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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MBONED Working Group H. Asaeda 3 Internet-Draft NICT 4 Intended status: Standards Track K. Meyer 5 Expires: April 17, 2018 Cisco 6 W. Lee, Ed. 7 October 14, 2017 9 Mtrace Version 2: Traceroute Facility for IP Multicast 10 draft-ietf-mboned-mtrace-v2-20 12 Abstract 14 This document describes the IP multicast traceroute facility, named 15 Mtrace version 2 (Mtrace2). Unlike unicast traceroute, Mtrace2 16 requires special implementations on the part of routers. This 17 specification describes the required functionality in multicast 18 routers, as well as how an Mtrace2 client invokes a query and 19 receives a reply. 21 Status of This Memo 23 This Internet-Draft is submitted in full conformance with the 24 provisions of BCP 78 and BCP 79. 26 Internet-Drafts are working documents of the Internet Engineering 27 Task Force (IETF). Note that other groups may also distribute 28 working documents as Internet-Drafts. The list of current Internet- 29 Drafts is at https://datatracker.ietf.org/drafts/current/. 31 Internet-Drafts are draft documents valid for a maximum of six months 32 and may be updated, replaced, or obsoleted by other documents at any 33 time. It is inappropriate to use Internet-Drafts as reference 34 material or to cite them other than as "work in progress." 36 This Internet-Draft will expire on April 17, 2018. 38 Copyright Notice 40 Copyright (c) 2017 IETF Trust and the persons identified as the 41 document authors. All rights reserved. 43 This document is subject to BCP 78 and the IETF Trust's Legal 44 Provisions Relating to IETF Documents 45 (https://trustee.ietf.org/license-info) in effect on the date of 46 publication of this document. Please review these documents 47 carefully, as they describe your rights and restrictions with respect 48 to this document. Code Components extracted from this document must 49 include Simplified BSD License text as described in Section 4.e of 50 the Trust Legal Provisions and are provided without warranty as 51 described in the Simplified BSD License. 53 This document may contain material from IETF Documents or IETF 54 Contributions published or made publicly available before November 55 10, 2008. The person(s) controlling the copyright in some of this 56 material may not have granted the IETF Trust the right to allow 57 modifications of such material outside the IETF Standards Process. 58 Without obtaining an adequate license from the person(s) controlling 59 the copyright in such materials, this document may not be modified 60 outside the IETF Standards Process, and derivative works of it may 61 not be created outside the IETF Standards Process, except to format 62 it for publication as an RFC or to translate it into languages other 63 than English. 65 Table of Contents 67 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 68 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 69 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 6 70 3. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 7 71 3.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . 8 72 3.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . 8 73 3.2.1. Mtrace2 Query . . . . . . . . . . . . . . . . . . . . 9 74 3.2.2. Mtrace2 Request . . . . . . . . . . . . . . . . . . . 11 75 3.2.3. Mtrace2 Reply . . . . . . . . . . . . . . . . . . . . 11 76 3.2.4. IPv4 Mtrace2 Standard Response Block . . . . . . . . 12 77 3.2.5. IPv6 Mtrace2 Standard Response Block . . . . . . . . 15 78 3.2.6. Mtrace2 Augmented Response Block . . . . . . . . . . 18 79 3.2.7. Mtrace2 Extended Query Block . . . . . . . . . . . . 19 80 4. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 20 81 4.1. Receiving Mtrace2 Query . . . . . . . . . . . . . . . . . 20 82 4.1.1. Query Packet Verification . . . . . . . . . . . . . . 20 83 4.1.2. Query Normal Processing . . . . . . . . . . . . . . . 21 84 4.2. Receiving Mtrace2 Request . . . . . . . . . . . . . . . . 21 85 4.2.1. Request Packet Verification . . . . . . . . . . . . . 21 86 4.2.2. Request Normal Processing . . . . . . . . . . . . . . 22 87 4.3. Forwarding Mtrace2 Request . . . . . . . . . . . . . . . 23 88 4.3.1. Destination Address . . . . . . . . . . . . . . . . . 24 89 4.3.2. Source Address . . . . . . . . . . . . . . . . . . . 24 90 4.3.3. Appending Standard Response Block . . . . . . . . . . 24 91 4.4. Sending Mtrace2 Reply . . . . . . . . . . . . . . . . . . 25 92 4.4.1. Destination Address . . . . . . . . . . . . . . . . . 25 93 4.4.2. Source Address . . . . . . . . . . . . . . . . . . . 25 94 4.4.3. Appending Standard Response Block . . . . . . . . . . 25 95 4.5. Proxying Mtrace2 Query . . . . . . . . . . . . . . . . . 25 96 4.6. Hiding Information . . . . . . . . . . . . . . . . . . . 26 98 5. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 26 99 5.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 26 100 5.1.1. Destination Address . . . . . . . . . . . . . . . . . 27 101 5.1.2. Source Address . . . . . . . . . . . . . . . . . . . 27 102 5.2. Determining the Path . . . . . . . . . . . . . . . . . . 27 103 5.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 27 104 5.4. Last Hop Router (LHR) . . . . . . . . . . . . . . . . . . 27 105 5.5. First Hop Router (FHR) . . . . . . . . . . . . . . . . . 28 106 5.6. Broken Intermediate Router . . . . . . . . . . . . . . . 28 107 5.7. Non-Supported Router . . . . . . . . . . . . . . . . . . 28 108 5.8. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 28 109 5.8.1. Arriving at Source . . . . . . . . . . . . . . . . . 28 110 5.8.2. Fatal Error . . . . . . . . . . . . . . . . . . . . . 29 111 5.8.3. No Upstream Router . . . . . . . . . . . . . . . . . 29 112 5.8.4. Reply Timeout . . . . . . . . . . . . . . . . . . . . 29 113 5.9. Continuing after an Error . . . . . . . . . . . . . . . . 29 114 6. Protocol-Specific Considerations . . . . . . . . . . . . . . 29 115 6.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . 30 116 6.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . 30 117 6.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . 30 118 6.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . 30 119 7. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 31 120 7.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . 31 121 7.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 31 122 7.3. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 31 123 7.4. Link Utilization . . . . . . . . . . . . . . . . . . . . 32 124 7.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . 32 125 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 126 8.1. "Mtrace2 Forwarding Codes" Registry . . . . . . . . . . . 32 127 8.2. "Mtrace2 TLV Types" registry . . . . . . . . . . . . . . 32 128 8.3. UDP Destination Port . . . . . . . . . . . . . . . . . . 33 129 9. Security Considerations . . . . . . . . . . . . . . . . . . . 33 130 9.1. Addresses in Mtrace2 Header . . . . . . . . . . . . . . . 33 131 9.2. Filtering of Clients . . . . . . . . . . . . . . . . . . 33 132 9.3. Topology Discovery . . . . . . . . . . . . . . . . . . . 33 133 9.4. Characteristics of Multicast Channel . . . . . . . . . . 33 134 9.5. Limiting Query/Request Rates . . . . . . . . . . . . . . 33 135 9.6. Limiting Reply Rates . . . . . . . . . . . . . . . . . . 34 136 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 34 137 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 34 138 11.1. Normative References . . . . . . . . . . . . . . . . . . 34 139 11.2. Informative References . . . . . . . . . . . . . . . . . 35 140 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35 142 1. Introduction 144 Given a multicast distribution tree, tracing from a multicast source 145 to a receiver is difficult, since we do not know which branch of the 146 multicast tree the receiver lies. This means that we have to flood 147 the whole tree to find the path from a source to a receiver. On the 148 other hand, walking up the tree from a receiver to a source is easy, 149 as most existing multicast routing protocols know the upstream router 150 for each source. Tracing from a receiver to a source can involve 151 only the routers on the direct path. 153 This document specifies the multicast traceroute facility named 154 Mtrace version 2 or Mtrace2 which allows the tracing of an IP 155 multicast routing path. Mtrace2 is usually initiated from an Mtrace2 156 client by sending an Mtrace2 Query to a Last Hop Router (LHR) or to a 157 Rendezvous Point (RP). The RP is a special router where sources and 158 receivers meet in PIM-SM [5]. From the LHR/RP receiving the query, 159 the tracing is directed towards a specified source if a source 160 address is specified and source specific state exists on the 161 receiving router. If no source address is specified or if no source 162 specific state exists on a receiving LHR, the tracing is directed 163 toward the RP for the specified group address. Moreover, Mtrace2 164 provides additional information such as the packet rates and losses, 165 as well as other diagnostic information. Mtrace2 is primarily 166 intended for the following purposes: 168 o To trace the path that a packet would take from a source to a 169 receiver. 171 o To isolate packet loss problems (e.g., congestion). 173 o To isolate configuration problems (e.g., TTL threshold). 175 Figure 1 shows a typical case on how Mtrace2 is used. FHR represents 176 the first-hop router, LHR represents the last-hop router, and the 177 arrow lines represent the Mtrace2 messages that are sent from one 178 node to another. The numbers before the Mtrace2 messages represent 179 the sequence of the messages that would happen. Source, Receiver and 180 Mtrace2 client are typically hosts. 182 2. Request 2. Request 183 +----+ +----+ 184 | | | | 185 v | v | 186 +--------+ +-----+ +-----+ +----------+ 187 | Source |----| FHR |----- The Internet -----| LHR |----| Receiver | 188 +--------+ +-----+ | +-----+ +----------+ 189 \ | ^ 190 \ | / 191 \ | / 192 \ | / 193 3. Reply \ | / 1. Query 194 \ | / 195 \ | / 196 \ +---------+ / 197 v | Mtrace2 |/ 198 | client | 199 +---------+ 201 Figure 1 203 When an Mtrace2 client initiates a multicast trace, it sends an 204 Mtrace2 Query packet to the LHR or RP for a multicast group and, 205 optionally, a source address. The LHR/RP turns the Query packet into 206 a Request. The Request message type enables each of the upstream 207 routers processing the message to apply different packet and message 208 validation rules than those required for handling of a Query message. 209 The LHR/RP then appends a standard response block containing its 210 interface addresses and packet statistics to the Request packet, then 211 forwards the packet towards the source/RP. The Request packet is 212 either unicasted to its upstream router towards the source/RP, or 213 multicasted to the group if the upstream router's IP address is not 214 known. In a similar fashion, each router along the path to the 215 source/RP appends a standard response block to the end of the Request 216 packet before forwarding it to its upstream router. When the FHR 217 receives the Request packet, it appends its own standard response 218 block, turns the Request packet into a Reply, and unicasts the Reply 219 back to the Mtrace2 client. 221 The Mtrace2 Reply may be returned before reaching the FHR under some 222 circumstances. This can happen if a Request packet is received at an 223 RP or gateway, or when any of several types of error or exception 224 conditions occur which prevent sending of a request to the next 225 upstream router. 227 The Mtrace2 client waits for the Mtrace2 Reply message and displays 228 the results. When not receiving an Mtrace2 Reply message due to 229 network congestion, a broken router (see Section 5.6), or a non- 230 responding router (see Section 5.7), the Mtrace2 client may resend 231 another Mtrace2 Query with a lower hop count (see Section 3.2.1), and 232 repeat the process until it receives an Mtrace2 Reply message. The 233 details are Mtrace2 client specific, and it is outside the scope of 234 this document. 236 Note that when a router's control plane and forwarding plane are out 237 of sync, the Mtrace2 Requests might be forwarded based on the control 238 states instead. In which case, the traced path might not represent 239 the real path the data packets would follow. 241 Mtrace2 supports both IPv4 and IPv6. Unlike the previous version of 242 Mtrace, which implements its query and response as IGMP messages [8], 243 all Mtrace2 messages are UDP-based. Although the packet formats of 244 IPv4 and IPv6 Mtrace2 are different because of the address families, 245 the syntax between them is similar. 247 This document describes the base specification of Mtrace2 that can 248 serve as a basis for future proposals such as Mtrace2 for AMT [9] and 249 Mtrace2 for MVPN [10]. They are therefore out of the scope of this 250 document. 252 2. Terminology 254 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 255 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", 256 and "OPTIONAL" are to be interpreted as described in RFC 2119 [1], 257 and indicate requirement levels for compliant Mtrace2 258 implementations. 260 2.1. Definitions 262 Since Mtrace2 Queries and Requests flow in the opposite direction to 263 the data flow, we refer to "upstream" and "downstream" with respect 264 to data, unless explicitly specified. 266 Incoming interface 267 The interface on which data is expected to arrive from the 268 specified source and group. 270 Outgoing interface 271 This is one of the interfaces to which data from the source or RP 272 is expected to be transmitted for the specified source and group. 273 It is also the interface on which the Mtrace2 Request was 274 received. 276 Upstream router 277 The router, connecting to the Incoming interface of the current 278 router, which is responsible for forwarding data for the specified 279 source and group to the current router. 281 First-hop router (FHR) 282 The router that is directly connected to the source the Mtrace2 283 Query specifies. 285 Last-hop router (LHR) 286 A router that is directly connected to a receiver. It is also the 287 router that receives the Mtrace2 Query from an Mtrace2 client. 289 Group state 290 It is the state a shared-tree protocol, such as PIM-SM [5], uses 291 to choose the upstream router towards the RP for the specified 292 group. In this state, source-specific state is not available for 293 the corresponding group address on the router. 295 Source-specific state 296 It is the state that is used to choose the path towards the source 297 for the specified source and group. 299 ALL-[protocol]-ROUTERS group 300 It is a link-local multicast address for multicast routers to 301 communicate with their adjacent routers that are running the same 302 routing protocol. For instance, the IPv4 'ALL-PIM-ROUTERS' group 303 is '224.0.0.13', and the IPv6 'ALL-PIM-ROUTERS' group is 'ff02::d' 304 [5]. 306 3. Packet Formats 308 This section describes the details of the packet formats for Mtrace2 309 messages. 311 All Mtrace2 messages are encoded in TLV format (see Section 3.1). 312 The first TLV of a message is a message header TLV specifying the 313 type of message and additional context information required for 314 processing of the message and for parsing of subsequent TLVs in the 315 message. Subsequent TLVs in a message, referred to as Blocks, are 316 appended after the header TLV to provide additional information 317 associated with the message. If an implementation receives an 318 unknown TLV type for the first TLV in a message, it SHOULD ignore and 319 silently discard the TLV and any subsequent TLVs in the packet 320 containing the TLV. If an implementation receives an unknown TLV 321 type for a subsequent TLV within a message, it SHOULD ignore and 322 silently discard the TLV. If the length of a TLV exceeds the 323 available space in the containing packet, the implementation MUST 324 ignore and silently discard the TLV and any remaining portion of the 325 containing packet. Any data in the packet after the specified TLV 326 length is considered to be outside the boundary of the TLV and MUST 327 be ignored during processing of the TLV. 329 All Mtrace2 messages are UDP packets. For IPv4, Mtrace2 Query and 330 Request messages MUST NOT be fragmented. For IPv6, the packet size 331 for the Mtrace2 messages MUST NOT exceed 1280 bytes, which is the 332 smallest MTU for an IPv6 interface [2]. The source port is uniquely 333 selected by the local host operating system. The destination port is 334 the IANA reserved Mtrace2 port number (see Section 8). All Mtrace2 335 messages MUST have a valid UDP checksum. 337 Additionally, Mtrace2 supports both IPv4 and IPv6, but not mixed. 338 For example, if an Mtrace2 Query or Request message arrives in as an 339 IPv4 packet, all addresses specified in the Mtrace2 messages MUST be 340 IPv4 as well. Same rule applies to IPv6 Mtrace2 messages. 342 3.1. Mtrace2 TLV format 344 0 1 2 3 345 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 1 346 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 347 | Type | Length | Value .... | 348 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 350 Type: 8 bits 352 Describes the format of the Value field. For all the available 353 types, please see Section 3.2 355 Length: 16 bits 357 Length of Type, Length, and Value fields in octets. Minimum 358 length required is 3 octets. The maximum TLV length is not 359 defined; however the entire Mtrace2 packet length SHOULD NOT 360 exceed the available MTU. 362 Value: variable length 364 The format is based on the Type value. The length of the value 365 field is Length field minus 3. All reserved fields in the Value 366 field MUST be transmitted as zeros and ignored on receipt. 368 3.2. Defined TLVs 370 The following TLV Types are defined: 372 Code Type 373 ==== ================================ 374 0x01 Mtrace2 Query 375 0x02 Mtrace2 Request 376 0x03 Mtrace2 Reply 377 0x04 Mtrace2 Standard Response Block 378 0x05 Mtrace2 Augmented Response Block 379 0x06 Mtrace2 Extended Query Block 381 Each Mtrace2 message MUST begin with either a Query, Request or Reply 382 TLV. The first TLV determines the type of each Mtrace2 message. 383 Following a Query TLV, there can be a sequence of optional Extended 384 Query Blocks. In the case of a Request or a Reply TLV, it is then 385 followed by a sequence of Standard Response Blocks, each from a 386 multicast router on the path towards the source or the RP. In the 387 case more information is needed, a Standard Response Block can be 388 followed by one or multiple Augmented Response Blocks. 390 We will describe each message type in detail in the next few 391 sections. 393 3.2.1. Mtrace2 Query 395 An Mtrace2 Query is usually originated by an Mtrace2 client which 396 sends an Mtrace2 Query message to the LHR. When tracing towards the 397 source or the RP, the intermediate routers MUST NOT modify the Query 398 message except the Type field. If the actual number of hops is not 399 known, an Mtrace2 client could send an initial Query message with a 400 large # Hops (e.g., 0xffffffff), in order to try to trace the full 401 path. 403 An Mtrace2 Query message is shown as follows: 405 0 1 2 3 406 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 1 407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 408 | Type | Length | # Hops | 409 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 410 | | 411 | Multicast Address | 412 | | 413 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 414 | | 415 | Source Address | 416 | | 417 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 418 | | 419 | Mtrace2 Client Address | 420 | | 421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 422 | Query ID | Client Port # | 423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 425 Figure 2 427 # Hops: 8 bits 428 This field specifies the maximum number of hops that the Mtrace2 429 client wants to trace. If there are some error conditions in the 430 middle of the path that prevent an Mtrace2 Reply from being 431 received by the client, the client MAY issue another Mtrace2 Query 432 with a lower number of hops until it receives a Reply. 434 Multicast Address: 32 bits or 128 bits 435 This field specifies an IPv4 or IPv6 address, which can be either: 437 m-1: a multicast group address to be traced; or, 439 m-2: all 1's in case of IPv4 or the unspecified address (::) in 440 case of IPv6 if no group-specific information is desired. 442 Source Address: 32 bits or 128 bits 443 This field specifies an IPv4 or IPv6 address, which can be either: 445 s-1: an unicast address of the source to be traced; or, 447 s-2: all 1's in case of IPv4 or the unspecified address (::) in 448 case of IPv6 if no source-specific information is desired. 449 For example, the client is tracing a (*,g) group state. 451 Note that it is invalid to have a source-group combination of 452 (s-2, m-2). If a router receives such combination in an Mtrace2 453 Query, it MUST silently discard the Query. 455 Mtrace2 Client Address: 32 bits or 128 bits 456 This field specifies the Mtrace2 client's IPv4 address or IPv6 457 global address. This address MUST be a valid unicast address, and 458 therefore, MUST NOT be all 1's or an unspecified address. The 459 Mtrace2 Reply will be sent to this address. 461 Query ID: 16 bits 462 This field is used as a unique identifier for this Mtrace2 Query 463 so that duplicate or delayed Reply messages may be detected. 465 Client Port #: 16 bits 466 This field specifies the destination UDP port number for receiving 467 the Mtrace2 Reply packet. 469 3.2.2. Mtrace2 Request 471 The format of an Mtrace2 Request message is similar to an Mtrace2 472 Query except the Type field is 0x02. 474 When a LHR receives an Mtrace2 Query message, it would turn the Query 475 into a Request by changing the Type field of the Query from 0x01 to 476 0x02. The LHR would then append an Mtrace2 Standard Response Block 477 (see Section 3.2.4) of its own to the Request message before sending 478 it upstream. The upstream routers would do the same without changing 479 the Type field until one of them is ready to send a Reply. 481 3.2.3. Mtrace2 Reply 483 The format of an Mtrace2 Reply message is similar to an Mtrace2 Query 484 except the Type field is 0x03. 486 When a FHR or a RP receives an Mtrace2 Request message which is 487 destined to itself, it would append an Mtrace2 Standard Response 488 Block (see Section 3.2.4) of its own to the Request message. Next, 489 it would turn the Request message into a Reply by changing the Type 490 field of the Request from 0x02 to 0x03. The Reply message would then 491 be unicasted to the Mtrace2 client specified in the Mtrace2 Client 492 Address field. 494 There are a number of cases an intermediate router might return a 495 Reply before a Request reaches the FHR or the RP. See Section 4.1.1, 496 Section 4.2.2, Section 4.3.3, and Section 4.5 for more details. 498 3.2.4. IPv4 Mtrace2 Standard Response Block 500 This section describes the message format of an IPv4 Mtrace2 Standard 501 Response Block. The Type field is 0x04. 503 0 1 2 3 504 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 1 505 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 506 | Type | Length | MBZ | 507 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 508 | Query Arrival Time | 509 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 510 | Incoming Interface Address | 511 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 512 | Outgoing Interface Address | 513 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 514 | Upstream Router Address | 515 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 516 | | 517 . Input packet count on incoming interface . 518 | | 519 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 520 | | 521 . Output packet count on outgoing interface . 522 | | 523 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 524 | | 525 . Total number of packets for this source-group pair . 526 | | 527 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 528 | Rtg Protocol | Multicast Rtg Protocol | 529 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 530 | Fwd TTL | MBZ |S| Src Mask |Forwarding Code| 531 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 533 MBZ: 8 bits 534 This field MUST be zeroed on transmission and ignored on 535 reception. 537 Query Arrival Time: 32 bits 538 The Query Arrival Time is a 32-bit NTP timestamp specifying the 539 arrival time of the Mtrace2 Query or Request packet at this 540 router. The 32-bit form of an NTP timestamp consists of the 541 middle 32 bits of the full 64-bit form; that is, the low 16 bits 542 of the integer part and the high 16 bits of the fractional part. 544 The following formula converts from a UNIX timeval to a 32-bit NTP 545 timestamp: 547 query_arrival_time 548 = ((tv.tv_sec + 32384) << 16) + ((tv.tv_nsec << 7) / 1953125) 550 The constant 32384 is the number of seconds from Jan 1, 1900 to 551 Jan 1, 1970 truncated to 16 bits. ((tv.tv_nsec << 7) / 1953125) 552 is a reduction of ((tv.tv_nsec / 1000000000) << 16). 554 Note that Mtrace2 does not require all the routers on the path to 555 have synchronized clocks in order to measure one-way latency. 557 Additionally, Query Arrival Time is useful for measuring the 558 packet rate. For example, suppose that a client issues two 559 queries, and the corresponding requests R1 and R2 arrive at router 560 X at time T1 and T2, then the client would be able to compute the 561 packet rate on router X by using the packet count information 562 stored in the R1 and R2, and the time T1 and T2. 564 Incoming Interface Address: 32 bits 565 This field specifies the address of the interface on which packets 566 from the source or the RP are expected to arrive, or 0 if unknown 567 or unnumbered. 569 Outgoing Interface Address: 32 bits 570 This field specifies the address of the interface on which packets 571 from the source or the RP are expected to transmit towards the 572 receiver, or 0 if unknown or unnumbered. This is also the address 573 of the interface on which the Mtrace2 Query or Request arrives. 575 Upstream Router Address: 32 bits 576 This field specifies the address of the upstream router from which 577 this router expects packets from this source. This may be a 578 multicast group (e.g., ALL-[protocol]-ROUTERS group) if the 579 upstream router is not known because of the workings of the 580 multicast routing protocol. However, it should be 0 if the 581 incoming interface address is unknown or unnumbered. 583 Input packet count on incoming interface: 64 bits 584 This field contains the number of multicast packets received for 585 all groups and sources on the incoming interface, or all 1's if no 586 count can be reported. This counter may have the same value as 587 ifHCInMulticastPkts from the IF-MIB [12] for this interface. 589 Output packet count on outgoing interface: 64 bit 590 This field contains the number of multicast packets that have been 591 transmitted or queued for transmission for all groups and sources 592 on the outgoing interface, or all 1's if no count can be reported. 593 This counter may have the same value as ifHCOutMulticastPkts from 594 the IF-MIB [12] for this interface. 596 Total number of packets for this source-group pair: 64 bits 597 This field counts the number of packets from the specified source 598 forwarded by the router to the specified group, or all 1's if no 599 count can be reported. If the S bit is set (see below), the count 600 is for the source network, as specified by the Src Mask field (see 601 below). If the S bit is set and the Src Mask field is 127, 602 indicating no source-specific state, the count is for all sources 603 sending to this group. This counter should have the same value as 604 ipMcastRoutePkts from the IPMROUTE-STD-MIB [13] for this 605 forwarding entry. 607 Rtg Protocol: 16 bits 608 This field describes the unicast routing protocol running between 609 this router and the upstream router, and it is used to determine 610 the RPF interface for the specified source or RP. This value 611 should have the same value as ipMcastRouteRtProtocol from the 612 IPMROUTE-STD-MIB [13] for this entry. If the router is not able 613 to obtain this value, all 0's must be specified. 615 Multicast Rtg Protocol: 16 bits 616 This field describes the multicast routing protocol in use between 617 the router and the upstream router. This value should have the 618 same value as ipMcastRouteProtocol from the IPMROUTE-STD-MIB [13] 619 for this entry. If the router cannot obtain this value, all 0's 620 must be specified. 622 Fwd TTL: 8 bits 623 This field contains the configured multicast TTL threshold, if 624 any, of the outgoing interface. 626 S: 1 bit 627 If this bit is set, it indicates that the packet count for the 628 source-group pair is for the source network, as determined by 629 masking the source address with the Src Mask field. 631 Src Mask: 7 bits 632 This field contains the number of 1's in the netmask the router 633 has for the source (i.e. a value of 24 means the netmask is 634 0xffffff00). If the router is forwarding solely on group state, 635 this field is set to 127 (0x7f). 637 Forwarding Code: 8 bits 638 This field contains a forwarding information/error code. Values 639 with the high order bit set (0x80-0xff) are intended for use as 640 error or exception codes. Section 4.1 and Section 4.2 explain how 641 and when the Forwarding Code is filled. Defined values are as 642 follows: 644 Value Name Description 645 ----- -------------- ---------------------------------------------- 646 0x00 NO_ERROR No error 647 0x01 WRONG_IF Mtrace2 Request arrived on an interface 648 to which this router would not forward for 649 the specified group towards the source or RP. 650 0x02 PRUNE_SENT This router has sent a prune upstream which 651 applies to the source and group in the 652 Mtrace2 Request. 653 0x03 PRUNE_RCVD This router has stopped forwarding for this 654 source and group in response to a request 655 from the downstream router. 656 0x04 SCOPED The group is subject to administrative 657 scoping at this router. 658 0x05 NO_ROUTE This router has no route for the source or 659 group and no way to determine a potential 660 route. 661 0x06 WRONG_LAST_HOP This router is not the proper LHR. 662 0x07 NOT_FORWARDING This router is not forwarding this source and 663 group out the outgoing interface for an 664 unspecified reason. 665 0x08 REACHED_RP Reached the Rendezvous Point. 666 0x09 RPF_IF Mtrace2 Request arrived on the expected 667 RPF interface for this source and group. 668 0x0A NO_MULTICAST Mtrace2 Request arrived on an interface 669 which is not enabled for multicast. 670 0x0B INFO_HIDDEN One or more hops have been hidden from this 671 trace. 672 0x0C REACHED_GW Mtrace2 Request arrived on a gateway (e.g., 673 a NAT or firewall) that hides the 674 information between this router and the 675 Mtrace2 client. 676 0x0D UNKNOWN_QUERY A non-transitive Extended Query Type was 677 received by a router which does not support 678 the type. 679 0x80 FATAL_ERROR A fatal error is one where the router may 680 know the upstream router but cannot forward 681 the message to it. 682 0x81 NO_SPACE There was not enough room to insert another 683 Standard Response Block in the packet. 684 0x83 ADMIN_PROHIB Mtrace2 is administratively prohibited. 686 3.2.5. IPv6 Mtrace2 Standard Response Block 688 This section describes the message format of an IPv6 Mtrace2 Standard 689 Response Block. The Type field is also 0x04. 691 0 1 2 3 692 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 1 693 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 694 | Type | Length | MBZ | 695 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 696 | Query Arrival Time | 697 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 698 | Incoming Interface ID | 699 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 700 | Outgoing Interface ID | 701 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 702 | | 703 * Local Address * 704 | | 705 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 706 | | 707 * Remote Address * 708 | | 709 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 710 | | 711 . Input packet count on incoming interface . 712 | | 713 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 714 | | 715 . Output packet count on outgoing interface . 716 | | 717 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 718 | | 719 . Total number of packets for this source-group pair . 720 | | 721 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 722 | Rtg Protocol | Multicast Rtg Protocol | 723 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 724 | MBZ 2 |S|Src Prefix Len |Forwarding Code| 725 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 727 MBZ: 8 bits 728 This field MUST be zeroed on transmission and ignored on 729 reception. 731 Query Arrival Time: 32 bits 732 Same definition as in IPv4. 734 Incoming Interface ID: 32 bits 735 This field specifies the interface ID on which packets from the 736 source or RP are expected to arrive, or 0 if unknown. This ID 737 should be the value taken from InterfaceIndex of the IF-MIB [12] 738 for this interface. 740 Outgoing Interface ID: 32 bits 741 This field specifies the interface ID to which packets from the 742 source or RP are expected to transmit, or 0 if unknown. This ID 743 should be the value taken from InterfaceIndex of the IF-MIB [12] 744 for this interface 746 Local Address: 128 bits 747 This field specifies a global IPv6 address that uniquely 748 identifies the router. An unique local unicast address [11] 749 SHOULD NOT be used unless the router is only assigned link-local 750 and unique local addresses. If the router is only assigned link- 751 local addresses, its link-local address can be specified in this 752 field. 754 Remote Address: 128 bits 755 This field specifies the address of the upstream router, which, in 756 most cases, is a link-local unicast address for the upstream 757 router. 759 Although a link-local address does not have enough information to 760 identify a node, it is possible to detect the upstream router with 761 the assistance of Incoming Interface ID and the current router 762 address (i.e., Local Address). 764 Note that this may be a multicast group (e.g., ALL-[protocol]- 765 ROUTERS group) if the upstream router is not known because of the 766 workings of a multicast routing protocol. However, it should be 767 the unspecified address (::) if the incoming interface address is 768 unknown. 770 Input packet count on incoming interface: 64 bits 771 Same definition as in IPv4. 773 Output packet count on outgoing interface: 64 bits 774 Same definition as in IPv4. 776 Total number of packets for this source-group pair: 64 bits 777 Same definition as in IPv4, except if the S bit is set (see 778 below), the count is for the source network, as specified by the 779 Src Prefix Len field. If the S bit is set and the Src Prefix Len 780 field is 255, indicating no source-specific state, the count is 781 for all sources sending to this group. This counter should have 782 the same value as ipMcastRoutePkts from the IPMROUTE-STD-MIB [13] 783 for this forwarding entry. 785 Rtg Protocol: 16 bits 786 Same definition as in IPv4. 788 Multicast Rtg Protocol: 16 bits 789 Same definition as in IPv4. 791 MBZ 2: 15 bits 792 This field MUST be zeroed on transmission and ignored on 793 reception. 795 S: 1 bit 796 Same definition as in IPv4, except the Src Prefix Len field is 797 used to mask the source address. 799 Src Prefix Len: 8 bits 800 This field contains the prefix length this router has for the 801 source. If the router is forwarding solely on group state, this 802 field is set to 255 (0xff). 804 Forwarding Code: 8 bits 805 Same definition as in IPv4. 807 3.2.6. Mtrace2 Augmented Response Block 809 In addition to the Standard Response Block, a multicast router on the 810 traced path can optionally add one or multiple Augmented Response 811 Blocks before sending the Request to its upstream router. 813 The Augmented Response Block is flexible for various purposes such as 814 providing diagnosis information (see Section 7) and protocol 815 verification. Its Type field is 0x05, and its format is as follows: 817 0 1 2 3 818 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 1 819 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 820 | Type | Length | MBZ | 821 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 822 | Augmented Response Type | Value .... | 823 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 825 MBZ: 8 bits 826 This field MUST be zeroed on transmission and ignored on 827 reception. 829 Augmented Response Type: 16 bits 830 This field specifies the type of various responses from a 831 multicast router that might need to communicate back to the 832 Mtrace2 client as well as the multicast routers on the traced 833 path. 835 The Augmented Response Type is defined as follows: 837 Code Type 838 ==== =============================================== 839 0x01 # of the returned Standard Response Blocks 841 When the NO_SPACE error occurs on a router, the router should send 842 the original Mtrace2 Request received from the downstream router 843 as a Reply back to the Mtrace2 client, and continue with a new 844 Mtrace2 Request. In the new Request, the router would add a 845 Standard Response Block followed by an Augmented Response Block 846 with 0x01 as the Augmented Response Type, and the number of the 847 returned Mtrace2 Standard Response Blocks as the Value. 849 Each upstream router would recognize the total number of hops the 850 Request has been traced so far by adding this number and the 851 number of the Standard Response Block in the current Request 852 message. 854 This document only defines one Augmented Response Type in the 855 Augmented Response Block. The description on how to provide 856 diagnosis information using the Augmented Response Block is out of 857 the scope of this document, and will be addressed in separate 858 documents. 860 Value: variable length 861 The format is based on the Augmented Response Type value. The 862 length of the value field is Length field minus 6. 864 3.2.7. Mtrace2 Extended Query Block 866 There may be a sequence of optional Extended Query Blocks that follow 867 an Mtrace2 Query to further specify any information needed for the 868 Query. For example, an Mtrace2 client might be interested in tracing 869 the path the specified source and group would take based on a certain 870 topology. In which case, the client can pass in the multi-topology 871 ID as the Value for an Extended Query Type (see below). The Extended 872 Query Type is extensible and the behavior of the new types will be 873 addressed by separate documents. 875 The Mtrace2 Extended Query Block's Type field is 0x06, and is 876 formatted as follows: 878 0 1 2 3 879 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 1 880 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 881 | Type | Length | MBZ |T| 882 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 883 | Extended Query Type | Value .... | 884 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 886 MBZ: 7 bits 887 This field MUST be zeroed on transmission and ignored on 888 reception. 890 T-bit (Transitive Attribute): 1 bit 891 If the TLV type is unrecognized by the receiving router, then this 892 TLV is either discarded or forwarded along with the Query, 893 depending on the value of this bit. If this bit is set, then the 894 router MUST forward this TLV. If this bit is clear, the router 895 MUST send an Mtrace2 Reply with an UNKNOWN_QUERY error. 897 Extended Query Type: 16 bits 898 This field specifies the type of the Extended Query Block. 900 Value: 16 bits 901 This field specifies the value of this Extended Query. 903 4. Router Behavior 905 This section describes the router behavior in the context of Mtrace2 906 in detail. 908 4.1. Receiving Mtrace2 Query 910 An Mtrace2 Query message is an Mtrace2 message with no response 911 blocks filled in, and uses TLV type of 0x01. 913 4.1.1. Query Packet Verification 915 Upon receiving an Mtrace2 Query message, a router MUST examine 916 whether the Multicast Address and the Source Address are a valid 917 combination as specified in Section 3.2.1, and whether the Mtrace2 918 Client Address is a valid IP unicast address. If either one is 919 invalid, the Query MUST be silently ignored. 921 Mtrace2 supports a non-local client to the LHR/RP. A router SHOULD, 922 however, support a mechanism to filter out queries from clients 923 beyond a specified administrative boundary. The potential approaches 924 are described in Section 9.2. 926 In the case where a local LHR client is required, the router must 927 then examine the Query to see if it is the proper LHR/RP for the 928 destination address in the packet. It is the proper local LHR if it 929 has a multicast-capable interface on the same subnet as the Mtrace2 930 Client Address and is the router that would forward traffic from the 931 given (S,G) or (*,G) onto that subnet. It is the proper RP if the 932 multicast group address specified in the query is 0 and if the IP 933 header destination address is a valid RP address on this router. 935 If the router determines that it is not the proper LHR/RP, or it 936 cannot make that determination, it does one of two things depending 937 on whether the Query was received via multicast or unicast. If the 938 Query was received via multicast, then it MUST be silently discarded. 939 If it was received via unicast, the router turns the Query into a 940 Reply message by changing the TLV type to 0x03 and appending a 941 Standard Response Block with a Forwarding Code of WRONG_LAST_HOP. 942 The rest of the fields in the Standard Response Block MUST be zeroed. 943 The router then sends the Reply message to the Mtrace2 Client Address 944 on the Client Port # as specified in the Mtrace2 Query. 946 Duplicate Query messages as identified by the tuple (Mtrace2 Client 947 Address, Query ID) SHOULD be ignored. This MAY be implemented using 948 a cache of previously processed queries keyed by the Mtrace2 Client 949 Address and Query ID pair. The duration of the cached entries is 950 implementation specific. Duplicate Request messages MUST NOT be 951 ignored in this manner. 953 4.1.2. Query Normal Processing 955 When a router receives an Mtrace2 Query and it determines that it is 956 the proper LHR/RP, it turns the Query to a Request by changing the 957 TLV type from 0x01 to 0x02, and performs the steps listed in 958 Section 4.2. 960 4.2. Receiving Mtrace2 Request 962 An Mtrace2 Request is an Mtrace2 message that uses TLV type of 0x02. 963 With the exception of the LHR, whose Request was just converted from 964 a Query, each Request received by a router should have at least one 965 Standard Response Block filled in. 967 4.2.1. Request Packet Verification 969 If the Mtrace2 Request does not come from an adjacent router, or if 970 the Request is not addressed to this router, or if the Request is 971 addressed to a multicast group which is not a link-scoped group 972 (i.e., 224.0.0.0/24 for IPv4, FFx2::/16 [3] for IPv6), it MUST be 973 silently ignored. GTSM [14] SHOULD be used by the router to 974 determine whether the router is adjacent or not. 976 If the sum of the number of the Standard Response Blocks in the 977 received Mtrace2 Request and the value of the Augmented Response Type 978 of 0x01, if any, is equal or more than the # Hops in the Mtrace2 979 Request, it MUST be silently ignored. 981 4.2.2. Request Normal Processing 983 When a router receives an Mtrace2 Request message, it performs the 984 following steps. Note that it is possible to have multiple 985 situations covered by the Forwarding Codes. The first one 986 encountered is the one that is reported, i.e. all "note Forwarding 987 Code N" should be interpreted as "if Forwarding Code is not already 988 set, set Forwarding Code to N". Note that in the steps described 989 below the "Outgoing Interface" is the one on which the Mtrace2 990 Request message arrives. 992 1. Prepare a Standard Response Block to be appended to the packet, 993 setting all fields to an initial default value of zero. 995 2. If Mtrace2 is administratively prohibited, note the Forwarding 996 Code of ADMIN_PROHIB and skip to step 4. 998 3. In the Standard Response Block, fill in the Query Arrival Time, 999 Outgoing Interface Address (for IPv4) or Outgoing Interface ID 1000 (for IPv6), Output Packet Count, and Fwd TTL (for IPv4). 1002 4. Attempt to determine the forwarding information for the 1003 specified source and group, using the same mechanisms as would 1004 be used when a packet is received from the source destined for 1005 the group. A state need not be instantiated, it can be a 1006 "phantom" state created only for the purpose of the trace, such 1007 as "dry-run." 1009 If using a shared-tree protocol and there is no source-specific 1010 state, or if no source-specific information is desired (i.e., 1011 all 1's for IPv4 or unspecified address (::) for IPv6), group 1012 state should be used. If there is no group state or no group- 1013 specific information is desired, potential source state (i.e., 1014 the path that would be followed for a source-specific Join) 1015 should be used. 1017 5. If no forwarding information can be determined, the router notes 1018 a Forwarding Code of NO_ROUTE, sets the remaining fields that 1019 have not yet been filled in to zero, and then sends an Mtrace2 1020 Reply back to the Mtrace2 client. 1022 6. If a Forwarding Code of ADMIN_PROHIB has been set, skip to step 1023 7. Otherwise, fill in the Incoming Interface Address (or 1024 Incoming Interface ID and Local Address for IPv6), Upstream 1025 Router Address (or Remote Address for IPv6), Input Packet Count, 1026 Total Number of Packets, Routing Protocol, S, and Src Mask (or 1027 Src Prefix Len for IPv6) using the forwarding information 1028 determined in step 4. 1030 7. If the Outgoing interface is not enabled for multicast, note 1031 Forwarding Code of NO_MULTICAST. If the Outgoing interface is 1032 the interface from which the router would expect data to arrive 1033 from the source, note forwarding code RPF_IF. If the Outgoing 1034 interface is not one to which the router would forward data from 1035 the source or RP to the group, a Forwarding code of WRONG_IF is 1036 noted. In the above three cases, the router will return an 1037 Mtrace2 Reply and terminate the trace. 1039 8. If the group is subject to administrative scoping on either the 1040 Outgoing or Incoming interfaces, a Forwarding Code of SCOPED is 1041 noted. 1043 9. If this router is the RP for the group for a non-source-specific 1044 query, note a Forwarding Code of REACHED_RP. The router will 1045 send an Mtrace2 Reply and terminate the trace. 1047 10. If this router is directly connected to the specified source or 1048 source network on the Incoming interface, it sets the Upstream 1049 Router Address (for IPv4) or the Remote Address (for IPv6) of 1050 the response block to zero. The router will send an Mtrace2 1051 Reply and terminate the trace. 1053 11. If this router has sent a prune upstream which applies to the 1054 source and group in the Mtrace2 Request, it notes a Forwarding 1055 Code of PRUNE_SENT. If the router has stopped forwarding 1056 downstream in response to a prune sent by the downstream router, 1057 it notes a Forwarding Code of PRUNE_RCVD. If the router should 1058 normally forward traffic downstream for this source and group 1059 but is not, it notes a Forwarding Code of NOT_FORWARDING. 1061 12. If this router is a gateway (e.g., a NAT or firewall) that hides 1062 the information between this router and the Mtrace2 client, it 1063 notes a Forwarding Code of REACHED_GW. The router continues the 1064 processing as described in Section 4.5. 1066 13. If the total number of the Standard Response Blocks, including 1067 the newly prepared one, and the value of the Augmented Response 1068 Type of 0x01, if any, is less than the # Hops in the Request, 1069 the packet is then forwarded to the upstream router as described 1070 in Section 4.3; otherwise, the packet is sent as an Mtrace2 1071 Reply to the Mtrace2 client as described in Section 4.4. 1073 4.3. Forwarding Mtrace2 Request 1075 This section describes how an Mtrace2 Request should be forwarded. 1077 4.3.1. Destination Address 1079 If the upstream router for the Mtrace2 Request is known for this 1080 request, the Mtrace2 Request is sent to that router. If the Incoming 1081 interface is known but the upstream router is not, the Mtrace2 1082 Request is sent to an appropriate multicast address on the Incoming 1083 interface. The multicast address SHOULD depend on the multicast 1084 routing protocol in use, such as ALL-[protocol]-ROUTERS group. It 1085 MUST be a link-scoped group (i.e., 224.0.0.0/24 for IPv4, FF02::/16 1086 for IPv6), and MUST NOT be the all-systems multicast group 1087 (224.0.0.1) for IPv4 and All Nodes Address (FF02::1) for IPv6. It 1088 MAY also be the all-routers multicast group (224.0.0.2) for IPv4 or 1089 All Routers Address (FF02::2) for IPv6 if the routing protocol in use 1090 does not define a more appropriate multicast address. 1092 4.3.2. Source Address 1094 An Mtrace2 Request should be sent with the address of the Incoming 1095 interface. However, if the Incoming interface is unnumbered, the 1096 router can use one of its numbered interface addresses as the source 1097 address. 1099 4.3.3. Appending Standard Response Block 1101 An Mtrace2 Request MUST be sent upstream towards the source or the RP 1102 after appending a Standard Response Block to the end of the received 1103 Mtrace2 Request. The Standard Response Block includes the multicast 1104 states and statistics information of the router described in 1105 Section 3.2.4. 1107 If appending the Standard Response Block would make the Mtrace2 1108 Request packet longer than the MTU of the Incoming Interface, or, in 1109 the case of IPv6, longer than 1280 bytes, the router MUST change the 1110 Forwarding Code in the last Standard Response Block of the received 1111 Mtrace2 Request into NO_SPACE. The router then turns the Request 1112 into a Reply, and sends the Reply as described in Section 4.4. 1114 The router will continue with a new Request by copying from the old 1115 Request excluding all the response blocks, followed by the previously 1116 prepared Standard Response Block, and an Augmented Response Block 1117 with Augmented Response Type of 0x01 and the number of the returned 1118 Standard Response Blocks as the value. The new Request is then 1119 forwarded upstream. 1121 4.4. Sending Mtrace2 Reply 1123 An Mtrace2 Reply MUST be returned to the client by a router if any of 1124 the following conditions occur: 1126 1. The total number of the traced routers are equal to the # of hops 1127 in the request (including the one just added) plus the number of 1128 the returned blocks, if any. 1130 2. Appending the Standard Response Block would make the Mtrace2 1131 Request packet longer than the MTU of the Incoming interface. 1132 (In case of IPv6 not more than 1280 bytes; see Section 4.3.3 for 1133 additional details on handling of this case.) 1135 3. The request has reached the RP for a non source specific query or 1136 has reached the first hop router for a source specific query (see 1137 Section 4.2.2, items 9 and 10 for additional details). 1139 4.4.1. Destination Address 1141 An Mtrace2 Reply MUST be sent to the address specified in the Mtrace2 1142 Client Address field in the Mtrace2 Request. 1144 4.4.2. Source Address 1146 An Mtrace2 Reply SHOULD be sent with the address of the router's 1147 Outgoing interface. However, if the Outgoing interface address is 1148 unnumbered, the router can use one of its numbered interface 1149 addresses as the source address. 1151 4.4.3. Appending Standard Response Block 1153 An Mtrace2 Reply MUST be sent with the prepared Standard Response 1154 Block appended at the end of the received Mtrace2 Request except in 1155 the case of NO_SPACE forwarding code. 1157 4.5. Proxying Mtrace2 Query 1159 When a gateway (e.g., a NAT or firewall), which needs to block 1160 unicast packets to the Mtrace2 client, or hide information between 1161 the gateway and the Mtrace2 client, receives an Mtrace2 Query from an 1162 adjacent host or Mtrace2 Request from an adjacent router, it appends 1163 a Standard Response Block with REACHED_GW as the Forwarding Code. It 1164 turns the Query or Request into a Reply, and sends the Reply back to 1165 the client. 1167 At the same time, the gateway originates a new Mtrace2 Query message 1168 by copying the original Mtrace2 header (the Query or Request without 1169 any of the response blocks), and makes the changes as follows: 1171 o sets the RPF interface's address as the Mtrace2 Client Address; 1173 o uses its own port number as the Client Port #; and, 1175 o decreases # Hops by ((number of the Standard Response Blocks that 1176 were just returned in a Reply) - 1). The "-1" in this expression 1177 accounts for the additional Standard Response Block appended by 1178 the gateway router. 1180 The new Mtrace2 Query message is then sent to the upstream router or 1181 to an appropriate multicast address on the RPF interface. 1183 When the gateway receives an Mtrace2 Reply whose Query ID matches the 1184 one in the original Mtrace2 header, it MUST relay the Mtrace2 Reply 1185 back to the Mtrace2 client by replacing the Reply's header with the 1186 original Mtrace2 header. If the gateway does not receive the 1187 corresponding Mtrace2 Reply within the [Mtrace Reply Timeout] period 1188 (see Section 5.8.4), then it silently discards the original Mtrace2 1189 Query or Request message, and terminates the trace. 1191 4.6. Hiding Information 1193 Information about a domain's topology and connectivity may be hidden 1194 from the Mtrace2 Requests. The Forwarding Code of INFO_HIDDEN may be 1195 used to note that. For example, the incoming interface address and 1196 packet count on the ingress router of a domain, and the outgoing 1197 interface address and packet count on the egress router of the domain 1198 can be specified as all 1's. Additionally, the source-group packet 1199 count (see Section 3.2.4 and Section 3.2.5) within the domain may be 1200 all 1's if it is hidden. 1202 5. Client Behavior 1204 This section describes the behavior of an Mtrace2 client in detail. 1206 5.1. Sending Mtrace2 Query 1208 An Mtrace2 client initiates an Mtrace2 Query by sending the Query to 1209 the LHR of interest. 1211 5.1.1. Destination Address 1213 If an Mtrace2 client knows the proper LHR, it unicasts an Mtrace2 1214 Query packet to that router; otherwise, it MAY send the Mtrace2 Query 1215 packet to the all-routers multicast group (224.0.0.2) for IPv4 or All 1216 Routers Address (FF02::2) for IPv6. This will ensure that the packet 1217 is received by the LHR on the subnet. 1219 See also Section 5.4 on determining the LHR. 1221 5.1.2. Source Address 1223 An Mtrace2 Query MUST be sent with the client's interface address, 1224 which would be the Mtrace2 Client Address. 1226 5.2. Determining the Path 1228 An Mtrace2 client could send an initial Query messages with a large # 1229 Hops, in order to try to trace the full path. If this attempt fails, 1230 one strategy is to perform a linear search (as the traditional 1231 unicast traceroute program does); set the # Hops field to 1 and try 1232 to get a Reply, then 2, and so on. If no Reply is received at a 1233 certain hop, the hop count can continue past the non-responding hop, 1234 in the hopes that further hops may respond. These attempts should 1235 continue until the [Mtrace Reply Timeout] timeout has occurred. 1237 See also Section 5.6 on receiving the results of a trace. 1239 5.3. Collecting Statistics 1241 After a client has determined that it has traced the whole path or as 1242 much as it can expect to (see Section 5.8), it might collect 1243 statistics by waiting a short time and performing a second trace. If 1244 the path is the same in the two traces, statistics can be displayed 1245 as described in Section 7.3 and Section 7.4. 1247 5.4. Last Hop Router (LHR) 1249 The Mtrace2 client may not know which is the last-hop router, or that 1250 router may be behind a firewall that blocks unicast packets but 1251 passes multicast packets. In these cases, the Mtrace2 Request should 1252 be multicasted to the all-routers multicast group (224.0.0.2) for 1253 IPv4 or All Routers Address (FF02::2) for IPv6. All routers except 1254 the correct last-hop router SHOULD ignore any Mtrace2 Request 1255 received via multicast. 1257 5.5. First Hop Router (FHR) 1259 The IANA assigned 224.0.1.32 as the default multicast group for old 1260 IPv4 mtrace (v1) responses, in order to support mtrace clients that 1261 are not unicast reachable from the first-hop router. Mtrace2, 1262 however, does not require any IPv4/IPv6 multicast addresses for the 1263 Mtrace2 Replies. Every Mtrace2 Reply is sent to the unicast address 1264 specified in the Mtrace2 Client Address field of the Mtrace2 Reply. 1266 5.6. Broken Intermediate Router 1268 A broken intermediate router might simply not understand Mtrace2 1269 packets, and drop them. The Mtrace2 client will get no Reply at all 1270 as a result. It should then perform a hop-by-hop search by setting 1271 the # Hops field until it gets an Mtrace2 Reply. The client may use 1272 linear or binary search; however, the latter is likely to be slower 1273 because a failure requires waiting for the [Mtrace Reply Timeout] 1274 period. 1276 5.7. Non-Supported Router 1278 When a non-supported router receives an Mtrace2 Query or Request 1279 message whose destination address is a multicast address, the router 1280 will silently discard the message. 1282 When the router receives an Mtrace2 Query which is destined to 1283 itself, the router would return an ICMP port unreachable to the 1284 Mtrace2 client. On the other hand, when the router receives an 1285 Mtrace2 Request which is destined to itself, the router would return 1286 an ICMP port unreachable to its adjacent router from which the 1287 Request receives. Therefore, the Mtrace2 client needs to terminate 1288 the trace when the [Mtrace Reply Timeout] timeout has occurred, and 1289 may then issue another Query with a lower number of # Hops. 1291 5.8. Mtrace2 Termination 1293 When performing an expanding hop-by-hop trace, it is necessary to 1294 determine when to stop expanding. 1296 5.8.1. Arriving at Source 1298 A trace can be determined to have arrived at the source if the 1299 Incoming Interface of the last router in the trace is non-zero, but 1300 the Upstream Router is zero. 1302 5.8.2. Fatal Error 1304 A trace has encountered a fatal error if the last Forwarding Error in 1305 the trace has the 0x80 bit set. 1307 5.8.3. No Upstream Router 1309 A trace can not continue if the last Upstream Router in the trace is 1310 set to 0. 1312 5.8.4. Reply Timeout 1314 This document defines the [Mtrace Reply Timeout] value, which is used 1315 to time out an Mtrace2 Reply as seen in Section 4.5, Section 5.2, and 1316 Section 5.7. The default [Mtrace Reply Timeout] value is 10 1317 (seconds), and can be manually changed on the Mtrace2 client and 1318 routers. 1320 5.9. Continuing after an Error 1322 When the NO_SPACE error occurs, as described in Section 4.2, a router 1323 will send back an Mtrace2 Reply to the Mtrace2 client, and continue 1324 with a new Request (see Section 4.3.3). In which case, the Mtrace2 1325 client may receive multiple Mtrace2 Replies from different routers 1326 along the path. When this happens, the client MUST treat them as a 1327 single Mtrace2 Reply message. 1329 If a trace times out, it is very likely that a router in the middle 1330 of the path does not support Mtrace2. That router's address will be 1331 in the Upstream Router field of the last Standard Response Block in 1332 the last received Reply. A client may be able to determine (via 1333 mrinfo or SNMP [11][13]) a list of neighbors of the non-responding 1334 router. If desired, each of those neighbors could be probed to 1335 determine the remainder of the path. Unfortunately, this heuristic 1336 may end up with multiple paths, since there is no way of knowing what 1337 the non-responding router's algorithm for choosing an upstream router 1338 is. However, if all paths but one flow back towards the non- 1339 responding router, it is possible to be sure that this is the correct 1340 path. 1342 6. Protocol-Specific Considerations 1344 This section describes the Mtrace2 behavior with the presence of 1345 different multicast protocols. 1347 6.1. PIM-SM 1349 When an Mtrace2 reaches a PIM-SM RP, and the RP does not forward the 1350 trace on, it means that the RP has not performed a source-specific 1351 join so there is no more state to trace. However, the path that 1352 traffic would use if the RP did perform a source-specific join can be 1353 traced by setting the trace destination to the RP, the trace source 1354 to the traffic source, and the trace group to 0. This Mtrace2 Query 1355 may be unicasted to the RP, and the RP takes the same actions as an 1356 LHR. 1358 6.2. Bi-Directional PIM 1360 Bi-directional PIM [6] is a variant of PIM-SM that builds bi- 1361 directional shared trees connecting multicast sources and receivers. 1362 Along the bi-directional shared trees, multicast data is natively 1363 forwarded from the sources to the Rendezvous Point Link (RPL), and 1364 from which, to receivers without requiring source-specific state. In 1365 contrast to PIM-SM, Bi-directional PIM always has the state to trace. 1367 A Designated Forwarder (DF) for a given Rendezvous Point Address 1368 (RPA) is in charge of forwarding downstream traffic onto its link, 1369 and forwarding upstream traffic from its link towards the RPL that 1370 the RPA belongs to. Hence Mtrace2 Reply reports DF addresses or RPA 1371 along the path. 1373 6.3. PIM-DM 1375 Routers running PIM Dense Mode [15] do not know the path packets 1376 would take unless traffic is flowing. Without some extra protocol 1377 mechanism, this means that in an environment with multiple possible 1378 paths with branch points on shared media, Mtrace2 can only trace 1379 existing paths, not potential paths. When there are multiple 1380 possible paths but the branch points are not on shared media, the 1381 upstream router is known, but the LHR may not know that it is the 1382 appropriate last hop. 1384 When traffic is flowing, PIM Dense Mode routers know whether or not 1385 they are the LHR for the link (because they won or lost an Assert 1386 battle) and know who the upstream router is (because it won an Assert 1387 battle). Therefore, Mtrace2 is always able to follow the proper path 1388 when traffic is flowing. 1390 6.4. IGMP/MLD Proxy 1392 When an IGMP/MLD Proxy [7] receives an Mtrace2 Query packet on an 1393 incoming interface, it notes a WRONG_IF in the Forwarding Code of the 1394 last Standard Response Block (see Section 3.2.4), and sends the 1395 Mtrace2 Reply back to the Mtrace2 client. On the other hand, when an 1396 Mtrace2 Query packet reaches an outgoing interface of the IGMP/MLD 1397 proxy, it is forwarded onto its incoming interface towards the 1398 upstream router. 1400 7. Problem Diagnosis 1402 This section describes different scenarios Mtrace2 can be used to 1403 diagnose the multicast problems. 1405 7.1. Forwarding Inconsistencies 1407 The Forwarding Error code can tell if a group is unexpectedly pruned 1408 or administratively scoped. 1410 7.2. TTL or Hop Limit Problems 1412 By taking the maximum of hops from the source and forwarding TTL 1413 threshold over all hops, it is possible to discover the TTL or hop 1414 limit required for the source to reach the destination. 1416 7.3. Packet Loss 1418 By taking two traces, it is possible to find packet loss information 1419 by comparing the difference in input packet counts to the difference 1420 in output packet counts for the specified source-group address pair 1421 at the previous hop. On a point-to-point link, any difference in 1422 these numbers implies packet loss. Since the packet counts may be 1423 changing as the Mtrace2 Request is propagating, there may be small 1424 errors (off by 1 or 2 or more) in these statistics. However, these 1425 errors will not accumulate if multiple traces are taken to expand the 1426 measurement period. On a shared link, the count of input packets can 1427 be larger than the number of output packets at the previous hop, due 1428 to other routers or hosts on the link injecting packets. This 1429 appears as "negative loss" which may mask real packet loss. 1431 In addition to the counts of input and output packets for all 1432 multicast traffic on the interfaces, the Standard Response Block 1433 includes a count of the packets forwarded by a node for the specified 1434 source-group pair. Taking the difference in this count between two 1435 traces and then comparing those differences between two hops gives a 1436 measure of packet loss just for traffic from the specified source to 1437 the specified receiver via the specified group. This measure is not 1438 affected by shared links. 1440 On a point-to-point link that is a multicast tunnel, packet loss is 1441 usually due to congestion in unicast routers along the path of that 1442 tunnel. On native multicast links, loss is more likely in the output 1443 queue of one hop, perhaps due to priority dropping, or in the input 1444 queue at the next hop. The counters in the Standard Response Block 1445 do not allow these cases to be distinguished. Differences in packet 1446 counts between the incoming and outgoing interfaces on one node 1447 cannot generally be used to measure queue overflow in the node. 1449 7.4. Link Utilization 1451 Again, with two traces, you can divide the difference in the input or 1452 output packet counts at some hop by the difference in time stamps 1453 from the same hop to obtain the packet rate over the link. If the 1454 average packet size is known, then the link utilization can also be 1455 estimated to see whether packet loss may be due to the rate limit or 1456 the physical capacity on a particular link being exceeded. 1458 7.5. Time Delay 1460 If the routers have synchronized clocks, it is possible to estimate 1461 propagation and queuing delay from the differences between the 1462 timestamps at successive hops. However, this delay includes control 1463 processing overhead, so is not necessarily indicative of the delay 1464 that data traffic would experience. 1466 8. IANA Considerations 1468 The following new registries are to be created and maintained under 1469 the "RFC Required" registry policy as specified in [4]. 1471 8.1. "Mtrace2 Forwarding Codes" Registry 1473 This is an integer in the range 0-255. Assignment of a Forwarding 1474 Code requires specification of a value and a name for the Forwarding 1475 Code. Initial values for the forwarding codes are given in the table 1476 at the end of Section 3.2.4. Additional values (specific to IPv6) 1477 may also be specified at the end of Section 3.2.5. Any additions to 1478 this registry are required to fully describe the conditions under 1479 which the new Forwarding Code is used. 1481 8.2. "Mtrace2 TLV Types" registry 1483 Assignment of a TLV Type requires specification of an integer value 1484 "Code" in the range 0-255 and a name ("Type"). Initial values for 1485 the TLV Types are given in the table at the beginning of Section 3.2. 1487 8.3. UDP Destination Port 1489 The Mtrace2 UDP destination port is assigned when this document is 1490 published as RFC. 1492 9. Security Considerations 1494 This section addresses some of the security considerations related to 1495 Mtrace2. 1497 9.1. Addresses in Mtrace2 Header 1499 An Mtrace2 header includes three addresses, source address, multicast 1500 address, and Mtrace2 client address. These addresses MUST be 1501 congruent with the definition defined in Section 3.2.1 and forwarding 1502 Mtrace2 messages having invalid addresses MUST be prohibited. For 1503 instance, if Mtrace2 Client Address specified in an Mtrace2 header is 1504 a multicast address, then a router that receives the Mtrace2 message 1505 MUST silently discard it. 1507 9.2. Filtering of Clients 1509 A router SHOULD support a mechanism to filter out queries from 1510 clients beyond a specified administrative boundary. Such a boundary 1511 could, for example, be specified via a list of allowed/disallowed 1512 client addresses or subnets. If a query is received from beyond the 1513 specified administrative boundary, the Query MUST NOT be processed. 1514 The router MAY, however, perform rate limited logging of such events. 1516 9.3. Topology Discovery 1518 Mtrace2 can be used to discover any actively-used topology. If your 1519 network topology is a secret, Mtrace2 may be restricted at the border 1520 of your domain, using the ADMIN_PROHIB forwarding code. 1522 9.4. Characteristics of Multicast Channel 1524 Mtrace2 can be used to discover what sources are sending to what 1525 groups and at what rates. If this information is a secret, Mtrace2 1526 may be restricted at the border of your domain, using the 1527 ADMIN_PROHIB forwarding code. 1529 9.5. Limiting Query/Request Rates 1531 A router may limit Mtrace2 Queries and Requests by ignoring some of 1532 the consecutive messages. The router MAY randomly ignore the 1533 received messages to minimize the processing overhead, i.e., to keep 1534 fairness in processing queries, or prevent traffic amplification. 1535 The rate limit is left to the router's implementation. 1537 9.6. Limiting Reply Rates 1539 The proxying and NO_SPACE behaviors may result in one Query returning 1540 multiple Reply messages. In order to prevent abuse, the routers in 1541 the traced path MAY need to rate-limit the Replies. The rate limit 1542 function is left to the router's implementation. 1544 10. Acknowledgements 1546 This specification started largely as a transcription of Van 1547 Jacobson's slides from the 30th IETF, and the implementation in 1548 mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve 1549 Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original 1550 multicast traceroute client, mtrace (version 1), has been implemented 1551 by Ajit Thyagarajan, Steve Casner and Bill Fenner. The idea of the 1552 "S" bit to allow statistics for a source subnet is due to Tom 1553 Pusateri. 1555 For the Mtrace version 2 specification, the authors would like to 1556 give special thanks to Tatsuya Jinmei, Bill Fenner, and Steve Casner. 1557 Also, extensive comments were received from David L. Black, Ronald 1558 Bonica, Yiqun Cai, Liu Hui, Bharat Joshi, Robert Kebler, John 1559 Kristoff, Mankamana Mishra, Heidi Ou, Pekka Savola, Shinsuke Suzuki, 1560 Dave Thaler, Achmad Husni Thamrin, Stig Venaas, and Cao Wei. 1562 11. References 1564 11.1. Normative References 1566 [1] Bradner, S., "Key words for use in RFCs to indicate 1567 requirement levels", RFC 2119, March 1997. 1569 [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1570 (IPv6) Specification", RFC 8200, July 2017. 1572 [3] Hinden, R. and S. Deering, "IP Version 6 Addressing 1573 Architecture", RFC 4291, February 2006. 1575 [4] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1576 Writing an IANA Considerations Section in RFCs", RFC 8126, 1577 June 2017. 1579 [5] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 1580 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 1581 Multicast - Sparse Mode (PIM-SM): Protocol Specification 1582 (Revised)", RFC 7761, March 2016. 1584 [6] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 1585 "Bidirectional Protocol Independent Multicast (BIDIR- 1586 PIM)", RFC 5015, October 2007. 1588 [7] Fenner, B., He, H., Haberman, B., and H. Sandick, 1589 "Internet Group Management Protocol (IGMP) / Multicast 1590 Listener Discovery (MLD)-Based Multicast Forwarding 1591 ("IGMP/MLD Proxying")", RFC 4605, August 2006. 1593 11.2. Informative References 1595 [8] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 1596 Thyagarajan, "Internet Group Management Protocol, Version 1597 3", RFC 3376, October 2002. 1599 [9] Bumgardner, G., "Automatic Multicast Tunneling", RFC 7450, 1600 February 2015. 1602 [10] Rosen, E. and R. Aggarwal, "Multicast in MPLS/BGP IP 1603 VPNs", RFC 6513, February 2012. 1605 [11] Draves, R. and D. Thaler, "Default Router Preferences and 1606 More-Specific Routes", RFC 4191, November 2005. 1608 [12] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 1609 MIB", RFC 2863, June 2000. 1611 [13] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast 1612 MIB", RFC 5132, December 2007. 1614 [14] Gill, V., Heasley, J., Meyer, D., Savola, P., and C. 1615 Pignataro, "The Generalized TTL Security Mechanism 1616 (GTSM)", RFC 5082, October 2007. 1618 [15] Adams, A., Nicholas, J., and W. Siadak, "Protocol 1619 Independent Multicast - Dense Mode (PIM-DM): Protocol 1620 Specification (Revised)", RFC 3973, January 2005. 1622 Authors' Addresses 1623 Hitoshi Asaeda 1624 National Institute of Information and Communications Technology 1625 4-2-1 Nukui-Kitamachi 1626 Koganei, Tokyo 184-8795 1627 Japan 1629 Email: asaeda@nict.go.jp 1631 Kerry Meyer 1632 Cisco Systems, Inc. 1633 510 McCarthy Blvd. 1634 Milpitas, CA 95035 1635 USA 1637 Email: kerrymey@cisco.com 1639 WeeSan Lee (editor) 1641 Email: weesan@weesan.com