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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: June 23, 2018 6 W. Lee, Ed. 7 December 20, 2017 9 Mtrace Version 2: Traceroute Facility for IP Multicast 10 draft-ietf-mboned-mtrace-v2-22 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 June 23, 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 . . . . . . . . 16 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 . . . . . . . . . . . . . . . 24 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 on which branch of 146 the multicast tree the receiver lies. This means that we have to 147 flood the whole tree to find the path from a source to a receiver. 148 On the other hand, walking up the tree from a receiver to a source is 149 easy, as most existing multicast routing protocols know the upstream 150 router for each source. Tracing from a receiver to a source can 151 involve 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 Protocol Independent Multicast - Sparse Mode (PIM- 159 SM) [5]. From the LHR/RP receiving the query, the tracing is 160 directed towards a specified source if a source address is specified 161 and source specific state exists on the receiving router. If no 162 source address is specified or if no source specific state exists on 163 a receiving LHR, the tracing is directed toward the RP for the 164 specified group address. Moreover, Mtrace2 provides additional 165 information such as the packet rates and losses, as well as other 166 diagnostic information. Mtrace2 is primarily intended for the 167 following purposes: 169 o To trace the path that a packet would take from a source to a 170 receiver. 172 o To isolate packet loss problems (e.g., congestion). 174 o To isolate configuration problems (e.g., Time to live (TTL) 175 threshold). 177 Figure 1 shows a typical case on how Mtrace2 is used. First-hop 178 router (FHR) represents the first-hop router, LHR represents the 179 last-hop router (LHR), and the arrow lines represent the Mtrace2 180 messages that are sent from one node to another. The numbers before 181 the Mtrace2 messages represent the sequence of the messages that 182 would happen. Source, Receiver and Mtrace2 client are typically 183 hosts. 185 2. Request 2. Request 186 +----+ +----+ 187 | | | | 188 v | v | 189 +--------+ +-----+ +-----+ +----------+ 190 | Source |----| FHR |----- The Internet -----| LHR |----| Receiver | 191 +--------+ +-----+ | +-----+ +----------+ 192 \ | ^ 193 \ | / 194 \ | / 195 \ | / 196 3. Reply \ | / 1. Query 197 \ | / 198 \ | / 199 \ +---------+ / 200 v | Mtrace2 |/ 201 | client | 202 +---------+ 204 Figure 1 206 When an Mtrace2 client initiates a multicast trace, it sends an 207 Mtrace2 Query packet to the LHR or RP for a multicast group and, 208 optionally, a source address. The LHR/RP turns the Query packet into 209 a Request. The Request message type enables each of the upstream 210 routers processing the message to apply different packet and message 211 validation rules than those required for handling of a Query message. 212 The LHR/RP then appends a standard response block containing its 213 interface addresses and packet statistics to the Request packet, then 214 forwards the packet towards the source/RP. The Request packet is 215 either unicasted to its upstream router towards the source/RP, or 216 multicasted to the group if the upstream router's IP address is not 217 known. In a similar fashion, each router along the path to the 218 source/RP appends a standard response block to the end of the Request 219 packet before forwarding it to its upstream router. When the FHR 220 receives the Request packet, it appends its own standard response 221 block, turns the Request packet into a Reply, and unicasts the Reply 222 back to the Mtrace2 client. 224 The Mtrace2 Reply may be returned before reaching the FHR under some 225 circumstances. This can happen if a Request packet is received at an 226 RP or gateway, or when any of several types of error or exception 227 conditions occur which prevent sending of a request to the next 228 upstream router. 230 The Mtrace2 client waits for the Mtrace2 Reply message and displays 231 the results. When not receiving an Mtrace2 Reply message due to 232 network congestion, a broken router (see Section 5.6), or a non- 233 responding router (see Section 5.7), the Mtrace2 client may resend 234 another Mtrace2 Query with a lower hop count (see Section 3.2.1), and 235 repeat the process until it receives an Mtrace2 Reply message. The 236 details are Mtrace2 client specific and outside the scope of this 237 document. 239 Note that when a router's control plane and forwarding plane are out 240 of sync, the Mtrace2 Requests might be forwarded based on the control 241 states instead. In this case, the traced path might not represent 242 the real path the data packets would follow. 244 Mtrace2 supports both IPv4 and IPv6. Unlike the previous version of 245 Mtrace, which implements its query and response as Internet Group 246 Management Protocol (IGMP) messages [8], all Mtrace2 messages are 247 UDP-based. Although the packet formats of IPv4 and IPv6 Mtrace2 are 248 different because of the address families, the syntax between them is 249 similar. 251 This document describes the base specification of Mtrace2 that can 252 serve as a basis for future proposals such as Mtrace2 for Automatic 253 Multicast Tunneling (AMT) [9] and Mtrace2 for Multicast in MPLS/BGP 254 IP VPNs (MVPN) [10]. They are therefore out of the scope of this 255 document. 257 2. Terminology 259 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 260 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", 261 and "OPTIONAL" are to be interpreted as described in RFC 2119 [1], 262 and indicate requirement levels for compliant Mtrace2 263 implementations. 265 2.1. Definitions 267 Since Mtrace2 Queries and Requests flow in the opposite direction to 268 the data flow, we refer to "upstream" and "downstream" with respect 269 to data, unless explicitly specified. 271 Incoming interface 272 The interface on which data is expected to arrive from the 273 specified source and group. 275 Outgoing interface 276 This is one of the interfaces to which data from the source or RP 277 is expected to be transmitted for the specified source and group. 278 It is also the interface on which the Mtrace2 Request was 279 received. 281 Upstream router 282 The router, connecting to the Incoming interface of the current 283 router, which is responsible for forwarding data for the specified 284 source and group to the current router. 286 First-hop router (FHR) 287 The router that is directly connected to the source the Mtrace2 288 Query specifies. 290 Last-hop router (LHR) 291 A router that is directly connected to a receiver. It is also the 292 router that receives the Mtrace2 Query from an Mtrace2 client. 294 Group state 295 It is the state a shared-tree protocol, such as PIM-SM [5], uses 296 to choose the upstream router towards the RP for the specified 297 group. In this state, source-specific state is not available for 298 the corresponding group address on the router. 300 Source-specific state 301 It is the state that is used to choose the path towards the source 302 for the specified source and group. 304 ALL-[protocol]-ROUTERS group 305 It is a link-local multicast address for multicast routers to 306 communicate with their adjacent routers that are running the same 307 routing protocol. For instance, the IPv4 'ALL-PIM-ROUTERS' group 308 is '224.0.0.13', and the IPv6 'ALL-PIM-ROUTERS' group is 'ff02::d' 309 [5]. 311 3. Packet Formats 313 This section describes the details of the packet formats for Mtrace2 314 messages. 316 All Mtrace2 messages are encoded in the Type/Length/Value (TLV) 317 format (see Section 3.1). The first TLV of a message is a message 318 header TLV specifying the type of message and additional context 319 information required for processing of the message and for parsing of 320 subsequent TLVs in the message. Subsequent TLVs in a message, 321 referred to as Blocks, are appended after the header TLV to provide 322 additional information associated with the message. If an 323 implementation receives an unknown TLV type for the first TLV in a 324 message (i.e., the header TLV), it SHOULD ignore and silently discard 325 the entire packet. If an implementation receives an unknown TLV type 326 for a subsequent TLV within a message, it SHOULD ignore and silently 327 discard the entire packet. If the length of a TLV exceeds the 328 available space in the containing packet, the implementation MUST 329 ignore and silently discard the TLV and any remaining portion of the 330 containing packet. 332 All Mtrace2 messages are UDP packets. For IPv4, Mtrace2 Query and 333 Request messages MUST NOT be fragmented. For IPv6, the packet size 334 for the Mtrace2 messages MUST NOT exceed 1280 bytes, which is the 335 smallest Maximum Transmission Unit (MTU) for an IPv6 interface [2]. 336 The source port is uniquely selected by the local host operating 337 system. The destination port is the IANA reserved Mtrace2 port 338 number (see Section 8). All Mtrace2 messages MUST have a valid UDP 339 checksum. 341 Additionally, Mtrace2 supports both IPv4 and IPv6, but not mixed. 342 For example, if an Mtrace2 Query or Request message arrives in as an 343 IPv4 packet, all addresses specified in the Mtrace2 messages MUST be 344 IPv4 as well. Same rule applies to IPv6 Mtrace2 messages. 346 3.1. Mtrace2 TLV format 348 0 1 2 3 349 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 1 350 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 351 | Type | Length | Value .... | 352 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 354 Type: 8 bits 356 Describes the format of the Value field. For all the available 357 types, please see Section 3.2 359 Length: 16 bits 361 Length of Type, Length, and Value fields in octets. Minimum 362 length required is 3 octets. The maximum TLV length is not 363 defined; however the entire Mtrace2 packet length SHOULD NOT 364 exceed the available MTU. 366 Value: variable length 368 The format is based on the Type value. The length of the value 369 field is Length field minus 3. All reserved fields in the Value 370 field MUST be transmitted as zeros and ignored on receipt. 372 3.2. Defined TLVs 374 The following TLV Types are defined: 376 Code Type 377 ==== ================================ 378 0x01 Mtrace2 Query 379 0x02 Mtrace2 Request 380 0x03 Mtrace2 Reply 381 0x04 Mtrace2 Standard Response Block 382 0x05 Mtrace2 Augmented Response Block 383 0x06 Mtrace2 Extended Query Block 385 Each Mtrace2 message MUST begin with either a Query, Request or Reply 386 TLV. The first TLV determines the type of each Mtrace2 message. 387 Following a Query TLV, there can be a sequence of optional Extended 388 Query Blocks. In the case of a Request or a Reply TLV, it is then 389 followed by a sequence of Standard Response Blocks, each from a 390 multicast router on the path towards the source or the RP. In the 391 case more information is needed, a Standard Response Block can be 392 followed by one or multiple Augmented Response Blocks. 394 We will describe each message type in detail in the next few 395 sections. 397 3.2.1. Mtrace2 Query 399 An Mtrace2 Query is usually originated by an Mtrace2 client which 400 sends an Mtrace2 Query message to the LHR. When tracing towards the 401 source or the RP, the intermediate routers MUST NOT modify the Query 402 message except the Type field. If the actual number of hops is not 403 known, an Mtrace2 client could send an initial Query message with a 404 large # Hops (e.g., 0xffffffff), in order to try to trace the full 405 path. 407 An Mtrace2 Query message is shown as follows: 409 0 1 2 3 410 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 1 411 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 412 | Type | Length | # Hops | 413 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 414 | | 415 | Multicast Address | 416 | | 417 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 418 | | 419 | Source Address | 420 | | 421 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 422 | | 423 | Mtrace2 Client Address | 424 | | 425 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 426 | Query ID | Client Port # | 427 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 429 Figure 2 431 # Hops: 8 bits 432 This field specifies the maximum number of hops that the Mtrace2 433 client wants to trace. If there are some error conditions in the 434 middle of the path that prevent an Mtrace2 Reply from being 435 received by the client, the client MAY issue another Mtrace2 Query 436 with a lower number of hops until it receives a Reply. 438 Multicast Address: 32 bits or 128 bits 439 This field specifies an IPv4 or IPv6 address, which can be either: 441 m-1: a multicast group address to be traced; or, 443 m-2: all 1's in case of IPv4 or the unspecified address (::) in 444 case of IPv6 if no group-specific information is desired. 446 Source Address: 32 bits or 128 bits 447 This field specifies an IPv4 or IPv6 address, which can be either: 449 s-1: a unicast address of the source to be traced; or, 451 s-2: all 1's in case of IPv4 or the unspecified address (::) in 452 case of IPv6 if no source-specific information is desired. 453 For example, the client is tracing a (*,g) group state. 455 Note that it is invalid to have a source-group combination of 456 (s-2, m-2). If a router receives such combination in an Mtrace2 457 Query, it MUST silently discard the Query. 459 Mtrace2 Client Address: 32 bits or 128 bits 460 This field specifies the Mtrace2 client's IPv4 address or IPv6 461 global address. This address MUST be a valid unicast address, and 462 therefore, MUST NOT be all 1's or an unspecified address. The 463 Mtrace2 Reply will be sent to this address. 465 Query ID: 16 bits 466 This field is used as a unique identifier for this Mtrace2 Query 467 so that duplicate or delayed Reply messages may be detected. 469 Client Port #: 16 bits 470 This field specifies the destination UDP port number for receiving 471 the Mtrace2 Reply packet. 473 3.2.2. Mtrace2 Request 475 The format of an Mtrace2 Request message is similar to an Mtrace2 476 Query except the Type field is 0x02. 478 When a LHR receives an Mtrace2 Query message, it would turn the Query 479 into a Request by changing the Type field of the Query from 0x01 to 480 0x02. The LHR would then append an Mtrace2 Standard Response Block 481 (see Section 3.2.4) of its own to the Request message before sending 482 it upstream. The upstream routers would do the same without changing 483 the Type field until one of them is ready to send a Reply. 485 3.2.3. Mtrace2 Reply 487 The format of an Mtrace2 Reply message is similar to an Mtrace2 Query 488 except the Type field is 0x03. 490 When a FHR or a RP receives an Mtrace2 Request message which is 491 destined to itself, it would append an Mtrace2 Standard Response 492 Block (see Section 3.2.4) of its own to the Request message. Next, 493 it would turn the Request message into a Reply by changing the Type 494 field of the Request from 0x02 to 0x03. The Reply message would then 495 be unicasted to the Mtrace2 client specified in the Mtrace2 Client 496 Address field. 498 There are a number of cases in which an intermediate router might 499 return a Reply before a Request reaches the FHR or the RP. See 500 Section 4.1.1, Section 4.2.2, Section 4.3.3, and Section 4.5 for more 501 details. 503 3.2.4. IPv4 Mtrace2 Standard Response Block 505 This section describes the message format of an IPv4 Mtrace2 Standard 506 Response Block. The Type field is 0x04. 508 0 1 2 3 509 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 1 510 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 511 | Type | Length | MBZ | 512 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 513 | Query Arrival Time | 514 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 515 | Incoming Interface Address | 516 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 517 | Outgoing Interface Address | 518 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 519 | Upstream Router Address | 520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 521 | | 522 . Input packet count on incoming interface . 523 | | 524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 525 | | 526 . Output packet count on outgoing interface . 527 | | 528 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 529 | | 530 . Total number of packets for this source-group pair . 531 | | 532 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 533 | Rtg Protocol | Multicast Rtg Protocol | 534 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 535 | Fwd TTL | MBZ |S| Src Mask |Forwarding Code| 536 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 538 MBZ: 8 bits 539 This field MUST be zeroed on transmission and ignored on 540 reception. 542 Query Arrival Time: 32 bits 543 The Query Arrival Time is a 32-bit Network Time Protocol (NTP) 544 timestamp specifying the arrival time of the Mtrace2 Query or 545 Request packet at this router. The 32-bit form of an NTP 546 timestamp consists of the middle 32 bits of the full 64-bit form; 547 that is, the low 16 bits of the integer part and the high 16 bits 548 of the fractional part. 550 The following formula converts from a timespec (fractional part in 551 nanoseconds) to a 32-bit NTP timestamp: 553 query_arrival_time 554 = ((tv.tv_sec + 32384) << 16) + ((tv.tv_nsec << 7) / 1953125) 556 The constant 32384 is the number of seconds from Jan 1, 1900 to 557 Jan 1, 1970 truncated to 16 bits. ((tv.tv_nsec << 7) / 1953125) 558 is a reduction of ((tv.tv_nsec / 1000000000) << 16). 560 Note that Mtrace2 does not require all the routers on the path to 561 have synchronized clocks in order to measure one-way latency. 563 Additionally, Query Arrival Time is useful for measuring the 564 packet rate. For example, suppose that a client issues two 565 queries, and the corresponding requests R1 and R2 arrive at router 566 X at time T1 and T2, then the client would be able to compute the 567 packet rate on router X by using the packet count information 568 stored in the R1 and R2, and the time T1 and T2. 570 Incoming Interface Address: 32 bits 571 This field specifies the address of the interface on which packets 572 from the source or the RP are expected to arrive, or 0 if unknown 573 or unnumbered. 575 Outgoing Interface Address: 32 bits 576 This field specifies the address of the interface on which packets 577 from the source or the RP are expected to transmit towards the 578 receiver, or 0 if unknown or unnumbered. This is also the address 579 of the interface on which the Mtrace2 Query or Request arrives. 581 Upstream Router Address: 32 bits 582 This field specifies the address of the upstream router from which 583 this router expects packets from this source. This may be a 584 multicast group (e.g., ALL-[protocol]-ROUTERS group) if the 585 upstream router is not known because of the workings of the 586 multicast routing protocol. However, it should be 0 if the 587 incoming interface address is unknown or unnumbered. 589 Input packet count on incoming interface: 64 bits 590 This field contains the number of multicast packets received for 591 all groups and sources on the incoming interface, or all 1's if no 592 count can be reported. This counter may have the same value as 593 ifHCInMulticastPkts from the Interfaces Group MIB (IF-MIB) [12] 594 for this interface. 596 Output packet count on outgoing interface: 64 bit 597 This field contains the number of multicast packets that have been 598 transmitted or queued for transmission for all groups and sources 599 on the outgoing interface, or all 1's if no count can be reported. 600 This counter may have the same value as ifHCOutMulticastPkts from 601 the IF-MIB [12] for this interface. 603 Total number of packets for this source-group pair: 64 bits 604 This field counts the number of packets from the specified source 605 forwarded by the router to the specified group, or all 1's if no 606 count can be reported. If the S bit is set (see below), the count 607 is for the source network, as specified by the Src Mask field (see 608 below). If the S bit is set and the Src Mask field is 127, 609 indicating no source-specific state, the count is for all sources 610 sending to this group. This counter should have the same value as 611 ipMcastRoutePkts from the IP Multicast MIB [13] for this 612 forwarding entry. 614 Rtg Protocol: 16 bits 615 This field describes the unicast routing protocol running between 616 this router and the upstream router, and it is used to determine 617 the RPF interface for the specified source or RP. This value 618 should have the same value as ipMcastRouteRtProtocol from the IP 619 Multicast MIB [13] for this entry. If the router is not able to 620 obtain this value, all 0's must be specified. 622 Multicast Rtg Protocol: 16 bits 623 This field describes the multicast routing protocol in use between 624 the router and the upstream router. This value should have the 625 same value as ipMcastRouteProtocol from the IP Multicast MIB [13] 626 for this entry. If the router cannot obtain this value, all 0's 627 must be specified. 629 Fwd TTL: 8 bits 630 This field contains the configured multicast TTL threshold, if 631 any, of the outgoing interface. 633 S: 1 bit 634 If this bit is set, it indicates that the packet count for the 635 source-group pair is for the source network, as determined by 636 masking the source address with the Src Mask field. 638 Src Mask: 7 bits 639 This field contains the number of 1's in the netmask the router 640 has for the source (i.e. a value of 24 means the netmask is 641 0xffffff00). If the router is forwarding solely on group state, 642 this field is set to 127 (0x7f). 644 Forwarding Code: 8 bits 645 This field contains a forwarding information/error code. Values 646 with the high order bit set (0x80-0xff) are intended for use as 647 error or exception codes. Section 4.1 and Section 4.2 explain how 648 and when the Forwarding Code is filled. Defined values are as 649 follows: 651 Value Name Description 652 ----- -------------- ---------------------------------------------- 653 0x00 NO_ERROR No error 654 0x01 WRONG_IF Mtrace2 Request arrived on an interface 655 to which this router would not forward for 656 the specified group towards the source or RP. 657 0x02 PRUNE_SENT This router has sent a prune upstream which 658 applies to the source and group in the 659 Mtrace2 Request. 660 0x03 PRUNE_RCVD This router has stopped forwarding for this 661 source and group in response to a request 662 from the downstream router. 663 0x04 SCOPED The group is subject to administrative 664 scoping at this router. 665 0x05 NO_ROUTE This router has no route for the source or 666 group and no way to determine a potential 667 route. 668 0x06 WRONG_LAST_HOP This router is not the proper LHR. 669 0x07 NOT_FORWARDING This router is not forwarding this source and 670 group out the outgoing interface for an 671 unspecified reason. 672 0x08 REACHED_RP Reached the Rendezvous Point. 673 0x09 RPF_IF Mtrace2 Request arrived on the expected 674 RPF interface for this source and group. 675 0x0A NO_MULTICAST Mtrace2 Request arrived on an interface 676 which is not enabled for multicast. 677 0x0B INFO_HIDDEN One or more hops have been hidden from this 678 trace. 679 0x0C REACHED_GW Mtrace2 Request arrived on a gateway (e.g., 680 a NAT or firewall) that hides the 681 information between this router and the 682 Mtrace2 client. 683 0x0D UNKNOWN_QUERY A non-transitive Extended Query Type was 684 received by a router which does not support 685 the type. 686 0x80 FATAL_ERROR A fatal error is one where the router may 687 know the upstream router but cannot forward 688 the message to it. 689 0x81 NO_SPACE There was not enough room to insert another 690 Standard Response Block in the packet. 691 0x83 ADMIN_PROHIB Mtrace2 is administratively prohibited. 693 3.2.5. IPv6 Mtrace2 Standard Response Block 695 This section describes the message format of an IPv6 Mtrace2 Standard 696 Response Block. The Type field is also 0x04. 698 0 1 2 3 699 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 1 700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 701 | Type | Length | MBZ | 702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 703 | Query Arrival Time | 704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 705 | Incoming Interface ID | 706 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 707 | Outgoing Interface ID | 708 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 709 | | 710 * Local Address * 711 | | 712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 713 | | 714 * Remote Address * 715 | | 716 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 717 | | 718 . Input packet count on incoming interface . 719 | | 720 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 721 | | 722 . Output packet count on outgoing interface . 723 | | 724 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 725 | | 726 . Total number of packets for this source-group pair . 727 | | 728 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 729 | Rtg Protocol | Multicast Rtg Protocol | 730 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 731 | MBZ 2 |S|Src Prefix Len |Forwarding Code| 732 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 734 MBZ: 8 bits 735 This field MUST be zeroed on transmission and ignored on 736 reception. 738 Query Arrival Time: 32 bits 739 Same definition as in IPv4. 741 Incoming Interface ID: 32 bits 742 This field specifies the interface ID on which packets from the 743 source or RP are expected to arrive, or 0 if unknown. This ID 744 should be the value taken from InterfaceIndex of the IF-MIB [12] 745 for this interface. 747 Outgoing Interface ID: 32 bits 748 This field specifies the interface ID to which packets from the 749 source or RP are expected to transmit, or 0 if unknown. This ID 750 should be the value taken from InterfaceIndex of the IF-MIB [12] 751 for this interface 753 Local Address: 128 bits 754 This field specifies a global IPv6 address that uniquely 755 identifies the router. A unique local unicast address [11] SHOULD 756 NOT be used unless the router is only assigned link-local and 757 unique local addresses. If the router is only assigned link-local 758 addresses, its link-local address can be specified in this field. 760 Remote Address: 128 bits 761 This field specifies the address of the upstream router, which, in 762 most cases, is a link-local unicast address for the upstream 763 router. 765 Although a link-local address does not have enough information to 766 identify a node, it is possible to detect the upstream router with 767 the assistance of Incoming Interface ID and the current router 768 address (i.e., Local Address). 770 Note that this may be a multicast group (e.g., ALL-[protocol]- 771 ROUTERS group) if the upstream router is not known because of the 772 workings of a multicast routing protocol. However, it should be 773 the unspecified address (::) if the incoming interface address is 774 unknown. 776 Input packet count on incoming interface: 64 bits 777 Same definition as in IPv4. 779 Output packet count on outgoing interface: 64 bits 780 Same definition as in IPv4. 782 Total number of packets for this source-group pair: 64 bits 783 Same definition as in IPv4, except if the S bit is set (see 784 below), the count is for the source network, as specified by the 785 Src Prefix Len field. If the S bit is set and the Src Prefix Len 786 field is 255, indicating no source-specific state, the count is 787 for all sources sending to this group. This counter should have 788 the same value as ipMcastRoutePkts from the IP Multicast MIB [13] 789 for this forwarding entry. 791 Rtg Protocol: 16 bits 792 Same definition as in IPv4. 794 Multicast Rtg Protocol: 16 bits 795 Same definition as in IPv4. 797 MBZ 2: 15 bits 798 This field MUST be zeroed on transmission and ignored on 799 reception. 801 S: 1 bit 802 Same definition as in IPv4, except the Src Prefix Len field is 803 used to mask the source address. 805 Src Prefix Len: 8 bits 806 This field contains the prefix length this router has for the 807 source. If the router is forwarding solely on group state, this 808 field is set to 255 (0xff). 810 Forwarding Code: 8 bits 811 Same definition as in IPv4. 813 3.2.6. Mtrace2 Augmented Response Block 815 In addition to the Standard Response Block, a multicast router on the 816 traced path can optionally add one or multiple Augmented Response 817 Blocks before sending the Request to its upstream router. 819 The Augmented Response Block is flexible for various purposes such as 820 providing diagnosis information (see Section 7) and protocol 821 verification. Its Type field is 0x05, and its format is as follows: 823 0 1 2 3 824 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 1 825 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 826 | Type | Length | MBZ | 827 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 828 | Augmented Response Type | Value .... | 829 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 831 MBZ: 8 bits 832 This field MUST be zeroed on transmission and ignored on 833 reception. 835 Augmented Response Type: 16 bits 836 This field specifies the type of various responses from a 837 multicast router that might need to communicate back to the 838 Mtrace2 client as well as the multicast routers on the traced 839 path. 841 The Augmented Response Type is defined as follows: 843 Code Type 844 ==== =============================================== 845 0x01 # of the returned Standard Response Blocks 847 When the NO_SPACE error occurs on a router, the router should send 848 the original Mtrace2 Request received from the downstream router 849 as a Reply back to the Mtrace2 client and continue with a new 850 Mtrace2 Request. In the new Request, the router would add a 851 Standard Response Block followed by an Augmented Response Block 852 with 0x01 as the Augmented Response Type, and the number of the 853 returned Mtrace2 Standard Response Blocks as the Value. 855 Each upstream router would recognize the total number of hops the 856 Request has been traced so far by adding this number and the 857 number of the Standard Response Block in the current Request 858 message. 860 This document only defines one Augmented Response Type in the 861 Augmented Response Block. The description on how to provide 862 diagnosis information using the Augmented Response Block is out of 863 the scope of this document, and will be addressed in separate 864 documents. 866 Value: variable length 867 The format is based on the Augmented Response Type value. The 868 length of the value field is Length field minus 6. 870 3.2.7. Mtrace2 Extended Query Block 872 There may be a sequence of optional Extended Query Blocks that follow 873 an Mtrace2 Query to further specify any information needed for the 874 Query. For example, an Mtrace2 client might be interested in tracing 875 the path the specified source and group would take based on a certain 876 topology. In this case, the client can pass in the multi-topology ID 877 as the Value for an Extended Query Type (see below). The Extended 878 Query Type is extensible and the behavior of the new types will be 879 addressed by separate documents. 881 The Mtrace2 Extended Query Block's Type field is 0x06, and is 882 formatted as follows: 884 0 1 2 3 885 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 1 886 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 887 | Type | Length | MBZ |T| 888 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 889 | Extended Query Type | Value .... | 890 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 892 MBZ: 7 bits 893 This field MUST be zeroed on transmission and ignored on 894 reception. 896 T-bit (Transitive Attribute): 1 bit 897 If the TLV type is unrecognized by the receiving router, then this 898 TLV is either discarded or forwarded along with the Query, 899 depending on the value of this bit. If this bit is set, then the 900 router MUST forward this TLV. If this bit is clear, the router 901 MUST send an Mtrace2 Reply with an UNKNOWN_QUERY error. 903 Extended Query Type: 16 bits 904 This field specifies the type of the Extended Query Block. 906 Value: 16 bits 907 This field specifies the value of this Extended Query. 909 4. Router Behavior 911 This section describes the router behavior in the context of Mtrace2 912 in detail. 914 4.1. Receiving Mtrace2 Query 916 An Mtrace2 Query message is an Mtrace2 message with no response 917 blocks filled in, and uses TLV type of 0x01. 919 4.1.1. Query Packet Verification 921 Upon receiving an Mtrace2 Query message, a router MUST examine 922 whether the Multicast Address and the Source Address are a valid 923 combination as specified in Section 3.2.1, and whether the Mtrace2 924 Client Address is a valid IP unicast address. If either one is 925 invalid, the Query MUST be silently ignored. 927 Mtrace2 supports a non-local client to the LHR/RP. A router SHOULD, 928 however, support a mechanism to filter out queries from clients 929 beyond a specified administrative boundary. The potential approaches 930 are described in Section 9.2. 932 In the case where a local LHR client is required, the router must 933 then examine the Query to see if it is the proper LHR/RP for the 934 destination address in the packet. It is the proper local LHR if it 935 has a multicast-capable interface on the same subnet as the Mtrace2 936 Client Address and is the router that would forward traffic from the 937 given (S,G) or (*,G) onto that subnet. It is the proper RP if the 938 multicast group address specified in the query is 0 and if the IP 939 header destination address is a valid RP address on this router. 941 If the router determines that it is not the proper LHR/RP, or it 942 cannot make that determination, it does one of two things depending 943 on whether the Query was received via multicast or unicast. If the 944 Query was received via multicast, then it MUST be silently discarded. 945 If it was received via unicast, the router turns the Query into a 946 Reply message by changing the TLV type to 0x03 and appending a 947 Standard Response Block with a Forwarding Code of WRONG_LAST_HOP. 948 The rest of the fields in the Standard Response Block MUST be zeroed. 949 The router then sends the Reply message to the Mtrace2 Client Address 950 on the Client Port # as specified in the Mtrace2 Query. 952 Duplicate Query messages as identified by the tuple (Mtrace2 Client 953 Address, Query ID) SHOULD be ignored. This MAY be implemented using 954 a cache of previously processed queries keyed by the Mtrace2 Client 955 Address and Query ID pair. The duration of the cached entries is 956 implementation specific. Duplicate Request messages MUST NOT be 957 ignored in this manner. 959 4.1.2. Query Normal Processing 961 When a router receives an Mtrace2 Query and it determines that it is 962 the proper LHR/RP, it turns the Query to a Request by changing the 963 TLV type from 0x01 to 0x02, and performs the steps listed in 964 Section 4.2. 966 4.2. Receiving Mtrace2 Request 968 An Mtrace2 Request is an Mtrace2 message that uses TLV type of 0x02. 969 With the exception of the LHR, whose Request was just converted from 970 a Query, each Request received by a router should have at least one 971 Standard Response Block filled in. 973 4.2.1. Request Packet Verification 975 If the Mtrace2 Request does not come from an adjacent router, or if 976 the Request is not addressed to this router, or if the Request is 977 addressed to a multicast group which is not a link-scoped group 978 (i.e., 224.0.0.0/24 for IPv4, FFx2::/16 [3] for IPv6), it MUST be 979 silently ignored. The Generalized TTL Security Mechanism (GTSM) [14] 980 SHOULD be used by the router to determine whether the router is 981 adjacent or not. 983 If the sum of the number of the Standard Response Blocks in the 984 received Mtrace2 Request and the value of the Augmented Response Type 985 of 0x01, if any, is equal or more than the # Hops in the Mtrace2 986 Request, it MUST be silently ignored. 988 4.2.2. Request Normal Processing 990 When a router receives an Mtrace2 Request message, it performs the 991 following steps. Note that it is possible to have multiple 992 situations covered by the Forwarding Codes. The first one 993 encountered is the one that is reported, i.e. all "note Forwarding 994 Code N" should be interpreted as "if Forwarding Code is not already 995 set, set Forwarding Code to N". Note that in the steps described 996 below the "Outgoing Interface" is the one on which the Mtrace2 997 Request message arrives. 999 1. Prepare a Standard Response Block to be appended to the packet, 1000 setting all fields to an initial default value of zero. 1002 2. If Mtrace2 is administratively prohibited, note the Forwarding 1003 Code of ADMIN_PROHIB and skip to step 4. 1005 3. In the Standard Response Block, fill in the Query Arrival Time, 1006 Outgoing Interface Address (for IPv4) or Outgoing Interface ID 1007 (for IPv6), Output Packet Count, and Fwd TTL (for IPv4). 1009 4. Attempt to determine the forwarding information for the 1010 specified source and group, using the same mechanisms as would 1011 be used when a packet is received from the source destined for 1012 the group. A state need not be instantiated, it can be a 1013 "phantom" state created only for the purpose of the trace, such 1014 as "dry-run." 1016 If using a shared-tree protocol and there is no source-specific 1017 state, or if no source-specific information is desired (i.e., 1018 all 1's for IPv4 or unspecified address (::) for IPv6), group 1019 state should be used. If there is no group state or no group- 1020 specific information is desired, potential source state (i.e., 1021 the path that would be followed for a source-specific Join) 1022 should be used. 1024 5. If no forwarding information can be determined, the router notes 1025 a Forwarding Code of NO_ROUTE, sets the remaining fields that 1026 have not yet been filled in to zero, and then sends an Mtrace2 1027 Reply back to the Mtrace2 client. 1029 6. If a Forwarding Code of ADMIN_PROHIB has been set, skip to step 1030 7. Otherwise, fill in the Incoming Interface Address (or 1031 Incoming Interface ID and Local Address for IPv6), Upstream 1032 Router Address (or Remote Address for IPv6), Input Packet Count, 1033 Total Number of Packets, Routing Protocol, S, and Src Mask (or 1034 Src Prefix Len for IPv6) using the forwarding information 1035 determined in step 4. 1037 7. If the Outgoing interface is not enabled for multicast, note 1038 Forwarding Code of NO_MULTICAST. If the Outgoing interface is 1039 the interface from which the router would expect data to arrive 1040 from the source, note forwarding code RPF_IF. If the Outgoing 1041 interface is not one to which the router would forward data from 1042 the source or RP to the group, a Forwarding code of WRONG_IF is 1043 noted. In the above three cases, the router will return an 1044 Mtrace2 Reply and terminate the trace. 1046 8. If the group is subject to administrative scoping on either the 1047 Outgoing or Incoming interfaces, a Forwarding Code of SCOPED is 1048 noted. 1050 9. If this router is the RP for the group for a non-source-specific 1051 query, note a Forwarding Code of REACHED_RP. The router will 1052 send an Mtrace2 Reply and terminate the trace. 1054 10. If this router is directly connected to the specified source or 1055 source network on the Incoming interface, it sets the Upstream 1056 Router Address (for IPv4) or the Remote Address (for IPv6) of 1057 the response block to zero. The router will send an Mtrace2 1058 Reply and terminate the trace. 1060 11. If this router has sent a prune upstream which applies to the 1061 source and group in the Mtrace2 Request, it notes a Forwarding 1062 Code of PRUNE_SENT. If the router has stopped forwarding 1063 downstream in response to a prune sent by the downstream router, 1064 it notes a Forwarding Code of PRUNE_RCVD. If the router should 1065 normally forward traffic downstream for this source and group 1066 but is not, it notes a Forwarding Code of NOT_FORWARDING. 1068 12. If this router is a gateway (e.g., a NAT or firewall) that hides 1069 the information between this router and the Mtrace2 client, it 1070 notes a Forwarding Code of REACHED_GW. The router continues the 1071 processing as described in Section 4.5. 1073 13. If the total number of the Standard Response Blocks, including 1074 the newly prepared one, and the value of the Augmented Response 1075 Type of 0x01, if any, is less than the # Hops in the Request, 1076 the packet is then forwarded to the upstream router as described 1077 in Section 4.3; otherwise, the packet is sent as an Mtrace2 1078 Reply to the Mtrace2 client as described in Section 4.4. 1080 4.3. Forwarding Mtrace2 Request 1082 This section describes how an Mtrace2 Request should be forwarded. 1084 4.3.1. Destination Address 1086 If the upstream router for the Mtrace2 Request is known for this 1087 request, the Mtrace2 Request is sent to that router. If the Incoming 1088 interface is known but the upstream router is not, the Mtrace2 1089 Request is sent to an appropriate multicast address on the Incoming 1090 interface. The multicast address SHOULD depend on the multicast 1091 routing protocol in use, such as ALL-[protocol]-ROUTERS group. It 1092 MUST be a link-scoped group (i.e., 224.0.0.0/24 for IPv4, FF02::/16 1093 for IPv6), and MUST NOT be the all-systems multicast group 1094 (224.0.0.1) for IPv4 and All Nodes Address (FF02::1) for IPv6. It 1095 MAY also be the all-routers multicast group (224.0.0.2) for IPv4 or 1096 All Routers Address (FF02::2) for IPv6 if the routing protocol in use 1097 does not define a more appropriate multicast address. 1099 4.3.2. Source Address 1101 An Mtrace2 Request should be sent with the address of the Incoming 1102 interface. However, if the Incoming interface is unnumbered, the 1103 router can use one of its numbered interface addresses as the source 1104 address. 1106 4.3.3. Appending Standard Response Block 1108 An Mtrace2 Request MUST be sent upstream towards the source or the RP 1109 after appending a Standard Response Block to the end of the received 1110 Mtrace2 Request. The Standard Response Block includes the multicast 1111 states and statistics information of the router described in 1112 Section 3.2.4. 1114 If appending the Standard Response Block would make the Mtrace2 1115 Request packet longer than the MTU of the Incoming Interface, or, in 1116 the case of IPv6, longer than 1280 bytes, the router MUST change the 1117 Forwarding Code in the last Standard Response Block of the received 1118 Mtrace2 Request into NO_SPACE. The router then turns the Request 1119 into a Reply and sends the Reply as described in Section 4.4. 1121 The router will continue with a new Request by copying from the old 1122 Request excluding all the response blocks, followed by the previously 1123 prepared Standard Response Block, and an Augmented Response Block 1124 with Augmented Response Type of 0x01 and the number of the returned 1125 Standard Response Blocks as the value. The new Request is then 1126 forwarded upstream. 1128 4.4. Sending Mtrace2 Reply 1130 An Mtrace2 Reply MUST be returned to the client by a router if any of 1131 the following conditions occur: 1133 1. The total number of the traced routers are equal to the # of hops 1134 in the request (including the one just added) plus the number of 1135 the returned blocks, if any. 1137 2. Appending the Standard Response Block would make the Mtrace2 1138 Request packet longer than the MTU of the Incoming interface. 1139 (In case of IPv6 not more than 1280 bytes; see Section 4.3.3 for 1140 additional details on handling of this case.) 1142 3. The request has reached the RP for a non source specific query or 1143 has reached the first hop router for a source specific query (see 1144 Section 4.2.2, items 9 and 10 for additional details). 1146 4.4.1. Destination Address 1148 An Mtrace2 Reply MUST be sent to the address specified in the Mtrace2 1149 Client Address field in the Mtrace2 Request. 1151 4.4.2. Source Address 1153 An Mtrace2 Reply SHOULD be sent with the address of the router's 1154 Outgoing interface. However, if the Outgoing interface address is 1155 unnumbered, the router can use one of its numbered interface 1156 addresses as the source address. 1158 4.4.3. Appending Standard Response Block 1160 An Mtrace2 Reply MUST be sent with the prepared Standard Response 1161 Block appended at the end of the received Mtrace2 Request except in 1162 the case of NO_SPACE forwarding code. 1164 4.5. Proxying Mtrace2 Query 1166 When a gateway (e.g., a NAT or firewall), which needs to block 1167 unicast packets to the Mtrace2 client, or hide information between 1168 the gateway and the Mtrace2 client, receives an Mtrace2 Query from an 1169 adjacent host or Mtrace2 Request from an adjacent router, it appends 1170 a Standard Response Block with REACHED_GW as the Forwarding Code. It 1171 turns the Query or Request into a Reply, and sends the Reply back to 1172 the client. 1174 At the same time, the gateway originates a new Mtrace2 Query message 1175 by copying the original Mtrace2 header (the Query or Request without 1176 any of the response blocks), and makes the changes as follows: 1178 o sets the RPF interface's address as the Mtrace2 Client Address; 1180 o uses its own port number as the Client Port #; and, 1182 o decreases # Hops by ((number of the Standard Response Blocks that 1183 were just returned in a Reply) - 1). The "-1" in this expression 1184 accounts for the additional Standard Response Block appended by 1185 the gateway router. 1187 The new Mtrace2 Query message is then sent to the upstream router or 1188 to an appropriate multicast address on the RPF interface. 1190 When the gateway receives an Mtrace2 Reply whose Query ID matches the 1191 one in the original Mtrace2 header, it MUST relay the Mtrace2 Reply 1192 back to the Mtrace2 client by replacing the Reply's header with the 1193 original Mtrace2 header. If the gateway does not receive the 1194 corresponding Mtrace2 Reply within the [Mtrace Reply Timeout] period 1195 (see Section 5.8.4), then it silently discards the original Mtrace2 1196 Query or Request message, and terminates the trace. 1198 4.6. Hiding Information 1200 Information about a domain's topology and connectivity may be hidden 1201 from the Mtrace2 Requests. The Forwarding Code of INFO_HIDDEN may be 1202 used to note that. For example, the incoming interface address and 1203 packet count on the ingress router of a domain, and the outgoing 1204 interface address and packet count on the egress router of the domain 1205 can be specified as all 1's. Additionally, the source-group packet 1206 count (see Section 3.2.4 and Section 3.2.5) within the domain may be 1207 all 1's if it is hidden. 1209 5. Client Behavior 1211 This section describes the behavior of an Mtrace2 client in detail. 1213 5.1. Sending Mtrace2 Query 1215 An Mtrace2 client initiates an Mtrace2 Query by sending the Query to 1216 the LHR of interest. 1218 5.1.1. Destination Address 1220 If an Mtrace2 client knows the proper LHR, it unicasts an Mtrace2 1221 Query packet to that router; otherwise, it MAY send the Mtrace2 Query 1222 packet to the all-routers multicast group (224.0.0.2) for IPv4 or All 1223 Routers Address (FF02::2) for IPv6. This will ensure that the packet 1224 is received by the LHR on the subnet. 1226 See also Section 5.4 on determining the LHR. 1228 5.1.2. Source Address 1230 An Mtrace2 Query MUST be sent with the client's interface address, 1231 which would be the Mtrace2 Client Address. 1233 5.2. Determining the Path 1235 An Mtrace2 client could send an initial Query messages with a large # 1236 Hops, in order to try to trace the full path. If this attempt fails, 1237 one strategy is to perform a linear search (as the traditional 1238 unicast traceroute program does); set the # Hops field to 1 and try 1239 to get a Reply, then 2, and so on. If no Reply is received at a 1240 certain hop, the hop count can continue past the non-responding hop, 1241 in the hopes that further hops may respond. These attempts should 1242 continue until the [Mtrace Reply Timeout] timeout has occurred. 1244 See also Section 5.6 on receiving the results of a trace. 1246 5.3. Collecting Statistics 1248 After a client has determined that it has traced the whole path or as 1249 much as it can expect to (see Section 5.8), it might collect 1250 statistics by waiting a short time and performing a second trace. If 1251 the path is the same in the two traces, statistics can be displayed 1252 as described in Section 7.3 and Section 7.4. 1254 5.4. Last Hop Router (LHR) 1256 The Mtrace2 client may not know which is the last-hop router, or that 1257 router may be behind a firewall that blocks unicast packets but 1258 passes multicast packets. In these cases, the Mtrace2 Request should 1259 be multicasted to the all-routers multicast group (224.0.0.2) for 1260 IPv4 or All Routers Address (FF02::2) for IPv6. All routers except 1261 the correct last-hop router SHOULD ignore any Mtrace2 Request 1262 received via multicast. 1264 5.5. First Hop Router (FHR) 1266 The IANA assigned 224.0.1.32 as the default multicast group for old 1267 IPv4 mtrace (v1) responses, in order to support mtrace clients that 1268 are not unicast reachable from the first-hop router. Mtrace2, 1269 however, does not require any IPv4/IPv6 multicast addresses for the 1270 Mtrace2 Replies. Every Mtrace2 Reply is sent to the unicast address 1271 specified in the Mtrace2 Client Address field of the Mtrace2 Reply. 1273 5.6. Broken Intermediate Router 1275 A broken intermediate router might simply not understand Mtrace2 1276 packets, and drop them. The Mtrace2 client will get no Reply at all 1277 as a result. It should then perform a hop-by-hop search by setting 1278 the # Hops field until it gets an Mtrace2 Reply. The client may use 1279 linear or binary search; however, the latter is likely to be slower 1280 because a failure requires waiting for the [Mtrace Reply Timeout] 1281 period. 1283 5.7. Non-Supported Router 1285 When a non-supported router receives an Mtrace2 Query or Request 1286 message whose destination address is a multicast address, the router 1287 will silently discard the message. 1289 When the router receives an Mtrace2 Query which is destined to 1290 itself, the router would return an Internet Control Message Protocol 1291 (ICMP) port unreachable to the Mtrace2 client. On the other hand, 1292 when the router receives an Mtrace2 Request which is destined to 1293 itself, the router would return an ICMP port unreachable to its 1294 adjacent router from which the Request receives. Therefore, the 1295 Mtrace2 client needs to terminate the trace when the [Mtrace Reply 1296 Timeout] timeout has occurred, and may then issue another Query with 1297 a lower number of # Hops. 1299 5.8. Mtrace2 Termination 1301 When performing an expanding hop-by-hop trace, it is necessary to 1302 determine when to stop expanding. 1304 5.8.1. Arriving at Source 1306 A trace can be determined to have arrived at the source if the 1307 Incoming Interface of the last router in the trace is non-zero, but 1308 the Upstream Router is zero. 1310 5.8.2. Fatal Error 1312 A trace has encountered a fatal error if the last Forwarding Error in 1313 the trace has the 0x80 bit set. 1315 5.8.3. No Upstream Router 1317 A trace cannot continue if the last Upstream Router in the trace is 1318 set to 0. 1320 5.8.4. Reply Timeout 1322 This document defines the [Mtrace Reply Timeout] value, which is used 1323 to time out an Mtrace2 Reply as seen in Section 4.5, Section 5.2, and 1324 Section 5.7. The default [Mtrace Reply Timeout] value is 10 1325 (seconds), and can be manually changed on the Mtrace2 client and 1326 routers. 1328 5.9. Continuing after an Error 1330 When the NO_SPACE error occurs, as described in Section 4.2, a router 1331 will send back an Mtrace2 Reply to the Mtrace2 client, and continue 1332 with a new Request (see Section 4.3.3). In this case, the Mtrace2 1333 client may receive multiple Mtrace2 Replies from different routers 1334 along the path. When this happens, the client MUST treat them as a 1335 single Mtrace2 Reply message. 1337 If a trace times out, it is very likely that a router in the middle 1338 of the path does not support Mtrace2. That router's address will be 1339 in the Upstream Router field of the last Standard Response Block in 1340 the last received Reply. A client may be able to determine (via 1341 mrinfo or the Simple Network Management Protocol (SNMP) [11][13]) a 1342 list of neighbors of the non-responding router. The neighbors 1343 obtained in this way could then be probed (via the multicast MIB 1344 [13]) to determine which one is the upstream neighbor (i.e., Reverse 1345 Path Forwarding (RPF) neighbor) of the non-responding router. This 1346 algorithm can identify the upstream neighbor because, even though 1347 there may be multiple neighbors, the non-responding router should 1348 only have sent a "join" to the one neighbor corresponding to its 1349 selected RPF path. Because of this, only the RPF neighbor should 1350 contain the non-responding router as a multicast next hop in its MIB 1351 output list for the affected multicast route. 1353 6. Protocol-Specific Considerations 1355 This section describes the Mtrace2 behavior with the presence of 1356 different multicast protocols. 1358 6.1. PIM-SM 1360 When an Mtrace2 reaches a PIM-SM RP, and the RP does not forward the 1361 trace on, it means that the RP has not performed a source-specific 1362 join so there is no more state to trace. However, the path that 1363 traffic would use if the RP did perform a source-specific join can be 1364 traced by setting the trace destination to the RP, the trace source 1365 to the traffic source, and the trace group to 0. This Mtrace2 Query 1366 may be unicasted to the RP, and the RP takes the same actions as an 1367 LHR. 1369 6.2. Bi-Directional PIM 1371 Bi-directional PIM [6] is a variant of PIM-SM that builds bi- 1372 directional shared trees connecting multicast sources and receivers. 1373 Along the bi-directional shared trees, multicast data is natively 1374 forwarded from the sources to the Rendezvous Point Link (RPL), and 1375 from which, to receivers without requiring source-specific state. In 1376 contrast to PIM-SM, Bi-directional PIM always has the state to trace. 1378 A Designated Forwarder (DF) for a given Rendezvous Point Address 1379 (RPA) is in charge of forwarding downstream traffic onto its link, 1380 and forwarding upstream traffic from its link towards the RPL that 1381 the RPA belongs to. Hence Mtrace2 Reply reports DF addresses or RPA 1382 along the path. 1384 6.3. PIM-DM 1386 Routers running PIM Dense Mode [15] do not know the path packets 1387 would take unless traffic is flowing. Without some extra protocol 1388 mechanism, this means that in an environment with multiple possible 1389 paths with branch points on shared media, Mtrace2 can only trace 1390 existing paths, not potential paths. When there are multiple 1391 possible paths but the branch points are not on shared media, the 1392 upstream router is known, but the LHR may not know that it is the 1393 appropriate last hop. 1395 When traffic is flowing, PIM Dense Mode routers know whether or not 1396 they are the LHR for the link (because they won or lost an Assert 1397 battle) and know who the upstream router is (because it won an Assert 1398 battle). Therefore, Mtrace2 is always able to follow the proper path 1399 when traffic is flowing. 1401 6.4. IGMP/MLD Proxy 1403 When an IGMP or Multicast Listener Discovery (MLD) Proxy [7] receives 1404 an Mtrace2 Query packet on an incoming interface, it notes a WRONG_IF 1405 in the Forwarding Code of the last Standard Response Block (see 1406 Section 3.2.4), and sends the Mtrace2 Reply back to the Mtrace2 1407 client. On the other hand, when an Mtrace2 Query packet reaches an 1408 outgoing interface of the IGMP/MLD proxy, it is forwarded onto its 1409 incoming interface towards the upstream router. 1411 7. Problem Diagnosis 1413 This section describes different scenarios Mtrace2 can be used to 1414 diagnose the multicast problems. 1416 7.1. Forwarding Inconsistencies 1418 The Forwarding Error code can tell if a group is unexpectedly pruned 1419 or administratively scoped. 1421 7.2. TTL or Hop Limit Problems 1423 By taking the maximum of hops from the source and forwarding TTL 1424 threshold over all hops, it is possible to discover the TTL or hop 1425 limit required for the source to reach the destination. 1427 7.3. Packet Loss 1429 By taking multiple traces, it is possible to find packet loss 1430 information by tracking the difference between the output packet 1431 count for the specified source-group address pair at a given upstream 1432 router and the input packet count on the next hop downstream router. 1433 On a point-to-point link, any steadily increasing difference in these 1434 counts implies packet loss. Although the packet counts will differ 1435 due to Mtrace2 Request propagation delay, the difference should 1436 remain essentially constant (except for jitter caused by differences 1437 in propagation time among the trace iterations). However, this 1438 difference will display a steady increase if packet loss is 1439 occurring. On a shared link, the count of input packets can be 1440 larger than the number of output packets at the previous hop, due to 1441 other routers or hosts on the link injecting packets. This appears 1442 as "negative loss" which may mask real packet loss. 1444 In addition to the counts of input and output packets for all 1445 multicast traffic on the interfaces, the Standard Response Block 1446 includes a count of the packets forwarded by a node for the specified 1447 source-group pair. Taking the difference in this count between two 1448 traces and then comparing those differences between two hops gives a 1449 measure of packet loss just for traffic from the specified source to 1450 the specified receiver via the specified group. This measure is not 1451 affected by shared links. 1453 On a point-to-point link that is a multicast tunnel, packet loss is 1454 usually due to congestion in unicast routers along the path of that 1455 tunnel. On native multicast links, loss is more likely in the output 1456 queue of one hop, perhaps due to priority dropping, or in the input 1457 queue at the next hop. The counters in the Standard Response Block 1458 do not allow these cases to be distinguished. Differences in packet 1459 counts between the incoming and outgoing interfaces on one node 1460 cannot generally be used to measure queue overflow in the node. 1462 7.4. Link Utilization 1464 Again, with two traces, you can divide the difference in the input or 1465 output packet counts at some hop by the difference in time stamps 1466 from the same hop to obtain the packet rate over the link. If the 1467 average packet size is known, then the link utilization can also be 1468 estimated to see whether packet loss may be due to the rate limit or 1469 the physical capacity on a particular link being exceeded. 1471 7.5. Time Delay 1473 If the routers have synchronized clocks, it is possible to estimate 1474 propagation and queuing delay from the differences between the 1475 timestamps at successive hops. However, this delay includes control 1476 processing overhead, so is not necessarily indicative of the delay 1477 that data traffic would experience. 1479 8. IANA Considerations 1481 The following new registries are to be created and maintained under 1482 the "RFC Required" registry policy as specified in [4]. 1484 8.1. "Mtrace2 Forwarding Codes" Registry 1486 This is an integer in the range 0-255. Assignment of a Forwarding 1487 Code requires specification of a value and a name for the Forwarding 1488 Code. Initial values for the forwarding codes are given in the table 1489 at the end of Section 3.2.4. Additional values (specific to IPv6) 1490 may also be specified at the end of Section 3.2.5. Any additions to 1491 this registry are required to fully describe the conditions under 1492 which the new Forwarding Code is used. 1494 8.2. "Mtrace2 TLV Types" registry 1496 Assignment of a TLV Type requires specification of an integer value 1497 "Code" in the range 0-255 and a name ("Type"). Initial values for 1498 the TLV Types are given in the table at the beginning of Section 3.2. 1500 8.3. UDP Destination Port 1502 IANA has assigned UDP user port 33435 (mtrace) for use by this 1503 protocol as the Mtrace2 UDP destination port. 1505 9. Security Considerations 1507 This section addresses some of the security considerations related to 1508 Mtrace2. 1510 9.1. Addresses in Mtrace2 Header 1512 An Mtrace2 header includes three addresses, source address, multicast 1513 address, and Mtrace2 client address. These addresses MUST be 1514 congruent with the definition defined in Section 3.2.1 and forwarding 1515 Mtrace2 messages having invalid addresses MUST be prohibited. For 1516 instance, if Mtrace2 Client Address specified in an Mtrace2 header is 1517 a multicast address, then a router that receives the Mtrace2 message 1518 MUST silently discard it. 1520 9.2. Filtering of Clients 1522 A router SHOULD support a mechanism to filter out queries from 1523 clients beyond a specified administrative boundary. Such a boundary 1524 could, for example, be specified via a list of allowed/disallowed 1525 client addresses or subnets. If a query is received from beyond the 1526 specified administrative boundary, the Query MUST NOT be processed. 1527 The router MAY, however, perform rate limited logging of such events. 1529 9.3. Topology Discovery 1531 Mtrace2 can be used to discover any actively-used topology. If your 1532 network topology is a secret, Mtrace2 may be restricted at the border 1533 of your domain, using the ADMIN_PROHIB forwarding code. 1535 9.4. Characteristics of Multicast Channel 1537 Mtrace2 can be used to discover what sources are sending to what 1538 groups and at what rates. If this information is a secret, Mtrace2 1539 may be restricted at the border of your domain, using the 1540 ADMIN_PROHIB forwarding code. 1542 9.5. Limiting Query/Request Rates 1544 A router may limit Mtrace2 Queries and Requests by ignoring some of 1545 the consecutive messages. The router MAY randomly ignore the 1546 received messages to minimize the processing overhead, i.e., to keep 1547 fairness in processing queries, or prevent traffic amplification. 1548 The rate limit is left to the router's implementation. 1550 9.6. Limiting Reply Rates 1552 The proxying and NO_SPACE behaviors may result in one Query returning 1553 multiple Reply messages. In order to prevent abuse, the routers in 1554 the traced path MAY need to rate-limit the Replies. The rate limit 1555 function is left to the router's implementation. 1557 10. Acknowledgements 1559 This specification started largely as a transcription of Van 1560 Jacobson's slides from the 30th IETF, and the implementation in 1561 mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve 1562 Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original 1563 multicast traceroute client, mtrace (version 1), has been implemented 1564 by Ajit Thyagarajan, Steve Casner and Bill Fenner. The idea of the 1565 "S" bit to allow statistics for a source subnet is due to Tom 1566 Pusateri. 1568 For the Mtrace version 2 specification, the authors would like to 1569 give special thanks to Tatsuya Jinmei, Bill Fenner, and Steve Casner. 1570 Also, extensive comments were received from David L. Black, Ronald 1571 Bonica, Yiqun Cai, Liu Hui, Bharat Joshi, Robert Kebler, John 1572 Kristoff, Mankamana Mishra, Heidi Ou, Pekka Savola, Shinsuke Suzuki, 1573 Dave Thaler, Achmad Husni Thamrin, Stig Venaas, and Cao Wei. 1575 11. References 1577 11.1. Normative References 1579 [1] Bradner, S., "Key words for use in RFCs to indicate 1580 requirement levels", RFC 2119, March 1997. 1582 [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 1583 (IPv6) Specification", RFC 8200, July 2017. 1585 [3] Hinden, R. and S. Deering, "IP Version 6 Addressing 1586 Architecture", RFC 4291, February 2006. 1588 [4] Cotton, M., Leiba, B., and T. Narten, "Guidelines for 1589 Writing an IANA Considerations Section in RFCs", RFC 8126, 1590 June 2017. 1592 [5] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I., 1593 Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent 1594 Multicast - Sparse Mode (PIM-SM): Protocol Specification 1595 (Revised)", RFC 7761, March 2016. 1597 [6] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 1598 "Bidirectional Protocol Independent Multicast (BIDIR- 1599 PIM)", RFC 5015, October 2007. 1601 [7] Fenner, B., He, H., Haberman, B., and H. Sandick, 1602 "Internet Group Management Protocol (IGMP) / Multicast 1603 Listener Discovery (MLD)-Based Multicast Forwarding 1604 ("IGMP/MLD Proxying")", RFC 4605, August 2006. 1606 11.2. Informative References 1608 [8] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 1609 Thyagarajan, "Internet Group Management Protocol, Version 1610 3", RFC 3376, October 2002. 1612 [9] Bumgardner, G., "Automatic Multicast Tunneling", RFC 7450, 1613 February 2015. 1615 [10] Rosen, E. and R. Aggarwal, "Multicast in MPLS/BGP IP 1616 VPNs", RFC 6513, February 2012. 1618 [11] Draves, R. and D. Thaler, "Default Router Preferences and 1619 More-Specific Routes", RFC 4191, November 2005. 1621 [12] McCloghrie, K. and F. Kastenholz, "The Interfaces Group 1622 MIB", RFC 2863, June 2000. 1624 [13] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast 1625 MIB", RFC 5132, December 2007. 1627 [14] Gill, V., Heasley, J., Meyer, D., Savola, P., and C. 1628 Pignataro, "The Generalized TTL Security Mechanism 1629 (GTSM)", RFC 5082, October 2007. 1631 [15] Adams, A., Nicholas, J., and W. Siadak, "Protocol 1632 Independent Multicast - Dense Mode (PIM-DM): Protocol 1633 Specification (Revised)", RFC 3973, January 2005. 1635 Authors' Addresses 1636 Hitoshi Asaeda 1637 National Institute of Information and Communications Technology 1638 4-2-1 Nukui-Kitamachi 1639 Koganei, Tokyo 184-8795 1640 Japan 1642 Email: asaeda@nict.go.jp 1644 Kerry Meyer 1646 Email: kerry.meyer@me.com 1648 WeeSan Lee (editor) 1650 Email: weesan@weesan.com