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All references will be assumed normative when checking for downward references. ** There are 9 instances of too long lines in the document, the longest one being 2 characters in excess of 72. == There are 5 instances of lines with non-RFC6890-compliant IPv4 addresses in the document. If these are example addresses, they should be changed. == There are 2 instances of lines with private range IPv4 addresses in the document. If these are generic example addresses, they should be changed to use any of the ranges defined in RFC 6890 (or successor): 192.0.2.x, 198.51.100.x or 203.0.113.x. Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the RFC 3978 Section 5.4 Copyright Line does not match the current year == Line 2783 has weird spacing: '...RIBs-In and t...' == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'MUST not' in this paragraph: The information carried by the AdvertisementPath attribute is checked for ITAD loops. ITAD loop detection is done by scanning the full AdvertisementPath, and checking that the ITAD number of the local ITAD does not appear in the AdvertisementPath. If the local ITAD number appears in the AdvertisementPath, then the route MAY be stored in the Adj-TRIB-In, but unless the LS is configured to accept routes with its own ITAD in the advertisement path, the route MUST not be passed to the TRIP Decision Process. The operation of an LS that is configured to accept routes with its own ITAD number in the advertisement path are outside the scope of this document. -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. 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'8') (Obsoleted by RFC 3261, RFC 3262, RFC 3263, RFC 3264, RFC 3265) ** Obsolete normative reference: RFC 2373 (ref. '10') (Obsoleted by RFC 3513) ** Obsolete normative reference: RFC 2434 (ref. '11') (Obsoleted by RFC 5226) ** Obsolete normative reference: RFC 2401 (ref. '12') (Obsoleted by RFC 4301) ** Obsolete normative reference: RFC 2402 (ref. '13') (Obsoleted by RFC 4302, RFC 4305) ** Obsolete normative reference: RFC 2406 (ref. '14') (Obsoleted by RFC 4303, RFC 4305) ** Obsolete normative reference: RFC 2409 (ref. '15') (Obsoleted by RFC 4306) Summary: 12 errors (**), 0 flaws (~~), 6 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 IPTEL Working Group J. Rosenberg, dynamicsoft 3 Internet Draft H. Salama, Cisco Systems 4 draft-ietf-iptel-trip-09.txt M. Squire, WindWire 5 August 2001 6 Expiration Date: February 2002 8 Telephony Routing over IP (TRIP) 10 Status of this Memo 12 This document is an Internet-Draft and is in full conformance with 13 all provisions of Section 10 of RFC2026. 15 Internet-Drafts are working documents of the Internet Engineering 16 Task Force (IETF), its areas, and its working groups. Note that other 17 groups may also distribute working documents as Internet-Drafts. 19 Internet-Drafts are draft documents valid for a maximum of six months 20 and may be updated, replaced, or obsoleted by other documents at any 21 time. It is inappropriate to use Internet-Drafts as reference 22 material or to cite them other than as "work in progress." 24 The list of current Internet-Drafts can be accessed at 25 http://www.ietf.org/ietf/1id-abstracts.txt. 27 The list of Internet-Draft Shadow Directories can be accessed at 28 http://www.ietf.org/shadow.html. 30 Abstract 32 This document presents the Telephony Routing over IP (TRIP). TRIP is 33 a policy driven inter-administrative domain protocol for advertising 34 the reachability of telephony destinations between location servers, 35 and for advertising attributes of the routes to those destinations. 36 TRIP's operation is independent of any signaling protocol, hence TRIP 37 can serve as the telephony routing protocol for any signaling 38 protocol. 40 The Border Gateway Protocol (BGP-4) is used to distribute routing 41 information between administrative domains. TRIP is used to 42 distribute telephony routing information between telephony 43 administrative domains. The similarity between the two protocols is 44 obvious, and hence TRIP is modeled after BGP-4. 46 Table of Contents 48 1 Terminology and Definitions .............................. 3 49 2 Introduction ............................................. 4 50 3 Summary of Operation ..................................... 6 51 3.1 Peering Session Establishment and Maintenance ............ 6 52 3.2 Database Exchanges ....................................... 6 53 3.3 Internal Versus External Synchronization ................. 6 54 3.4 Advertising TRIP Routes .................................. 7 55 3.5 Telephony Routing Information Bases ...................... 8 56 3.6 Routes in TRIP ........................................... 9 57 3.7 Aggregation .............................................. 9 58 4 Message Formats .......................................... 10 59 4.1 Message Header Format .................................... 10 60 4.2 OPEN Message Format ...................................... 11 61 4.3 UPDATE Message Format .................................... 16 62 4.4 KEEPALIVE Message Format ................................ 23 63 4.5 NOTIFICATION Message Format ............................. 24 64 5 TRIP Attributes ......................................... 25 65 5.1 WithdrawnRoutes .......................................... 25 66 5.2 ReachableRoutes .......................................... 29 67 5.3 NextHopServer ........................................... 30 68 5.4 AdvertisementPath ....................................... 32 69 5.5 RoutedPath ............................................... 36 70 5.6 AtomicAggregate ......................................... 38 71 5.7 LocalPreference ......................................... 39 72 5.8 MultiExitDisc ............................................ 40 73 5.9 Communities .............................................. 41 74 5.10 ITAD Topology .......................................... 43 75 5.11 ConvertedRoute ........................................... 45 76 5.12 Considerations for Defining New TRIP Attributes ......... 46 77 6 TRIP Error Detection and Handling ....................... 47 78 6.1 Message Header Error Detection and Handling ............. 47 79 6.2 OPEN Message Error Detection and Handling ............... 48 80 6.3 UPDATE Message Error Detection and Handling ............. 49 81 6.4 NOTIFICATION Message Error Detection and Handling ....... 50 82 6.5 Hold Timer Expired Error Handling ....................... 50 83 6.6 Finite State Machine Error Handling ..................... 50 84 6.7 Cease ................................................... 51 85 6.8 Connection Collision Detection .......................... 51 86 7 TRIP Version Negotiation ................................ 52 87 8 TRIP Capability Negotiation ............................. 52 88 9 TRIP Finite State Machine ............................... 52 89 10 UPDATE Message Handling ................................. 57 90 10.1 Flooding Process ........................................ 58 91 10.2 Decision Process ........................................ 61 92 10.3 Update-Send Process ..................................... 65 93 10.4 Route Selection Criteria ................................ 70 94 10.5 Originating TRIP Routes ................................. 70 95 11 TRIP Transport .......................................... 70 96 12 ITAD Topology ........................................... 71 97 13 IANA Considerations ...................................... 71 98 13.1 TRIP Capabilities ....................................... 71 99 13.2 TRIP Attributes ........................................ 72 100 13.3 Destination Address Families ............................ 72 101 13.4 TRIP Application Protocols .............................. 72 102 13.5 ITAD Numbers ............................................ 73 103 14 Security Considerations ................................. 73 104 Appendix 1: TRIP FSM State Transitions and Actions ...... 74 105 Appendix 2: Implementation Recommendations .............. 76 106 Acknowledgments .......................................... 78 107 References ............................................... 78 108 Authors' Addresses ....................................... 79 109 Intellectual Property Notice ............................. 80 110 Full Copyright Statement ................................. 81 112 1. Terminology and Definitions 114 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 115 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 116 document are to be interpreted as described in RFC 2119 [1]. 118 A framework for a Telephony Routing over IP (TRIP) is described in 119 [2]. We assume the reader is familiar with the framework and 120 terminology of [2]. We define and use the following terms in addition 121 to those defined in [2]. 123 Telephony Routing Information Base (TRIB): The database of reachable 124 telephony destinations built and maintained at an LS as a result of 125 its participation in TRIP. 127 IP Telephony Administrative Domain (ITAD): The set of resources 128 (gateways, location servers, etc.) under the control of a single 129 administrative authority. End users are customers of an ITAD. 131 Less/More Specific Route: A route X is said to be less specific than 132 a route Y if every destination in Y is also a destination in X, and X 133 and Y are not equal. In this case, Y is also said to be more specific 134 than X. 136 Aggregation: Aggregation is the process by which multiple routes are 137 combined into a single less specific route that covers the same set 138 of destinations. Aggregation is used to reduce the size of the TRIB 139 synchronized with peer LSs by reducing the number of exported TRIP 140 routes. 142 Peers: Two LSs that share a logical association (a transport 143 connection). If the LSs are in the same ITAD, they are internal 144 peers. Otherwise, they are external peers. The logical association 145 between two peer LSs is called a peering session. 147 Telephony Routing Information Protocol (TRIP): The protocol defined 148 in this specification. The function of TRIP is to advertise the 149 reachability of telephony destinations, attributes associated with 150 the destinations, as well as the attributes of the path towards those 151 destinations. 153 TRIP destination: TRIP can be used to manage routing tables for 154 multiple protocols (SIP, H323, etc.). In TRIP, a destination is the 155 combination of (a) a set of addresses (given by an address family and 156 address prefix), and (b) an application protocol (SIP, H323, etc). 158 2. Introduction 160 The gateway location and routing problem has been introduced in [2]. 161 It is considered one of the more difficult problems in IP telephony. 162 The selection of an egress gateway for a telephony call, traversing 163 an IP network towards an ultimate destination in the PSTN, is driven 164 in large part by the policies of the various parties along the path, 165 and by the relationships established between these parties. As such, 166 a global directory of egress gateways in which users look up 167 destination phone numbers is not a feasible solution. Rather, 168 information about the availability of egress gateways is exchanged 169 between providers, and subject to policy, made available locally and 170 then propagated to other providers in other ITADs, thus creating 171 routes towards these egress gateways. This would allow each provider 172 to create its own database of reachable phone numbers and the 173 associated routes - such a database could be very different for each 174 provider depending on policy. 176 TRIP is an inter-domain (i.e., inter-ITAD) gateway location and 177 routing protocol. The primary function of a TRIP speaker, called a 178 location server (LS), is to exchange information with other LSs. This 179 information includes the reachability of telephony destinations, the 180 routes towards these destinations, and information about gateways 181 towards those telephony destinations residing in the PSTN. The TRIP 182 requirements are set forth in [2]. 184 LSs exchange sufficient routing information to construct a graph of 185 ITAD connectivity so that routing loops may be prevented. In 186 addition, TRIP can be used to exchange attributes necessary to 187 enforce policies and to select routes based on path or gateway 188 characteristics. This specification defines TRIP's transport and 189 synchronization mechanisms, its finite state machine, and the TRIP 190 data. This specification defines the basic attributes of TRIP. The 191 TRIP attribute set is extendible, so additional attributes may be 192 defined in future drafts. 194 TRIP is modeled after the Border Gateway Protocol 4 (BGP-4) [3] and 195 enhanced with some link state features as in the Open Shortest Path 196 First (OSPF) protocol [4], IS-IS [5], and the Server Cache 197 Synchronization Protocol (SCSP) [6]. TRIP uses BGP's inter-domain 198 transport mechanism, BGP's peer communication, BGP's finite state 199 machine, and similar formats and attributes as BGP. Unlike BGP 200 however, TRIP permits generic intra-domain LS topologies, which 201 simplifies configuration and increases scalability in contrast to 202 BGP's full mesh requirement of internal BGP speakers. TRIP uses an 203 intra-domain flooding mechanism similar to that used in OSPF [4], 204 IS-IS [5], and SCSP [6]. 206 TRIP permits aggregation of routes as they are advertised through the 207 network. TRIP does not define a specific route selection algorithm. 209 TRIP runs over a reliable transport protocol. This eliminates the 210 need to implement explicit fragmentation, retransmission, 211 acknowledgment, and sequencing. The error notification mechanism used 212 in TRIP assumes that the transport protocol supports a graceful 213 close, i.e., that all outstanding data will be delivered before the 214 connection is closed. 216 TRIP's operation is independent of any particular telephony signaling 217 protocol. Therefore, TRIP can be used as the routing protocol for any 218 of these protocols, e.g., H.323 [7] and SIP [8]. 220 The LS peering topology is independent of the physical topology of 221 the network. In addition, the boundaries of ITAD are independent of 222 the boundaries of the layer 3 routing autonomous systems. Neither 223 internal nor external TRIP peers need be physically adjacent. 225 3. Summary of Operation 227 This section summarizes the operation of TRIP. Details are provided 228 in later sections. 230 3.1. Peering Session Establishment and Maintenance 232 Two peer LSs form a transport protocol connection between one 233 another. They exchange messages to open and confirm the connection 234 parameters, and to negotiate the capabilities of each LS as well as 235 the type of information to be advertised over this connection. 237 KeepAlive messages are sent periodically to ensure adjacent peers are 238 operational. Notification messages are sent in response to errors or 239 special conditions. If a connection encounters an error condition, a 240 Notification message is sent and the connection is closed. 242 3.2. Database Exchanges 244 Once the peer connection has been established, the initial data flow 245 is a dump of all routes relevant to the new peer (In case of an 246 external peer, all routes in the LS's Adj-TRIB-Out for that external 247 peer. In case of an internal peer, all routes in the Ext-TRIB and all 248 Adj-TRIBs-In). Note that the different TRIBs are defined in Section 249 3.5. 251 Incremental updates are sent as the TRIP routing tables (TRIBs) 252 change. TRIP does not require periodic refresh of the routes. 253 Therefore, an LS must retain the current version of all routing 254 entries. 256 If a particular ITAD has multiple LSs and is providing transit 257 service for other ITADs, then care must be taken to ensure a 258 consistent view of routing within the ITAD. When synchronized the 259 TRIP routing tables, i.e., the Loc-TRIBs, of all internal peers are 260 identical. 262 3.3. Internal Versus External Synchronization 264 As with BGP, TRIP distinguishes between internal and external peers. 265 Within an ITAD, internal TRIP uses link-state mechanisms to flood 266 database updates over an arbitrary topology. Externally, TRIP uses 267 point-to-point peering relationships to exchange database 268 information. 270 To achieve internal synchronization, internal peer connections are 271 configured between LSs of the same ITAD such that the resulting 272 intra-domain LS topology is connected and sufficiently redundant. 273 This is different from BGP's approach that requires all internal 274 peers to be connected in a full mesh topology, which may result in 275 scaling problems. When an update is received from an internal peer, 276 the routes in the update are checked to determine if they are newer 277 than the version already in the database. Newer routes are then 278 flooded to all other peers in the same domain. 280 3.4. Advertising TRIP Routes 282 In TRIP, a route is defined as the combination of (a) a set of 283 destination addresses (given by an address family indicator and an 284 address prefix), and (b) an application protocol (e.g. SIP, H323, 285 etc.). Generally, there are additional attributes associated with 286 each route (for example, the next-hop server). 288 TRIP routes are advertised between a pair of LSs in UPDATE messages. 289 The destination addresses are included in the ReachableRoutes 290 attribute of the UPDATE, while other attributes describe things like 291 the path or egress gateway. 293 If an LS chooses to advertise the TRIP route, it may add to or modify 294 the attributes of the route before advertising it to a peer. TRIP 295 provides mechanisms by which an LS can inform its peer that a 296 previously advertised route is no longer available for use. There are 297 three methods by which a given LS can indicate that a route has been 298 withdrawn from service: 300 - Include the route in the WithdrawnRoutes Attribute in an UPDATE 301 message, thus marking the associated destinations as being no 302 longer available for use. 303 - Advertise a replacement route with the same set of destinations 304 in the ReachableRoutes Attribute. 305 - For external peers where flooding is not in use, the LS-to-LS 306 peer connection can be closed, which implicitly removes from 307 service all routes which the pair of LSs had advertised to each 308 other over that peer session. Note that terminating an internal 309 peering session does not necessarily remove the routes advertised 310 by the peer LS as the same routes may have been received from 311 multiple internal peers because of flooding. If an LS determines 312 that the another internal LS is no longer active (from the ITAD 313 Topology attributes of the UPDATE messages from other internal 314 peers), then it MUST remove all routes originated into the LS by 315 that LS and rerun its decision process. 317 3.5. Telephony Routing Information Bases 319 A TRIP LS processes three types of routes: 321 - External routes: An external route is a route received from an 322 external peer LS 323 - Internal routes: An internal route is a route received from an 324 internal LS in the same ITAD. 325 - Local routes: A local route is a route locally injected into 326 TRIP, e.g. by configuration or by route redistribution from 327 another routing protocol. 329 The Telephony Routing Information Base (TRIB) within an LS consists 330 of four distinct parts: 332 - Adj-TRIBs-In: The Adj-TRIBs-In store routing information that has 333 been learned from inbound UPDATE messages. Their contents 334 represent TRIP routes that are available as an input to the 335 Decision Process. These are the "unprocessed" routes received. 336 The routes from each external peer LS and each internal LS are 337 maintained in this database independently, so that updates from 338 one peer do not affect the routes received from another LS. Note 339 that there is an Adj-TRIBs-In for every LS within the domain, 340 even those with which the LS is not directly peered. 341 - Ext-TRIB: There is only one Ext-TRIB database per LS. The LS runs 342 the route selection algorithm on all external routes (stored in 343 the Adj-TRIBs-In of the external peers) and local routes (may be 344 stored in an Adj-TRIB-In representing the local LS) and selects 345 the best route for a given destination and stores it in the Ext- 346 TRIB. The use of Ext-TRIB will be explained further in Section 347 10.3.1 348 - Loc-TRIB: The Loc-TRIB contains the local TRIP routing 349 information that the LS has selected by applying its local 350 policies to the routing information contained in its Adj-TRIBs-In 351 of internal LSs and the Ext-TRIB. 352 - Adj-TRIBs-Out: The Adj-TRIBs-Out store the information that the 353 local LS has selected for advertisement to its external peers. 354 The routing information stored in the Adj-TRIBs-Out will be 355 carried in the local LS's UPDATE messages and advertised to its 356 peers. 358 Figure 1 illustrates the relationship between the three parts of the 359 routing information base. 361 Loc-TRIB 362 ^ 363 | 364 Decision Process 365 ^ ^ | 366 | | | 367 Adj-TRIBs-In | V 368 (Internal LSs) | Adj-TRIBs-Out 369 | 370 | 371 | 372 Ext-TRIB 373 ^ ^ 374 | | 375 Adj-TRIB-In Local Routes 376 (External Peers) 378 Figure 1: TRIB Relationships 380 Although the conceptual model distinguishes between Adj-TRIBs-In, 381 Loc-TRIB, and Adj-TRIBs-Out, this neither implies nor requires that 382 an implementation must maintain three separate copies of the routing 383 information. The choice of implementation (for example, 3 copies of 384 the information vs. 1 copy with pointers) is not constrained by the 385 protocol. 387 3.6. Routes in TRIP 389 A route in TRIP specifies a range of numbers by being a prefix of 390 those numbers (the exact definition & syntax of route are in 5.1.1). 391 Arbitrary ranges of numbers are not atomically representable by a 392 route in TRIP. A prefix range is the only type of range supported 393 atomicly. An arbitrary range can be accomplished by using multiple 394 prefixes in a ReachableRoutes attribute (see Section 5.1 & 5.2). For 395 example, 222-xxxx thru 999-xxxx could be represented by including the 396 prefixes 222, 223, 224,...,23,24,...,3,4,...,9 in a ReachableRoutes 397 attribute. 399 3.7. Aggregation 401 Aggregation is a scaling enhancement used by an LS to reduce the 402 number of routing entries that it has to synchronize with its peers. 403 Aggregation may be peformed by an LS when there is a set of routes 404 {R1, R2, ...} in its TRIB such that there exists a less specific 405 route R where every valid destination in R is also a valid 406 destination in {R1, R2, ...} and vice-versa. Section 5 includes a 407 description of how to combine each attribute (by type) on the {R1, 408 R2, ...} routes into an attribute for R. 410 Note that there is no mechanism within TRIP to communicate that a 411 particular address prefix is not used or valid within a particular 412 address family, and thus that these addresses could be skipped during 413 aggregation. LSs may use methods outside of TRIP to learn of invalid 414 prefixes that may be ignored during aggregation. 416 An LS is not required to perform aggregation, however it is 417 recommended whenever maintaining a smaller TRIB is important. 418 Whether an LS aggregate routes is considered a local policy decision. 420 Whenever an LS aggregates multiple routes where the NextHopServer is 421 not identical in all aggregated routes, the NextHopServer attribute 422 of the aggregate route must be set to a signalling server in the 423 aggregating LS's domain. 425 When an LS resets the NextHopServer of any route, and this may be 426 performed because of aggregation or other reasons, it has the effect 427 of adding another signalling server along the signalling path to 428 these desinations. The end result is that the signalling path 429 between two destinations may consist of multiple signalling servers 430 across multiple domains. 432 4. Message Formats 434 This section describes message formats used by TRIP. Messages are 435 sent over a reliable transport protocol connection. A message MUST be 436 processed only after it is entirely received. The maximum message 437 size is 4096 octets. All implementations MUST support this maximum 438 message size. The smallest message that MAY be sent consists of a 439 TRIP header without a data portion, or 3 octets. 441 4.1. Message Header Format 443 Each message has a fixed-size header. There may or may not be a data 444 portion following the header depending on the message type. The 445 layout of the header fields is shown in Figure 2. 447 0 1 2 448 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 449 +--------------+----------------+---------------+ 450 | Length | Type | 451 +--------------+----------------+---------------+ 453 Figure 2: TRIP Header 455 Length: 456 This 2-octet unsigned integer indicates the total length of the 457 message, including the header, in octets. Thus, it allows one to 458 locate in the transport-level stream the beginning of the next 459 message. The value of the Length field must always be at least 3 and 460 no greater than 4096, and may be further constrained depending on the 461 message type. No padding of extra data after the message is allowed, 462 so the Length field must have the smallest value possible given the 463 rest of the message. 465 Type: 466 This 1-octet unsigned integer indicates the type code of the message. 467 The following type codes are defined: 469 1 - OPEN 470 2 - UPDATE 471 3 - NOTIFICATION 472 4 - KEEPALIVE 474 4.2. OPEN Message Format 476 After a transport protocol connection is established, the first 477 message sent by each side is an OPEN message. If the OPEN message is 478 acceptable, a KEEPALIVE message confirming the OPEN is sent back. 479 Once the OPEN is confirmed, UPDATE, KEEPALIVE, and NOTIFICATION 480 messages may be exchanged. 482 The minimum length of the OPEN message is 14 octets (including 483 message header). OPEN messages not meeting this minimum requirement 484 are handled as defined in Section 6.2. 486 In addition to the fixed-size TRIP header, the OPEN message contains 487 the following fields: 489 0 1 2 3 490 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 491 +---------------+---------------+--------------+----------------+ 492 | Version | Reserved | Hold Time | 493 +---------------+---------------+--------------+----------------+ 494 | My ITAD | 495 +---------------+---------------+--------------+----------------+ 496 | TRIP Identifier | 497 +---------------+---------------+--------------+----------------+ 498 | Optional Parameters Len |Optional Parameters (variable)... 499 +---------------+---------------+--------------+----------------+ 500 Figure 3: TRIP OPEN Header 502 Version: 503 This 1-octet unsigned integer indicates the protocol version of the 504 message. The current TRIP version number is 1. 506 Hold Time: 507 This 2-octet unsigned integer indicates the number of seconds that 508 the sender proposes for the value of the Hold Timer. Upon receipt of 509 an OPEN message, an LS MUST calculate the value of the Hold Timer by 510 using the smaller of its configured Hold Time and the Hold Time 511 received in the OPEN message. The Hold Time MUST be either zero or at 512 least three seconds. An implementation MAY reject connections on the 513 basis of the Hold Time. The calculated value indicates the maximum 514 number of seconds that may elapse between the receipt of successive 515 KEEPALIVE and/or UPDATE messages by the sender. 517 This 4-octet unsigned integer indicates the ITAD number of the 518 sender. The ITAD number must be unique for this domain within this 519 confederation of cooperating LSs. 521 ITAD numbers are assigned by IANA as specified in Section 13. This 522 document reserves ITAD number 0. ITAD numbers from 1 to 255 are 523 designated for private use. 525 TRIP Identifier: 526 This 4-octet unsigned integer indicates the TRIP Identifier of the 527 sender. The TRIP Identifier MUST uniquely identify this LS within its 528 ITAD. A given LS MAY set the value of its TRIP Identifier to an IPv4 529 address assigned to that LS. The value of the TRIP Identifier is 530 determined on startup and MUST be the same for all peer connections. 531 When comparing two TRIP identifiers, the TRIP Identifier is 532 interpreted as a numerical 4-octet unsigned integer. 534 Optional Parameters Length: 535 This 2-octet unsigned integer indicates the total length of the 536 Optional Parameters field in octets. If the value of this field is 537 zero, no Optional Parameters are present. 539 Optional Parameters: 540 This field may contain a list of optional parameters, where each 541 parameter is encoded as a triplet. 544 0 1 2 545 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 546 +---------------+---------------+--------------+----------------+ 547 | Parameter Type | Parameter Length | 548 +---------------+---------------+--------------+----------------+ 549 | Parameter Value (variable)... 550 +---------------+---------------+--------------+----------------+ 552 Figure 4: Optional Parameter Encoding 554 Parameter Type: 555 This is a 2-octet field that unambiguously identifies individual 556 parameters. 558 Parameter Length: 559 This is a 2-octet field that contains the length of the Parameter 560 Value field in octets. 562 Parameter Value: 563 This is a variable length field that is interpreted according to the 564 value of the Parameter Type field. 566 4.2.1. Open Message Optional Parameters 568 This document defines the following Optional Parameters for the OPEN 569 message. 571 4.2.1.1. Capability Information 573 Capability Information uses Optional Parameter type 1. This is an 574 optional parameter used by an LS to convey to its peer the list of 575 capabilities supported by the LS. This permits an LS to learn of the 576 capabilities of its peer LSs. Capability negotiation is defined in 577 Section 8. 579 The parameter contains one or more triples , where each triple is encoded as 581 shown below: 583 0 1 2 584 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 585 +---------------+---------------+--------------+----------------+ 586 | Capability Code | Capability Length | 587 +---------------+---------------+--------------+----------------+ 588 | Capability Value (variable)... 589 +---------------+---------------+--------------+----------------+ 591 Figure 5: Capability Optional Parameter 593 Capability Code: 594 Capability Code is a 2-octet field that unambiguously identifies 595 individual capabilities. 597 Capability Length: 598 Capability Length is a 2-octet field that contains the length of the 599 Capability Value field in octets. 601 Capability Value: 602 Capability Value is a variable length field that is interpreted 603 according to the value of the Capability Code field. 605 Any particular capability, as identified by its Capability Code, may 606 appear more than once within the Optional Parameter. 608 This document reserves Capability Codes 32768-65535 for vendor- 609 specific applications (these are the codes with the first bit of the 610 code value equal to 1). This document reserves value 0. Capability 611 Codes (other than those reserved for vendor specific use) are 612 controlled by IANA. See Section 13 for IANA considerations. 614 The following Capability Codes are defined by this specification: 616 Code Capability 617 1 Route Types Supported 618 2 Send Receive Capability 620 4.2.1.1.1. Route Types Supported 622 The Route Types Supported Capability Code lists the route types 623 supported in this peering session by the transmitting LS. An LS MUST 624 NOT use route types that are not supported by the peer LS in any 625 particular peering session. If the route types supported by a peer 626 are not satisfactory, an LS SHOULD terminate the peering session. The 627 format for a Route Type is: 629 0 1 2 630 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 631 +---------------+---------------+--------------+----------------+ 632 | Address Family | Application Protocol | 633 +---------------+---------------+--------------+----------------+ 635 Figure 6: Route Types Supported Capability 637 The Address Family and Application Protocol are as defined in Section 638 5.1.1. Address Family gives the address family being routed (within 639 the ReachableRoutes attribute). The application protocol lists the 640 application for which the routes apply. As an example, a route type 641 for TRIP could be , indicating a set of POTS destinations 642 for the SIP protocol. 644 The Route Types Supported Capability MAY contain multiple route types 645 in the capability. The number of route types within the capability is 646 the maximum number that can fit given the capability length. The 647 Capability Code is 1 and the length is variable. 649 4.2.1.1.2. Send Receive Capability 651 This capability specifies the mode in which the LS will operate with 652 this particular peer. The possible modes are: Send Only mode, Receive 653 Only mode, or Send Receive mode. The default mode is Send Receive 654 mode. 656 In Send Only mode, an LS transmits UPDATE messages to its peer, but 657 the peer MUST NOT transmit UPDATE messages to that LS. If an LS in 658 Send Only mode receives an UPDATE message from its peer, it MUST 659 discard that message, but no further action should be taken. 661 The UPDATE messages sent by an LS in Send Only mode to its intra- 662 domain peer MUST include the ITAD Topology attribute whenever the 663 topology changes. A useful application of an LS in Send Only mode 664 with an external peer is to enable gateway termination services. 666 If a service provider terminates calls to a set of gateways it owns, 667 but never initiates calls, it can set its LSs to operate in Send Only 668 mode, since they only ever need to generate UPDATE messages, not 669 receive them. 671 If an LS in Send Receive mode has a peering session with a peer in 672 Send Only mode, that LS MUST set its route dissemination policy such 673 that it does not send any UPDATE messages to its peer. 675 In Receive Only mode, the LS acts as a passive TRIP listener. It 676 receives and processes UPDATE messages from its peer, but it MUST NOT 677 transmit any UPDATE messages to its peer. This is useful for 678 management stations that wish to collect topology information for 679 display purposes. 681 The behavior of an LS in Send Receive mode is the default TRIP 682 operation specified throughout this document. 684 The Send Receive capability is a 4-octet unsigned numeric value. It 685 can only take one of the following three values: 687 1 - Send Receive mode 688 2 - Send only mode 689 3 - Receive Only mode 691 A peering session MUST NOT be established between two LSs, both of 692 them in either Send Only mode or in Receive Only mode. If a peer LS 693 detects such a capability mismatch when processing an OPEN message, 694 it MUST respond with a NOTIFICATION message and close the peer 695 session. The error code in the NOTIFICATION message must be set to 696 "Capability Mismatch." 698 An LS MUST be configured in the same Send Receive mode for all peers. 700 4.3. UPDATE Message Format 702 UPDATE messages are used to transfer routing information between LSs. 703 The information in the UPDATE packet can be used to construct a graph 704 describing the relationships between the various ITADs. By applying 705 rules to be discussed, routing information loops and some other 706 anomalies can be prevented. 708 An UPDATE message is used to both advertise and withdraw routes from 709 service. An UPDATE message may simultaneously advertise and withdraw 710 TRIP routes. 712 In addition to the TRIP header, the TRIP UPDATE contains a list of 713 routing attributes as shown in Figure 7. There is no padding between 714 routing attributes. 716 +------------------------------------------------+--... 717 | First Route Attribute | Second Route Attribute | ... 718 +------------------------------------------------+--... 720 Figure 7: TRIP UPDATE Format 722 The minimum length of an UPDATE message 11 octets (the TRIP header 723 plus at least the WithdrawnRoutes and ReachableRoutes attributes). 725 4.3.1. Routing Attributes 727 A variable length sequence of routing attributes is present in every 728 UPDATE message. Each attribute is a triple of variable length. 731 0 1 2 3 732 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 733 +---------------+---------------+--------------+----------------+ 734 | Attr. Flags |Attr. Type Code| Attr. Length | 735 +---------------+---------------+--------------+----------------+ 736 | Attribute Value (variable) | 737 +---------------+---------------+--------------+----------------+ 739 Figure 8: Routing Attribute Format 741 Attribute Type is a two-octet field that consists of the Attribute 742 Flags octet followed by the Attribute Type Code octet. 744 The Attribute Type Code defines the type of attribute. The basic 745 TRIP-defined Attribute Type Codes are discussed later in this 746 section. Attributes MUST appear in the UPDATE message in numerical 747 order of the Attribute Type Code. An attribute MUST NOT be included 748 more than once in the same UPDATE message. Attribute Flags are used 749 to control attribute processing when the attribute type is unknown. 750 Attribute Flags are further defined in Section 4.3.2. 752 This document reserves Attribute Type Codes 224-255 for vendor- 753 specific applications (these are the codes with the first three bits 754 of the code equal to 1). This document reserves value 0. Attribute 755 Type Codes (other than those reserved for vendor specific use) are 756 controlled by IANA. See Section 13 for IANA considerations. 758 The third and the fourth octets of the route attribute contain the 759 length of the attribute value field in octets. 761 The remaining octets of the attribute represent the Attribute Value 762 and are interpreted according to the Attribute Flags and the 763 Attribute Type Code. The basic supported attribute types, their 764 values, and their uses are defined in this specification. These are 765 the attributes necessary for proper loop free operation of TRIP, both 766 inter-domain and intra-domain. Additional attributes may be defined 767 in future documents. 769 4.3.2. Attribute Flags 771 It is clear that the set of attributes for TRIP will evolve over 772 time. Hence it is essential that mechanisms be provided to handle 773 attributes with unrecognized types. The handling of unrecognized 774 attributes is controlled via the flags field of the attribute. 775 Recognized attributes should be processed according to their specific 776 definition. 778 The following are the attribute flags defined by this specification: 779 Bit Flag 780 0 Well-Known Flag 781 1 Transitive Flag 782 2 Dependent Flag 783 3 Partial Flag 784 4 Link-state Encapsulated Flag 786 The high-order bit (bit 0) of the Attribute Flags octet is the Well- 787 Known Bit. It defines whether the attribute is not well-known (if set 788 to 1) or well-known (if set to 0). Implementations are not required 789 to support not well-known attributes, but MUST support well-known 790 attributes. 792 The second high-order bit (bit 1) of the Attribute Flags octet is the 793 Transitive bit. It defines whether a not well-known attribute is 794 transitive (if set to 1) or non-transitive (if set to 0). For well- 795 known attributes, the Transitive bit MUST be zero on transmit and 796 MUST be ignored on receipt. 798 The third high-order bit (bit 2) of the Attribute Flags octet is the 799 Dependent bit. It defines whether a transitive attribute is dependent 800 (if set to 1) or independent (if set to 0). For well-known attributes 801 and for non-transitive attributes, the Dependent bit is irrelevant, 802 and MUST be set to zero on transmit and MUST be ignored on receipt. 804 The fourth high-order bit (bit 3) of the Attribute Flags octet is the 805 Partial bit. It defines whether the information contained in the not 806 well-known transitive attribute is partial (if set to 1) or complete 807 (if set to 0). For well-known attributes and for non- transitive 808 attributes the Partial bit MUST be set to 0 on transmit and MUST be 809 ignored on receipt. 811 The fifth high-order bit (bit 4) of the Attribute Flags octet is the 812 Link-state Encapsulation bit. This bit is only applicable to certain 813 attributes (ReachableRoutes and WithdrawnRoutes) and determines the 814 encapsulation of the routes within those attributes. If this bit is 815 set, link-state encapsulation is used within the attribute. 816 Otherwise, standard encapsulation is used within the attribute. The 817 Link-state Encapsulation technique is described in Section 4.3.2.4. 818 This flag is only valid on the ReachableRoutes and WithdrawnRoutes 819 attributes. It MUST be cleared on transmit and MUST be ignored on 820 receipt for all other attributes. 822 The other bits of the Attribute Flags octet are unused. They MUST be 823 zeroed on transmit and ignored on receipt. 825 4.3.2.1. Attribute Flags and Route Selection 827 Any recognized attribute can be used as input to the route selection 828 process, although the utility of some attributes in route selection 829 is minimal. 831 4.3.2.2. Attribute Flags and Route Dissemination 833 TRIP provides for two variations of transitivity due to the fact that 834 intermediate LSs need not modify the NextHopServer when propagating 835 routes. Attributes may be non-transitive, dependent transitive, or 836 independent transitive. An attribute cannot be both dependent 837 transitive and independent transitive. 839 Unrecognized independent transitive attributes may be propagated by 840 any intermediate LS. Unrecognized dependent transitive attributes MAY 841 only be propagated if the LS is NOT changing the next-hop server. The 842 transitivity variations permit some unrecognized attributes to be 843 carried end-to-end (independent transitive), some to be carried 844 between adjacent next-hop servers (dependent transitive), and other 845 to be restricted to peer LSs (non- transitive). 847 An LS that passes an unrecognized transitive attribute to a peer MUST 848 set the Partial flag on that attribute. Any LS along a path MAY 849 insert a transitive attribute into a route. If any LS except the 850 originating LS inserts a new independent transitive attribute into a 851 route, then it MUST set the Partial flag on that attribute. If any 852 LS except an LS that modifies the NextHopServer inserts a new 853 dependent transitive attribute into a route, then it MUST set the 854 Partial flag on that attribute. The Partial flag indicates that not 855 every LS along the relevant path has processed and understood the 856 attribute. For independent transitive attributes, the "relevant path" 857 is the path given in the AdvertisementPath attribute. For dependent 858 transitive attributes, the relevant path consists only of those 859 domains thru which this object has passed since the NextHopServer was 860 last modified. The Partial flag in an independent transitive 861 attribute MUST NOT be unset by any other LS along the path. The 862 Partial flag in a dependent transitive attribute MUST be reset 863 whenever the NextHopServer is changed, but MUST NOT be unset by any 864 LS that is not changing the NextHopServer. 866 The rules governing the addition of new non-transitive attributes are 867 defined independently for each non-transitive attribute. Any 868 attribute MAY be updated by an LS in the path. 870 4.3.2.3. Attribute Flags and Route Aggregation 872 Each attribute defines how it is to be handled during route 873 aggregation. 875 The rules governing the handling of unknown attributes are guided by 876 the Attribute Flags. Unrecognized transitive attributes are dropped 877 during aggregation. There should be no unrecognized non-transitive 878 attributes during aggregation because non-transitive attributes must 879 be processed by the local LS in order to be propagated. 881 4.3.2.4. Attribute Flags and Encapsulation 883 Normally attributes have the simple format as described in Section 884 4.3.1. If the Link-state Encapsulation Flag is set, then the two 885 additional fields are added to the attribute header as shown in 886 Figure 9. 888 0 1 2 3 889 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 890 +---------------+---------------+--------------+----------------+ 891 | Attr. Flags |Attr. Type Code| Attr. Length | 892 +---------------+---------------+--------------+----------------+ 893 | Originator TRIP Identifier | 894 +---------------+---------------+--------------+----------------+ 895 | Sequence Number | 896 +---------------+---------------+--------------+----------------+ 897 | Attribute Value (variable) | 898 +---------------+---------------+--------------+----------------+ 900 Figure 9: Link State Encapsulation 902 The Originator TRIP ID and Sequence Number are used to control the 903 flooding of routing updates within a collection of servers. These 904 fields are used to detect duplicate and old routes so that they are 905 not further propagated within the servers. The use of these fields is 906 defined in Section 10.1. 908 4.3.3. Mandatory Attributes 910 There are no Mandatory attributes in TRIP. However, there are 911 Conditional Mandatory attributes. A conditional mandatory attribute 912 is an attribute, which MUST be included in an UPDATE message if 913 another attribute is included in that message. For example, if an 914 UPDATE message includes a ReachableRoutes attribute, it MUST include 915 an AdvertisementPath attribute as well. 917 The three base attributes in TRIP are WithdrawnRoutes, 918 ReachableRoutes, and ITAD Topology. Their presence in an UPDATE 919 message is entirely optional and independent of any other attributes. 921 4.3.4. TRIP UPDATE Attributes 923 This section summarizes the attributes that may be carried in an 924 UPDATE message. Attributes MUST appear in the UPDATE message in 925 increasing order of the Attribute Type Code. Additional details are 926 provided in Section 5. 928 4.3.4.1. WithdrawnRoutes 930 This attribute lists a set of routes that are being withdrawn from 931 service. The transmitting LS has determined that these routes should 932 no longer be advertised, and is propagating this information to its 933 peers. 935 4.3.4.2. ReachableRoutes 937 This attribute lists set of routes that are being added to service. 938 These routes will have the potential to be inserted into the Adj- 939 TRIBs-In of the receiving LS and the route selection process will be 940 applied to them. 942 4.3.4.3. NextHopServer 944 This attribute gives the identity of the entity to which messages 945 should be sent along this routed path. It specifies the identity of 946 the next hop server as either a host domain name or an IP address. It 947 MAY optionally specify the UDP/TCP port number for the next hop 948 signaling server. If not specified, then the default port SHOULD be 949 used. The NextHopServer is specific to the set of destinations and 950 application protocol defined in the ReachableRoutes attribute. Note 951 that this is NOT the address to which media (voice, video, etc.) 952 should be transmitted, it is only for the application protocol as 953 given in the ReachableRoutes attribute. 955 4.3.4.4. AdvertisementPath 957 The AdvertisementPath is analogous to the AS_PATH in BGP4 [3]. The 958 attribute records the sequence of domains through which this 959 advertisement has passed. The attribute is used to detect when the 960 routing advertisement is looping. This attribute does NOT reflect the 961 path through which messages following this route would traverse. 962 Since the next-hop need not be modified by each LS, the actual path 963 to the destination might not have to traverse every domain in the 964 AdvertisementPath. 966 4.3.4.5. RoutedPath 968 The RoutedPath attribute is analogous to the AdvertisementPath 969 attribute, except that it records the actual path (given by the list 970 of domains) *to* the destinations. Unlike AdvertisementPath, which is 971 modified each time the route is propagated, RoutedPath is only 972 modified when the NextHopServer attribute changes. Thus, it records 973 the subset of the AdvertisementPath over which messages following 974 this particular route would traverse. 976 4.3.4.6. AtomicAggregate 978 The AtomicAggregate attribute indicates that a route may actually 979 include domains not listed in the RoutedPath. If an LS, when 980 presented with a set of overlapping routes from a peer LS, selects a 981 less specific route without selecting the more specific route, then 982 the LS MUST include the AtomicAggregate attribute with the route. An 983 LS receiving a route with an AtomicAggregate attribute MUST NOT make 984 the set of destinations more specific when advertising it to other 985 LSs. 987 4.3.4.7. LocalPreference 989 The LocalPreference attribute is an intra-domain attribute used to 990 inform other LSs of the local LSs preference for a given route. The 991 preference of a route is calculated at the ingress to a domain and 992 passed as an attribute with that route throughout the domain. Other 993 LSs within the same ITAD use this attribute in their route selection 994 process. This attribute has no significance between domains. 996 4.3.4.8. MultiExitDisc 998 There may be more than one LS peering relationship between 999 neighboring domains. The MultiExitDisc attribute is used by an LS to 1000 express a preference for one link between the domains over another 1001 link between the domains. The use of the MultiExitDisc attribute is 1002 controlled by local policy. 1004 4.3.4.9. Communities 1006 The Communities attribute is a not well-known attribute used to 1007 facilitate and simplify the control of routing information by 1008 grouping destinations into communities. 1010 4.3.4.10. ITAD Topology 1012 The ITAD topology attribute is an intra-domain attribute that is used 1013 by LSs to indicate their intra-domain topology to other LSs in the 1014 domain. 1016 4.3.4.11. ConvertedRoute 1018 The ConvertedRoute attribute indicates that an intermediate LS has 1019 altered the route by changing the route's Application Protocol. 1021 4.4. KEEPALIVE Message Format 1023 TRIP does not use any transport-based keep-alive mechanism to 1024 determine if peers are reachable. Instead, KEEPALIVE messages are 1025 exchanged between peers often enough as not to cause the Hold Timer 1026 to expire. A reasonable maximum time between KEEPALIVE messages would 1027 be one third of the Hold Time interval. KEEPALIVE messages MUST NOT 1028 be sent more than once every 3 seconds. An implementation SHOULD 1029 adjust the rate at which it sends KEEPALIVE messages as a function of 1030 the negotiated Hold Time interval. 1032 If the negotiated Hold Time interval is zero, then periodic KEEPALIVE 1033 messages MUST NOT be sent. 1035 KEEPALIVE message consists of only message header and has a length of 1036 3 octets. 1038 4.5. NOTIFICATION Message Format 1040 A NOTIFICATION message is sent when an error condition is detected. 1041 The TRIP transport connection is closed immediately after sending a 1042 NOTIFICATION message 1044 In addition to the fixed-size TRIP header, the NOTIFICATION message 1045 contains the following fields: 1047 0 1 2 3 1048 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1049 +---------------+---------------+--------------+----------------+ 1050 | Error Code | Error Subcode | Data... (variable) 1051 +---------------+---------------+--------------+----------------+ 1053 Figure 10: TRIP NOTIFICATION Format 1055 Error Code: 1056 This 1-octet unsigned integer indicates the type of NOTIFICATION. 1057 The following Error Codes have been defined: 1059 Error Code Symbolic Name Reference 1060 1 Message Header Error Section 6.1 1061 2 OPEN Message Error Section 6.2 1062 3 UPDATE Message Error Section 6.3 1063 4 Hold Timer Expired Section 6.5 1064 5 Finite State Machine Error Section 6.6 1065 6 Cease Section 6.7 1067 Error Subcode: 1068 This 1-octet unsigned integer provides more specific information 1069 about the nature of the reported error. Each Error Code may have one 1070 or more Error Subcodes associated with it. If no appropriate Error 1071 Subcode is defined, then a zero (Unspecific) value is used for the 1072 Error Subcode field. 1074 Message Header Error Subcodes: 1075 1 - Bad Message Length. 1076 2 - Bad Message Type. 1078 OPEN Message Error Subcodes: 1079 1 - Unsupported Version Number. 1080 2 - Bad Peer ITAD. 1081 3 - Bad TRIP Identifier. 1082 4 - Unsupported Optional Parameter. 1083 5 - Unacceptable Hold Time. 1084 6 - Unsupported Capability. 1085 7 - Capability Mismatch. 1087 UPDATE Message Error Subcodes: 1088 1 - Malformed Attribute List. 1089 2 - Unrecognized Well-known Attribute. 1090 3 - Missing Well-known Mandatory Attribute. 1091 4 - Attribute Flags Error. 1092 5 - Attribute Length Error. 1093 6 - Invalid Attribute. 1095 Data: 1096 This variable-length field is used to diagnose the reason for the 1097 NOTIFICATION. The contents of the Data field depend upon the Error 1098 Code and Error Subcode. 1100 Note that the length of the data can be determined from the message 1101 length field by the formula: 1103 Data Length = Message Length - 5 1105 The minimum length of the NOTIFICATION message is 5 octets (including 1106 message header). 1108 5. TRIP Attributes 1110 This section provides details on the syntax and semantics of each 1111 TRIP UPDATE attribute. 1113 5.1. WithdrawnRoutes 1115 Conditional Mandatory: False. 1116 Required Flags: Well-known. 1117 Potential Flags: Link-State Encapsulation (when flooding). 1118 TRIP Type Code: 1 1120 The WithdrawnRoutes attribute MUST be included in every UPDATE 1121 message. It specifies a set of routes that are to be removed from 1122 service by the receiving LS(s). The set of routes MAY be empty, 1123 indicated by a length field of zero. 1125 5.1.1. Syntax of WithdrawnRoutes 1127 The WithdrawnRoutes Attribute encodes a sequence of routes in its 1128 value field. The format for individual routes is given in Section 1129 5.1.1.1. The WithdrawnRoutes Attribute lists the individual routes 1130 sequentially with no padding as shown in Figure 11. Each route 1131 includes a length field so that the individual routes within the 1132 attribute can be delineated. 1134 +---------------------+---------------------+... 1135 | WithdrawnRoute1... | WithdrawnRoute2... |... 1136 +---------------------+---------------------+... 1138 Figure 11: WithdrawnRoutes Format 1140 5.1.1.1. Generic TRIP Route Format 1142 The generic format for a TRIP route is given in Figure 12. 1144 0 1 2 3 1145 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1146 +---------------+---------------+--------------+----------------+ 1147 | Address Family | Application Protocol | 1148 +---------------+---------------+--------------+----------------+ 1149 | Length | Address (variable) ... 1150 +---------------+---------------+--------------+----------------+ 1152 Figure 12: Generic TRIP Route Format 1154 Address Family: 1155 The address family field gives the type of address for the route. Two 1156 address families are defined in this Section: 1158 Code Address Family 1159 1 Decimal Routing Numbers 1160 2 PentaDecimal Routing Numbers 1161 3 E.164 Numbers 1163 This document reserves address family code 0. This document reserves 1164 address family codes 32768-65535 for vendor-specific applications 1165 (these are the codes with the first bit of the code value equal to 1166 1).Additional address families may be defined in the future. 1167 Assignment of address family codes is controlled by IANA. See 1168 Section 13 for IANA considerations. 1170 Application Protocol: 1171 The application protocol gives the protocol for which this routing 1172 table is maintained. The currently defined application protocols are: 1174 Code Protocol 1175 1 SIP 1176 2 H.323-H.225.0-Q.931 1177 3 H.323-H.225.0-RAS 1178 4 H.323-H.225.0-Annex-G 1180 This document reserves application protocol code 0. This document 1181 reserves application protocol codes 32768-65535 for vendor-specific 1182 applications (these are the codes with the first bit of the code 1183 value equal to 1). Additional application protocols may be defined in 1184 the future. Assignment of application protocol codes is controlled by 1185 IANA. See Section 13 for IANA considerations. 1187 Length: 1188 The length of the address field, in bytes. 1190 Address: 1191 This is an address (prefix) of the family type given by Address 1192 Family. The octet length of the address is variable and is determined 1193 by the length field of the route. 1195 5.1.1.2. Decimal Routing Numbers 1197 The Decimal Routing Numbers address family is a super set of all 1198 E.164 numbers, national numbers, local numbers, and private numbers. 1199 It can also be used to represent the decimal routing numbers used in 1200 conjunction with Number Portability in some countries/regions. A set 1201 of telephone numbers is specified by a Decimal Routing Number prefix. 1202 Decimal Routing Number prefixes are represented by a string of 1203 digits, each digit encoded by its ASCII character representation. 1204 This routing object covers all phone numbers starting with this 1205 prefix. The syntax for the Decimal Routing Number prefix is: 1207 Decimal-routing-number = *decimal-digit 1208 decimal-digit = DECIMAL-DIGIT 1209 DECIMAL-DIGIT = "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9" 1211 This DECIMAL Routing Number prefix is not bound in length. This 1212 format is similar to the format for a global telephone number as 1213 defined in SIP [8] without visual separators and without the "+" 1214 prefix for international numbers. This format facilitates efficient 1215 comparison when using TRIP to route SIP or H323, both of which use 1216 character based representations of phone numbers. The prefix length 1217 is determined from the length field of the route. The type of Decimal 1218 Routing Number (private, local, national, or international) can be 1219 deduced from the first few digits of the prefix. 1221 5.1.1.3. PentaDecimal Routing Numbers 1223 This address family is used to represent PentaDecimal Routing Numbers 1224 used in conjunction with Number Portability in some 1225 countries/regions. PentaDecimal Routing Number prefixes are 1226 represented by a string of digits, each digit encoded by its ASCII 1227 character representation. This routing object covers all routing 1228 numbers starting with this prefix. The syntax for the PentaDecimal 1229 Routing Number prefix is: 1231 PentaDecimal-routing-number = *pentadecimal-digit 1232 pentadecimal-routing-digit = PENTADECIMAL-DIGIT 1233 PENTADECIMAL-DIGIT = "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"| 1234 "8"|"9"|"A"|"B"|"C"|"D"|"E" 1236 Note the difference in alphabets between Decimal Routing Numbers and 1237 PentaDecimal Routing Numbers. A PentaDecimal Routing Number prefix is 1238 not bound in length. 1240 Note that the address family, which suits the routing numbers of a 1241 specific country/region depends on the alphabets used for routing 1242 numbers in that country/region. For example, North American routing 1243 numbers SHOULD use the Decimal Routing Numbers address family, 1244 because their alphabet is limited to the digits "0" through "9". 1245 Another example, in most European countries routing numbers use the 1246 alphabet "0" through "9" and "A" through "F", and hence these 1247 countries SHOULD use the PentaDecimal Routing Numbers address family. 1249 5.1.1.4. E.164 Numbers 1251 The E.164 Numbers address family is dedicated to fully qualified 1252 E.164 numbers. A set of telephone numbers is specified by a E.164 1253 prefix. E.164 prefixes are represented by a string of digits, each 1254 digit encoded by its ASCII character representation. This routing 1255 object covers all phone numbers starting with this prefix. The syntax 1256 for the E.164 prefix is: 1258 E164-number = *e164-digit 1259 E164-digit = E164-DIGIT 1260 E164-DIGIT = "0"|"1"|"2"|"3"|"4"|"5"|"6"|"7"|"8"|"9" 1262 This format facilitates efficient comparison when using TRIP to route 1263 SIP or H323, both of which use character based representations of 1264 phone numbers. The prefix length is determined from the length field 1265 of the route. 1267 The E.164 Numbers address family and the Decimal Routing Numbers 1268 address family have the same alphabet. The E.164 Numbers address 1269 family SHOULD be used whenever possible. The Decimal Routing Numbers 1270 address family can be used in case of private numbering plans or 1271 applications that do not desire to advertise fully expanded, fully 1272 qualified telephone numbers. If Decimal routing Numbers are used to 1273 advertise non-fully qualified prefixes, the prefixes may have to be 1274 manipulated (e.g. expanded) at the boundary between ITADs. This adds 1275 significant complexity to the egress LS, because, it has to map the 1276 prefixes from the format used in its own ITAD to the format used in 1277 the peer ITAD. 1279 5.2. ReachableRoutes 1281 Conditional Mandatory: False. 1282 Required Flags: Well-known. 1283 Potential Flags: Link-State Encapsulation (when flooding). 1284 TRIP Type Code: 2 1286 The ReachableRoutes attribute MUST be included in every UPDATE 1287 message. It specifies a set of routes that are to be added to service 1288 by the receiving LS(s). The set of routes MAY be empty, this is 1289 indicated by setting the length field to zero. 1291 5.2.1. Syntax of ReachableRoutes 1293 The ReachableRoutes Attribute has the same syntax as the 1294 WithdrawnRoutes Attribute. See Section 5.1.1. 1296 5.2.2. Route Origination and ReachableRoutes 1298 Routes are injected into TRIP by a method outside the scope of this 1299 specification. Possible methods include a front-end protocol, an 1300 intra-domain routing protocol, or static configuration. 1302 5.2.3. Route Selection and ReachableRoutes 1304 The routes in ReachableRoutes are necessary for route selection. 1306 5.2.4. Aggregation and ReachableRoutes 1308 To aggregate multiple routes, the set of ReachableRoutes to be 1309 aggregated MUST combine to form a less specific set. 1311 There is no mechanism within TRIP to communicate that a particular 1312 address prefix is not used and thus that these addresses could be 1313 skipped during aggregation. LSs MAY use methods outside of TRIP to 1314 learn of invalid prefixes that may be ignored during aggregation. 1316 If an LS advertises an aggregated route, it MUST include the 1317 AtomicAggregate attribute. 1319 5.2.5. Route Dissemination and ReachableRoutes 1321 The ReachableRoutes attribute is recomputed at each LS except where 1322 flooding is being used (e.g., within a domain). It is therefore 1323 possible for an LS to change Application Protocol field of a route 1324 before advertising that route to an external peer. 1326 If an LS changes the Application Protocol of a route it advertises, 1327 it MUST include the ConvertedRoute attribute in the UPDATE message. 1329 5.2.6. Aggregation Specifics for Decimal Routing Numbers, E.164 Numbers, 1330 and PentaDecimal Routing Numbers 1332 An LS that has routes to all valid numbers in a specific prefix 1333 SHOULD advertise that prefix as the ReachableRoutes, even if there 1334 are more specific prefixes that do not actually exist on the PSTN. 1335 Generally, it takes 10 Decimal Routing/E.164 prefixes, or 15 1336 PentaDecimal Routing prefixes, of length n to aggregate into a prefix 1337 of length n-1. However, if an LS is aware that a prefix is an invalid 1338 Decimal Routing/E.164 prefix, or PentaDecimal Routing prefix, then 1339 the LS MAY aggregate by skipping this prefix. For example, if the 1340 Decimal Routing prefix 19191 is known not to exist, then an LS can 1341 aggregate to 1919 without 19191. A prefix representing an invalid set 1342 of PSTN destinations is sometimes referred to as a "black-hole." 1343 The method by which an LS is aware of black-holes is not within the 1344 scope of TRIP, but if an LS has such knowledge, it can use the 1345 knowledge when aggregating. 1347 5.3. NextHopServer 1349 Conditional Mandatory: True (if ReachableRoutes and/or 1350 WithdrawnRoutes attribute is present). 1351 Required Flags: Well-known. 1352 Potential Flags: None. 1353 TRIP Type Code: 3. 1355 Given a route with application protocol A and destinations D, the 1356 NextHopServer indicates the next-hop that messages of protocol A 1357 destined for D should be sent. This may or may not represent the 1358 ultimate destination of those messages. 1360 5.3.1. NextHopServer Syntax 1362 For generality, the address of the next-hop server may be of various 1363 types (domain name, IPv4, IPv6, etc). The NextHopServer attribute 1364 includes the ITAD number of next-hop server, a length field , and a 1365 next-hop name or address. 1367 The syntax for the NextHopServer is given in Figure 13. 1369 0 1 2 3 1370 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1371 +---------------+---------------+--------------+----------------+ 1372 | Next Hop ITAD | 1373 +---------------+---------------+--------------+----------------+ 1374 | Length | Server (variable) ... 1375 +---------------+---------------+--------------+----------------+ 1377 Figure 13: NextHopServer Syntax 1379 The Next-Hop ITAD indicates the domain of the next-hop. Length field 1380 gives the number of octets in the Server field, and the Server field 1381 contains the name or address of the next-hop server. The server field 1382 is represented as a string of ASCII characters. It is defined as 1383 follows: 1385 Server = host [":" port ] 1386 host = < A legal Internet host domain name 1387 or an IPv4 address using the textual representation 1388 defined in Section 2.1 of RFC 1123 [9] 1389 or an IPv6 address using the textual representation 1390 defined in Section 2.2 of RFC 2373 [10]. The IPv6 1391 address MUST be enclosed in "[" and "]" 1392 characters.> 1393 port = *DIGIT 1395 If the port is empty or not given, the default port is assumed (e.g., 1396 port 5060 if the application protocol is SIP). 1398 5.3.2. Route Origination and NextHopServer 1400 When an LS originates a routing object into TRIP, it MUST include a 1401 NextHopServer within its domain. The NextHopServer could be an 1402 address of the egress gateway or of a signaling proxy. 1404 5.3.3. Route Selection and NextHopServer 1406 LS policy may prefer certain next-hops or next-hop domains over 1407 others. 1409 5.3.4. Aggregation and NextHopServer 1411 When aggregating multiple routing objects into a single routing 1412 object, an LS MUST insert a new signaling server from within its 1413 domain as the new NextHopServer unless all of the routes being 1414 aggregated have the same next-hop. 1416 5.3.5. Route Dissemination and NextHopServer 1418 When propagating routing objects to peers, an LS may choose to insert 1419 a signaling proxy within its domain as the new next-hop, or it may 1420 leave the next-hop unchanged. Inserting a new next-hop will cause the 1421 signaling messages to be sent to that address, and will provide finer 1422 control over the signaling path. Leaving the next-hop unchanged will 1423 yield a more efficient signaling path (fewer hops). It is a local 1424 policy decision of the LS to decide whether to propagate or change 1425 the NextHopServer. 1427 5.4. AdvertisementPath 1429 Conditional Mandatory: True (if ReachableRoutes and/or 1430 WithdrawnRoutes attribute is present). 1431 Required Flags: Well-known. 1432 Potential Flags: None. 1433 TRIP Type Code: 4. 1435 This attribute identifies the ITADs through which routing information 1436 carried in an advertisement has passed. The AdvertisementPath 1437 attribute is analogous to the AS_PATH attribute in BGP. The 1438 attributes differ in that BGP's AS_PATH also reflects the path to the 1439 destination. In TRIP, not every domain need modify the next-hop, so 1440 the AdvertisementPath may include many more hops than the actual path 1441 to the destination. The RoutedPath attribute (Section 5.5) reflects 1442 the actual path to the destination. 1444 5.4.1. AdvertisementPath Syntax 1446 AdvertisementPath is a variable length attribute that is composed of 1447 a sequence of ITAD path segments. Each ITAD path segment is 1448 represented by a type-length-value triple. 1450 The path segment type is a 1-octet long field with the following 1451 values defined: 1453 Value Segment Type 1454 1 AP_SET: unordered set of ITADs a route in the 1455 advertisement message has traversed 1456 2 AP_SEQUENCE: ordered set of ITADs a route in 1457 the advertisement message has traversed 1459 The path segment length is a 1-octet long field containing the number 1460 of ITADs in the path segment value field. 1462 The path segment value field contains one or more ITAD numbers, each 1463 encoded as a 4-octets long field. ITAD numbers uniquely identify an 1464 Internet Telephony Administrative Domain, and must be obtained from 1465 IANA. See Section 13 for procedures to obtain an ITAD number from 1466 IANA. 1468 5.4.2. Route Origination and AdvertisementPath 1470 When an LS originates a route then: 1472 - The originating LS shall include its own ITAD number in the 1473 AdvertisementPath attribute of all advertisements sent to LSs 1474 located in neighboring ITADs. In this case, the ITAD number of 1475 the originating LS's ITAD will be the only entry in the 1476 AdvertisementPath attribute. 1477 - The originating LS shall include an empty AdvertisementPath 1478 attribute in all advertisements sent to LSs located in its own 1479 ITAD. An empty AdvertisementPath attribute is one whose length 1480 field contains the value zero. 1482 5.4.3. Route Selection and AdvertisementPath 1484 The AdvertisementPath may be used for route selection. Possible 1485 criteria to be used are the number of hops on the path and the 1486 presence or absence of particular ITADs on the path. 1488 As discussed in Section 10, the AdvertisementPath is used to prevent 1489 routing information from looping. If an LS receives a route with its 1490 own ITAD already in the AdvertisementPath, the route MUST be 1491 discarded. 1493 5.4.4. Aggregation and AdvertisementPath 1495 The rules for aggregating AdvertisementPath attributes are given in 1496 the following sections, where the term "path" used in Section 5.4.4.1 1497 and 5.4.4.2 is understood to mean AdvertisementPath. 1499 5.4.4.1. Aggregating Routes with Identical Paths 1501 If all routes to be aggregated have identical path attributes, then 1502 the aggregated route has the same path attribute as the individual 1503 routes. 1505 5.4.4.2. Aggregating Routes with Different Paths 1507 For the purpose of aggregating path attributes we model each ITAD 1508 within the path as a pair , where "type" identifies a 1509 type of the path segment (AP_SEQUENCE or AP_SET), and "value" is the 1510 ITAD number. Two ITADs are said to be the same if their corresponding 1511 are the same. 1513 If the routes to be aggregated have different path attributes, then 1514 the aggregated path attribute shall satisfy all of the following 1515 conditions: 1517 - All pairs of the type AP_SEQUENCE in the aggregated path MUST 1518 appear in all of the paths of routes to be aggregated. 1519 - All pairs of the type AP_SET in the aggregated path MUST appear 1520 in at least one of the paths of the initial set (they may appear 1521 as either AP_SET or AP_SEQUENCE types). 1522 - For any pair X of the type AP_SEQUENCE that precedes pair Y in 1523 the aggregated path, X precedes Y in each path of the initial set 1524 that contains Y, regardless of the type of Y. 1525 - No pair with the same value shall appear more than once in the 1526 aggregated path, regardless of the pair's type. 1528 An implementation may choose any algorithm that conforms to these 1529 rules. At a minimum a conformant implementation MUST be able to 1530 perform the following algorithm that meets all of the above 1531 conditions: 1533 - Determine the longest leading sequence of tuples (as defined 1534 above) common to all the paths of the routes to be aggregated. 1535 Make this sequence the leading sequence of the aggregated path. 1536 - Set the type of the rest of the tuples from the paths of the 1537 routes to be aggregated to AP_SET, and append them to the 1538 aggregated path. 1539 - If the aggregated path has more than one tuple with the same 1540 value (regardless of tuple's type), eliminate all but one such 1541 tuple by deleting tuples of the type AP_SET from the aggregated 1542 path. 1544 An implementation that chooses to provide a path aggregation 1545 algorithm that retains significant amounts of path information 1546 may wish to use the procedure of Section 5.4.4.3. 1548 5.4.4.3. Example Path Aggregation Algorithm 1550 An example algorithm to aggregate two paths works as follows: 1552 - Identify the ITADs (as defined in Section 5.4.1) within each path 1553 attribute that are in the same relative order within both path 1554 attributes. Two ITADs, X and Y, are said to be in the same order 1555 if either X precedes Y in both paths, or if Y precedes X in both 1556 paths. 1557 - The aggregated path consists of ITADs identified in (a) in 1558 exactly the same order as they appear in the paths to be 1559 aggregated. If two consecutive ITADs identified in (a) do not 1560 immediately follow each other in both of the paths to be 1561 aggregated, then the intervening ITADs (ITADs that are between 1562 the two consecutive ITADs that are the same) in both attributes 1563 are combined into an AP_SET path segment that consists of the 1564 intervening ITADs from both paths; this segment is then placed in 1565 between the two consecutive ITADs identified in (a) of the 1566 aggregated attribute. If two consecutive ITADs identified in (a) 1567 immediately follow each other in one attribute, but do not follow 1568 in another, then the intervening ITADs of the latter are combined 1569 into an AP_SET path segment; this segment is then placed in 1570 between the two consecutive ITADs identified in (a) of the 1571 aggregated path. 1573 If as a result of the above procedure a given ITAD number appears 1574 more than once within the aggregated path, all, but the last instance 1575 (rightmost occurrence) of that ITAD number should be removed from the 1576 aggregated path. 1578 5.4.5. Route Dissemination and AdvertisementPath 1580 When an LS propagates a route which it has learned from another LS, 1581 it shall modify the route's AdvertisementPath attribute based on the 1582 location of the LS to which the route will be sent. 1584 - When a LS advertises a route to another LS located in its own 1585 ITAD, the advertising LS MUST NOT modify the AdvertisementPath 1586 attribute associated with the route. 1587 - When a LS advertises a route to an LS located in a neighboring 1588 ITAD, then the advertising LS MUST update the AdvertisementPath 1589 attribute as follows: 1591 * If the first path segment of the AdvertisementPath is of type 1592 AP_SEQUENCE, the local system shall prepend its own ITAD 1593 number as the last element of the sequence (put it in the 1594 leftmost position). 1595 * If the first path segment of the AdvertisementPath is of type 1596 AP_SET, the local system shall prepend a new path segment of 1597 type AP_SEQUENCE to the AdvertisementPath, including its own 1598 ITAD number in that segment. 1600 5.5. RoutedPath 1602 Conditional Mandatory: True (if ReachableRoutes attribute is present). 1603 Required Flags: Well-known. 1604 Potential Flags: None. 1605 TRIP Type Code: 5. 1607 This attribute identifies the ITADs through which messages sent using 1608 this route would pass. The ITADs in this path are a subset of those 1609 in the AdvertisementPath. 1611 5.5.1. RoutedPath Syntax 1613 The syntax of the RoutedPath attribute is the same as that of the 1614 AdvertisementPath attribute. See Section 5.4.1. 1616 5.5.2. Route Origination and RoutedPath 1618 When an LS originates a route it MUST include the RoutedPath 1619 attribute. 1621 - The originating LS shall include its own ITAD number in the 1622 RoutedPath attribute of all advertisements sent to LSs located in 1623 neighboring ITADs. In this case, the ITAD number of the 1624 originating LS's ITAD will be the only entry in the RoutedPath 1625 attribute. 1626 - The originating LS shall include an empty RoutedPath attribute in 1627 all advertisements sent to LSs located in its own ITAD. An empty 1628 RoutedPath attribute is one whose length field contains the value 1629 zero. 1631 5.5.3. Route Selection and RoutedPath 1633 The RoutedPath MAY be used for route selection, and in most cases is 1634 preferred over the AdvertisementPath for this role. Some possible 1635 criteria to be used are the number of hops on the path and the 1636 presence or absence of particular ITADs on the path. 1638 5.5.4. Aggregation and RoutedPath 1640 The rules for aggregating RoutedPath attributes are given in Section 1641 5.4.4.1 and 5.4.4.2, where the term "path" used in Section 5.4.4.1 1642 and 5.4.4.2 is understood to mean RoutedPath. 1644 5.5.5. Route Dissemination and RoutedPath 1646 When an LS propagates a route that it learned from another LS, it 1647 modifies the route's RoutedPath attribute based on the location of 1648 the LS to which the route is sent. 1650 - When a LS advertises a route to another LS located in its own 1651 ITAD, the advertising LS MUST NOT modify the RoutedPath attribute 1652 associated with the route. 1653 - If the LS has not changed the NextHopServer attribute, then the 1654 LS MUST NOT change the RoutedPath attribute. 1655 - Otherwise, the LS changed the NextHopServer and is advertising 1656 the route to an LS in another ITAD. The advertising LS MUST 1657 update the RoutedPath attribute as follows: 1659 * If the first path segment of the RoutedPath is of type 1660 AP_SEQUENCE, the local system shall prepend its own ITAD 1661 number as the last element of the sequence (put it in the 1662 leftmost position). 1664 * If the first path segment of the RoutedPath is of type 1665 AP_SET, the local system shall prepend a new path segment of 1666 type AP_SEQUENCE to the RoutedPath, including its own ITAD 1667 number in that segment. 1669 5.6. AtomicAggregate 1671 Conditional Mandatory: False. 1672 Required Flags: Well-known. 1673 Potential Flags: None. 1674 TRIP Type Code: 6. 1676 The AtomicAggregate attribute indicates that a route may traverse 1677 domains not listed in the RoutedPath. If an LS, when presented with a 1678 set of overlapping routes from a peer LS, selects the less specific 1679 route without selecting the more specific route, then the LS includes 1680 the AtomicAggregate attribute with the routing object. 1682 5.6.1. AtomicAggregate Syntax 1684 This attribute has length zero (0); the value field is empty. 1686 5.6.2. Route Origination and AtomicAggregate 1688 Routes are never originated with the AtomicAggregate attribute. 1690 5.6.3. Route Selection and AtomicAggregate 1692 The AtomicAggregate attribute may be used in route selection - it 1693 indicates that the RoutedPath may be incomplete. 1695 5.6.4. Aggregation and AtomicAggregate 1697 If any of the routes to aggregate has the AtomicAggregate attribute, 1698 then so MUST the resultant aggregate. 1700 5.6.5. Route Dissemination and AtomicAggregate 1702 If an LS, when presented with a set of overlapping routes from a peer 1703 LS, selects the less specific route (see Section 0) without selecting 1704 the more specific route, then the LS MUST include the AtomicAggregate 1705 attribute with the routing object (if it is not already present). 1707 An LS receiving a routing object with an AtomicAggregate attribute 1708 MUST NOT make the set of destinations more specific when advertising 1709 it to other LSs, and MUST NOT remove the attribute when propagating 1710 this object to a peer LS. 1712 5.7. LocalPreference 1714 Conditional Mandatory: False. 1715 Required Flags: Well-known. 1716 Potential Flags: None. 1717 TRIP Type Code: 7. 1719 The LocalPreference attribute is only used intra-domain, it indicates 1720 the local LS's preference for the routing object to other LSs within 1721 the same domain. This attribute MUST NOT be included when 1722 communicating to an LS in another domain, and MUST be included over 1723 intra-domain links. 1725 5.7.1. LocalPreference Syntax 1727 The LocalPreference attribute is a 4-octet unsigned numeric value. A 1728 higher value indicates a higher preference. 1730 5.7.2. Route Origination and LocalPreference 1732 Routes MUST NOT be originated with the LocalPreference attribute to 1733 inter-domain peers. Routes to intra-domain peers MUST be originated 1734 with the LocalPreference attribute. 1736 5.7.3. Route Selection and LocalPreference 1738 The LocalPreference attribute allows one LS in a domain to calculate 1739 a preference for a route, and to communicate this preference to other 1740 LSs within the domain. 1742 5.7.4. Aggregation and LocalPreference 1744 The LocalPreference attribute is not affected by aggregation. 1746 5.7.5. Route Dissemination and LocalPreference 1748 An LS MUST include the LocalPreference attribute when communicating 1749 with peer LSs within its own domain. An LS MUST NOT include the 1750 LocalPreference attribute when communicating with LSs in other 1751 domains. LocalPreference attributes received from inter-domain peers 1752 MUST be ignored. 1754 5.8. MultiExitDisc 1756 Conditional Mandatory: False. 1757 Required Flags: Well-known. 1758 Potential Flags: None. 1759 TRIP Type Code: 8. 1761 When two ITADs are connected by more than one set of peers, the 1762 MultiExitDisc attribute may be used to specify preferences for routes 1763 received over one of those links versus routes received over other 1764 links. The MultiExitDisc parameter is used only for route selection. 1766 5.8.1. MultiExitDisc Syntax 1768 The MultiExitDisc attribute carries a 4-octet unsigned numeric value. 1769 A higher value represents a more preferred routing object. 1771 5.8.2. Route Origination and MultiExitDisc 1773 Routes originated to intra-domain peers MUST NOT be originated with 1774 the MultiExitDisc attribute. When originating a route to an inter- 1775 domain peer, the MultiExitDisc attribute may be included. 1777 5.8.3. Route Selection and MultiExitDisc 1779 The MultiExitDisc attribute is used to express a preference when 1780 there are multiple links between two domains. If all other factors 1781 are equal, then a route with a higher MultiExitDisc attribute is 1782 preferred over a route with a lower MultiExitDisc attribute. 1784 5.8.4. Aggregation and MultiExitDisc 1786 Routes with differing MultiExitDisc parameters MUST NOT be 1787 aggregated. Routes with the same value in the MultiExitDisc attribute 1788 MAY be aggregated and the same MultiExitDisc attribute attached to 1789 the aggregated object. 1791 5.8.5. Route Dissemination and MultiExitDisc 1793 If received from a peer LS in another domain, an LS MAY propagate the 1794 MultiExitDisc to other LSs within its domain. The MultiExitDisc 1795 attribute MUST NOT be propagated to LSs in other domains. 1797 An LS may add the MultiExitDisc attribute when propagating routing 1798 objects to an LS in another domain. The inclusion of the 1799 MultiExitDisc attribute is a matter of policy, as is the value of the 1800 attribute. 1802 5.9. Communities 1804 Conditional Mandatory: False. 1805 Required Flags: Not Well-Known, Independent Transitive. 1806 Potential Flags: None. 1807 TRIP Type Code: 9. 1809 A community is a group of destinations that share some common 1810 property. 1812 The Communities attribute is used to group destinations so that the 1813 routing decision can be based on the identity of the group. Using the 1814 Communities attribute should significantly simplify the distribution 1815 of routing information by providing an administratively defined 1816 aggregation unit. 1818 Each ITAD administrator may define the communities to which a 1819 particular route belongs. By default, all routes belong to the 1820 general Internet Telephony community. 1822 As an example, the Communities attribute could be used to define an 1823 alliance between a group of Internet Telephony service providers for 1824 a specific subset of routing information. In this case, members of 1825 that alliance would accept only routes for destinations in this group 1826 that are advertised by other members of the alliance. Other 1827 destinations would be more freely accepted. To achieve this, a member 1828 would tag each route with a designated Community attribute value 1829 before disseminating it. This relieves the members of such an 1830 alliance from the responsibility of keeping track of the identities 1831 of all other members of that alliance. 1833 Another example use of the Communities attribute is with aggregation. 1834 It is often useful to advertise both the aggregate route and the 1835 component more-specific routes that were used to form the aggregate. 1836 These component information are only useful to the neighboring TRIP 1837 peer, and perhaps the ITAD of the neighboring TRIP peer, so it is 1838 desirable to filter out the component routes. This can be achieved by 1839 specifying a Community attribute value that the neighboring peers 1840 will match and filter on. That way it can be assured that the more 1841 specific routes will not propagate beyond their desired scope. 1843 5.9.1. Syntax of Communities 1845 The Communities attribute is of variable length. It consists of set 1846 of 8-octet values, each of which specifies a community. The first 4 1847 octets of the Community value are the Community ITAD Number and the 1848 next 4 octets are the Community ID. 1850 0 1 2 3 1851 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1852 +---------------+---------------+--------------+----------------+ 1853 | Community ITAD Number 1 | 1854 +---------------+---------------+--------------+----------------+ 1855 | Community ID 1 | 1856 +---------------+---------------+--------------+----------------+ 1857 | . . . . . . . . . 1858 +---------------+---------------+--------------+----------------+ 1860 Figure 14: Communities Syntax 1862 For administrative assignment, the following assumptions may be made: 1864 The Community attribute values starting with a Community ITAD 1865 Number of 0x00000000 are hereby reserved. 1867 The following communities have global significance and their 1868 operation MUST be implemented in any Community attribute-aware TRIP 1869 LS. 1871 - NO_EXPORT (Community ITAD Number = 0x00000000 and Community ID = 1872 0xFFFFFF01). Any received route with a community attribute 1873 containing this value MUST NOT be advertised outside of the 1874 receiving TRIP ITAD. 1876 Other community values MUST be encoded using an ITAD number in the 1877 four most significant octets. The semantics of the final four octets 1878 (the Community ID octets) may be defined by the ITAD (e.g., ITAD 690 1879 may define research, educational, and commercial community IDs that 1880 may be used for policy routing as defined by the operators of that 1881 ITAD). 1883 5.9.2. Route Origination and Communities 1885 The Communities attribute is not well-known. If a route has a 1886 Communities attribute associated with it, the LS MUST include that 1887 attribute in advertisement it originates. 1889 5.9.3. Route Selection and Communities 1891 The Communities attribute may be used for route selection. A route 1892 that is a member of a certain community may be preferred over another 1893 route that is not a member of that community. Likewise, routes 1894 without a certain community value may be excluded from consideration. 1896 5.9.4. Aggregation and Communities 1898 If a set of routes is to be aggregated and the resultant aggregate 1899 does not carry an Atomic_Aggregate attribute, then the resulting 1900 aggregate should have a Communities attribute that contains the union 1901 of the Community attributes of the aggregated routes. 1903 5.9.5. Route Dissemination and Communities 1905 An LS may manipulate the Communities attribute before disseminating a 1906 route to a peer. Community attribute manipulation may include adding 1907 communities, removing communities, adding a Communities attribute (if 1908 none exists), deleting the Communities attribute, etc. 1910 5.10. ITAD Topology 1912 Conditional Mandatory: False. 1913 Required Flags: Well-known, Link-State encapsulated. 1914 Potential Flags: None. 1915 TRIP Type Code: 10. 1917 Within an ITAD, each LS must know the status of other LSs so that LS 1918 failure can be detected. To do this, each LS advertises its internal 1919 topology to other LSs within the domain. When an LS detects that 1920 another LS is no longer active, the information sourced by that LS 1921 can be deleted (the Adj-TRIB-In for that peer may be cleared). The 1922 ITAD Topology attribute is used to communicate this information to 1923 other LSs within the domain. 1925 An LS MUST send a topology update each time it detects a change in 1926 its internal peer set. The topology update may be sent in an UPDATE 1927 message by itself or it may be piggybacked on an UPDATE message which 1928 includes ReachableRoutes and/or WithdrawnRoutes information. 1930 When an LS receives a topology update from an internal LS, it MUST 1931 recalculate to which LSs are active within their domain via a 1932 connectivity algorithm on the topology. 1934 5.10.1. ITAD Topology Syntax 1936 The ITAD Topology attribute indicates the LSs with which the LS is 1937 currently peering. The attribute consists of a list of the TRIP 1938 Identifiers with which the LS is currently peering, the format is 1939 given in Figure 15. This attribute MUST use the link-state 1940 encapsulation as defined in Section 4.3.2.4. 1942 0 1 2 3 1943 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 1944 +---------------+---------------+--------------+----------------+ 1945 | TRIP Identifier 1 | 1946 +---------------+---------------+--------------+----------------+ 1947 | TRIP Identifier 2 ... | 1948 +---------------+---------------+--------------+----------------+ 1950 Figure 15: ITAD Topology Syntax 1952 5.10.2. Route Origination and ITAD Topology 1954 The ITAD Topology attribute is independent of any routes in the 1955 UPDATE. Whenever the set of internal peers of a LS changes, it 1956 MUST 1957 originate an UPDATE with the ITAD Topology Attribute included 1958 listing the current set of internal peers. The LS MUST include 1959 this attribute in the first UPDATE it sends to a peer after the 1960 peering session is established. 1962 5.10.3. Route Selection and ITAD Topology 1964 This attribute is independent of any routing information in the 1965 UPDATE. When an LS receives an UPDATE with an ITAD Topology 1966 attribute, it MUST compute the set of LSs currently active in the 1967 domain by performing a connectivity test on the ITAD topology as 1968 given by the set of originated ITAD Topology attributes. The LS MUST 1969 locally purge the Adj-TRIB-In for any LS that is no longer active in 1970 the domain. The LS MUST NOT propagate this purging information to 1971 other LSs as they will make a similar decision. 1973 5.10.4. Aggregation and ITAD Topology 1975 This information is not aggregated. 1977 5.10.5. Route Dissemination and ITAD Topology 1979 An LS MUST ignore the attribute if received from a peer in another 1980 domain. An LS MUST NOT send this attribute to an inter-domain peer. 1982 5.11. ConvertedRoute 1984 Conditional Mandatory: False. 1985 Required Flags: Well-known. 1986 Potential Flags: None. 1987 TRIP Type Code: 12. 1989 The ConvertedRoute attribute indicates that an intermediate LS has 1990 altered the route by changing the route's Application Protocol. For 1991 example, if an LS receives a route with Application Protocol X and 1992 changes the Application Protocol to Y before advertising the route to 1993 an external peer, the LS MUST include the ConvertedRoute attribute. 1994 The attribute is an indication that the advertised application 1995 protocol will not be used end-to-end, i.e., the information 1996 advertised about this route is not complete. 1998 5.11.1. ConvertedRoute Syntax 2000 This attribute has length zero (0); the value field is empty. 2002 5.11.2. Route Origination and ConvertedRoute 2004 Routes are never originated with the ConvertedRoute attribute. 2006 5.11.3. Route Selection and ConvertedRoute 2008 The ConvertedRoute attribute may be used in route selection - it 2009 indicates that advertised routing information is not complete. 2011 5.11.4. Aggregation and ConvertedRoute 2013 If any of the routes to aggregate has the ConvertedRoute attribute, 2014 then so MUST the resultant aggregate. 2016 5.11.5. Route Dissemination and ConvertedRoute 2018 If an LS changes the Application Protocol of route before advertising 2019 the route to an external peer, the LS MUST include the ConvertedRoute 2020 attribute. 2022 5.12. Considerations for Defining New TRIP Attributes 2024 Any proposal for defining new TRIP attributes should specify the 2025 following: 2027 - the use of this attribute, 2028 - the attribute's flags, 2029 - the attribute's syntax, 2030 - how the attribute works with route origination, 2031 - how the attribute works with route aggregation, and 2032 - how the attribute works with route dissemination and the 2033 attribute's scope (e.g., intra-domain only like LocalPreference) 2035 IANA will manage the assignment of TRIP attribute type codes to new 2036 attributes. 2038 6. TRIP Error Detection and Handling 2040 This section describes errors to be detected and the actions to be 2041 taken while processing TRIP messages. 2043 When any of the conditions described here are detected, a 2044 NOTIFICATION message with the indicated Error Code, Error Subcode, 2045 and Data fields MUST be sent, and the TRIP connection MUST be closed. 2046 If no Error Subcode is specified, then a zero Subcode MUST be used. 2048 The phrase "the TRIP connection is closed" means that the transport 2049 protocol connection has been closed and that all resources for that 2050 TRIP connection have been de-allocated. If the connection was inter- 2051 domain, then routing table entries associated with the remote peer 2052 MUST be marked as invalid. Routing table entries MUST NOT be marked 2053 as invalid if an internal peering session is terminated. The fact 2054 that the routes have been marked as invalid is passed to other TRIP 2055 peers before the routes are deleted from the system. 2057 Unless specified explicitly, the Data field of the NOTIFICATION 2058 message that is sent to indicate an error MUST be empty. 2060 6.1. Message Header Error Detection and Handling 2062 All errors detected while processing the Message Header are indicated 2063 by sending the NOTIFICATION message with Error Code Message Header 2064 Error. The Error Subcode elaborates on the specific nature of the 2065 error. The error checks in this section MUST be performed by each LS 2066 on receipt of every message. 2068 If the Length field of the message header is less than 3 or greater 2069 than 4096, or if the Length field of an OPEN message is less than the 2070 minimum length of the OPEN message, or if the Length field of an 2071 UPDATE message is less than the minimum length of the UPDATE message, 2072 or if the Length field of a KEEPALIVE message is not equal to 3, or 2073 if the Length field of a NOTIFICATION message is less than the 2074 minimum length of the NOTIFICATION message, then the Error Subcode 2075 MUST be set to Bad Message Length. The Data field contains the 2076 erroneous Length field. 2078 If the Type field of the message header is not recognized, then the 2079 Error Subcode MUST be set to "Bad Message Type." The Data field 2080 contains the erroneous Type field. 2082 6.2. OPEN Message Error Detection and Handling 2084 All errors detected while processing the OPEN message are indicated 2085 by sending the NOTIFICATION message with Error Code "OPEN Message 2086 Error." The Error Subcode elaborates on the specific nature of the 2087 error. The error checks in this section MUST be performed by each LS 2088 on receipt of every OPEN message. 2090 If the version number contained in the Version field of the received 2091 OPEN message is not supported, then the Error Subcode MUST be set to 2092 "Unsupported Version Number." The Data field is a 1-octet unsigned 2093 integer, which indicates the largest locally supported version number 2094 less than the version the remote TRIP peer bid (as indicated in the 2095 received OPEN message). 2097 If the ITAD field of the OPEN message is unacceptable, then the Error 2098 Subcode MUST be set to "Bad Peer ITAD." The determination of 2099 acceptable ITAD numbers is outside the scope of this protocol. 2101 If the Hold Time field of the OPEN message is unacceptable, then the 2102 Error Subcode MUST be set to "Unacceptable Hold Time." An 2103 implementation MUST reject Hold Time values of one or two seconds. An 2104 implementation MAY reject any proposed Hold Time. An implementation 2105 that accepts a Hold Time MUST use the negotiated value for the Hold 2106 Time. 2108 If the TRIP Identifier field of the OPEN message is not valid, then 2109 the Error Subcode MUST be set to "Bad TRIP Identifier." A TRIP 2110 identifier is 4-octets and can take any value. An LS considers the 2111 TRIP Identifier invalid if it has an already open connection with 2112 another peer LS that has the same ITAD and TRIP Identifier. 2114 Any two LSs within the same ITAD MUST NOT have equal TRIP Identifier 2115 values. This restriction does not apply to LSs in different ITADs 2116 since the purpose is to uniquely identify an LS using its TRIP 2117 Identifier and its ITAD number. 2119 If one of the Optional Parameters in the OPEN message is not 2120 recognized, then the Error Subcode MUST be set to "Unsupported 2121 Optional Parameters." 2123 If the Optional Parameters of the OPEN message include Capability 2124 Information with an unsupported capability (unsupported in either 2125 capability type or value), then the Error Subcode MUST be set to 2126 "Unsupported Capability," and the entirety of the unsupported 2127 capabilities MUST be listed in the Data field of the NOTIFICATION 2128 message. 2130 If the Optional Parameters of the OPEN message include Capability 2131 Information which do not match the receiving LS's capabilities, then 2132 the Error Subcode MUST be set to "Capability Mismatch," and the 2133 entirety of the mismatched capabilities MUST be listed in the Data 2134 field of the NOTIFICATION message. 2136 6.3. UPDATE Message Error Detection and Handling 2138 All errors detected while processing the UPDATE message are indicated 2139 by sending the NOTIFICATION message with Error Code "UPDATE Message 2140 Error." The Error Subcode elaborates on the specific nature of the 2141 error. The error checks in this section MUST be performed by each LS 2142 on receipt of every UPDATE message. These error checks MUST occur 2143 before flooding procedures are invoked with internal peers. 2145 If any recognized attribute has Attribute Flags that conflict with 2146 the Attribute Type Code, then the Error Subcode MUST be set to 2147 "Attribute Flags Error." The Data field contains the erroneous 2148 attribute (type, length and value). 2150 If any recognized attribute has Attribute Length that conflicts with 2151 the expected length (based on the attribute type code), then the 2152 Error Subcode MUST be set to "Attribute Length Error." The Data 2153 field contains the erroneous attribute (type, length and value). 2155 If any of the mandatory (i.e., conditional mandatory attribute and 2156 the conditions for including it in the UPDATE message are fulfilled) 2157 well-known attributes are not present, then the Error Subcode MUST be 2158 set to "Missing Well-known Mandatory Attribute." The Data field 2159 contains the Attribute Type Code of the missing well-known 2160 conditional mandatory attributes. 2162 If any of the well-known attributes are not recognized, then the 2163 Error Subcode MUST be set to "Unrecognized Well-known Attribute." The 2164 Data field contains the unrecognized attribute (type, length and 2165 value). 2167 If any attribute has a syntactically incorrect value, or an undefined 2168 value, then the Error Subcode is set to "Invalid Attribute." The 2169 Data field contains the incorrect attribute (type, length and value). 2170 Such a NOTIFICATION message is sent, for example, when a 2171 NextHopServer attribute is received with an invalid address. 2173 The information carried by the AdvertisementPath attribute is checked 2174 for ITAD loops. ITAD loop detection is done by scanning the full 2175 AdvertisementPath, and checking that the ITAD number of the local 2176 ITAD does not appear in the AdvertisementPath. If the local ITAD 2177 number appears in the AdvertisementPath, then the route MAY be stored 2178 in the Adj-TRIB-In, but unless the LS is configured to accept routes 2179 with its own ITAD in the advertisement path, the route MUST not be 2180 passed to the TRIP Decision Process. The operation of an LS that is 2181 configured to accept routes with its own ITAD number in the 2182 advertisement path are outside the scope of this document. 2184 If the UPDATE message was received from an internal peer and either 2185 the WithdrawnRoutes, ReachableRoutes, or ITAD Topology attribute does 2186 not have the Link-State Encapsulation flag set, then the Error 2187 Subcode is set to "Invalid Attribute" and the data field contains the 2188 attribute. Likewise, the attribute is invalid if received from an 2189 external peer and the Link-State Flag is set. 2191 If any attribute appears more than once in the UPDATE message, then 2192 the Error Subcode is set to "Malformed Attribute List." 2194 6.4. NOTIFICATION Message Error Detection and Handling 2196 If a peer sends a NOTIFICATION message, and there is an error in that 2197 message, there is unfortunately no means of reporting this error via 2198 a subsequent NOTIFICATION message. Any such error, such as an 2199 unrecognized Error Code or Error Subcode, should be noticed, logged 2200 locally, and brought to the attention of the administration of the 2201 peer. The means to do this, however, are outside the scope of this 2202 document. 2204 6.5. Hold Timer Expired Error Handling 2206 If a system does not receive successive messages within the period 2207 specified by the negotiated Hold Time, then a NOTIFICATION message 2208 with "Hold Timer Expired" Error Code MUST be sent and the TRIP 2209 connection MUST be closed. 2211 6.6. Finite State Machine Error Handling 2213 An error detected by the TRIP Finite State Machine (e.g., receipt of 2214 an unexpected event) MUST result in sending a NOTIFICATION message 2215 with Error Code "Finite State Machine Error" and the TRIP connection 2216 MUST be closed. 2218 6.7. Cease 2220 In the absence of any fatal errors (that are indicated in this 2221 section), a TRIP peer MAY choose at any given time to close its TRIP 2222 connection by sending the NOTIFICATION message with Error Code 2223 "Cease." However, the Cease NOTIFICATION message MUST NOT be used 2224 when a fatal error indicated by this section exists. 2226 6.8. Connection Collision Detection 2228 If a pair of LSs try simultaneously to establish a transport 2229 connection to each other, then two parallel connections between this 2230 pair of speakers might well be formed. We refer to this situation as 2231 connection collision. Clearly, one of these connections must be 2232 closed. 2234 Based on the value of the TRIP Identifier a convention is established 2235 for detecting which TRIP connection is to be preserved when a 2236 collision occurs. The convention is to compare the TRIP Identifiers 2237 of the peers involved in the collision and to retain only the 2238 connection initiated by the LS with the higher-valued TRIP 2239 Identifier. 2241 Upon receipt of an OPEN message, the local LS MUST examine all of its 2242 connections that are in the OpenConfirm state. An LS MAY also examine 2243 connections in an OpenSent state if it knows the TRIP Identifier of 2244 the peer by means outside of the protocol. If among these connections 2245 there is a connection to a remote LS whose TRIP Identifier equals the 2246 one in the OPEN message, then the local LS MUST perform the following 2247 collision resolution procedure: 2249 The TRIP Identifier and ITAD of the local LS is compared to the TRIP 2250 Identifier and ITAD of the remote LS (as specified in the OPEN 2251 message). TRIP Identifiers are treated as 4-octet unsigned integers 2252 for comparison. 2254 If the value of the local TRIP Identifier is less than the remote 2255 one, or if the two TRIP Identifiers are equal and the value of ITAD 2256 of the local LS is less than value of the ITAD of the remote LS, then 2257 the local LS MUST close the TRIP connection that already exists (the 2258 one that is already in the OpenConfirm state), and accepts the TRIP 2259 connection initiated by the remote LS: 2261 1. Otherwise, the local LS closes newly created TRIP connection 2262 continues to use the existing one (the one that is already in 2263 the OpenConfirm state). 2265 2. If a connection collision occurs with an existing TRIP 2266 connection that is in the Established state, then the LS MUST 2267 unconditionally close of the newly created connection. Note 2268 that a connection collision cannot be detected with connections 2269 that are in Idle, Connect, or Active states. 2270 3. To close the TRIP connection (that results from the collision 2271 resolution procedure), an LS MUST send a NOTIFICATION message 2272 with the Error Code "Cease" and the TRIP connection MUST be 2273 closed. 2275 7. TRIP Version Negotiation 2277 Peer LSs may negotiate the version of the protocol by making multiple 2278 attempts to open a TRIP connection, starting with the highest version 2279 number each supports. If an open attempt fails with an Error Code 2280 "OPEN Message Error" and an Error Subcode "Unsupported Version 2281 Number," then the LS has available the version number it tried, the 2282 version number its peer tried, the version number passed by its peer 2283 in the NOTIFICATION message, and the version numbers that it 2284 supports. If the two peers support one or more common versions, then 2285 this will allow them to rapidly determine the highest common version. 2286 In order to support TRIP version negotiation, future versions of TRIP 2287 must retain the format of the OPEN and NOTIFICATION messages. 2289 8. TRIP Capability Negotiation 2291 An LS MAY include the Capabilities Option in its OPEN message to a 2292 peer to indicate the capabilities supported by the LS. An LS 2293 receiving an OPEN message MUST NOT use any capabilities that were not 2294 included in the OPEN message of the peer when communicating with that 2295 peer. 2297 9. TRIP Finite State Machine 2299 This section specifies TRIP operation in terms of a Finite State 2300 Machine (FSM). Following is a brief summary and overview of TRIP 2301 operations by state as determined by this FSM. A condensed version of 2302 the TRIP FSM is found in Appendix 1. There is a TRIP FSM per peer and 2303 these FSMs operate independently. 2305 Idle state: 2306 Initially TRIP is in the Idle state for each peer. In this state, 2307 TRIP refuses all incoming connections. No resources are allocated to 2308 the peer. In response to the Start event (initiated by either the 2309 system or the operator), the local system initializes all TRIP 2310 resources, starts the ConnectRetry timer, initiates a transport 2311 connection to the peer, starts listening for a connection that may be 2312 initiated by the remote TRIP peer, and changes its state to Connect. 2313 The exact value of the ConnectRetry timer is a local matter, but 2314 should be sufficiently large to allow TCP initialization. 2316 If an LS detects an error, it closes the transport connection and 2317 changes its state to Idle. Transitioning from the Idle state requires 2318 generation of the Start event. If such an event is generated 2319 automatically, then persistent TRIP errors may result in persistent 2320 flapping of the LS. To avoid such a condition, Start events MUST NOT 2321 be generated immediately for a peer that was previously transitioned 2322 to Idle due to an error. For a peer that was previously transitioned 2323 to Idle due to an error, the time between consecutive Start events, 2324 if such events are generated automatically, MUST exponentially 2325 increase. The value of the initial timer SHOULD be 60 seconds, and 2326 the time SHOULD be at least doubled for each consecutive retry up to 2327 some maximum value. 2329 Any other event received in the Idle state is ignored. 2331 Connect state: 2332 In this state, an LS is waiting for a transport protocol connection 2333 to be completed to the peer, and is listening for inbound transport 2334 connections from the peer. 2336 If the transport protocol connection succeeds, the local LS clears 2337 the ConnectRetry timer, completes initialization, sends an OPEN 2338 message to its peer, sets its Hold Timer to a large value, and 2339 changes its state to OpenSent. A Hold Timer value of 4 minutes is 2340 suggested. 2342 If the transport protocol connect fails (e.g., retransmission 2343 timeout), the local system restarts the ConnectRetry timer, continues 2344 to listen for a connection that may be initiated by the remote LS, 2345 and changes its state to Active state. 2347 In response to the ConnectRetry timer expired event, the local LS 2348 cancels any outstanding transport connection to the peer, restarts 2349 the ConnectRetry timer, initiates a transport connection to the 2350 remote LS, continues to listen for a connection that may be initiated 2351 by the remote LS, and stays in the Connect state. 2353 If the local LS detects that a remote peer is trying to establish a 2354 connection to it and the IP address of the peer is not an expected 2355 one, then the local LS rejects the attempted connection and continues 2356 to listen for a connection from its expected peers without changing 2357 state. 2359 If an inbound transport protocol connection succeeds, the local LS 2360 clears the ConnectRetry timer, completes initialization, sends an 2361 OPEN message to its peer, sets its Hold Timer to a large value, and 2362 changes its state to OpenSent. A Hold Timer value of 4 minutes is 2363 suggested. 2365 The Start event is ignored in the Connect state. 2367 In response to any other event (initiated by either the system or the 2368 operator), the local system releases all TRIP resources associated 2369 with this connection and changes its state to Idle. 2371 Active state: 2372 In this state, an LS is listening for an inbound connection from the 2373 peer, but is not in the process of initiating a connection to the 2374 peer. 2376 If an inbound transport protocol connection succeeds, the local LS 2377 clears the ConnectRetry timer, completes initialization, sends an 2378 OPEN message to its peer, sets its Hold Timer to a large value, and 2379 changes its state to OpenSent. A Hold Timer value of 4 minutes is 2380 suggested. 2382 In response to the ConnectRetry timer expired event, the local system 2383 restarts the ConnectRetry timer, initiates a transport connection to 2384 the TRIP peer, continues to listen for a connection that may be 2385 initiated by the remote TRIP peer, and changes its state to Connect. 2387 If the local LS detects that a remote peer is trying to establish a 2388 connection to it and the IP address of the peer is not an expected 2389 one, then the local LS rejects the attempted connection and continues 2390 to listen for a connection from its expected peers without changing 2391 state. 2393 Start event is ignored in the Active state. 2395 In response to any other event (initiated by either the system or the 2396 operator), the local system releases all TRIP resources associated 2397 with this connection and changes its state to Idle. 2399 OpenSent state: 2400 In this state, an LS has sent an OPEN message to its peer and is 2401 waiting for an OPEN message from its peer. When an OPEN message is 2402 received, all fields are checked for correctness. If the TRIP message 2403 header checking or OPEN message checking detects an error (see 2404 Section 6.2) or a connection collision (see Section 6.8), the local 2405 system sends a NOTIFICATION message and changes its state to Idle. 2407 If there are no errors in the OPEN message, TRIP sends a KEEPALIVE 2408 message and sets a KeepAlive timer. The Hold Timer, which was 2409 originally set to a large value (see above), is replaced with the 2410 negotiated Hold Time value (see Section 4.2). If the negotiated Hold 2411 Time value is zero, then the Hold Time timer and KeepAlive timers are 2412 not started. If the value of the ITAD field is the same as the local 2413 ITAD number, then the connection is an "internal" connection; 2414 otherwise, it is "external" (this will affect UPDATE processing). 2415 Finally, the state is changed to OpenConfirm. 2417 If the local LS detects that a remote peer is trying to establish a 2418 connection to it and the IP address of the peer is not an expected 2419 one, then the local LS rejects the attempted connection and continues 2420 to listen for a connection from its expected peers without changing 2421 state. 2423 If a disconnect notification is received from the underlying 2424 transport protocol, the local LS closes the transport connection, 2425 restarts the ConnectRetry timer, continues to listen for a connection 2426 that may be initiated by the remote TRIP peer, and goes into the 2427 Active state. 2429 If the Hold Timer expires, the local LS sends NOTIFICATION message 2430 with Error Code "Hold Timer Expired" and changes its state to Idle. 2432 In response to the Stop event (initiated by either system or 2433 operator) the local LS sends NOTIFICATION message with Error Code 2434 "Cease" and changes its state to Idle. 2436 The Start event is ignored in the OpenSent state. 2438 In response to any other event the local LS sends NOTIFICATION 2439 message with Error Code "Finite State Machine Error" and changes its 2440 state to Idle. 2442 Whenever TRIP changes its state from OpenSent to Idle, it closes the 2443 transport connection and releases all resources associated with that 2444 connection. 2446 OpenConfirm state: 2447 In this state, an LS has sent an OPEN to its peer, received an OPEN 2448 from its peer, and sent a KEEPALIVE in response to the OPEN. The LS 2449 is now waiting for a KEEPALIVE or NOTIFICATION message in response to 2450 its OPEN. 2452 If the local LS receives a KEEPALIVE message, it changes its state to 2453 Established. 2455 If the Hold Timer expires before a KEEPALIVE message is received, the 2456 local LS sends NOTIFICATION message with Error Code "Hold Timer 2457 Expired" and changes its state to Idle. 2459 If the local LS receives a NOTIFICATION message, it changes its state 2460 to Idle. 2462 If the KeepAlive timer expires, the local LS sends a KEEPALIVE 2463 message and restarts its KeepAlive timer. 2465 If a disconnect notification is received from the underlying 2466 transport protocol, the local LS closes the transport connection, 2467 restarts the ConnectRetry timer, continues to listen for a connection 2468 that may be initiated by the remote TRIP peer, and goes into the 2469 Active state. 2471 In response to the Stop event (initiated by either the system or the 2472 operator) the local LS sends NOTIFICATION message with Error Code 2473 "Cease" and changes its state to Idle. 2475 Start event is ignored in the OpenConfirm state. 2477 In response to any other event the local LS sends NOTIFICATION 2478 message with Error Code "Finite State Machine Error" and changes its 2479 state to Idle. 2481 Whenever TRIP changes its state from OpenConfirm to Idle, it closes 2482 the transport connection and releases all resources associated with 2483 that connection. 2485 Established state: 2486 In the Established state, an LS can exchange UPDATE, NOTIFICATION, 2487 and KEEPALIVE messages with its peer. 2489 If the negotiated Hold Timer is zero, then no procedures are 2490 necessary for keeping a peering session alive. If the negotiated Hold 2491 Time value is non-zero, the procedures of this paragraph apply. If 2492 the Hold Timer expires, the local LS sends a NOTIFICATION message 2493 with Error Code "Hold Timer Expired" and changes its state to Idle. 2494 If the KeepAlive Timer expires, then the local LS sends a KeepAlive 2495 message and restarts the KeepAlive Timer. If the local LS receives an 2496 UPDATE or KEEPALIVE message, then it restarts its Hold Timer. Each 2497 time the LS sends an UPDATE or KEEPALIVE message, it restarts its 2498 KeepAlive Timer. 2500 If the local LS receives a NOTIFICATION message, it changes its state 2501 to Idle. 2503 If the local LS receives an UPDATE message and the UPDATE message 2504 error handling procedure (see Section6.3) detects an error, the local 2505 LS sends a NOTIFICATION message and changes its state to Idle. 2507 If a disconnect notification is received from the underlying 2508 transport protocol, the local LS changes its state to Idle. 2510 In response to the Stop event (initiated by either the system or the 2511 operator), the local LS sends a NOTIFICATION message with Error Code 2512 "Cease" and changes its state to Idle. 2514 The Start event is ignored in the Established state. 2516 In response to any other event, the local LS sends NOTIFICATION 2517 message with Error Code "Finite State Machine Error" and changes its 2518 state to Idle. 2520 Whenever TRIP changes its state from Established to Idle, it closes 2521 the transport) connection, releases all resources associated with 2522 that connection. Additionally, if the peer is an external peer, the 2523 LS deletes all routes derived from that connection. 2525 10. UPDATE Message Handling 2527 An UPDATE message may be received only in the Established state. When 2528 an UPDATE message is received, each field is checked for validity as 2529 specified in Section 6.3. The rest of this section presumes that the 2530 UPDATE message has passed the error-checking procedures of Section 2531 6.3. 2533 If the UPDATE message was received from an internal peer, the 2534 flooding procedures of Section 10.1 MUST be applied. The flooding 2535 process synchronizes the Loc-TRIBs of all LSs within the domain. 2536 Certain routes within the UPDATE may be marked as old or duplicates 2537 by the flooding process and are ignored during the rest of the UPDATE 2538 processing. 2540 If the UPDATE message contains withdrawn routes, then the 2541 corresponding previously advertised routes shall be removed from the 2542 Adj-TRIB-In. This LS MUST run its Decision Process since the 2543 previously advertised route is no longer available for use. 2545 If the UPDATE message contains a route, then the route MUST be placed 2546 in the appropriate Adj-TRIB-In, and the following additional actions 2547 MUST be taken: 2549 1. If its destinations are identical to those of a route currently 2550 stored in the Adj-TRIB-In, then the new route MUST replace the 2551 older route in the Adj-TRIB-In, thus implicitly withdrawing the 2552 older route from service. The LS MUST run its Decision Process 2553 since the older route is no longer available for use. 2554 2. If the new route is more specific than an earlier route 2555 contained in the Adj-TRIB-In and has identical attributes, then 2556 no further actions are necessary. 2557 3. If the new route is more specific than an earlier route 2558 contained in the Adj-TRIB-In but does not have identical 2559 attributes, then the LS MUST run its Decision Process since the 2560 more specific route has implicitly made a portion of the less 2561 specific route unavailable for use. 2562 4. If the new route has destinations that are not present in any 2563 of the routes currently stored in the Adj-TRIB-In, then the LS 2564 MUST run its Decision Process. 2565 5. If the new route is less specific than an earlier route 2566 contained in the Adj-TRIB-In, the LS MUST run its Decision 2567 Process on the set of destinations that are described only by 2568 the less specific route. 2570 10.1. Flooding Process 2572 When an LS receives an UPDATE message from an internal peer, the LS 2573 floods the new information from that message to all of its other 2574 internal peers. Flooding is used to efficiently synchronize all of 2575 the LSs within a domain without putting any constraints on the 2576 domain's internal topology. The flooding mechanism is based on the 2577 techniques used in OSPF [4] and SCSP [6]. One may argue that TRIP's 2578 flooding process is in reality a controlled broadcast mechanism. 2580 10.1.1. Database Information 2582 The LS MUST maintain the sequence number and originating TRIP 2583 identifier for each link-state encapsulated attribute in an internal 2584 Adj-TRIB-In. These values are included with the route in the 2585 ReachableRoutes, WithdrawnRoutes, and ITAD Topology attributes. The 2586 originating TRIP identifier gives the internal LS that originated 2587 this route into the ITAD, the sequence number gives the version of 2588 this route at the originating LS. 2590 10.1.2. Determining Newness 2592 For each route in the ReachableRoutes or WithdrawnRoutes field, the 2593 LS decides if the route is new or old. This is determined by 2594 comparing the Sequence Number of the route in the UPDATE with the 2595 Sequence Number of the route saved in the Adj-TRIB-In. The route is 2596 new if either the route does not exist in the Adj-TRIB-In for the 2597 originating LS, or if the route does exist in the Adj-TRIB-In but the 2598 Sequence Number in the UPDATE is greater than the Sequence Number 2599 saved in the Adj-TRIBs-In. Note that the newness test is 2600 independently applied to each link-state encapsulated attribute in 2601 the UPDATE (WithdrawnRoutes or ReachableRoutes). 2603 10.1.3. Flooding 2605 Each route in the ReachableRoutes or WithdrawnRoutes field that is 2606 determined to be old is ignored in further processing. If the route 2607 is determined to be new then the following actions occur. 2609 If the route is being withdrawn, then the LS MUST flood the withdrawn 2610 route to all other internal peers, and MUST mark the route as 2611 withdrawn. An LS MUST maintain routes marked as withdrawn in its 2612 databases for MaxPurgeTime seconds. 2614 If the route is being updated, then the LS MUST update the route in 2615 the Adj-TRIB-In and MUST flood it to all other internal peers. 2617 If these procedures result in changes to the Adj-TRIB-In, then the 2618 route is also made available for local route processing as described 2619 early in Section 10. 2621 To implement flooding, the following is recommended. All routes 2622 received in a single UPDATE message that are determined to be new 2623 should be forwarded to all other internal peers in a single UPDATE 2624 message. Other variations on flooding are possible, but the local LS 2625 MUST ensure that each new route (and any associated attributes) 2626 received from an internal peer get forwarded to every other internal 2627 peer. 2629 10.1.4. Sequence Number Considerations 2631 The Sequence Number is used to determine when one version of a Route 2632 is newer than another version of a route. A larger Sequence Number 2633 indicates a newer version. The Sequence Number is assigned by the LS 2634 originating the route into the local ITAD. The Sequence Number is an 2635 unsigned 4-octet integer in the range of 1 thru 2^31-1 MinSequenceNum 2636 thru MaxSequenceNum). The value 0 is reserved. When an LS first 2637 originates a route (including when the LS restarts/reboots) into its 2638 ITAD, it MUST originate it with a Sequence Number of MinSequenceNum. 2639 Each time the route is updated within the ITAD by the originator, the 2640 Sequence Number MUST be increased. 2642 If it is ever the case that the sequence number is MaxSequenceNum-1 2643 and it needs to be increased, then the TRIP module of the LS MUST be 2644 disabled for a period of TripDisableTime so that all routes 2645 originated by this LS with high sequence numbers can be removed. 2647 10.1.5. Purging a Route Within the ITAD 2649 To withdraw a route that it originated within the ITAD, an LS 2650 includes the route in the WithdrawnRoutes field of an UPDATE message. 2651 The Sequence Number MUST be greater than the last valid version of 2652 the route. The LS MAY choose to use a sequence number of 2653 MaxSequenceNum when withdrawing routes within its ITAD, but this is 2654 not required. 2656 After withdrawing a route, an LS MUST mark the route as "withdrawn" 2657 in its database, and maintain the withdrawn route in its database for 2658 MaxPurgeTime seconds. If the LS needs to re-originate a route that 2659 had been purged but is still in its database, it can either re- 2660 originate the route immediately using a Sequence Number that is 2661 greater than that used in the withdraw, or the LS may wait until 2662 MaxPurgeTime seconds have expired since the route was withdrawn. 2664 10.1.6. Receiving Self-Originated Routes 2666 It is common for an LS to receive UPDATES for routes that it 2667 originated within the ITAD via the flooding procedure. If the LS 2668 receives an UPDATE for a route that it originated that is newer (has 2669 a higher sequence number) than the LSs current version, then special 2670 actions must be taken. This should be a relatively rare occurrence 2671 and indicates that a route still exists within the ITAD since the LSs 2672 last restart/reboot. 2674 If an LS receives a self-originated route update that is newer than 2675 the current version of the route at the LS, then the following 2676 actions MUST be taken. If the LS still wishes to advertise the 2677 information in the route, then the LS MUST increase the Sequence 2678 Number of the route to a value greater than that received in the 2679 UPDATE and re-originate the route. If the LS does not wish to 2680 continue to advertise the route, then it MUST purge the route as 2681 described in Section 10.1.5. 2683 10.1.7. Removing Withdrawn Routes 2685 An LS SHOULD ensure that routes marked as withdrawn are removed from 2686 the database in a timely fashion after the MaxPurgeTime has expired. 2687 This could be done, for example, by periodically sweeping the 2688 database, and deleting those entries that were withdrawn more than 2689 MaxPurgeTime seconds ago. 2691 10.2. Decision Process 2693 The Decision Process selects routes for subsequent advertisement by 2694 applying the policies in the local Policy Information Base (PIB) to 2695 the routes stored in its Adj-TRIBs-In. The output of the Decision 2696 Process is the set of routes that will be advertised to all peers; 2697 the selected routes will be stored in the local LS's Adj-TRIBs-Out. 2699 The selection process is formalized by defining a function that takes 2700 the attributes of a given route as an argument and returns a non- 2701 negative integer denoting the degree of preference for the route. The 2702 function that calculates the degree of preference for a given route 2703 shall not use as its inputs any of the following: the existence of 2704 other routes, the non-existence of other routes, or the attributes of 2705 other routes. Route selection then consists of individual application 2706 of the degree of preference function to each feasible route, followed 2707 by the choice of the one with the highest degree of preference. 2709 All internal LSs in an ITAD MUST run the Decision Process and apply 2710 the same decision criteria, otherwise it will not be possible to 2711 synchronize their Loc-TRIBs. 2713 The Decision Process operates on routes contained in each Adj-TRIBs- 2714 In, and is responsible for: 2716 - selection of routes to be advertised to internal peers 2717 - selection of routes to be advertised to external peers 2718 - route aggregation and route information reduction 2720 The Decision Process takes place in three distinct phases, each 2721 triggered by a different event: 2723 - Phase 1 is responsible for calculating the degree of preference 2724 for each route received from an external peer. 2725 - Phase 2 is invoked on completion of phase 1. It is responsible 2726 for choosing the best route out of all those available for each 2727 distinct destination, and for installing each chosen route into 2728 the Loc-TRIB. 2730 - Phase 3 is invoked after the Loc-TRIB has been modified. It is 2731 responsible for disseminating routes in the Loc-TRIB to each 2732 external peer, according to the policies contained in the PIB. 2733 Route aggregation and information reduction can optionally be 2734 performed within this phase. 2736 10.2.1. Phase 1: Calculation of Degree of Preference 2738 The Phase 1 decision function shall be invoked whenever the local LS 2739 receives from a peer an UPDATE message that advertises a new route, a 2740 replacement route, or a withdrawn route. 2742 The Phase 1 decision function is a separate process that completes 2743 when it has no further work to do. 2745 The Phase 1 decision function shall lock an Adj-TRIB-In prior to 2746 operating on any route contained within it, and shall unlock it after 2747 operating on all new or replacement routes contained within it. 2749 The local LS MUST determine a degree of preference for each newly 2750 received or replacement route. If the route is learned from an 2751 internal peer, the value of the LocalPreference attribute MUST be 2752 taken as the degree of preference. If the route is learned from an 2753 external peer, then the degree of preference MUST be computed based 2754 on pre-configured policy information and used as the LocalPreference 2755 value in any intra-domain TRIP advertisement. The exact nature of 2756 this policy information and the computation involved is a local 2757 matter. 2759 The output of the degree of preference determination process is the 2760 local preference of a route. The local LS computes the local 2761 preference of routes learned from external peers or originated 2762 internally at that LS. The local preference of a route learned from 2763 an internal peer is included in the LocalPreference attribute 2764 associated with that route. 2766 10.2.2. Phase 2: Route Selection 2768 The Phase 2 decision function shall be invoked on completion of Phase 2769 1. The Phase 2 function is a separate process that completes when it 2770 has no further work to do. Phase 2 consists of two sub- phases: 2a 2771 and 2b. The same route selection function is applied in both sub- 2772 phases, but the inputs to each phase are different. The Phase 2a 2773 process MUST consider as inputs all external routes, that are present 2774 in the Adj-TRIBs-In of external peers, and all local routes. The 2775 output of Phase 2a is inserted into the Ext-TRIB. The Phase 2b 2776 process shall be invoked upon completion of Phase 2a and it MUST 2777 consider as inputs all routes in the Ext-TRIB and all routes that are 2778 present in the Adj-TRIBs-In of internal LSs. The output of Phase 2b 2779 is stored in the Loc-TRIB. 2781 The Phase 2 decision function MUST be blocked from running while the 2782 Phase 3 decision function is in process. The Phase 2 function MUST 2783 lock all Adj-TRIBs-In and the Ext-TRIB prior to commencing its 2784 function, and MUST unlock them on completion. 2786 If the LS determines that the NextHopServer listed in a route is 2787 unreachable, then the route MAY be excluded from the Phase 2 decision 2788 function. The means by which such a determination is made is not 2789 mandated here. 2791 For each set of destinations for which one or more routes exist, the 2792 local LS's route selection function MUST identify the route that has: 2794 - the highest degree of preference, or 2795 - is selected as a result of the tie breaking rules specified in 2796 10.2.2.1. 2798 Withdrawn routes MUST be removed from the Loc-TRIB, Ext-TRIB, and the 2799 Adj-TRIBs-In. 2801 10.2.2.1. Breaking Ties (Phase 2) 2803 Several routes to the same destination that have the same degree of 2804 preference may be input to the Phase 2 route selection function. The 2805 local LS can select only one of these routes for inclusion in the 2806 associated Ext-TRIB (Phase 2a) or Loc-TRIB (Phase 2b). The local LS 2807 considers all routes with the same degrees of preference. The 2808 following algorithm shall be used to break ties. 2810 - If the local LS is configured to use the MultiExitDisc attribute 2811 to break ties, and candidate routes received from the same 2812 neighboring ITAD differ in the value of the MultiExitDisc 2813 attribute, then select the route that has the larger value of 2814 MultiExitDisc. 2815 - If at least one of the routes was originated by an internal LS, 2816 select the route route that was advertised by the internal LS 2817 that has the lowest TRIP ID. 2818 - Otherwise, select the route that was advertised by the neighbor 2819 domain that has the lowest ITAD number. 2821 10.2.3. Phase 3: Route Dissemination 2823 The Phase 3 decision function MUST be invoked upon completion of 2824 Phase 2 if Phase 2 results in changes to the Loc-TRIB or when a new 2825 LS-to-LS peer session is established. 2827 The Phase 3 function is a separate process that completes when it has 2828 no further work to do. The Phase 3 routing decision function MUST be 2829 blocked from running while the Phase 2 decision function is in 2830 process. 2832 All routes in the Loc-TRIB shall be processed into a corresponding 2833 entry in the associated Adj-TRIBs-Out. Route aggregation and 2834 information reduction techniques (see 10.3.4) MAY optionally be 2835 applied. 2837 When the updating of the Adj-TRIBs-Out is complete, the local LS MUST 2838 run the external update process of 10.3.2. 2840 10.2.4. Overlapping Routes 2842 When overlapping routes are present in the same Adj-TRIB-In, the more 2843 specific route shall take precedence, in order from more specific to 2844 least specific. 2846 The set of destinations described by the overlap represents a portion 2847 of the less specific route that is feasible, but is not currently in 2848 use. If a more specific route is later withdrawn, the set of 2849 destinations described by the more specific route will still be 2850 reachable using the less specific route. 2852 If an LS receives overlapping routes, the Decision Process MUST take 2853 into account the semantics of the overlapping routes. In particular, 2854 if an LS accepts the less specific route while rejecting the more 2855 specific route from the same peer, then the destinations represented 2856 by the overlap may not forward along the domains listed in the 2857 AdvertisementPath attribute of that route. Therefore, an LS has the 2858 following choices: 2860 1. Install both the less and the more specific routes 2861 2. Install the more specific route only 2862 3. Install the non-overlapping part of the less specific route 2863 only (that implies disaggregation of the less-specific route) 2864 4. Aggregate the two routes and install the aggregated route 2865 5. Install the less specific route only 2866 6. Install neither route 2868 If an LS chooses 5), then it SHOULD add AtomicAggregate attribute to 2869 the route. A route that carries AtomicAggregate attribute MUST NOT be 2870 de-aggregated. That is, the route cannot be made more specific. 2871 Forwarding along such a route does not guarantee that route traverses 2872 only domains listed in the RoutedPath of the route. If an LS chooses 2873 1), then it MUST NOT advertise the more general route without the 2874 more specific route. 2876 10.3. Update-Send Process 2878 The Update-Send process is responsible for advertising UPDATE 2879 messages to all peers. For example, it distributes the routes chosen 2880 by the Decision Process to other LSs that may be located in either 2881 the same ITAD or a neighboring ITAD. Rules for information exchange 2882 between peer LSs located in different ITADs are given in 10.3.2; 2883 rules for information exchange between peer LSs located in the same 2884 ITAD are given in 10.3.1. 2886 Before forwarding routes to peers, an LS MUST determine which 2887 attributes should be forwarded along with that route. If a not well- 2888 known non-transitive attribute is unrecognized, it is quietly 2889 ignored. If a not well-known dependent-transitive attribute is 2890 unrecognized, and the NextHopServer attribute has been changed by the 2891 LS, the unrecognized attribute is quietly ignored. If a not well- 2892 known dependent-transitive attribute is unrecognized, and the 2893 NextHopServer attribute has not been modified by the LS, the Partial 2894 bit in the attribute flags octet is set to 1, and the attribute is 2895 retained for propagation to other TRIP speakers. Similarly, if an not 2896 well-known independent-transitive attribute is unrecognized, the 2897 Partial bit in the attribute flags octet is set to 1, and the 2898 attribute is retained for propagation to other TRIP speakers. 2900 If a not well-known attribute is recognized, and has a valid value, 2901 then, depending on the type of the not well-known attribute, it is 2902 updated, if necessary, for possible propagation to other TRIP 2903 speakers. 2905 10.3.1. Internal Updates 2907 The Internal update process is concerned with the distribution of 2908 routing information to internal peers. 2910 When an LS receives an UPDATE message from another TRIP LS located in 2911 its own ITAD, it is flooded as described in Section 10.1. 2913 When an LS receives a new route from an LS in a neighboring ITAD, or 2914 if a local route is injected into TRIP, the LS determines the 2915 preference of that route. If the new route has the highest degree of 2916 preference for all external routes and local routes to a given 2917 destination (or if the route was selected via a tie-breaking 2918 procedure as specified in 10.3.1.1), the LS MUST insert that new 2919 route into the Ext-TRIB database and the LS MUST advertise that route 2920 to all other LSs in its ITAD by means of an UPDATE message. The LS 2921 MUST advertise itself as the Originator of that route within the 2922 ITAD. 2924 When an LS receives an UPDATE message with a non-empty 2925 WithdrawnRoutes attribute from an external peer, or if a local route 2926 is withdrawn from TRIP, the LS MUST remove from its Adj-TRIB-In all 2927 routes whose destinations were carried in this field. If the 2928 withdrawn route was previously selected into the Ext-TRIB, the LS 2929 MUST take the following additional steps: 2931 - If a new route is selected for advertisement for those 2932 destinations, then the LS MUST insert the replacement route into 2933 Ext-TRIB to replace the withdrawn route and advertise it to all 2934 internal LSs. 2935 - If a replacement route is not available for advertisement, then 2936 the LS MUST include the destinations of the route in the 2937 WithdrawnRoutes attribute of an UPDATE message, and MUST send 2938 this message to each internal peer. The LS MUST also remove the 2939 withdrawn route from the Ext-TRIB. 2941 10.3.1.1. Breaking Ties (Routes Received from External Peers) 2943 If an LS has connections to several external peers, there will be 2944 multiple Adj-TRIBs-In associated with these peers. These databases 2945 might contain several equally preferable routes to the same 2946 destination, all of which were advertised by external peers. The 2947 local LS shall select one of these routes according to the following 2948 rules: 2950 - If the LS is configured to use the MultiExitDisc attribute to 2951 break ties, and the candidate routes differ in the value of the 2952 MultiExitDisc attribute, then select the route that has the 2953 lowest value of MultiExitDisc, else 2954 - Select the route that was advertised by the external LS that has 2955 the lowest TRIP Identifier. 2957 10.3.2. External Updates 2959 The external update process is concerned with the distribution of 2960 routing information to external peers. As part of Phase 3 route 2961 selection process, the LS has updated its Adj-TRIBs-Out. All newly 2962 installed routes and all newly unfeasible routes for which there is 2963 no replacement route MUST be advertised to external peers by means of 2964 UPDATE messages. 2966 Any routes in the Loc-TRIB marked as withdrawn MUST be removed. 2967 Changes to the reachable destinations within its own ITAD SHALL also 2968 be advertised in an UPDATE message. 2970 10.3.3. Controlling Routing Traffic Overhead 2972 The TRIP protocol constrains the amount of routing traffic (that is, 2973 UPDATE messages) in order to limit both the link bandwidth needed to 2974 advertise UPDATE messages and the processing power needed by the 2975 Decision Process to digest the information contained in the UPDATE 2976 messages. 2978 10.3.3.1. Frequency of Route Advertisement 2980 The parameter MinRouteAdvertisementInterval determines the minimum 2981 amount of time that must elapse between advertisements of routes to a 2982 particular destination from a single LS. This rate limiting procedure 2983 applies on a per-destination basis, although the value of 2984 MinRouteAdvertisementInterval is set on a per LS peer basis. 2986 Two UPDATE messages sent from a single LS that advertise feasible 2987 routes to some common set of destinations received from external 2988 peers MUST be separated by at least MinRouteAdvertisementInterval. 2989 Clearly, this can only be achieved precisely by keeping a separate 2990 timer for each common set of destinations. This would be unwarranted 2991 overhead. Any technique which ensures that the interval between two 2992 UPDATE messages sent from a single LS that advertise feasible routes 2993 to some common set of destinations received from external peers will 2994 be at least MinRouteAdvertisementInterval, and will also ensure a 2995 constant upper bound on the interval is acceptable. 2997 Two UPDATE messages, sent from a single LS to an external peer, that 2998 advertise feasible routes to some common set of destinations received 2999 from internal peers MUST be separated by at least 3000 MinRouteAdvertisementInterval. 3002 Since fast convergence is needed within an ITAD, this rate limiting 3003 procedure does not apply to routes received from internal peers and 3004 being broadcast to other internal peers. To avoid long-lived black 3005 holes, the procedure does not apply to the explicit withdrawal of 3006 routes (that is, routes whose destinations explicitly withdrawn by 3007 UPDATE messages. 3009 This procedure does not limit the rate of route selection, but only 3010 the rate of route advertisement. If new routes are selected multiple 3011 times while awaiting the expiration of MinRouteAdvertisementInterval, 3012 the last route selected shall be advertised at the end of 3013 MinRouteAdvertisementInterval. 3015 10.3.3.2. Frequency of Route Origination 3017 The parameter MinITADOriginationInterval determines the minimum 3018 amount of time that must elapse between successive advertisements of 3019 UPDATE messages that report changes within the advertising LS's own 3020 ITAD. 3022 10.3.3.3. Jitter 3024 To minimize the likelihood that the distribution of TRIP messages by 3025 a given LS will contain peaks, jitter should be applied to the timers 3026 associated with MinITADOriginationInterval, KeepAlive, and 3027 MinRouteAdvertisementInterval. A given LS shall apply the same jitter 3028 to each of these quantities regardless of the destinations to which 3029 the updates are being sent; that is, jitter will not be applied on a 3030 "per peer" basis. 3032 The amount of jitter to be introduced shall be determined by 3033 multiplying the base value of the appropriate timer by a random 3034 factor that is uniformly distributed in the range from 0.75 to 1.0. 3036 10.3.4. Efficient Organization of Routing Information 3038 Having selected the routing information that it will advertise, a 3039 TRIP speaker may use methods to organize this information in an 3040 efficient manner. These methods are discussed in the following 3041 sections. 3043 10.3.4.1. Information Reduction 3045 Information reduction may imply a reduction in granularity of policy 3046 control - after information is collapsed, the same policies will 3047 apply to all destinations and paths in the equivalence class. 3049 The Decision Process may optionally reduce the amount of information 3050 that it will place in the Adj-TRIBs-Out by any of the following 3051 methods: 3053 - ReachableRoutes: A set of destinations can be usually represented 3054 in compact form. For example, a set of E.164 phone numbers can be 3055 represented in more compact form using E.164 prefixes. 3056 - AdvertisementPath: AdvertisementPath information can be 3057 represented as ordered AP_SEQUENCEs or unordered AP_SETs. AP_SETs 3058 are used in the route aggregation algorithm described in Section 3059 5.4.4. They reduce the size of the AP_PATH information by listing 3060 each ITAD number only once, regardless of how many times it may 3061 have appeared in multiple advertisement paths that were 3062 aggregated. 3064 An AP_SET implies that the destinations advertised in the UPDATE 3065 message can be reached through paths that traverse at least some of 3066 the constituent ITADs. AP_SETs provide sufficient information to 3067 avoid route looping; however their use may prune potentially feasible 3068 paths, since such paths are no longer listed individually as in the 3069 form of AP_SEQUENCEs. In practice this is not likely to be a problem, 3070 since once a call arrives at the edge of a group of ITADs, the LS at 3071 that point is likely to have more detailed path information and can 3072 distinguish individual paths to destinations. 3074 10.3.4.2. Aggregating Routing Information 3076 Aggregation is the process of combining the characteristics of 3077 several different routes in such a way that a single route can be 3078 advertised. Aggregation can occur as part of the decision process to 3079 reduce the amount of routing information that is placed in the Adj- 3080 TRIBs-Out. 3082 Aggregation reduces the amount of information an LS must store and 3083 exchange with other LSs. Routes can be aggregated by applying the 3084 following procedure separately to attributes of like type. 3086 Routes that have the following attributes shall not be aggregated 3087 unless the corresponding attributes of each route are identical: 3088 MultiExitDisc, NextHopServer. 3090 Attributes that have different type codes cannot be aggregated. 3091 Attributes of the same type code may be aggregated. The rules for 3092 aggregating each attribute MUST be provided together with attribute 3093 definition. For example, aggregation rules for TRIP's basic 3094 attributes, e.g., ReachableRoutes and AdvertisementPath, are given in 3095 Section 5. 3097 10.4. Route Selection Criteria 3099 Generally speaking, additional rules for comparing routes among 3100 several alternatives are outside the scope of this document. There 3101 are two exceptions: 3103 - If the local ITAD appears in the AdvertisementPath of the new 3104 route being considered, then that new route cannot be viewed as 3105 better than any other route. If such a route were ever used, a 3106 routing loop could result (see Section 6.3). 3107 - In order to achieve successful distributed operation, only routes 3108 with a likelihood of stability can be chosen. Thus, an ITAD must 3109 avoid using unstable routes, and it must not make rapid 3110 spontaneous changes to its choice of route. Quantifying the terms 3111 "unstable" and "rapid" in the previous sentence will require 3112 experience, but the principle is clear. 3114 10.5. Originating TRIP Routes 3116 An LS may originate local routes by injecting routing information 3117 acquired by some other means (e.g. via an intra-domain routing 3118 protocol or through manual configuration or some dynamic registration 3119 mechanism/protocol) into TRIP. An LS that originates TRIP routes 3120 shall assign the degree of preference to these routes by passing them 3121 through the Decision Process (see Section 10.2). To TRIP local routes 3122 are identical to external routes and are subjected to the same two 3123 phase route selection mechanism. A local route which is selected into 3124 the Ext-TRIB MUST be advertised to all internal LSs. The decision 3125 whether to distribute non-TRIP acquired routes within an ITAD via 3126 TRIP or not depends on the environment within the ITAD (e.g. type of 3127 intra-domain routing protocol) and should be controlled via 3128 configuration. 3130 11. TRIP Transport 3132 This specification defines the use of TCP as the transport layer for 3133 TRIP. TRIP uses TCP port 6069. Running TRIP over other transport 3134 protocols is for further study. 3136 12. ITAD Topology 3138 There are no restrictions on the intra-domain topology of TRIP LSs. 3139 For example, LSs in an ITAD can be configured in a full mesh, star, 3140 or any other connected topology. Similarly, there are no restrictions 3141 on the topology of TRIP ITADs. For example, the ITADs can be 3142 organized in a flat topology (mesh or ring) or in multi-level 3143 hierarchy or any other topology. 3145 The border between two TRIP ITADs may be located either on the link 3146 between two TRIP LSs or it may coincide on a TRIP LS. In the latter 3147 case, the same TRIP LS will be member in more than one ITAD, and it 3148 appears to be an internal peer to LSs in each ITAD it is member of. 3150 13. IANA Considerations 3152 This document creates a new IANA registry for TRIP parameters. The 3153 following TRIP parameters are included in the registry: 3154 - TRIP Capabilities 3155 - TRIP Attributes 3156 - TRIP Address Families 3157 - TRIP Application Protocols 3158 - TRIP ITAD Numbers 3160 Protocol parameters are frequently initialized/reset to 0. This 3161 document reserves the value 0 of each of the above TRIP parameters in 3162 order to clearly distinguish between an unset parameter and any other 3163 registered values for that parameter. 3165 The sub-registries for each of the above parameters are discussed in 3166 the sections below. 3168 13.1. TRIP Capabilities 3170 Requests to add TRIP capabilities other than those defined in Section 3171 4.2.1.1 must be submitted to iana@iana.org. Following the assigned 3172 number policies outlined in [11], Capability Codes in the range 3173 32768-65535 are reserved for Private Use (these are the codes with 3174 the first bit of the code value equal to 1). This document reserves 3175 value 0. Capability Codes 1 and 2 have been assigned in Section 3176 4.2.1.1. Capability Codes in the range 2-32767 are controlled by 3177 IANA, and are allocated subject to the Specification Required (IETF 3178 RFC or equivalent) condition. The specification MUST include a 3179 description of the capability, the possible values it may take, and 3180 what constitutes a capability mismatch. 3182 13.2. TRIP Attributes 3184 This document reserves Attribute Type Codes 224-255 for Private Use 3185 (these are the codes with the first three bits of the code equal to 3186 1). This document reserves value 0. Attribute Type Codes 1 through 11 3187 have already been allocated by this document. Attribute Type Codes 1 3188 through 11 are defined in Sections 5.1 through 5.11. 3190 Attribute Type Codes in the range 12-223 are controlled by IANA, and 3191 require a Specification document (RFC or equivalent). The 3192 specification MUST provide all information required in Section 5.12 3193 of this document. 3195 Attribute Type Code registration requests must be sent to 3196 iana@iana.org. In addition to the specification requirement, the 3197 request MUST include an indication of who has change control over the 3198 attribute and contact information (postal and email address). 3200 13.3. Destination Address Families 3202 This document reserves address family 0. Requests to add TRIP address 3203 families other than those defined in Section 5.1.1.1 ( address 3204 families 1, 2, and 3), i.e., in the range 3-32767, must be submitted 3205 to iana@iana.org. The request MUST include a brief description of the 3206 address family, its alphabet, and special processing rules and 3207 guidelines, such as guidelines for aggregation, if any. The requests 3208 are subject to Expert Review. This document reserves addresss family 3209 codes 32768-65535 for vendor-specific applications. 3211 13.4. TRIP Application Protocols 3213 This document creates a new IANA registry for TRIP application 3214 protocols. This document reserves application protocol code 0. 3215 Requests to add TRIP application protocols other than those defined 3216 in Section 5.1.1.1 (application protocols 1 through 4), i.e., in the 3217 range 5- 32767 must be submitted to iana@iana.org. The request MUST 3218 include a brief background on the application protocol, and a 3219 description of how TRIP can be used to advertise routes for that 3220 protocol. The requests are subject to Expert Review. This document 3221 reserves application protocol codes 32768-65535 for vendor-specific 3222 applications. 3224 13.5. ITAD Numbers 3226 This document reserves ITAD number 0. ITAD numbers in the range 1- 3227 255 are designated for Private Use. ITAD numbers in the range from 3228 256 to (2**32-1) are allocated by IANA on a First-Come-First-Serve 3229 basis. Requests for ITAD numbers must be submitted to iana@iana.org. 3230 The requests MUST include the following: 3231 - Information about the organization that will administer the ITAD. 3232 - Contact information (postal and email address). 3234 14. Security Considerations 3236 This section covers security between peer TRIP LSs when TRIP runs 3237 over TCP in an IP environment. 3239 A security mechanism is clearly needed to prevent unauthorized 3240 entities from using the protocol defined in this document for setting 3241 up unauthorized peer sessions with other TRIP LSs or interfering with 3242 authorized peer sessions. The security mechanism for the protocol 3243 when transported over TCP in an IP network is IPsec [12]. IPsec uses 3244 two protocols to provide traffic security: Authentication Header (AH) 3245 [13] and Encapsulating Security Payload (ESP) [14]. 3247 The AH header affords data origin authentication, connectionless 3248 integrity and optional anti-replay protection of messages passed 3249 between the peer LSs. The ESP header provides origin authentication, 3250 connectionless integrity, anti-replay protection, and, in addition, 3251 confidentiality of messages. 3253 Implementations of the protocol defined in this document employing 3254 the ESP header SHALL comply with section 5 of [14], which defines a 3255 minimum set of algorithms for integrity checking and encryption. 3256 Similarly, implementations employing the AH header SHALL comply with 3257 section 5 of [13], which defines a minimum set of algorithms for 3258 integrity checking using manual keys. 3260 Implementations SHOULD use IKE [15] to permit more robust keying 3261 options. Implementations employing IKE SHOULD support authentication 3262 with RSA signatures and RSA public key encryption. 3264 A Security Association (SA) [12] is a simplex "connection" that 3265 affords security services to the traffic carried by it. Security 3266 services are afforded to an SA by the use of AH, or ESP, but not 3267 both. Two types of SAs are defined: transport mode and tunnel mode 3268 [12]. A transport mode SA is a security association between two 3269 hosts, and is appropriate for protecting the TRIP session between two 3270 peer LSs. 3272 Appendix 1: TRIP FSM State Transitions and Actions 3274 This Appendix discusses the transitions between states in the TRIP 3275 FSM in response to TRIP events. The following is the list of these 3276 states and events when the negotiated Hold Time value is non-zero. 3278 TRIP States: 3279 1 - Idle 3280 2 - Connect 3281 3 - Active 3282 4 - OpenSent 3283 5 - OpenConfirm 3284 6 - Established 3286 TRIP Events: 3287 1 - TRIP Start 3288 2 - TRIP Stop 3289 3 - TRIP Transport connection open 3290 4 - TRIP Transport connection closed 3291 5 - TRIP Transport connection open failed 3292 6 - TRIP Transport fatal error 3293 7 - ConnectRetry timer expired 3294 8 - Hold Timer expired 3295 9 - KeepAlive timer expired 3296 10 - Receive OPEN message 3297 11 - Receive KEEPALIVE message 3298 12 - Receive UPDATE messages 3299 13 - Receive NOTIFICATION message 3301 The following table describes the state transitions of the TRIP FSM 3302 and the actions triggered by these transitions. 3304 Event Actions Message Sent Next State 3305 -------------------------------------------------------------------- 3306 Idle (1) 3307 1 Initialize resources none 2 3308 Start ConnectRetry timer 3309 Initiate a transport connection 3310 others none none 1 3312 Connect(2) 3313 1 none none 2 3314 3 Complete initialization OPEN 4 3315 Clear ConnectRetry timer 3316 5 Restart ConnectRetry timer none 3 3317 7 Restart ConnectRetry timer none 2 3318 Initiate a transport connection 3319 others Release resources none 1 3321 Active (3) 3322 1 none none 3 3323 3 Complete initialization OPEN 4 3324 Clear ConnectRetry timer 3325 5 Close connection 3 3326 Restart ConnectRetry timer 3327 7 Restart ConnectRetry timer none 2 3328 Initiate a transport connection 3329 others Release resources none 1 3331 OpenSent(4) 3332 1 none none 4 3333 4 Close transport connection none 3 3334 Restart ConnectRetry timer 3335 6 Release resources none 1 3336 10 Process OPEN is OK KEEPALIVE 5 3337 Process OPEN failed NOTIFICATION 1 3338 others Close transport connection NOTIFICATION 1 3339 Release resources 3341 OpenConfirm (5) 3342 1 none none 5 3343 4 Release resources none 1 3344 6 Release resources none 1 3345 9 Restart KeepAlive timer KEEPALIVE 5 3346 11 Complete initialization none 6 3347 Restart Hold Timer 3348 13 Close transport connection 1 3349 Release resources 3350 others Close transport connection NOTIFICATION 1 3351 Release resources 3353 Established (6) 3354 1 none none 6 3355 4 Release resources none 1 3356 6 Release resources none 1 3357 9 Restart KeepAlive timer KEEPALIVE 6 3358 11 Restart Hold Timer none 6 3359 12 Process UPDATE is OK UPDATE 6 3360 Process UPDATE failed NOTIFICATION 1 3361 13 Close transport connection 1 3362 Release resources 3363 others Close transport connection NOTIFICATION 1 3364 Release resources 3365 ----------------------------------------------------------------- 3367 The following is a condensed version of the above state transition 3368 table. 3370 Events| Idle | Connect | Active | OpenSent | OpenConfirm | Estab 3371 | (1) | (2) | (3) | (4) | (5) | (6) 3372 |---------------------------------------------------------- 3373 1 | 2 | 2 | 3 | 4 | 5 | 6 3374 | | | | | | 3375 2 | 1 | 1 | 1 | 1 | 1 | 1 3376 | | | | | | 3377 3 | 1 | 4 | 4 | 1 | 1 | 1 3378 | | | | | | 3379 4 | 1 | 1 | 1 | 3 | 1 | 1 3380 | | | | | | 3381 5 | 1 | 3 | 3 | 1 | 1 | 1 3382 | | | | | | 3383 6 | 1 | 1 | 1 | 1 | 1 | 1 3384 | | | | | | 3385 7 | 1 | 2 | 2 | 1 | 1 | 1 3386 | | | | | | 3387 8 | 1 | 1 | 1 | 1 | 1 | 1 3388 | | | | | | 3389 9 | 1 | 1 | 1 | 1 | 5 | 6 3390 | | | | | | 3391 10 | 1 | 1 | 1 | 1 or 5 | 1 | 1 3392 | | | | | | 3393 11 | 1 | 1 | 1 | 1 | 6 | 6 3394 | | | | | | 3395 12 | 1 | 1 | 1 | 1 | 1 | 1 or 6 3396 | | | | | | 3397 13 | 1 | 1 | 1 | 1 | 1 | 1 3398 | | | | | | 3399 -------------------------------------------------------------- 3401 Appendix 2: Implementation Recommendations 3403 This section presents some implementation recommendations. 3405 A.2.1: Multiple Networks Per Message 3407 The TRIP protocol allows for multiple address prefixes with the same 3408 advertisement path and next-hop server to be specified in one 3409 message. Making use of this capability is highly recommended. With 3410 one address prefix per message there is a substantial increase in 3411 overhead in the receiver. Not only does the system overhead increase 3412 due to the reception of multiple messages, but the overhead of 3413 scanning the routing table for updates to TRIP peers is incurred 3414 multiple times as well. One method of building messages containing 3415 many address prefixes per advertisement path and next hop from a 3416 routing table that is not organized per advertisement path is to 3417 build many messages as the routing table is scanned. As each address 3418 prefix is processed, a message for the associated advertisement path 3419 and next hop is allocated, if it does not exist, and the new address 3420 prefix is added to it. If such a message exists, the new address 3421 prefix is just appended to it. If the message lacks the space to hold 3422 the new address prefix, it is transmitted, a new message is 3423 allocated, and the new address prefix is inserted into the new 3424 message. When the entire routing table has been scanned, all 3425 allocated messages are sent and their resources released. Maximum 3426 compression is achieved when all the destinations covered by the 3427 address prefixes share a next hop server and common attributes, 3428 making it possible to send many address prefixes in one 4096-byte 3429 message. 3431 When peering with a TRIP implementation that does not compress 3432 multiple address prefixes into one message, it may be necessary to 3433 take steps to reduce the overhead from the flood of data received 3434 when a peer is acquired or a significant network topology change 3435 occurs. One method of doing this is to limit the rate of updates. 3436 This will eliminate the redundant scanning of the routing table to 3437 provide flash updates for TRIP peers. A disadvantage of this approach 3438 is that it increases the propagation latency of routing information. 3439 By choosing a minimum flash update interval that is not much greater 3440 than the time it takes to process the multiple messages this latency 3441 should be minimized. A better method would be to read all received 3442 messages before sending updates. 3444 A.2.2: Processing Messages on a Stream Protocol 3446 TRIP uses TCP as a transport mechanism. Due to the stream nature of 3447 TCP, all the data for received messages does not necessarily arrive 3448 at the same time. This can make it difficult to process the data as 3449 messages, especially on systems where it is not possible to determine 3450 how much data has been received but not yet processed. 3452 One method that can be used in this situation is to first try to read 3453 just the message header. For the KEEPALIVE message type, this is a 3454 complete message; for other message types, the header should first be 3455 verified, in particular the total length. If all checks are 3456 successful, the specified length, minus the size of the message 3457 header is the amount of data left to read. An implementation that 3458 would "hang" the routing information process while trying to read 3459 from a peer could set up a message buffer (4096 bytes) per peer and 3460 fill it with data as available until a complete message has been 3461 received. 3463 A.2.3: Reducing Route Flapping 3465 To avoid excessive route flapping an LS which needs to withdraw a 3466 destination and send an update about a more specific or less specific 3467 route SHOULD combine them into the same UPDATE message. 3469 A.2.4: TRIP Timers 3471 TRIP employs seven timers: ConnectRetry, Hold Time, KeepAlive, 3472 MaxPurgeTime, TripDisableTime, MinITADOriginationInterval, and 3473 MinRouteAdvertisementInterval The suggested value for the 3474 ConnectRetry timer is 120 seconds. The suggested value for the Hold 3475 Time is 90 seconds. The suggested value for the KeepAlive timer is 30 3476 seconds. The suggested value for the MaxPurgeTime timer is 10 3477 seconds. The suggested value for the TripDisableTime timer is 180 3478 seconds. The suggested value for the MinITADOriginationInterval is 30 3479 seconds. The suggested value for the MinRouteAdvertisementInterval is 3480 30 seconds. 3482 An implementation of TRIP MUST allow these timers to be configurable. 3484 A.2.5: AP_SET Sorting 3486 Another useful optimization that can be done to simplify this 3487 situation is to sort the ITAD numbers found in an AP_SET. This 3488 optimization is entirely optional. 3490 Acknowledgments 3492 We wish to thank Dave Oran for his insightful comments and 3493 suggestions. 3495 References 3497 [1] S. Bradner, "Keywords for use in RFCs to Indicate Requirement 3498 Levels," IETF RFC 2119, March 1997. 3500 [2] J. Rosenberg and H. Schulzrinne, "A Framework for a Gateway 3501 Location Protocol," IETF RFC 2871, June 2000. 3503 [3] Y. Rekhter and T. Li, "Border Gateway Protocol 4 (BGP-4)," IETF 3504 RFC 1771, March 1995. 3506 [4] J. Moy, "Open Shortest Path First Version 2," IETF RFC 2328, 3507 April, 1998. 3509 [5] "Intermediate System to Intermediate System Intra-Domain Routing 3510 Exchange Protocol for use in Conjunction with the 3511 Protocol for Providing the Connectionless-mode Network Service (ISO 3512 8473)," ISO DP 10589, February 1990. 3514 [6] J. Luciani, et al, "Server Cache Synchronization Protocol 3515 (SCSP)," IETF RFC 2334, April, 1998. 3517 [7] International Telecommunication Union, "Visual Telephone Systems 3518 and Equipment for Local Area Networks which Provide a Non-Guaranteed 3519 Quality of Service," Recommendation H.323, Telecommunication 3520 Standardization Sector of ITU, Geneva, Switzerland, May 1996. 3522 [8] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP: 3523 Session Initiation Protocol," IETF RFC 2543, March 1999. 3525 [9] R. Braden, "Requirements for Internet Hosts -- Application and 3526 Support," IETF RFC 1123, October 1989. 3528 [10] R. Hinden and S. Deering, "IP Version 6 Addressing 3529 Architecture," IETF RFC 2373, July 1998. 3531 [11] T. Narten and H. Alvestrand, "Guidelines for Writing an IANA 3532 Considerations Section in RFCs," IETF RFC 2434, October 1998. 3534 [12] S. Kent and R. Atkinson, "Security Architecture for the Internet 3535 Protocol," IETF RFC 2401, November 1998. 3537 [13] S. Kent and R. Atkinson, "IP Authentication Header," IETF RFC 3538 2402, November 1998. 3540 [14] S. Kent and R. Atkinson, "IP Encapsulating Security Payload 3541 (ESP)," IETF RFC 2406, November 1998. 3543 [15] D. Harkins and D. Carrel, "The Internet Key Exchange (IKE)," 3544 IETF RFC 2409, November 1998. 3546 Authors' Addresses 3548 Jonathan Rosenberg 3549 dynamicsoft 3550 72 Eagle Rock Avenue 3551 First Floor 3552 East Hanover, NJ 07936 3553 973-952-5000 3554 email: jdrosen@dynamicsoft.com 3556 Hussein F. Salama 3557 Cisco Systems 3558 Mail Stop SJ-6/3 3559 170 W. Tasman Drive 3560 San Jose, CA 95134 3561 408-527-7147 3562 email: hsalama@cisco.com 3564 Matt Squire 3565 WindWire 3566 4825 Creekstone Drive 3567 Durham, NC 27703 3568 919-247-0820 3569 email: msquire@windwire.com 3571 Intellectual Property Notice 3573 The IETF takes no position regarding the validity or scope of any 3574 intellectual property or other rights that might be claimed to 3575 pertain to the implementation or use of the technology described in 3576 this document or the extent to which any license under such rights 3577 might or might not be available; neither does it represent that it 3578 has made any effort to identify any such rights. Information on the 3579 IETF's procedures with respect to rights in standards-track and 3580 standards-related documentation can be found in BCP-11. 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