idnits 2.17.1 draft-ietf-mboned-mtrace-v2-18.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == There are 7 instances of lines with non-RFC2606-compliant FQDNs in the document. == There are 3 instances of lines with multicast IPv4 addresses in the document. If these are generic example addresses, they should be changed to use the 233.252.0.x range defined in RFC 5771 Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust and authors Copyright Line does not match the current year == The document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords. (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (August 28, 2017) is 2405 days in the past. Is this intentional? -- Found something which looks like a code comment -- if you have code sections in the document, please surround them with '' and '' lines. Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: 'TBD' on line 1476 ** Obsolete normative reference: RFC 2460 (ref. '2') (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 5226 (ref. '4') (Obsoleted by RFC 8126) Summary: 2 errors (**), 0 flaws (~~), 4 warnings (==), 4 comments (--). 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: March 1, 2018 Cisco 6 W. Lee, Ed. 7 August 28, 2017 9 Mtrace Version 2: Traceroute Facility for IP Multicast 10 draft-ietf-mboned-mtrace-v2-18 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 http://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 March 1, 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 (http://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 Table of Contents 55 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 56 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 57 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 6 58 3. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 7 59 3.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . 7 60 3.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . 8 61 3.2.1. Mtrace2 Query . . . . . . . . . . . . . . . . . . . . 9 62 3.2.2. Mtrace2 Request . . . . . . . . . . . . . . . . . . . 10 63 3.2.3. Mtrace2 Reply . . . . . . . . . . . . . . . . . . . . 10 64 3.2.4. IPv4 Mtrace2 Standard Response Block . . . . . . . . 11 65 3.2.5. IPv6 Mtrace2 Standard Response Block . . . . . . . . 15 66 3.2.6. Mtrace2 Augmented Response Block . . . . . . . . . . 18 67 3.2.7. Mtrace2 Extended Query Block . . . . . . . . . . . . 19 68 4. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 20 69 4.1. Receiving Mtrace2 Query . . . . . . . . . . . . . . . . . 20 70 4.1.1. Query Packet Verification . . . . . . . . . . . . . . 20 71 4.1.2. Query Normal Processing . . . . . . . . . . . . . . . 21 72 4.2. Receiving Mtrace2 Request . . . . . . . . . . . . . . . . 21 73 4.2.1. Request Packet Verification . . . . . . . . . . . . . 21 74 4.2.2. Request Normal Processing . . . . . . . . . . . . . . 22 75 4.3. Forwarding Mtrace2 Request . . . . . . . . . . . . . . . 23 76 4.3.1. Destination Address . . . . . . . . . . . . . . . . . 24 77 4.3.2. Source Address . . . . . . . . . . . . . . . . . . . 24 78 4.3.3. Appending Standard Response Block . . . . . . . . . . 24 79 4.4. Sending Mtrace2 Reply . . . . . . . . . . . . . . . . . . 25 80 4.4.1. Destination Address . . . . . . . . . . . . . . . . . 25 81 4.4.2. Source Address . . . . . . . . . . . . . . . . . . . 25 82 4.4.3. Appending Standard Response Block . . . . . . . . . . 25 83 4.5. Proxying Mtrace2 Query . . . . . . . . . . . . . . . . . 25 84 4.6. Hiding Information . . . . . . . . . . . . . . . . . . . 26 85 5. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 26 86 5.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 26 87 5.1.1. Destination Address . . . . . . . . . . . . . . . . . 27 88 5.1.2. Source Address . . . . . . . . . . . . . . . . . . . 27 89 5.2. Determining the Path . . . . . . . . . . . . . . . . . . 27 90 5.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 27 91 5.4. Last Hop Router (LHR) . . . . . . . . . . . . . . . . . . 27 92 5.5. First Hop Router (FHR) . . . . . . . . . . . . . . . . . 28 93 5.6. Broken Intermediate Router . . . . . . . . . . . . . . . 28 94 5.7. Non-Supported Router . . . . . . . . . . . . . . . . . . 28 95 5.8. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 28 96 5.8.1. Arriving at Source . . . . . . . . . . . . . . . . . 28 97 5.8.2. Fatal Error . . . . . . . . . . . . . . . . . . . . . 29 98 5.8.3. No Upstream Router . . . . . . . . . . . . . . . . . 29 99 5.8.4. Reply Timeout . . . . . . . . . . . . . . . . . . . . 29 100 5.9. Continuing after an Error . . . . . . . . . . . . . . . . 29 101 6. Protocol-Specific Considerations . . . . . . . . . . . . . . 29 102 6.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . 30 103 6.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . 30 104 6.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . 30 105 6.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . 30 106 7. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 31 107 7.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . 31 108 7.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 31 109 7.3. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 31 110 7.4. Link Utilization . . . . . . . . . . . . . . . . . . . . 32 111 7.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . 32 112 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 113 8.1. "Mtrace2 Forwarding Codes" Registry . . . . . . . . . . . 32 114 8.2. "Mtrace2 TLV Types" registry . . . . . . . . . . . . . . 32 115 8.3. UDP Destination Port . . . . . . . . . . . . . . . . . . 33 116 9. Security Considerations . . . . . . . . . . . . . . . . . . . 33 117 9.1. Addresses in Mtrace2 Header . . . . . . . . . . . . . . . 33 118 9.2. Filtering of Clients . . . . . . . . . . . . . . . . . . 33 119 9.3. Topology Discovery . . . . . . . . . . . . . . . . . . . 33 120 9.4. Characteristics of Multicast Channel . . . . . . . . . . 33 121 9.5. Limiting Query/Request Rates . . . . . . . . . . . . . . 33 122 9.6. Limiting Reply Rates . . . . . . . . . . . . . . . . . . 34 123 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 34 124 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 34 125 11.1. Normative References . . . . . . . . . . . . . . . . . . 34 126 11.2. Informative References . . . . . . . . . . . . . . . . . 35 127 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 35 129 1. Introduction 131 Given a multicast distribution tree, tracing from a multicast source 132 to a receiver is difficult, since we do not know which branch of the 133 multicast tree the receiver lies. This means that we have to flood 134 the whole tree to find the path from a source to a receiver. On the 135 other hand, walking up the tree from a receiver to a source is easy, 136 as most existing multicast routing protocols know the upstream router 137 for each source. Tracing from a receiver to a source can involve 138 only the routers on the direct path. 140 This document specifies the multicast traceroute facility named 141 Mtrace version 2 or Mtrace2 which allows the tracing of an IP 142 multicast routing path. Mtrace2 is usually initiated from an Mtrace2 143 client by sending an Mtrace2 Query to a Last Hop Router (LHR) or to a 144 Rendezvous Point (RP). The RP is a special router where sources and 145 receivers meet in PIM-SM [5]. From the LHR/RP receiving the query, 146 the tracing is directed towards a specified source if a source 147 address is specified and source specific state exists on the 148 receiving router. If no source address is specified or if no source 149 specific state exists on a receiving LHR, the tracing is directed 150 toward the RP for the specified group address. Moreover, Mtrace2 151 provides additional information such as the packet rates and losses, 152 as well as other diagnostic information. Mtrace2 is primarily 153 intended for the following purposes: 155 o To trace the path that a packet would take from a source to a 156 receiver. 158 o To isolate packet loss problems (e.g., congestion). 160 o To isolate configuration problems (e.g., TTL threshold). 162 Figure 1 shows a typical case on how Mtrace2 is used. FHR represents 163 the first-hop router, LHR represents the last-hop router, and the 164 arrow lines represent the Mtrace2 messages that are sent from one 165 node to another. The numbers before the Mtrace2 messages represent 166 the sequence of the messages that would happen. Source, Receiver and 167 Mtrace2 client are typically hosts. 169 2. Request 2. Request 170 +----+ +----+ 171 | | | | 172 v | v | 173 +--------+ +-----+ +-----+ +----------+ 174 | Source |----| FHR |----- The Internet -----| LHR |----| Receiver | 175 +--------+ +-----+ | +-----+ +----------+ 176 \ | ^ 177 \ | / 178 \ | / 179 \ | / 180 3. Reply \ | / 1. Query 181 \ | / 182 \ | / 183 \ +---------+ / 184 v | Mtrace2 |/ 185 | client | 186 +---------+ 188 Figure 1 190 When an Mtrace2 client initiates a multicast trace, it sends an 191 Mtrace2 Query packet to the LHR or RP for a multicast group and, 192 optionally, a source address. The LHR/RP turns the Query packet into 193 a Request. The Request message type enables each of the upstream 194 routers processing the message to apply different packet and message 195 validation rules than those required for handling of a Query message. 196 The LHR/RP then appends a standard response block containing its 197 interface addresses and packet statistics to the Request packet, then 198 forwards the packet towards the source/RP. The Request packet is 199 either unicasted to its upstream router towards the source/RP, or 200 multicasted to the group if the upstream router's IP address is not 201 known. In a similar fashion, each router along the path to the 202 source/RP appends a standard response block to the end of the Request 203 packet before forwarding it to its upstream router. When the FHR 204 receives the Request packet, it appends its own standard response 205 block, turns the Request packet into a Reply, and unicasts the Reply 206 back to the Mtrace2 client. 208 The Mtrace2 Reply may be returned before reaching the FHR under some 209 circumstances. This can happen if a Request packet is received at an 210 RP or gateway, or when any of several types of error or exception 211 conditions occur which prevent sending of a request to the next 212 upstream router. 214 The Mtrace2 client waits for the Mtrace2 Reply message and displays 215 the results. When not receiving an Mtrace2 Reply message due to 216 network congestion, a broken router (see Section 5.6), or a non- 217 responding router (see Section 5.7), the Mtrace2 client may resend 218 another Mtrace2 Query with a lower hop count (see Section 3.2.1), and 219 repeat the process until it receives an Mtrace2 Reply message. The 220 details are Mtrace2 client specific, and it is outside the scope of 221 this document. 223 Note that when a router's control plane and forwarding plane are out 224 of sync, the Mtrace2 Requests might be forwarded based on the control 225 states instead. In which case, the traced path might not represent 226 the real path the data packets would follow. 228 Mtrace2 supports both IPv4 and IPv6. Unlike the previous version of 229 Mtrace, which implements its query and response as IGMP messages [8], 230 all Mtrace2 messages are UDP-based. Although the packet formats of 231 IPv4 and IPv6 Mtrace2 are different because of the address families, 232 the syntax between them is similar. 234 This document describes the base specification of Mtrace2 that can 235 serve as a basis for future proposals such as Mtrace2 for AMT [9] and 236 Mtrace2 for MVPN [10]. They are therefore out of the scope of this 237 document. 239 2. Terminology 241 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 242 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", 243 and "OPTIONAL" are to be interpreted as described in RFC 2119 [1], 244 and indicate requirement levels for compliant Mtrace2 245 implementations. 247 2.1. Definitions 249 Since Mtrace2 Queries and Requests flow in the opposite direction to 250 the data flow, we refer to "upstream" and "downstream" with respect 251 to data, unless explicitly specified. 253 Incoming interface 254 The interface on which data is expected to arrive from the 255 specified source and group. 257 Outgoing interface 258 This is one of the interfaces to which data from the source or RP 259 is expected to be transmitted for the specified source and group. 260 It is also the interface on which the Mtrace2 Request was 261 received. 263 Upstream router 264 The router, connecting to the Incoming interface of the current 265 router, which is responsible for forwarding data for the specified 266 source and group to the current router. 268 First-hop router (FHR) 269 The router that is directly connected to the source the Mtrace2 270 Query specifies. 272 Last-hop router (LHR) 273 A router that is directly connected to a receiver. It is also the 274 router that receives the Mtrace2 Query from an Mtrace2 client. 276 Group state 277 It is the state a shared-tree protocol, such as PIM-SM [5], uses 278 to choose the upstream router towards the RP for the specified 279 group. In this state, source-specific state is not available for 280 the corresponding group address on the router. 282 Source-specific state 283 It is the state that is used to choose the path towards the source 284 for the specified source and group. 286 ALL-[protocol]-ROUTERS.MCAST.NET 287 It is a link-local multicast address for multicast routers to 288 communicate with their adjacent routers that are running the same 289 routing protocol. For instance, the address of ALL-PIM- 290 ROUTERS.MCAST.NET [5] is '224.0.0.13' for IPv4 and 'ff02::d' for 291 IPv6. 293 3. Packet Formats 295 This section describes the details of the packet formats for Mtrace2 296 messages. 298 All Mtrace2 messages are encoded in TLV format (see Section 3.1). 299 The first TLV of a message is a message header TLV specifying the 300 type of message and additional context information required for 301 processing of the message and for parsing of subsequent TLVs in the 302 message. Subsequent TLVs in a message, referred to as Blocks, are 303 appended after the header TLV to provide additional information 304 associated with the message. If an implementation receives an 305 unknown TLV type for the first TLV in a message, it SHOULD ignore and 306 silently discard the TLV and any subsequent TLVs in the packet 307 containing the TLV. If an implementation receives an unknown TLV 308 type for a subsequent TLV within a message, it SHOULD ignore and 309 silently discard the TLV. If the length of a TLV exceeds the 310 available space in the containing packet, the implementation MUST 311 ignore and silently discard the TLV and any remaining portion of the 312 containing packet. Any data in the packet after the specified TLV 313 length is considered to be outside the boundary of the TLV and MUST 314 be ignored during processing of the TLV. 316 All Mtrace2 messages are UDP packets. For IPv4, Mtrace2 Query and 317 Request messages MUST NOT be fragmented. For IPv6, the packet size 318 for the Mtrace2 messages MUST NOT exceed 1280 bytes, which is the 319 smallest MTU for an IPv6 interface [2]. The source port is uniquely 320 selected by the local host operating system. The destination port is 321 the IANA reserved Mtrace2 port number (see Section 8). All Mtrace2 322 messages MUST have a valid UDP checksum. 324 Additionally, Mtrace2 supports both IPv4 and IPv6, but not mixed. 325 For example, if an Mtrace2 Query or Request message arrives in as an 326 IPv4 packet, all addresses specified in the Mtrace2 messages MUST be 327 IPv4 as well. Same rule applies to IPv6 Mtrace2 messages. 329 3.1. Mtrace2 TLV format 330 0 1 2 3 331 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 1 332 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 333 | Type | Length | Value .... | 334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 336 Type: 8 bits 338 Describes the format of the Value field. For all the available 339 types, please see Section 3.2 341 Length: 16 bits 343 Length of Type, Length, and Value fields in octets. Minimum 344 length required is 3 octets. The maximum TLV length is not 345 defined; however the entire Mtrace2 packet length SHOULD NOT 346 exceed the available MTU. 348 Value: variable length 350 The format is based on the Type value. The length of the value 351 field is Length field minus 3. All reserved fields in the Value 352 field MUST be transmitted as zeros and ignored on receipt. 354 3.2. Defined TLVs 356 The following TLV Types are defined: 358 Code Type 359 ==== ================================ 360 0x01 Mtrace2 Query 361 0x02 Mtrace2 Request 362 0x03 Mtrace2 Reply 363 0x04 Mtrace2 Standard Response Block 364 0x05 Mtrace2 Augmented Response Block 365 0x06 Mtrace2 Extended Query Block 367 Each Mtrace2 message MUST begin with either a Query, Request or Reply 368 TLV. The first TLV determines the type of each Mtrace2 message. 369 Following a Query TLV, there can be a sequence of optional Extended 370 Query Blocks. In the case of a Request or a Reply TLV, it is then 371 followed by a sequence of Standard Response Blocks, each from a 372 multicast router on the path towards the source or the RP. In the 373 case more information is needed, a Standard Response Block can be 374 followed by one or multiple Augmented Response Blocks. 376 We will describe each message type in detail in the next few 377 sections. 379 3.2.1. Mtrace2 Query 381 An Mtrace2 Query is usually originated by an Mtrace2 client which 382 sends an Mtrace2 Query message to the LHR. When tracing towards the 383 source or the RP, the intermediate routers MUST NOT modify the Query 384 message except the Type field. If the actual number of hops is not 385 known, an Mtrace2 client could send an initial Query message with a 386 large # Hops (e.g., 0xffffffff), in order to try to trace the full 387 path. 389 An Mtrace2 Query message is shown as follows: 391 0 1 2 3 392 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 1 393 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 394 | Type | Length | # Hops | 395 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 396 | | 397 | Multicast Address | 398 | | 399 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 400 | | 401 | Source Address | 402 | | 403 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 404 | | 405 | Mtrace2 Client Address | 406 | | 407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 408 | Query ID | Client Port # | 409 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 411 Figure 2 413 # Hops: 8 bits 414 This field specifies the maximum number of hops that the Mtrace2 415 client wants to trace. If there are some error conditions in the 416 middle of the path that prevent an Mtrace2 Reply from being 417 received by the client, the client MAY issue another Mtrace2 Query 418 with a lower number of hops until it receives a Reply. 420 Multicast Address: 32 bits or 128 bits 421 This field specifies an IPv4 or IPv6 address, which can be either: 423 m-1: a multicast group address to be traced; or, 425 m-2: all 1's in case of IPv4 or the unspecified address (::) in 426 case of IPv6 if no group-specific information is desired. 428 Source Address: 32 bits or 128 bits 429 This field specifies an IPv4 or IPv6 address, which can be either: 431 s-1: an unicast address of the source to be traced; or, 433 s-2: all 1's in case of IPv4 or the unspecified address (::) in 434 case of IPv6 if no source-specific information is desired. 435 For example, the client is tracing a (*,g) group state. 437 Note that it is invalid to have a source-group combination of 438 (s-2, m-2). If a router receives such combination in an Mtrace2 439 Query, it MUST silently discard the Query. 441 Mtrace2 Client Address: 32 bits or 128 bits 442 This field specifies the Mtrace2 client's IPv4 address or IPv6 443 global address. This address MUST be a valid unicast address, and 444 therefore, MUST NOT be all 1's or an unspecified address. The 445 Mtrace2 Reply will be sent to this address. 447 Query ID: 16 bits 448 This field is used as a unique identifier for this Mtrace2 Query 449 so that duplicate or delayed Reply messages may be detected. 451 Client Port #: 16 bits 452 This field specifies the destination UDP port number for receiving 453 the Mtrace2 Reply packet. 455 3.2.2. Mtrace2 Request 457 The format of an Mtrace2 Request message is similar to an Mtrace2 458 Query except the Type field is 0x02. 460 When a LHR receives an Mtrace2 Query message, it would turn the Query 461 into a Request by changing the Type field of the Query from 0x01 to 462 0x02. The LHR would then append an Mtrace2 Standard Response Block 463 (see Section 3.2.4) of its own to the Request message before sending 464 it upstream. The upstream routers would do the same without changing 465 the Type field until one of them is ready to send a Reply. 467 3.2.3. Mtrace2 Reply 469 The format of an Mtrace2 Reply message is similar to an Mtrace2 Query 470 except the Type field is 0x03. 472 When a FHR or a RP receives an Mtrace2 Request message which is 473 destined to itself, it would append an Mtrace2 Standard Response 474 Block (see Section 3.2.4) of its own to the Request message. Next, 475 it would turn the Request message into a Reply by changing the Type 476 field of the Request from 0x02 to 0x03. The Reply message would then 477 be unicasted to the Mtrace2 client specified in the Mtrace2 Client 478 Address field. 480 There are a number of cases an intermediate router might return a 481 Reply before a Request reaches the FHR or the RP. See Section 4.1.1, 482 Section 4.2.2, Section 4.3.3, and Section 4.5 for more details. 484 3.2.4. IPv4 Mtrace2 Standard Response Block 486 This section describes the message format of an IPv4 Mtrace2 Standard 487 Response Block. The Type field is 0x04. 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 | Type | Length | MBZ | 493 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 494 | Query Arrival Time | 495 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 496 | Incoming Interface Address | 497 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 498 | Outgoing Interface Address | 499 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 500 | Upstream Router Address | 501 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 502 | | 503 . Input packet count on incoming interface . 504 | | 505 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 506 | | 507 . Output packet count on outgoing interface . 508 | | 509 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 510 | | 511 . Total number of packets for this source-group pair . 512 | | 513 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 514 | Rtg Protocol | Multicast Rtg Protocol | 515 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 516 | Fwd TTL | MBZ |S| Src Mask |Forwarding Code| 517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 519 MBZ: 8 bits 520 This field MUST be zeroed on transmission and ignored on 521 reception. 523 Query Arrival Time: 32 bits 524 The Query Arrival Time is a 32-bit NTP timestamp specifying the 525 arrival time of the Mtrace2 Query or Request packet at this 526 router. The 32-bit form of an NTP timestamp consists of the 527 middle 32 bits of the full 64-bit form; that is, the low 16 bits 528 of the integer part and the high 16 bits of the fractional part. 530 The following formula converts from a UNIX timeval to a 32-bit NTP 531 timestamp: 533 query_arrival_time 534 = ((tv.tv_sec + 32384) << 16) + ((tv.tv_nsec << 7) / 1953125) 536 The constant 32384 is the number of seconds from Jan 1, 1900 to 537 Jan 1, 1970 truncated to 16 bits. ((tv.tv_nsec << 7) / 1953125) 538 is a reduction of ((tv.tv_nsec / 1000000000) << 16). 540 Note that Mtrace2 does not require all the routers on the path to 541 have synchronized clocks in order to measure one-way latency. 543 Additionally, Query Arrival Time is useful for measuring the 544 packet rate. For example, suppose that a client issues two 545 queries, and the corresponding requests R1 and R2 arrive at router 546 X at time T1 and T2, then the client would be able to compute the 547 packet rate on router X by using the packet count information 548 stored in the R1 and R2, and the time T1 and T2. 550 Incoming Interface Address: 32 bits 551 This field specifies the address of the interface on which packets 552 from the source or the RP are expected to arrive, or 0 if unknown 553 or unnumbered. 555 Outgoing Interface Address: 32 bits 556 This field specifies the address of the interface on which packets 557 from the source or the RP are expected to transmit towards the 558 receiver, or 0 if unknown or unnumbered. This is also the address 559 of the interface on which the Mtrace2 Query or Request arrives. 561 Upstream Router Address: 32 bits 562 This field specifies the address of the upstream router from which 563 this router expects packets from this source. This may be a 564 multicast group (e.g. ALL-[protocol]-ROUTERS.MCAST.NET) if the 565 upstream router is not known because of the workings of the 566 multicast routing protocol. However, it should be 0 if the 567 incoming interface address is unknown or unnumbered. 569 Input packet count on incoming interface: 64 bits 570 This field contains the number of multicast packets received for 571 all groups and sources on the incoming interface, or all 1's if no 572 count can be reported. This counter may have the same value as 573 ifHCInMulticastPkts from the IF-MIB [12] for this interface. 575 Output packet count on outgoing interface: 64 bit 576 This field contains the number of multicast packets that have been 577 transmitted or queued for transmission for all groups and sources 578 on the outgoing interface, or all 1's if no count can be reported. 579 This counter may have the same value as ifHCOutMulticastPkts from 580 the IF-MIB [12] for this interface. 582 Total number of packets for this source-group pair: 64 bits 583 This field counts the number of packets from the specified source 584 forwarded by the router to the specified group, or all 1's if no 585 count can be reported. If the S bit is set (see below), the count 586 is for the source network, as specified by the Src Mask field (see 587 below). If the S bit is set and the Src Mask field is 127, 588 indicating no source-specific state, the count is for all sources 589 sending to this group. This counter should have the same value as 590 ipMcastRoutePkts from the IPMROUTE-STD-MIB [13] for this 591 forwarding entry. 593 Rtg Protocol: 16 bits 594 This field describes the unicast routing protocol running between 595 this router and the upstream router, and it is used to determine 596 the RPF interface for the specified source or RP. This value 597 should have the same value as ipMcastRouteRtProtocol from the 598 IPMROUTE-STD-MIB [13] for this entry. If the router is not able 599 to obtain this value, all 0's must be specified. 601 Multicast Rtg Protocol: 16 bits 602 This field describes the multicast routing protocol in use between 603 the router and the upstream router. This value should have the 604 same value as ipMcastRouteProtocol from the IPMROUTE-STD-MIB [13] 605 for this entry. If the router cannot obtain this value, all 0's 606 must be specified. 608 Fwd TTL: 8 bits 609 This field contains the configured multicast TTL threshold, if 610 any, of the outgoing interface. 612 S: 1 bit 613 If this bit is set, it indicates that the packet count for the 614 source-group pair is for the source network, as determined by 615 masking the source address with the Src Mask field. 617 Src Mask: 7 bits 618 This field contains the number of 1's in the netmask the router 619 has for the source (i.e. a value of 24 means the netmask is 620 0xffffff00). If the router is forwarding solely on group state, 621 this field is set to 127 (0x7f). 623 Forwarding Code: 8 bits 624 This field contains a forwarding information/error code. Values 625 with the high order bit set (0x80-0xff) are intended for use as 626 error or exception codes. Section 4.1 and Section 4.2 explain how 627 and when the Forwarding Code is filled. Defined values are as 628 follows: 630 Value Name Description 631 ----- -------------- ---------------------------------------------- 632 0x00 NO_ERROR No error 633 0x01 WRONG_IF Mtrace2 Request arrived on an interface 634 to which this router would not forward for 635 the specified group towards the source or RP. 636 0x02 PRUNE_SENT This router has sent a prune upstream which 637 applies to the source and group in the 638 Mtrace2 Request. 639 0x03 PRUNE_RCVD This router has stopped forwarding for this 640 source and group in response to a request 641 from the downstream router. 642 0x04 SCOPED The group is subject to administrative 643 scoping at this router. 644 0x05 NO_ROUTE This router has no route for the source or 645 group and no way to determine a potential 646 route. 647 0x06 WRONG_LAST_HOP This router is not the proper LHR. 648 0x07 NOT_FORWARDING This router is not forwarding this source and 649 group out the outgoing interface for an 650 unspecified reason. 651 0x08 REACHED_RP Reached the Rendezvous Point. 652 0x09 RPF_IF Mtrace2 Request arrived on the expected 653 RPF interface for this source and group. 654 0x0A NO_MULTICAST Mtrace2 Request arrived on an interface 655 which is not enabled for multicast. 656 0x0B INFO_HIDDEN One or more hops have been hidden from this 657 trace. 658 0x0C REACHED_GW Mtrace2 Request arrived on a gateway (e.g., 659 a NAT or firewall) that hides the 660 information between this router and the 661 Mtrace2 client. 662 0x0D UNKNOWN_QUERY A non-transitive Extended Query Type was 663 received by a router which does not support 664 the type. 665 0x80 FATAL_ERROR A fatal error is one where the router may 666 know the upstream router but cannot forward 667 the message to it. 668 0x81 NO_SPACE There was not enough room to insert another 669 Standard Response Block in the packet. 670 0x83 ADMIN_PROHIB Mtrace2 is administratively prohibited. 672 3.2.5. IPv6 Mtrace2 Standard Response Block 674 This section describes the message format of an IPv6 Mtrace2 Standard 675 Response Block. The Type field is also 0x04. 677 0 1 2 3 678 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 1 679 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 680 | Type | Length | MBZ | 681 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 682 | Query Arrival Time | 683 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 684 | Incoming Interface ID | 685 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 686 | Outgoing Interface ID | 687 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 688 | | 689 * Local Address * 690 | | 691 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 692 | | 693 * Remote Address * 694 | | 695 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 696 | | 697 . Input packet count on incoming interface . 698 | | 699 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 700 | | 701 . Output packet count on outgoing interface . 702 | | 703 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 704 | | 705 . Total number of packets for this source-group pair . 706 | | 707 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 708 | Rtg Protocol | Multicast Rtg Protocol | 709 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 710 | MBZ 2 |S|Src Prefix Len |Forwarding Code| 711 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 713 MBZ: 8 bits 714 This field MUST be zeroed on transmission and ignored on 715 reception. 717 Query Arrival Time: 32 bits 718 Same definition as in IPv4. 720 Incoming Interface ID: 32 bits 721 This field specifies the interface ID on which packets from the 722 source or RP are expected to arrive, or 0 if unknown. This ID 723 should be the value taken from InterfaceIndex of the IF-MIB [12] 724 for this interface. 726 Outgoing Interface ID: 32 bits 727 This field specifies the interface ID to which packets from the 728 source or RP are expected to transmit, or 0 if unknown. This ID 729 should be the value taken from InterfaceIndex of the IF-MIB [12] 730 for this interface 732 Local Address: 128 bits 733 This field specifies a global IPv6 address that uniquely 734 identifies the router. An unique local unicast address [11] 735 SHOULD NOT be used unless the router is only assigned link-local 736 and unique local addresses. If the router is only assigned link- 737 local addresses, its link-local address can be specified in this 738 field. 740 Remote Address: 128 bits 741 This field specifies the address of the upstream router, which, in 742 most cases, is a link-local unicast address for the upstream 743 router. 745 Although a link-local address does not have enough information to 746 identify a node, it is possible to detect the upstream router with 747 the assistance of Incoming Interface ID and the current router 748 address (i.e., Local Address). 750 Note that this may be a multicast group (e.g., ALL-[protocol]- 751 ROUTERS.MCAST.NET) if the upstream router is not known because of 752 the workings of a multicast routing protocol. However, it should 753 be the unspecified address (::) if the incoming interface address 754 is unknown. 756 Input packet count on incoming interface: 64 bits 757 Same definition as in IPv4. 759 Output packet count on outgoing interface: 64 bits 760 Same definition as in IPv4. 762 Total number of packets for this source-group pair: 64 bits 763 Same definition as in IPv4, except if the S bit is set (see 764 below), the count is for the source network, as specified by the 765 Src Prefix Len field. If the S bit is set and the Src Prefix Len 766 field is 255, indicating no source-specific state, the count is 767 for all sources sending to this group. This counter should have 768 the same value as ipMcastRoutePkts from the IPMROUTE-STD-MIB [13] 769 for this forwarding entry. 771 Rtg Protocol: 16 bits 772 Same definition as in IPv4. 774 Multicast Rtg Protocol: 16 bits 775 Same definition as in IPv4. 777 MBZ 2: 15 bits 778 This field MUST be zeroed on transmission and ignored on 779 reception. 781 S: 1 bit 782 Same definition as in IPv4, except the Src Prefix Len field is 783 used to mask the source address. 785 Src Prefix Len: 8 bits 786 This field contains the prefix length this router has for the 787 source. If the router is forwarding solely on group state, this 788 field is set to 255 (0xff). 790 Forwarding Code: 8 bits 791 Same definition as in IPv4. 793 3.2.6. Mtrace2 Augmented Response Block 795 In addition to the Standard Response Block, a multicast router on the 796 traced path can optionally add one or multiple Augmented Response 797 Blocks before sending the Request to its upstream router. 799 The Augmented Response Block is flexible for various purposes such as 800 providing diagnosis information (see Section 7) and protocol 801 verification. Its Type field is 0x05, and its format is as follows: 803 0 1 2 3 804 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 1 805 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 806 | Type | Length | MBZ | 807 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 808 | Augmented Response Type | Value .... | 809 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 811 MBZ: 8 bits 812 This field MUST be zeroed on transmission and ignored on 813 reception. 815 Augmented Response Type: 16 bits 816 This field specifies the type of various responses from a 817 multicast router that might need to communicate back to the 818 Mtrace2 client as well as the multicast routers on the traced 819 path. 821 The Augmented Response Type is defined as follows: 823 Code Type 824 ==== =============================================== 825 0x01 # of the returned Standard Response Blocks 827 When the NO_SPACE error occurs on a router, the router should send 828 the original Mtrace2 Request received from the downstream router 829 as a Reply back to the Mtrace2 client, and continue with a new 830 Mtrace2 Request. In the new Request, the router would add a 831 Standard Response Block followed by an Augmented Response Block 832 with 0x01 as the Augmented Response Type, and the number of the 833 returned Mtrace2 Standard Response Blocks as the Value. 835 Each upstream router would recognize the total number of hops the 836 Request has been traced so far by adding this number and the 837 number of the Standard Response Block in the current Request 838 message. 840 This document only defines one Augmented Response Type in the 841 Augmented Response Block. The description on how to provide 842 diagnosis information using the Augmented Response Block is out of 843 the scope of this document, and will be addressed in separate 844 documents. 846 Value: variable length 847 The format is based on the Augmented Response Type value. The 848 length of the value field is Length field minus 6. 850 3.2.7. Mtrace2 Extended Query Block 852 There may be a sequence of optional Extended Query Blocks that follow 853 an Mtrace2 Query to further specify any information needed for the 854 Query. For example, an Mtrace2 client might be interested in tracing 855 the path the specified source and group would take based on a certain 856 topology. In which case, the client can pass in the multi-topology 857 ID as the Value for an Extended Query Type (see below). The Extended 858 Query Type is extensible and the behavior of the new types will be 859 addressed by separate documents. 861 The Mtrace2 Extended Query Block's Type field is 0x06, and is 862 formatted as follows: 864 0 1 2 3 865 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 1 866 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 867 | Type | Length | MBZ |T| 868 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 869 | Extended Query Type | Value .... | 870 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 872 MBZ: 7 bits 873 This field MUST be zeroed on transmission and ignored on 874 reception. 876 T-bit (Transitive Attribute): 1 bit 877 If the TLV type is unrecognized by the receiving router, then this 878 TLV is either discarded or forwarded along with the Query, 879 depending on the value of this bit. If this bit is set, then the 880 router MUST forward this TLV. If this bit is clear, the router 881 MUST send an Mtrace2 Reply with an UNKNOWN_QUERY error. 883 Extended Query Type: 16 bits 884 This field specifies the type of the Extended Query Block. 886 Value: 16 bits 887 This field specifies the value of this Extended Query. 889 4. Router Behavior 891 This section describes the router behavior in the context of Mtrace2 892 in detail. 894 4.1. Receiving Mtrace2 Query 896 An Mtrace2 Query message is an Mtrace2 message with no response 897 blocks filled in, and uses TLV type of 0x01. 899 4.1.1. Query Packet Verification 901 Upon receiving an Mtrace2 Query message, a router MUST examine 902 whether the Multicast Address and the Source Address are a valid 903 combination as specified in Section 3.2.1, and whether the Mtrace2 904 Client Address is a valid IP unicast address. If either one is 905 invalid, the Query MUST be silently ignored. 907 Mtrace2 supports a non-local client to the LHR/RP. A router SHOULD, 908 however, support a mechanism to filter out queries from clients 909 beyond a specified administrative boundary. The potential approaches 910 are described in Section 9.2. 912 In the case where a local LHR client is required, the router must 913 then examine the Query to see if it is the proper LHR/RP for the 914 destination address in the packet. It is the proper local LHR if it 915 has a multicast-capable interface on the same subnet as the Mtrace2 916 Client Address and is the router that would forward traffic from the 917 given (S,G) or (*,G) onto that subnet. It is the proper RP if the 918 multicast group address specified in the query is 0 and if the IP 919 header destination address is a valid RP address on this router. 921 If the router determines that it is not the proper LHR/RP, or it 922 cannot make that determination, it does one of two things depending 923 on whether the Query was received via multicast or unicast. If the 924 Query was received via multicast, then it MUST be silently discarded. 925 If it was received via unicast, the router turns the Query into a 926 Reply message by changing the TLV type to 0x03 and appending a 927 Standard Response Block with a Forwarding Code of WRONG_LAST_HOP. 928 The rest of the fields in the Standard Response Block MUST be zeroed. 929 The router then sends the Reply message to the Mtrace2 Client Address 930 on the Client Port # as specified in the Mtrace2 Query. 932 Duplicate Query messages as identified by the tuple (Mtrace2 Client 933 Address, Query ID) SHOULD be ignored. This MAY be implemented using 934 a cache of previously processed queries keyed by the Mtrace2 Client 935 Address and Query ID pair. The duration of the cached entries is 936 implementation specific. Duplicate Request messages MUST NOT be 937 ignored in this manner. 939 4.1.2. Query Normal Processing 941 When a router receives an Mtrace2 Query and it determines that it is 942 the proper LHR/RP, it turns the Query to a Request by changing the 943 TLV type from 0x01 to 0x02, and performs the steps listed in 944 Section 4.2. 946 4.2. Receiving Mtrace2 Request 948 An Mtrace2 Request is an Mtrace2 message that uses TLV type of 0x02. 949 With the exception of the LHR, whose Request was just converted from 950 a Query, each Request received by a router should have at least one 951 Standard Response Block filled in. 953 4.2.1. Request Packet Verification 955 If the Mtrace2 Request does not come from an adjacent router, or if 956 the Request is not addressed to this router, or if the Request is 957 addressed to a multicast group which is not a link-scoped group (i.e. 958 224.0.0.0/24 for IPv4, FFx2::/16 [3] for IPv6), it MUST be silently 959 ignored. GTSM [14] SHOULD be used by the router to determine whether 960 the router is adjacent or not. 962 If the sum of the number of the Standard Response Blocks in the 963 received Mtrace2 Request and the value of the Augmented Response Type 964 of 0x01, if any, is equal or more than the # Hops in the Mtrace2 965 Request, it MUST be silently ignored. 967 4.2.2. Request Normal Processing 969 When a router receives an Mtrace2 Request message, it performs the 970 following steps. Note that it is possible to have multiple 971 situations covered by the Forwarding Codes. The first one 972 encountered is the one that is reported, i.e. all "note Forwarding 973 Code N" should be interpreted as "if Forwarding Code is not already 974 set, set Forwarding Code to N". Note that in the steps described 975 below the "Outgoing Interface" is the one on which the Mtrace2 976 Request message arrives. 978 1. Prepare a Standard Response Block to be appended to the packet, 979 setting all fields to an initial default value of zero. 981 2. If Mtrace2 is administratively prohibited, note the Forwarding 982 Code of ADMIN_PROHIB and skip to step 4. 984 3. In the Standard Response Block, fill in the Query Arrival Time, 985 Outgoing Interface Address (for IPv4) or Outgoing Interface ID 986 (for IPv6), Output Packet Count, and Fwd TTL (for IPv4). 988 4. Attempt to determine the forwarding information for the 989 specified source and group, using the same mechanisms as would 990 be used when a packet is received from the source destined for 991 the group. A state need not be instantiated, it can be a 992 "phantom" state created only for the purpose of the trace, such 993 as "dry-run." 995 If using a shared-tree protocol and there is no source-specific 996 state, or if no source-specific information is desired (i.e., 997 all 1's for IPv4 or unspecified address (::) for IPv6), group 998 state should be used. If there is no group state or no group- 999 specific information is desired, potential source state (i.e., 1000 the path that would be followed for a source-specific Join) 1001 should be used. 1003 5. If no forwarding information can be determined, the router notes 1004 a Forwarding Code of NO_ROUTE, sets the remaining fields that 1005 have not yet been filled in to zero, and then sends an Mtrace2 1006 Reply back to the Mtrace2 client. 1008 6. If a Forwarding Code of ADMIN_PROHIB has been set, skip to step 1009 7. Otherwise, fill in the Incoming Interface Address (or 1010 Incoming Interface ID and Local Address for IPv6), Upstream 1011 Router Address (or Remote Address for IPv6), Input Packet Count, 1012 Total Number of Packets, Routing Protocol, S, and Src Mask (or 1013 Src Prefix Len for IPv6) using the forwarding information 1014 determined in step 4. 1016 7. If the Outgoing interface is not enabled for multicast, note 1017 Forwarding Code of NO_MULTICAST. If the Outgoing interface is 1018 the interface from which the router would expect data to arrive 1019 from the source, note forwarding code RPF_IF. If the Outgoing 1020 interface is not one to which the router would forward data from 1021 the source or RP to the group, a Forwarding code of WRONG_IF is 1022 noted. In the above three cases, the router will return an 1023 Mtrace2 Reply and terminate the trace. 1025 8. If the group is subject to administrative scoping on either the 1026 Outgoing or Incoming interfaces, a Forwarding Code of SCOPED is 1027 noted. 1029 9. If this router is the RP for the group for a non-source-specific 1030 query, note a Forwarding Code of REACHED_RP. The router will 1031 send an Mtrace2 Reply and terminate the trace. 1033 10. If this router is directly connected to the specified source or 1034 source network on the Incoming interface, it sets the Upstream 1035 Router Address (for IPv4) or the Remote Address (for IPv6) of 1036 the response block to zero. The router will send an Mtrace2 1037 Reply and terminate the trace. 1039 11. If this router has sent a prune upstream which applies to the 1040 source and group in the Mtrace2 Request, it notes a Forwarding 1041 Code of PRUNE_SENT. If the router has stopped forwarding 1042 downstream in response to a prune sent by the downstream router, 1043 it notes a Forwarding Code of PRUNE_RCVD. If the router should 1044 normally forward traffic downstream for this source and group 1045 but is not, it notes a Forwarding Code of NOT_FORWARDING. 1047 12. If this router is a gateway (e.g., a NAT or firewall) that hides 1048 the information between this router and the Mtrace2 client, it 1049 notes a Forwarding Code of REACHED_GW. The router continues the 1050 processing as described in Section 4.5. 1052 13. If the total number of the Standard Response Blocks, including 1053 the newly prepared one, and the value of the Augmented Response 1054 Type of 0x01, if any, is less than the # Hops in the Request, 1055 the packet is then forwarded to the upstream router as described 1056 in Section 4.3; otherwise, the packet is sent as an Mtrace2 1057 Reply to the Mtrace2 client as described in Section 4.4. 1059 4.3. Forwarding Mtrace2 Request 1061 This section describes how an Mtrace2 Request should be forwarded. 1063 4.3.1. Destination Address 1065 If the upstream router for the Mtrace2 Request is known for this 1066 request, the Mtrace2 Request is sent to that router. If the Incoming 1067 interface is known but the upstream router is not, the Mtrace2 1068 Request is sent to an appropriate multicast address on the Incoming 1069 interface. The multicast address SHOULD depend on the multicast 1070 routing protocol in use, such as ALL-[protocol]-ROUTERS.MCAST.NET. 1071 It MUST be a link-scoped group (i.e. 224.0.0.0/24 for IPv4, FF02::/16 1072 for IPv6), and MUST NOT be ALL-SYSTEMS.MCAST.NET (224.0.0.1) for IPv4 1073 and All Nodes Address (FF02::1) for IPv6. It MAY also be ALL- 1074 ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All Routers Address 1075 (FF02::2) for IPv6 if the routing protocol in use does not define a 1076 more appropriate multicast address. 1078 4.3.2. Source Address 1080 An Mtrace2 Request should be sent with the address of the Incoming 1081 interface. However, if the Incoming interface is unnumbered, the 1082 router can use one of its numbered interface addresses as the source 1083 address. 1085 4.3.3. Appending Standard Response Block 1087 An Mtrace2 Request MUST be sent upstream towards the source or the RP 1088 after appending a Standard Response Block to the end of the received 1089 Mtrace2 Request. The Standard Response Block includes the multicast 1090 states and statistics information of the router described in 1091 Section 3.2.4. 1093 If appending the Standard Response Block would make the Mtrace2 1094 Request packet longer than the MTU of the Incoming Interface, or, in 1095 the case of IPv6, longer than 1280 bytes, the router MUST change the 1096 Forwarding Code in the last Standard Response Block of the received 1097 Mtrace2 Request into NO_SPACE. The router then turns the Request 1098 into a Reply, and sends the Reply as described in Section 4.4. 1100 The router will continue with a new Request by copying from the old 1101 Request excluding all the response blocks, followed by the previously 1102 prepared Standard Response Block, and an Augmented Response Block 1103 with Augmented Response Type of 0x01 and the number of the returned 1104 Standard Response Blocks as the value. The new Request is then 1105 forwarded upstream. 1107 4.4. Sending Mtrace2 Reply 1109 An Mtrace2 Reply MUST be returned to the client by a router if any of 1110 the following conditions occur: 1112 1. The total number of the traced routers are equal to the # of hops 1113 in the request (including the one just added) plus the number of 1114 the returned blocks, if any. 1116 2. Appending the Standard Response Block would make the Mtrace2 1117 Request packet longer than the MTU of the Incoming interface. 1118 (In case of IPv6 not more than 1280 bytes; see Section 4.3.3 for 1119 additional details on handling of this case.) 1121 3. The request has reached the RP for a non source specific query or 1122 has reached the first hop router for a source specific query (see 1123 Section 4.2.2, items 9 and 10 for additional details). 1125 4.4.1. Destination Address 1127 An Mtrace2 Reply MUST be sent to the address specified in the Mtrace2 1128 Client Address field in the Mtrace2 Request. 1130 4.4.2. Source Address 1132 An Mtrace2 Reply SHOULD be sent with the address of the router's 1133 Outgoing interface. However, if the Outgoing interface address is 1134 unnumbered, the router can use one of its numbered interface 1135 addresses as the source address. 1137 4.4.3. Appending Standard Response Block 1139 An Mtrace2 Reply MUST be sent with the prepared Standard Response 1140 Block appended at the end of the received Mtrace2 Request except in 1141 the case of NO_SPACE forwarding code. 1143 4.5. Proxying Mtrace2 Query 1145 When a gateway (e.g., a NAT or firewall), which needs to block 1146 unicast packets to the Mtrace2 client, or hide information between 1147 the gateway and the Mtrace2 client, receives an Mtrace2 Query from an 1148 adjacent host or Mtrace2 Request from an adjacent router, it appends 1149 a Standard Response Block with REACHED_GW as the Forwarding Code. It 1150 turns the Query or Request into a Reply, and sends the Reply back to 1151 the client. 1153 At the same time, the gateway originates a new Mtrace2 Query message 1154 by copying the original Mtrace2 header (the Query or Request without 1155 any of the response blocks), and makes the changes as follows: 1157 o sets the RPF interface's address as the Mtrace2 Client Address; 1159 o uses its own port number as the Client Port #; and, 1161 o decreases # Hops by ((number of the Standard Response Blocks that 1162 were just returned in a Reply) - 1). The "-1" in this expression 1163 accounts for the additional Standard Response Block appended by 1164 the gateway router. 1166 The new Mtrace2 Query message is then sent to the upstream router or 1167 to an appropriate multicast address on the RPF interface. 1169 When the gateway receives an Mtrace2 Reply whose Query ID matches the 1170 one in the original Mtrace2 header, it MUST relay the Mtrace2 Reply 1171 back to the Mtrace2 client by replacing the Reply's header with the 1172 original Mtrace2 header. If the gateway does not receive the 1173 corresponding Mtrace2 Reply within the [Mtrace Reply Timeout] period 1174 (see Section 5.8.4), then it silently discards the original Mtrace2 1175 Query or Request message, and terminates the trace. 1177 4.6. Hiding Information 1179 Information about a domain's topology and connectivity may be hidden 1180 from the Mtrace2 Requests. The Forwarding Code of INFO_HIDDEN may be 1181 used to note that. For example, the incoming interface address and 1182 packet count on the ingress router of a domain, and the outgoing 1183 interface address and packet count on the egress router of the domain 1184 can be specified as all 1's. Additionally, the source-group packet 1185 count (see Section 3.2.4 and Section 3.2.5) within the domain may be 1186 all 1's if it is hidden. 1188 5. Client Behavior 1190 This section describes the behavior of an Mtrace2 client in detail. 1192 5.1. Sending Mtrace2 Query 1194 An Mtrace2 client initiates an Mtrace2 Query by sending the Query to 1195 the LHR of interest. 1197 5.1.1. Destination Address 1199 If an Mtrace2 client knows the proper LHR, it unicasts an Mtrace2 1200 Query packet to that router; otherwise, it MAY send the Mtrace2 Query 1201 packet to the ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All 1202 Routers Address (FF02::2) for IPv6. This will ensure that the packet 1203 is received by the LHR on the subnet. 1205 See also Section 5.4 on determining the LHR. 1207 5.1.2. Source Address 1209 An Mtrace2 Query MUST be sent with the client's interface address, 1210 which would be the Mtrace2 Client Address. 1212 5.2. Determining the Path 1214 An Mtrace2 client could send an initial Query messages with a large # 1215 Hops, in order to try to trace the full path. If this attempt fails, 1216 one strategy is to perform a linear search (as the traditional 1217 unicast traceroute program does); set the # Hops field to 1 and try 1218 to get a Reply, then 2, and so on. If no Reply is received at a 1219 certain hop, the hop count can continue past the non-responding hop, 1220 in the hopes that further hops may respond. These attempts should 1221 continue until the [Mtrace Reply Timeout] timeout has occurred. 1223 See also Section 5.6 on receiving the results of a trace. 1225 5.3. Collecting Statistics 1227 After a client has determined that it has traced the whole path or as 1228 much as it can expect to (see Section 5.8), it might collect 1229 statistics by waiting a short time and performing a second trace. If 1230 the path is the same in the two traces, statistics can be displayed 1231 as described in Section 7.3 and Section 7.4. 1233 5.4. Last Hop Router (LHR) 1235 The Mtrace2 client may not know which is the last-hop router, or that 1236 router may be behind a firewall that blocks unicast packets but 1237 passes multicast packets. In these cases, the Mtrace2 Request should 1238 be multicasted to ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All 1239 Routers Address (FF02::2) for IPv6. All routers except the correct 1240 last-hop router SHOULD ignore any Mtrace2 Request received via 1241 multicast. 1243 5.5. First Hop Router (FHR) 1245 The IANA assigned 224.0.1.32, MTRACE.MCAST.NET as the default 1246 multicast group for old IPv4 mtrace (v1) responses, in order to 1247 support mtrace clients that are not unicast reachable from the first- 1248 hop router. Mtrace2, however, does not require any IPv4/IPv6 1249 multicast addresses for the Mtrace2 Replies. Every Mtrace2 Reply is 1250 sent to the unicast address specified in the Mtrace2 Client Address 1251 field of the Mtrace2 Reply. 1253 5.6. Broken Intermediate Router 1255 A broken intermediate router might simply not understand Mtrace2 1256 packets, and drop them. The Mtrace2 client will get no Reply at all 1257 as a result. It should then perform a hop-by-hop search by setting 1258 the # Hops field until it gets an Mtrace2 Reply. The client may use 1259 linear or binary search; however, the latter is likely to be slower 1260 because a failure requires waiting for the [Mtrace Reply Timeout] 1261 period. 1263 5.7. Non-Supported Router 1265 When a non-supported router receives an Mtrace2 Query or Request 1266 message whose destination address is a multicast address, the router 1267 will silently discard the message. 1269 When the router receives an Mtrace2 Query which is destined to 1270 itself, the router would return an ICMP port unreachable to the 1271 Mtrace2 client. On the other hand, when the router receives an 1272 Mtrace2 Request which is destined to itself, the router would return 1273 an ICMP port unreachable to its adjacent router from which the 1274 Request receives. Therefore, the Mtrace2 client needs to terminate 1275 the trace when the [Mtrace Reply Timeout] timeout has occurred, and 1276 may then issue another Query with a lower number of # Hops. 1278 5.8. Mtrace2 Termination 1280 When performing an expanding hop-by-hop trace, it is necessary to 1281 determine when to stop expanding. 1283 5.8.1. Arriving at Source 1285 A trace can be determined to have arrived at the source if the 1286 Incoming Interface of the last router in the trace is non-zero, but 1287 the Upstream Router is zero. 1289 5.8.2. Fatal Error 1291 A trace has encountered a fatal error if the last Forwarding Error in 1292 the trace has the 0x80 bit set. 1294 5.8.3. No Upstream Router 1296 A trace can not continue if the last Upstream Router in the trace is 1297 set to 0. 1299 5.8.4. Reply Timeout 1301 This document defines the [Mtrace Reply Timeout] value, which is used 1302 to time out an Mtrace2 Reply as seen in Section 4.5, Section 5.2, and 1303 Section 5.7. The default [Mtrace Reply Timeout] value is 10 1304 (seconds), and can be manually changed on the Mtrace2 client and 1305 routers. 1307 5.9. Continuing after an Error 1309 When the NO_SPACE error occurs, as described in Section 4.2, a router 1310 will send back an Mtrace2 Reply to the Mtrace2 client, and continue 1311 with a new Request (see Section 4.3.3). In which case, the Mtrace2 1312 client may receive multiple Mtrace2 Replies from different routers 1313 along the path. When this happens, the client MUST treat them as a 1314 single Mtrace2 Reply message. 1316 If a trace times out, it is very likely that a router in the middle 1317 of the path does not support Mtrace2. That router's address will be 1318 in the Upstream Router field of the last Standard Response Block in 1319 the last received Reply. A client may be able to determine (via 1320 mrinfo or SNMP [11][13]) a list of neighbors of the non-responding 1321 router. If desired, each of those neighbors could be probed to 1322 determine the remainder of the path. Unfortunately, this heuristic 1323 may end up with multiple paths, since there is no way of knowing what 1324 the non-responding router's algorithm for choosing an upstream router 1325 is. However, if all paths but one flow back towards the non- 1326 responding router, it is possible to be sure that this is the correct 1327 path. 1329 6. Protocol-Specific Considerations 1331 This section describes the Mtrace2 behavior with the presence of 1332 different multicast protocols. 1334 6.1. PIM-SM 1336 When an Mtrace2 reaches a PIM-SM RP, and the RP does not forward the 1337 trace on, it means that the RP has not performed a source-specific 1338 join so there is no more state to trace. However, the path that 1339 traffic would use if the RP did perform a source-specific join can be 1340 traced by setting the trace destination to the RP, the trace source 1341 to the traffic source, and the trace group to 0. This Mtrace2 Query 1342 may be unicasted to the RP, and the RP takes the same actions as an 1343 LHR. 1345 6.2. Bi-Directional PIM 1347 Bi-directional PIM [6] is a variant of PIM-SM that builds bi- 1348 directional shared trees connecting multicast sources and receivers. 1349 Along the bi-directional shared trees, multicast data is natively 1350 forwarded from the sources to the Rendezvous Point Link (RPL), and 1351 from which, to receivers without requiring source-specific state. In 1352 contrast to PIM-SM, Bi-directional PIM always has the state to trace. 1354 A Designated Forwarder (DF) for a given Rendezvous Point Address 1355 (RPA) is in charge of forwarding downstream traffic onto its link, 1356 and forwarding upstream traffic from its link towards the RPL that 1357 the RPA belongs to. Hence Mtrace2 Reply reports DF addresses or RPA 1358 along the path. 1360 6.3. PIM-DM 1362 Routers running PIM Dense Mode [15] do not know the path packets 1363 would take unless traffic is flowing. Without some extra protocol 1364 mechanism, this means that in an environment with multiple possible 1365 paths with branch points on shared media, Mtrace2 can only trace 1366 existing paths, not potential paths. When there are multiple 1367 possible paths but the branch points are not on shared media, the 1368 upstream router is known, but the LHR may not know that it is the 1369 appropriate last hop. 1371 When traffic is flowing, PIM Dense Mode routers know whether or not 1372 they are the LHR for the link (because they won or lost an Assert 1373 battle) and know who the upstream router is (because it won an Assert 1374 battle). Therefore, Mtrace2 is always able to follow the proper path 1375 when traffic is flowing. 1377 6.4. IGMP/MLD Proxy 1379 When an IGMP/MLD Proxy [7] receives an Mtrace2 Query packet on an 1380 incoming interface, it notes a WRONG_IF in the Forwarding Code of the 1381 last Standard Response Block (see Section 3.2.4), and sends the 1382 Mtrace2 Reply back to the Mtrace2 client. On the other hand, when an 1383 Mtrace2 Query packet reaches an outgoing interface of the IGMP/MLD 1384 proxy, it is forwarded onto its incoming interface towards the 1385 upstream router. 1387 7. Problem Diagnosis 1389 This section describes different scenarios Mtrace2 can be used to 1390 diagnose the multicast problems. 1392 7.1. Forwarding Inconsistencies 1394 The Forwarding Error code can tell if a group is unexpectedly pruned 1395 or administratively scoped. 1397 7.2. TTL or Hop Limit Problems 1399 By taking the maximum of hops from the source and forwarding TTL 1400 threshold over all hops, it is possible to discover the TTL or hop 1401 limit required for the source to reach the destination. 1403 7.3. Packet Loss 1405 By taking two traces, it is possible to find packet loss information 1406 by comparing the difference in input packet counts to the difference 1407 in output packet counts for the specified source-group address pair 1408 at the previous hop. On a point-to-point link, any difference in 1409 these numbers implies packet loss. Since the packet counts may be 1410 changing as the Mtrace2 Request is propagating, there may be small 1411 errors (off by 1 or 2 or more) in these statistics. However, these 1412 errors will not accumulate if multiple traces are taken to expand the 1413 measurement period. On a shared link, the count of input packets can 1414 be larger than the number of output packets at the previous hop, due 1415 to other routers or hosts on the link injecting packets. This 1416 appears as "negative loss" which may mask real packet loss. 1418 In addition to the counts of input and output packets for all 1419 multicast traffic on the interfaces, the Standard Response Block 1420 includes a count of the packets forwarded by a node for the specified 1421 source-group pair. Taking the difference in this count between two 1422 traces and then comparing those differences between two hops gives a 1423 measure of packet loss just for traffic from the specified source to 1424 the specified receiver via the specified group. This measure is not 1425 affected by shared links. 1427 On a point-to-point link that is a multicast tunnel, packet loss is 1428 usually due to congestion in unicast routers along the path of that 1429 tunnel. On native multicast links, loss is more likely in the output 1430 queue of one hop, perhaps due to priority dropping, or in the input 1431 queue at the next hop. The counters in the Standard Response Block 1432 do not allow these cases to be distinguished. Differences in packet 1433 counts between the incoming and outgoing interfaces on one node 1434 cannot generally be used to measure queue overflow in the node. 1436 7.4. Link Utilization 1438 Again, with two traces, you can divide the difference in the input or 1439 output packet counts at some hop by the difference in time stamps 1440 from the same hop to obtain the packet rate over the link. If the 1441 average packet size is known, then the link utilization can also be 1442 estimated to see whether packet loss may be due to the rate limit or 1443 the physical capacity on a particular link being exceeded. 1445 7.5. Time Delay 1447 If the routers have synchronized clocks, it is possible to estimate 1448 propagation and queuing delay from the differences between the 1449 timestamps at successive hops. However, this delay includes control 1450 processing overhead, so is not necessarily indicative of the delay 1451 that data traffic would experience. 1453 8. IANA Considerations 1455 The following new registries are to be created and maintained under 1456 the "RFC Required" registry policy as specified in [4]. 1458 8.1. "Mtrace2 Forwarding Codes" Registry 1460 This is an integer in the range 0-255. Assignment of a Forwarding 1461 Code requires specification of a value and a name for the Forwarding 1462 Code. Initial values for the forwarding codes are given in the table 1463 at the end of Section 3.2.4. Additional values (specific to IPv6) 1464 may also be specified at the end of Section 3.2.5. Any additions to 1465 this registry are required to fully describe the conditions under 1466 which the new Forwarding Code is used. 1468 8.2. "Mtrace2 TLV Types" registry 1470 Assignment of a TLV Type requires specification of an integer value 1471 "Code" in the range 0-255 and a name ("Type"). Initial values for 1472 the TLV Types are given in the table at the beginning of Section 3.2. 1474 8.3. UDP Destination Port 1476 The Mtrace2 UDP destination port is [TBD]. 1478 9. Security Considerations 1480 This section addresses some of the security considerations related to 1481 Mtrace2. 1483 9.1. Addresses in Mtrace2 Header 1485 An Mtrace2 header includes three addresses, source address, multicast 1486 address, and Mtrace2 client address. These addresses MUST be 1487 congruent with the definition defined in Section 3.2.1 and forwarding 1488 Mtrace2 messages having invalid addresses MUST be prohibited. For 1489 instance, if Mtrace2 Client Address specified in an Mtrace2 header is 1490 a multicast address, then a router that receives the Mtrace2 message 1491 MUST silently discard it. 1493 9.2. Filtering of Clients 1495 A router SHOULD support a mechanism to filter out queries from 1496 clients beyond a specified administrative boundary. Such a boundary 1497 could, for example, be specified via a list of allowed/disallowed 1498 client addresses or subnets. If a query is received from beyond the 1499 specified administrative boundary, the Query MUST NOT be processed. 1500 The router MAY, however, perform rate limited logging of such events. 1502 9.3. Topology Discovery 1504 Mtrace2 can be used to discover any actively-used topology. If your 1505 network topology is a secret, Mtrace2 may be restricted at the border 1506 of your domain, using the ADMIN_PROHIB forwarding code. 1508 9.4. Characteristics of Multicast Channel 1510 Mtrace2 can be used to discover what sources are sending to what 1511 groups and at what rates. If this information is a secret, Mtrace2 1512 may be restricted at the border of your domain, using the 1513 ADMIN_PROHIB forwarding code. 1515 9.5. Limiting Query/Request Rates 1517 A router may limit Mtrace2 Queries and Requests by ignoring some of 1518 the consecutive messages. The router MAY randomly ignore the 1519 received messages to minimize the processing overhead, i.e., to keep 1520 fairness in processing queries, or prevent traffic amplification. 1521 The rate limit is left to the router's implementation. 1523 9.6. Limiting Reply Rates 1525 The proxying and NO_SPACE behaviors may result in one Query returning 1526 multiple Reply messages. In order to prevent abuse, the routers in 1527 the traced path MAY need to rate-limit the Replies. The rate limit 1528 function is left to the router's implementation. 1530 10. Acknowledgements 1532 This specification started largely as a transcription of Van 1533 Jacobson's slides from the 30th IETF, and the implementation in 1534 mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve 1535 Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original 1536 multicast traceroute client, mtrace (version 1), has been implemented 1537 by Ajit Thyagarajan, Steve Casner and Bill Fenner. The idea of the 1538 "S" bit to allow statistics for a source subnet is due to Tom 1539 Pusateri. 1541 For the Mtrace version 2 specification, the authors would like to 1542 give special thanks to Tatsuya Jinmei, Bill Fenner, and Steve Casner. 1543 Also, extensive comments were received from David L. Black, Ronald 1544 Bonica, Yiqun Cai, Liu Hui, Bharat Joshi, Robert Kebler, John 1545 Kristoff, Mankamana Mishra, Heidi Ou, Pekka Savola, Shinsuke Suzuki, 1546 Dave Thaler, Achmad Husni Thamrin, Stig Venaas, and Cao Wei. 1548 11. References 1550 11.1. Normative References 1552 [1] Bradner, S., "Key words for use in RFCs to indicate 1553 requirement levels", RFC 2119, March 1997. 1555 [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1556 (IPv6) Specification", RFC 2460, December 1998. 1558 [3] Hinden, R. and S. Deering, "IP Version 6 Addressing 1559 Architecture", RFC 4291, February 2006. 1561 [4] Narten, T. and H. Alvestrand, "Guidelines for Writing an 1562 IANA Considerations Section in RFCs", RFC 5226, May 2008. 1564 [5] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 1565 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 1566 Multicast - Sparse Mode (PIM-SM): Protocol Specification 1567 (Revised)", RFC 7761, March 2016. 1569 [6] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 1570 "Bidirectional Protocol Independent Multicast (BIDIR- 1571 PIM)", RFC 5015, October 2007. 1573 [7] Fenner, B., He, H., Haberman, B., and H. Sandick, 1574 "Internet Group Management Protocol (IGMP) / Multicast 1575 Listener Discovery (MLD)-Based Multicast Forwarding 1576 ("IGMP/MLD Proxying")", RFC 4605, August 2006. 1578 11.2. Informative References 1580 [8] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 1581 Thyagarajan, "Internet Group Management Protocol, Version 1582 3", RFC 3376, October 2002. 1584 [9] Bumgardner, G., "Automatic Multicast Tunneling", RFC 7450, 1585 February 2015. 1587 [10] Rosen, E. and R. Aggarwal, "Multicast in MPLS/BGP IP 1588 VPNs", RFC 6513, February 2012. 1590 [11] Draves, R. and D. Thaler, "Default Router Preferences and 1591 More-Specific Routes", RFC 4191, November 2005. 1593 [12] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 1594 MIB", RFC 2863, June 2000. 1596 [13] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast 1597 MIB", RFC 5132, December 2007. 1599 [14] Gill, V., Heasley, J., Meyer, D., Savola, P., and C. 1600 Pignataro, "The Generalized TTL Security Mechanism 1601 (GTSM)", RFC 5082, October 2007. 1603 [15] Adams, A., Nicholas, J., and W. Siadak, "Protocol 1604 Independent Multicast - Dense Mode (PIM-DM): Protocol 1605 Specification (Revised)", RFC 3973, January 2005. 1607 Authors' Addresses 1609 Hitoshi Asaeda 1610 National Institute of Information and Communications Technology 1611 4-2-1 Nukui-Kitamachi 1612 Koganei, Tokyo 184-8795 1613 Japan 1615 Email: asaeda@nict.go.jp 1616 Kerry Meyer 1617 Cisco Systems, Inc. 1618 510 McCarthy Blvd. 1619 Milpitas, CA 95035 1620 USA 1622 Email: kerrymey@cisco.com 1624 WeeSan Lee (editor) 1626 Email: weesan@weesan.com