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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 Keio University 4 Intended status: Standards Track T. Jinmei 5 Expires: May 7, 2009 ISC 6 W. Fenner 7 Arastra, Inc. 8 S. Casner 9 Packet Design, Inc. 10 November 3, 2008 12 Mtrace Version 2: Traceroute Facility for IP Multicast 13 draft-ietf-mboned-mtrace-v2-02 15 Status of this Memo 17 By submitting this Internet-Draft, each author represents that any 18 applicable patent or other IPR claims of which he or she is aware 19 have been or will be disclosed, and any of which he or she becomes 20 aware will be disclosed, in accordance with Section 6 of BCP 79. 22 Internet-Drafts are working documents of the Internet Engineering 23 Task Force (IETF), its areas, and its working groups. Note that 24 other groups may also distribute working documents as Internet- 25 Drafts. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 The list of current Internet-Drafts can be accessed at 33 http://www.ietf.org/ietf/1id-abstracts.txt. 35 The list of Internet-Draft Shadow Directories can be accessed at 36 http://www.ietf.org/shadow.html. 38 This Internet-Draft will expire on May 7, 2009. 40 Abstract 42 This document describes the IP multicast traceroute facility. Unlike 43 unicast traceroute, multicast traceroute requires special 44 implementations on the part of routers. This specification describes 45 the required functionality in multicast routers, as well as how 46 management applications can use the router functionality. 48 Table of Contents 50 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 51 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 52 3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 53 4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 8 54 4.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . . 8 55 4.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 8 56 5. Mtrace2 Query Header . . . . . . . . . . . . . . . . . . . . . 9 57 5.1. # hops: 8 bits . . . . . . . . . . . . . . . . . . . . . . 9 58 5.2. Multicast Address . . . . . . . . . . . . . . . . . . . . 10 59 5.3. Source Address . . . . . . . . . . . . . . . . . . . . . . 10 60 5.4. Destination Address . . . . . . . . . . . . . . . . . . . 10 61 5.5. Response Address . . . . . . . . . . . . . . . . . . . . . 10 62 5.6. Query ID: 16 bits . . . . . . . . . . . . . . . . . . . . 10 63 5.7. Client Port # . . . . . . . . . . . . . . . . . . . . . . 10 64 6. IPv4 Mtrace2 Standard Response Block . . . . . . . . . . . . . 11 65 6.1. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 11 66 6.2. Incoming Interface Address: 32 bits . . . . . . . . . . . 12 67 6.3. Outgoing Interface Address: 32 bits . . . . . . . . . . . 12 68 6.4. Previous-Hop Router Address: 32 bits . . . . . . . . . . . 12 69 6.5. Input packet count on incoming interface: 64 bits . . . . 12 70 6.6. Output packet count on incoming interface: 64 bits . . . . 12 71 6.7. Total number of packets for this source-group pair: 64 72 bits . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 73 6.8. Rtg Protocol: 8 bits . . . . . . . . . . . . . . . . . . . 13 74 6.9. Fwd TTL: 8 bits . . . . . . . . . . . . . . . . . . . . . 13 75 6.10. MBZ: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . 13 76 6.11. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 13 77 6.12. Src Mask: 6 bits . . . . . . . . . . . . . . . . . . . . . 13 78 6.13. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 13 79 7. IPv6 Mtrace2 Standard Response Block . . . . . . . . . . . . . 16 80 7.1. Query Arrival Time: 32 bits . . . . . . . . . . . . . . . 16 81 7.2. Incoming Interface ID: 32 bits . . . . . . . . . . . . . . 16 82 7.3. Outgoing Interface ID: 32 bits . . . . . . . . . . . . . . 17 83 7.4. Local Address . . . . . . . . . . . . . . . . . . . . . . 17 84 7.5. Remote Address . . . . . . . . . . . . . . . . . . . . . . 17 85 7.6. Input packet count on incoming interface . . . . . . . . . 17 86 7.7. Output packet count on incoming interface . . . . . . . . 17 87 7.8. Total number of packets for this source-group pair . . . . 17 88 7.9. Rtg Protocol: 8 bits . . . . . . . . . . . . . . . . . . . 18 89 7.10. MBZ: 7 bits . . . . . . . . . . . . . . . . . . . . . . . 18 90 7.11. S: 1 bit . . . . . . . . . . . . . . . . . . . . . . . . . 18 91 7.12. Src Prefix Len: 8 bits . . . . . . . . . . . . . . . . . . 18 92 7.13. Forwarding Code: 8 bits . . . . . . . . . . . . . . . . . 18 93 8. Mtrace2 Augmented Response Block . . . . . . . . . . . . . . . 19 94 9. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 20 95 9.1. Traceroute Query . . . . . . . . . . . . . . . . . . . . . 20 96 9.1.1. Packet Verification . . . . . . . . . . . . . . . . . 20 97 9.1.2. Normal Processing . . . . . . . . . . . . . . . . . . 20 98 9.2. Mtrace2 Request . . . . . . . . . . . . . . . . . . . . . 20 99 9.2.1. Packet Verification . . . . . . . . . . . . . . . . . 21 100 9.2.2. Normal Processing . . . . . . . . . . . . . . . . . . 21 101 9.3. Mtrace2 Response . . . . . . . . . . . . . . . . . . . . . 22 102 9.4. Forwarding Mtrace2 Requests . . . . . . . . . . . . . . . 22 103 9.5. Sending Mtrace2 Responses . . . . . . . . . . . . . . . . 23 104 9.5.1. Destination Address . . . . . . . . . . . . . . . . . 23 105 9.5.2. TTL and Hop Limit . . . . . . . . . . . . . . . . . . 23 106 9.5.3. Source Address . . . . . . . . . . . . . . . . . . . . 23 107 9.5.4. Sourcing Multicast Responses . . . . . . . . . . . . . 23 108 9.6. Hiding Information . . . . . . . . . . . . . . . . . . . . 23 109 10. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 25 110 10.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 25 111 10.2. Determining the Path . . . . . . . . . . . . . . . . . . . 25 112 10.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 25 113 10.4. Last Hop Router . . . . . . . . . . . . . . . . . . . . . 26 114 10.5. First Hop Router . . . . . . . . . . . . . . . . . . . . . 26 115 10.6. Broken Intermediate Router . . . . . . . . . . . . . . . . 26 116 10.7. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 26 117 10.7.1. Arriving at source . . . . . . . . . . . . . . . . . . 27 118 10.7.2. Fatal error . . . . . . . . . . . . . . . . . . . . . 27 119 10.7.3. No previous hop . . . . . . . . . . . . . . . . . . . 27 120 10.7.4. Traceroute shorter than requested . . . . . . . . . . 27 121 10.8. Continuing after an error . . . . . . . . . . . . . . . . 27 122 11. Protocol-Specific Considerations . . . . . . . . . . . . . . . 28 123 11.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 28 124 11.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . . 28 125 11.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . . 28 126 11.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . 28 127 11.5. AMT . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 128 12. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 30 129 12.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . . 30 130 12.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 30 131 12.3. Packet loss . . . . . . . . . . . . . . . . . . . . . . . 30 132 12.4. Link Utilization . . . . . . . . . . . . . . . . . . . . . 31 133 12.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . . 31 134 13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 135 13.1. Forwarding Codes . . . . . . . . . . . . . . . . . . . . . 32 136 13.2. UDP Destination Port and IPv6 Address . . . . . . . . . . 32 137 14. Security Considerations . . . . . . . . . . . . . . . . . . . 33 138 14.1. Topology Discovery . . . . . . . . . . . . . . . . . . . . 33 139 14.2. Traffic Rates . . . . . . . . . . . . . . . . . . . . . . 33 140 14.3. Unicast Replies . . . . . . . . . . . . . . . . . . . . . 33 141 15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 34 142 16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 35 143 16.1. Normative References . . . . . . . . . . . . . . . . . . . 35 144 16.2. Informative References . . . . . . . . . . . . . . . . . . 36 145 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37 146 Intellectual Property and Copyright Statements . . . . . . . . . . 38 148 1. Introduction 150 The unicast "traceroute" program allows the tracing of a path from 151 one machine to another. The key mechanism for unicast traceroute is 152 the ICMP TTL exceeded message, which is specifically precluded as a 153 response to multicast packets. On the other hand, the multicast 154 traceroute facility allows the tracing of an IP multicast routing 155 paths. In this document, we specify the multicast "traceroute" 156 facility to be implemented in multicast routers and accessed by 157 diagnostic programs. The multicast traceroute described in this 158 document named as mtrace version 2 or mtrace2 provides additional 159 information about packet rates and losses that the unicast traceroute 160 cannot, and generally requires fewer packets to be sent. 162 o. To be able to trace the path that a packet would take from some 163 source to some destination. 165 o. To be able to isolate packet loss problems (e.g., congestion). 167 o. To be able to isolate configuration problems (e.g., TTL 168 threshold). 170 o. To minimize packets sent (e.g. no flooding, no implosion). 172 This document supports both IPv4 and IPv6 multicast traceroute 173 facility. The protocol design, concept, and program behavior are 174 same between IPv4 and IPv6 mtrace2. While the original IPv4 175 multicast traceroute, mtrace, the query and response messages are 176 implemented as IGMP messages [4], all mtrace2 messages are carried on 177 UDP. The packet formats of IPv4 and IPv6 mtrace2 are different 178 because of the different address families, but the syntax is similar. 180 2. Terminology 182 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 183 NOT","SHOULD", "SHOULD NOT", "RECOMMENDED","MAY", and "OPTIONAL" in 184 this document are to be interpreted as described in RFC 2119 [1]. 186 Since multicast traceroutes flow in the opposite direction to the 187 data flow, we refer to "upstream" and "downstream" with respect to 188 data, unless explicitly specified. 190 Incoming interface: 191 The interface on which traffic is expected from the specified source 192 and group. 194 Outgoing interface: 195 The interface on which traffic is forwarded from the specified source 196 and group toward the destination. It is the interface on which the 197 multicast traceroute Request was received. 199 Previous-hop router: 200 The router that is on the link attached to the Incoming Interface and 201 is responsible for forwarding traffic for the specified source and 202 group. 204 Group state: 205 It is the state in which a shared-tree protocol (e.g., PIM-SM [9]) 206 running on a router chooses the previous-hop router toward the core 207 router or Rendezvous Point (RP) as its parent router. In this state, 208 source-specific state is not available for the corresponding 209 multicast address on the router. 211 Source-specific state: 212 It is the state in which a routing protocol running on a router 213 chooses the path that would be followed for a source-specific join. 215 ALL-[protocol]-ROUTERS.MCAST.NET: 216 It is a dedicated multicast address for a multicast router to 217 communicate with other routers that are working with the same routing 218 protocol. For instance,the address of ALL-PIM-ROUTERS.MCAST.NET is 219 '224.0.0.13' for IPv4 and 'ff02::d' for IPv6. 221 3. Overview 223 Given a multicast distribution tree, tracing from a source to a 224 multicast destination is hard, since you don't know down which branch 225 of the multicast tree the destination lies. This means that you have 226 to flood the whole tree to find the path from one source to one 227 destination. However, walking up the tree from destination to source 228 is easy, as most existing multicast routing protocols know the 229 previous hop for each source. Tracing from destination to source can 230 involve only routers on the direct path. 232 The party requesting the traceroute (which need be neither the source 233 nor the destination) sends a traceroute Query packet to the last-hop 234 multicast router for the given destination. The last-hop router 235 turns the Query into a Request packet by adding a response data block 236 containing its interface addresses and packet statistics, and then 237 forwards the Request packet via unicast to the router that it 238 believes is the proper previous hop for the given source and group. 239 Each hop adds its response data to the end of the Request packet, 240 then unicast forwards it to the previous hop. The first hop router 241 (the router that believes that packets from the source originate on 242 one of its directly connected networks) changes the packet type to 243 indicate a Response packet and sends the completed response to the 244 response destination address. The response may be returned before 245 reaching the first hop router if a fatal error condition such as "no 246 route" is encountered along the path. 248 Multicast traceroute uses any information available to it in the 249 router to attempt to determine a previous hop to forward the trace 250 towards. Multicast routing protocols vary in the type and amount of 251 state they keep; multicast traceroute endeavors to work with all of 252 them by using whatever is available. For example, if a PIM-SM router 253 is on the (*,G) tree, it chooses the parent towards the RP as the 254 previous hop. In these cases, no source/group-specific state is 255 available, but the path may still be traced. 257 4. Packet Formats 259 Mtrace2 message is encoded in TLV format. If an implementation 260 receives a TLV whose length exceeds the TLV length specified in the 261 Length field, the TLV SHOULD be accepted but any additional data 262 SHOULD be ignored. 264 4.1. Mtrace2 TLV format 266 0 1 2 3 267 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 1 268 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 269 | Type | Length | Value .... | 270 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 272 Type (8 bits) 274 Length (16 bits) 276 Value (variable length) 278 4.2. Defined TLVs 280 The following TLV Types are defined: 282 Code Type 283 ====== ====================================== 284 1 Mtrace2 Query 285 2 Mtrace2 Response 286 3 Mtrace2 Standard Response Block 287 4 Mtrace2 Augmented Response Block 289 An mtrace2 message MUST contain one Mtrace2 Query or Response. An 290 mtrace2 message MAY contain one or multiple Mtrace2 Standard and 291 Augmented Responses. A multicast router that sends mtrace2 request 292 MUST NOT contain multiple Mtrace2 Standard blocks but MAY contain 293 multiple Augmented Response blocks. 295 The type field is defined to be "0x1" for mtrace2 queries and 296 requests. The type field is changed to "0x2" when the packet is 297 completed and sent as a response from the first hop router to the 298 querier. Two codes are required so that multicast routers will not 299 attempt to process a completed response in those cases where the 300 initial query was issued from a router. 302 5. Mtrace2 Query Header 304 The mtrace2 message is carried as a UDP packet. The UDP source port 305 is uniquely selected by the local host operating system. The UDP 306 destination port is the IANA reserved mtrace2 port number (see 307 Section 13). The UDP checksum MUST be valid in mtrace2 messages. 309 The mtrace2 message includes the common mtrace2 Query header as 310 follows. The header is only filled in by the originator of the 311 mtrace2 Query; intermediate routers MUST NOT modify any of the 312 fields. 314 0 1 2 3 315 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 1 316 +-+-+-+-+-+-+-+-+ 317 | # hops | 318 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 319 | | 320 | Multicast Address | 321 | | 322 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 323 | | 324 | Source Address | 325 | | 326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 | | 328 | Destination Address | 329 | | 330 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 331 | | 332 | Response Address | 333 | | 334 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 335 | Query ID | Client Port # | 336 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 338 Figure 1 340 5.1. # hops: 8 bits 342 This field specifies the maximum number of hops that the requester 343 wants to trace. If there is some error condition in the middle of 344 the path that keeps the mtrace2 request from reaching the first-hop 345 router, this field can be used to perform an expanding-ring search to 346 trace the path to just before the problem. 348 5.2. Multicast Address 350 This field specifies the 32 bits length IPv4 or 128 bits length IPv6 351 multicast address to be traced, or is filled with "all 1" in case of 352 IPv4 or with the unspecified address (::) in case of IPv6 if no 353 group-specific information is desired. Note that non-group-specific 354 mtrace2 MUST specify source address. 356 5.3. Source Address 358 This field specifies the 32 bits length IPv4 or 128 bits length IPv6 359 address of the multicast source for the path being traced, or is 360 filled with "all 1" in case of IPv4 or with the unspecified address 361 (::) in case of IPv6 if no source-specific information is desired. 362 Note that non-source-specific traceroutes may not be possible with 363 certain multicast routing protocols. 365 5.4. Destination Address 367 This field specifies the 32 bits length IPv4 or 128 bits length IPv6 368 address of the multicast receiver for the path being traced. The 369 trace starts at this destination and proceeds toward the traffic 370 source. 372 5.5. Response Address 374 This field specifies 32 bits length IPv4 or 128 bits length IPv6 375 address to which the completed mtrace2 response packet gets sent. It 376 MUST be a global unicast address as explained in Section 9.2 378 5.6. Query ID: 16 bits 380 This field is used as a unique identifier for this traceroute request 381 so that duplicate or delayed responses may be detected and to 382 minimize collisions when a multicast response address is used. 384 5.7. Client Port # 386 Mtrace2 response is sent back to the address specified in a Response 387 Address field. This field specifies the UDP port number the router 388 will send Mtrace2 Response. This client port number MUST NOT be 389 changed by any router. 391 6. IPv4 Mtrace2 Standard Response Block 393 Each intermediate IPv4 router in a trace path appends "response data 394 block" to the forwarded trace packet. The standard response data 395 block looks as follows. 397 0 1 2 3 398 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 1 399 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 400 | Query Arrival Time | 401 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 402 | Incoming Interface Address | 403 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 404 | Outgoing Interface Address | 405 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 406 | Previous-Hop Router Address | 407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 408 | | 409 . Input packet count on incoming interface . 410 | | 411 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 412 | | 413 . Output packet count on outgoing interface . 414 | | 415 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 416 | | 417 . Total number of packets for this source-group pair . 418 | | 419 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 420 | | |M| | | | 421 | Rtg Protocol | Fwd TTL |B|S| Src Mask |Forwarding Code| 422 | | |Z| | | | 423 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 425 6.1. Query Arrival Time: 32 bits 427 The Query Arrival Time is a 32-bit NTP timestamp specifying the 428 arrival time of the traceroute request packet at this router. The 429 32-bit form of an NTP timestamp consists of the middle 32 bits of the 430 full 64-bit form; that is, the low 16 bits of the integer part and 431 the high 16 bits of the fractional part. 433 The following formula converts from a UNIX timeval to a 32-bit NTP 434 timestamp: 436 query_arrival_time 437 = (tv.tv_sec + 32384) << 16 + ((tv.tv_usec << 10) / 15625) 439 The constant 32384 is the number of seconds from Jan 1, 1900 to Jan 440 1, 1970 truncated to 16 bits. ((tv.tv_usec << 10) / 15625) is a 441 reduction of ((tv.tv_usec / 100000000) << 16). 443 6.2. Incoming Interface Address: 32 bits 445 This field specifies the address of the interface on which packets 446 from this source and group are expected to arrive, or 0 if unknown. 448 6.3. Outgoing Interface Address: 32 bits 450 This field specifies the address of the interface on which packets 451 from this source and group flow to the specified destination, or 0 if 452 unknown. 454 6.4. Previous-Hop Router Address: 32 bits 456 This field specifies the router from which this router expects 457 packets from this source. This may be a multicast group (e.g. ALL- 458 [protocol]-ROUTERS.MCAST.NET) if the previous hop is not known 459 because of the workings of the multicast routing protocol. However, 460 it should be 0 if the incoming interface address is unknown. 462 6.5. Input packet count on incoming interface: 64 bits 464 This field contains the number of multicast packets received for all 465 groups and sources on the incoming interface, or "all 1" if no count 466 can be reported. This counter may have the same value as 467 ifHCInMulticastPkts from the IF-MIB [14] for this interface. 469 6.6. Output packet count on incoming interface: 64 bits 471 This field contains the number of multicast packets that have been 472 transmitted or queued for transmission for all groups and sources on 473 the outgoing interface, or "all 1" if no count can be reported. This 474 counter may have the same value as ifHCOutMulticastPkts from the IF- 475 MIB for this interface. 477 6.7. Total number of packets for this source-group pair: 64 bits 479 This field counts the number of packets from the specified source 480 forwarded by this router to the specified group, or "all 1" if no 481 count can be reported. If the S bit is set, the count is for the 482 source network, as specified by the Src Mask field. If the S bit is 483 set and the Src Mask field is 63, indicating no source-specific 484 state, the count is for all sources sending to this group. This 485 counter should have the same value as ipMcastRoutePkts from the 486 IPMROUTE-STD-MIB [15] for this forwarding entry. 488 6.8. Rtg Protocol: 8 bits 490 This field describes the routing protocol in use between this router 491 and the previous-hop router. Specified values include: 493 0 Unknown 494 1 PIM 495 2 PIM using special routing table 496 3 PIM using a static route 497 4 PIM using MBGP route 498 5 PIM using state created by Assert processing 499 6 Bi-directional PIM 500 7 IGMP/MLD proxy 501 8 AMT Relay 502 9 AMT Gateway 504 To obtain these values, multicast routers access to 505 ipMcastRouteProtocol, ipMcastRouteRtProtocol, and ipMcastRouteRtType 506 in IpMcastRouteEntry specified in IPMROUTE-STD-MIB [15], and combine 507 these MIB values to recognize above routing protocol values. 509 6.9. Fwd TTL: 8 bits 511 This field contains the TTL that a packet is required to have before 512 it will be forwarded over the outgoing interface. 514 6.10. MBZ: 1 bit 516 Must be zeroed on transmission and ignored on reception. 518 6.11. S: 1 bit 520 This S bit indicates that the packet count for the source-group pair 521 is for the source network, as determined by masking the source 522 address with the Src Mask field. 524 6.12. Src Mask: 6 bits 526 This field contains the number of 1's in the netmask this router has 527 for the source (i.e. a value of 24 means the netmask is 0xffffff00). 528 If the router is forwarding solely on group state, this field is set 529 to 63 (0x3f). 531 6.13. Forwarding Code: 8 bits 533 This field contains a forwarding information/error code. Section 9.2 534 explains how and when the forwarding code is filled. Defined values 535 are as follows; 536 Value Name Description 538 ----- -------------- ------------------------------------------- 540 0x00 NO_ERROR No error 542 0x01 WRONG_IF Mtrace2 request arrived on an interface 543 to which this router would not forward for 544 this source, group, destination. 546 0x02 PRUNE_SENT This router has sent a prune upstream which 547 applies to the source and group in the 548 traceroute request. 550 0x03 PRUNE_RCVD This router has stopped forwarding for this 551 source and group in response to a request 552 from the next hop router. 554 0x04 SCOPED The group is subject to administrative 555 scoping at this hop. 557 0x05 NO_ROUTE This router has no route for the source or 558 group and no way to determine a potential 559 route. 561 0x06 WRONG_LAST_HOP This router is not the proper last-hop 562 router. 564 0x07 NOT_FORWARDING This router is not forwarding this source, 565 group out the outgoing interface for an 566 unspecified reason. 568 0x08 REACHED_RP Reached Rendezvous Point or Core 570 0x09 RPF_IF Mtrace2 request arrived on the expected 571 RPF interface for this source and group. 573 0x0A NO_MULTICAST Mtrace2 request arrived on an interface 574 which is not enabled for multicast. 576 0x0B INFO_HIDDEN One or more hops have been hidden from this 577 trace. 579 0x81 NO_SPACE There was not enough room to insert another 580 response data block in the packet. 582 0x82 OLD_ROUTER The previous-hop router does not understand 583 traceroute requests. 585 0x83 ADMIN_PROHIB Mtrace2 is administratively prohibited. 587 Note that if a router discovers there is not enough room in a packet 588 to insert its response, it puts the 0x81 error code in the previous 589 router's Forwarding Code field, overwriting any error the previous 590 router placed there. After the router sends the response to the 591 Response Address in the header, multicast traceroute client MAY 592 restart the trace at the last hop listed in the packet (as described 593 in Section 9.5 and Section 10.1). [TODO: What if the Response 594 Address is not the address of mtrace2 client?] 596 The 0x80 bit of the Forwarding Code is used to indicate a fatal 597 error. A fatal error is one where the router may know the previous 598 hop but cannot forward the message to it. 600 7. IPv6 Mtrace2 Standard Response Block 602 Each intermediate IPv6 router in a trace path appends "response data 603 block" to the forwarded trace packet. The standard response data 604 block looks as follows. 606 0 1 2 3 607 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 1 608 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 609 | Query Arrival Time | 610 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 611 | Incoming Interface ID | 612 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 613 | Outgoing Interface ID | 614 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 615 | | 616 * Local Address * 617 | | 618 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 619 | | 620 * Remote Address * 621 | | 622 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 623 | | 624 . Input packet count on incoming interface . 625 | | 626 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 627 | | 628 . Output packet count on outgoing interface . 629 | | 630 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 631 | | 632 . Total number of packets for this source-group pair . 633 | | 634 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 635 | Rtg Protocol | MBZ |S|Src Prefix Len |Forwarding Code| 636 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 638 7.1. Query Arrival Time: 32 bits 640 Same definition described in Section 6.1 642 7.2. Incoming Interface ID: 32 bits 644 This field specifies the interface ID on which packets from this 645 source and group are expected to arrive, or 0 if unknown. This ID 646 should be the value taken from InterfaceIndex of the IF-MIB [14] for 647 this interface. This field is carried in network byte order. 649 7.3. Outgoing Interface ID: 32 bits 651 This field specifies the interface ID on which packets from this 652 source and group flow to the specified destination, or 0 if unknown. 653 This ID should be the value taken from InterfaceIndex of the IF-MIB 654 for this interface. This field is carried in network byte order. 656 7.4. Local Address 658 This field specifies a global IPv6 address that uniquely identifies 659 the router. A unique local unicast address [13] SHOULD NOT be used 660 unless the router is only assigned link-local and unique local 661 addresses. If the router is only assigned link-local addresses, its 662 link-local address can be specified in this field. 664 7.5. Remote Address 666 This field specifies the address of the previous-hop router, which, 667 in most cases, is a link-local unicast address for the queried source 668 and destination addresses. 670 Although a link-local address does not have enough information to 671 identify a node, it is possible to detect the previous-hop router 672 with the assistance of Incoming Interface ID and the current router 673 address (i.e., Local Address). 675 This may be a multicast group (e.g., ALL-[protocol]- 676 ROUTERS.MCAST.NET) if the previous hop is not known because of the 677 workings of the multicast routing protocol. However, it should be 678 the unspecified address (::) if the incoming interface address is 679 unknown. 681 7.6. Input packet count on incoming interface 683 Same definition described in Section 6.5 685 7.7. Output packet count on incoming interface 687 Same definition described in Section 6.6 689 7.8. Total number of packets for this source-group pair 691 This field counts the number of packets from the specified source 692 forwarded by this router to the specified group, or "all 1" if no 693 count can be reported. If the S bit is set, the count is for the 694 source network, as specified by the Src Prefix Len field. If the S 695 bit is set and the Src Prefix Len field is 255, indicating no source- 696 specific state, the count is for all sources sending to this group. 698 This counter should have the same value as ipMcastRoutePkts from the 699 IPMROUTE-STD-MIB for this forwarding entry. 701 7.9. Rtg Protocol: 8 bits 703 Same definition described in Section 6.8 705 7.10. MBZ: 7 bits 707 Must be zeroed on transmission and ignored on reception. 709 7.11. S: 1 bit 711 This S bit indicates that the packet count for the source-group pair 712 is for the source network, as determined by masking the source 713 address with the Src Prefix Len field. 715 7.12. Src Prefix Len: 8 bits 717 This field contains the prefix length this router has for the source. 718 If the router is forwarding solely on group state, this field is set 719 to 255 (0xff) 721 7.13. Forwarding Code: 8 bits 723 Same definition described in Section 6.13 725 8. Mtrace2 Augmented Response Block 727 In addition to the standard response block, a multicast router on the 728 path will be able to add "augumented response block" when it sends 729 the request to its upstream router or sends the response to the 730 Response Address. This augmented response block is flexible to add 731 various information. 733 0 1 2 3 734 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 1 735 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 736 | Type | Value .... | 737 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 739 The augmented response block is always appended to mtrace2 TLV header 740 (0x04). The 16 bits Type filed of the augmented response block is 741 defined for various purposees, such as diagnosis (as in Section 12) 742 and protocol verification. The packet length of the augmented 743 response block is specified in the augmented response block TLV 744 header as see in Section 4.1. 746 [TODO: Define augmented response block types. Specify how to deal 747 with diagnosis information.] 749 9. Router Behavior 751 All of these actions are performed in addition to (NOT instead of) 752 forwarding the packet, if applicable. E.g. a multicast packet that 753 has TTL or the hop limit remaining MUST be forwarded normally, as 754 MUST a unicast packet that has TTL or the hop limit remaining and is 755 not addressed to this router. 757 9.1. Traceroute Query 759 An mtrace2 Query message is a traceroute message with no response 760 blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 mtrace2. 762 9.1.1. Packet Verification 764 Upon receiving an mtrace2 Query message, a router must examine the 765 Query to see if it is the proper last-hop router for the destination 766 address in the packet. It is the proper last-hop router if it has a 767 multicast-capable interface on the same subnet as the Destination 768 Address and is the router that would forward traffic from the given 769 (S,G) onto that subnet. 771 If the router determines that it is not the proper last-hop router, 772 or it cannot make that determination, it does one of two things 773 depending if the Query was received via multicast or unicast. If the 774 Query was received via multicast, then it MUST be silently dropped. 775 If it was received via unicast, a forwarding code of WRONG_LAST_HOP 776 is noted and processing continues as in Section 9.2 778 Duplicate Query messages as identified by the tuple (IP Source, Query 779 ID) SHOULD be ignored. This MAY be implemented using a simple 1-back 780 cache (i.e. remembering the IP source and Query ID of the previous 781 Query message that was processed, and ignoring future messages with 782 the same IP Source and Query ID). Duplicate Request messages MUST 783 NOT be ignored in this manner. 785 9.1.2. Normal Processing 787 When a router receives an mtrace2 Query and it determines that it is 788 the proper last-hop router, it treats it like an mtrace2 Request and 789 performs the steps listed in Section 9.2 791 9.2. Mtrace2 Request 793 An mtrace2 Request is a traceroute message with some number of 794 response blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 795 mtrace2. Routers can tell the difference between Queries and 796 Requests by checking the length of the packet. 798 9.2.1. Packet Verification 800 If the mtrace2 Request is not addressed to this router, or if the 801 Request is addressed to a multicast group which is not a link-scoped 802 group (i.e. 224/24 for IPv4, FFx2::/16 [3] for IPv6), it MUST be 803 silently ignored. 805 9.2.2. Normal Processing 807 When a router receives an mtrace2 Request, it performs the following 808 steps. Note that it is possible to have multiple situations covered 809 by the Forwarding Codes. The first one encountered is the one that 810 is reported, i.e. all "note forwarding code N" should be interpreted 811 as "if forwarding code is not already set, set forwarding code to N". 813 1. If there is room in the current buffer (or the router can 814 efficiently allocate more space to use), insert a new response 815 block into the packet and fill in the Query Arrival Time, 816 Outgoing Interface Address (for IPv4 mtrace2) or Outgoing 817 Interface ID (for IPv6 mtrace2), Output Packet Count, and Fwd 818 TTL (for IPv4 mtrace2). If there was no room, fill in the 819 response code "NO_SPACE" in the *previous* hop's response block, 820 and forward the packet to the requester as described in 821 Section 9.4. 823 2. Attempt to determine the forwarding information for the source 824 and group specified, using the same mechanisms as would be used 825 when a packet is received from the source destined for the 826 group. State need not be instantiated, it can be "phantom" 827 state created only for the purpose of the trace, such as "dry- 828 run". 830 If using a shared-tree protocol and there is no source-specific 831 state, or if the source is specified as "all 1", group state 832 should be used. If there is no group state or the group is 833 specified as 0, potential source state (i.e. the path that would 834 be followed for a source-specific Join) should be used. If this 835 router is the Core or RP and no source-specific information is 836 available, note an error code of REACHED_RP. 838 3. If no forwarding information can be determined, the router notes 839 an error code of NO_ROUTE, sets the remaining fields that have 840 not yet been filled in to zero, and then forwards the packet to 841 the requester as described in Section 9.4. 843 4. Fill in the Incoming Interface Address, Previous-Hop Router 844 Address, Input Packet Count, Total Number of Packets, Routing 845 Protocol, S, and Src Mask from the forwarding information that 846 was determined. 848 5. If mtrace2 is administratively prohibited or the previous hop 849 router does not understand mtrace2 requests, note the 850 appropriate forwarding code (ADMIN_PROHIB or OLD_ROUTER). If 851 mtrace2 is administratively prohibited and any of the fields as 852 filled in step 4 are considered private information, zero out 853 the applicable fields. Then the packet is forwarded to the 854 requester as described in Section 9.4. 856 6. If the reception interface is not enabled for multicast, note 857 forwarding code NO_MULTICAST. If the reception interface is the 858 interface from which the router would expect data to arrive from 859 the source, note forwarding code RPF_IF. Otherwise, if the 860 reception interface is not one to which the router would forward 861 data from the source to the group, a forwarding code of WRONG_IF 862 is noted. 864 7. If the group is subject to administrative scoping on either the 865 Outgoing or Incoming interfaces, a forwarding code of SCOPED is 866 noted. 868 8. If this router is the Rendezvous Point or Core for the group, a 869 forwarding code of REACHED_RP is noted. 871 9. If this router has sent a prune upstream which applies to the 872 source and group in the mtrace2 Request, it notes forwarding 873 code PRUNE_SENT. If the router has stopped forwarding 874 downstream in response to a prune sent by the next hop router, 875 it notes forwarding code PRUNE_RCVD. If the router should 876 normally forward traffic for this source and group downstream 877 but is not, it notes forwarding code NOT_FORWARDING. 879 10. The packet is then sent on to the previous hop or the requester 880 as described in Section 9.4. 882 9.3. Mtrace2 Response 884 A router must forward all mtrace2 response packets normally, with no 885 special processing. If a router has initiated an mtrace2 with a 886 Query or Request message, it may listen for Responses to that 887 traceroute and MUST forward them as well. 889 9.4. Forwarding Mtrace2 Requests 891 If the Previous-hop router is known for this request and the number 892 of response blocks is less than the number requested (i.e., the "# 893 hops" field in mtrace2 header), the packet is sent to that router. 895 If the Incoming Interface is known but the Previous-hop router is not 896 known, the packet is sent to an appropriate multicast address on the 897 Incoming Interface. The appropriate multicast address may depend on 898 the routing protocol in use, MUST be a link-scoped group (i.e. 224/24 899 for IPv4, FF02::/16 for IPv6), MUST NOT be ALL-SYSTEMS.MCAST.NET 900 (224.0.0.1) for IPv4 and All Nodes Address (FF02::1) for IPv6, and 901 MAY be ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All Routers 902 Address (FF02::2) for IPv6 if the routing protocol in use does not 903 define a more appropriate group. Otherwise, it is sent to the 904 Response Address in the header, as described in Section 9.5. 906 9.5. Sending Mtrace2 Responses 908 9.5.1. Destination Address 910 An mtrace2 response must be sent to the Response Address in the 911 mtrace2 header. 913 9.5.2. TTL and Hop Limit 915 If the Response Address is unicast, the router inserts its normal 916 unicast TTL or hop limit in the IP header. If the Response Address 917 is multicast, the router copies the Response TTL or hop limit from 918 the mtrace2 header into the IP header. 920 9.5.3. Source Address 922 If the Response Address is unicast, the router may use any of its 923 interface addresses as the source address. Since some multicast 924 routing protocols forward based on source address, if the Response 925 Address is multicast, the router MUST use an address that is known in 926 the multicast routing topology if it can make that determination. 928 9.5.4. Sourcing Multicast Responses 930 When a router sources a multicast response, the response packet MUST 931 be sent on a single interface, then forwarded as if it were received 932 on that interface. It MUST NOT source the response packet 933 individually on each interface, in order to avoid duplicate packets. 935 9.6. Hiding Information 937 Information about a domain's topology and connectivity may be hidden 938 from multicast traceroute requests. The exact mechanism is not 939 specified here; however, the INFO_HIDDEN forwarding code may be used 940 to note that, for example, the incoming interface address and packet 941 count are for the entrance to the domain and the outgoing interface 942 address and packet count are the exit from the domain. The source- 943 group packet count may be from either router or not specified (all 944 1). 946 10. Client Behavior 948 10.1. Sending Mtrace2 Query 950 When the destination of the mtrace2 is the machine running the 951 client, the mtrace2 Query packet can be sent to the ALL- 952 ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All Routers Address 953 (FF02::2) for IPv6. This will ensure that the packet is received by 954 the last-hop router on the subnet. Otherwise, if the proper last-hop 955 router is known for the mtrace2 destination, or if the mtrace2 client 956 wants to restart mtrace2 Query from the intermediate router that 957 responded with NO_SPACE in Forwarding Code of Standard Response Block 958 as specified in Section 6.13, the Query could be unicasted to that 959 router. Otherwise, the Query packet should be multicasted to the 960 group being queried; if the destination of the mtrace2 is a member of 961 the group, this will get the Query to the proper last-hop router. In 962 this final case, the packet should contain the Router Alert option 963 [7][8], to make sure that routers that are not members of the 964 multicast group notice the packet. 966 See also Section 10.4 on determining the last-hop router. 968 10.2. Determining the Path 970 The client could send a small number of initial query messages with a 971 large "# hops" field, in order to try to trace the full path. If 972 this attempt fails, one strategy is to perform a linear search (as 973 the traditional unicast traceroute program does); set the "# hops" 974 field to 1 and try to get a response, then 2, and so on. If no 975 response is received at a certain hop, the hop count can continue 976 past the non-responding hop, in the hopes that further hops may 977 respond. These attempts should continue until a user-defined timeout 978 has occurred. 980 See also Section 10.5 and Section 10.6 on receiving the results of a 981 trace. 983 10.3. Collecting Statistics 985 After a client has determined that it has traced the whole path or as 986 much as it can expect to (see Section 10.7), it might collect 987 statistics by waiting a short time and performing a second trace. If 988 the path is the same in the two traces, statistics can be displayed 989 as described in Section 12.3 and Section 12.4. 991 10.4. Last Hop Router 993 The mtrace2 querier may not know which is the last hop router, or 994 that router may be behind a firewall that blocks unicast packets but 995 passes multicast packets. In these cases, the mtrace2 request should 996 be multicasted to ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All 997 Routers Address (FF02::2) for IPv6. All routers except the correct 998 last hop router should ignore any mtrace2 request received via 999 multicast. Mtrace2 requests which are multicasted to the group being 1000 traced must include the Router Alert option[7][8]. 1002 Another alternative is to unicast to the trace destination. Mtrace2 1003 requests which are unicasted to the trace destination must include 1004 the Router Alert option, in order that the last-hop router is aware 1005 of the packet. 1007 10.5. First Hop Router 1009 The mtrace2 querier may not be unicast reachable from the first hop 1010 router. In this case, the querier should set the mtrace2 response 1011 address to a multicast address, and should set the response TTL (or 1012 hop limit) to a value sufficient for the response from the first hop 1013 router to reach the querier. It may be appropriate to start with a 1014 small TTL and increase in subsequent attempts until a sufficient TTL 1015 is reached, up to an appropriate maximum (such as 192). 1017 The IANA assigned 224.0.1.32, MTRACE.MCAST.NET as the default 1018 multicast group for IPv4 mtrace responses. However, mtrace2 does not 1019 reserve any IPv4/IPv6 multicast addresses for mtrace2 responses, 1020 because mtrace2 does not send its responses with multicast. 1022 10.6. Broken Intermediate Router 1024 A broken intermediate router might simply not understand mtrace2 1025 packets, and drop them. The querier would then get no response at 1026 all from its mtrace2 requests. It should then perform a hop-by-hop 1027 search by setting the number of responses field until it gets a 1028 response (both linear and binary search are options, but binary is 1029 likely to be slower because a failure requires waiting for a 1030 timeout). 1032 10.7. Mtrace2 Termination 1034 When performing an expanding hop-by-hop trace, it is necessary to 1035 determine when to stop expanding. 1037 10.7.1. Arriving at source 1039 A trace can be determined to have arrived at the source if the 1040 Incoming Interface of the last router in the trace is non-zero, but 1041 the Previous Hop router is zero. 1043 10.7.2. Fatal error 1045 A trace has encountered a fatal error if the last Forwarding Error in 1046 the trace has the 0x80 bit set. 1048 10.7.3. No previous hop 1050 A trace can not continue if the last Previous Hop in the trace is set 1051 to 0. 1053 10.7.4. Traceroute shorter than requested 1055 If the trace that is returned is shorter than requested (i.e. the 1056 number of response blocks is smaller than the "# hops" field), the 1057 trace encountered an error and could not continue. 1059 10.8. Continuing after an error 1061 When the NO_SPACE error occurs, the client might try to continue the 1062 trace by starting it at the last hop in the trace. It can do this by 1063 unicasting to this router's outgoing interface address, keeping all 1064 fields the same. If this results in a single hop and a "WRONG_IF" 1065 error, the client may try setting the trace destination to the same 1066 outgoing interface address. 1068 If a trace times out, it is likely to be because a router in the 1069 middle of the path does not support multicast traceroute. That 1070 router's address will be in the Previous Hop field of the last entry 1071 in the last response packet received. A client may be able to 1072 determine (via mrinfo or SNMP [13][15]) a list of neighbors of the 1073 non-responding router. If desired, each of those neighbors could be 1074 probed to determine the remainder of the path. Unfortunately, this 1075 heuristic may end up with multiple paths, since there is no way of 1076 knowing what the non-responding router's algorithm for choosing a 1077 previous-hop router is. However, if all paths but one flow back 1078 towards the non-responding router, it is possible to be sure that 1079 this is the correct path. 1081 11. Protocol-Specific Considerations 1083 11.1. PIM-SM 1085 When a multicast traceroute reaches a PIM-SM RP and the RP does not 1086 forward the trace on, it means that the RP has not performed a 1087 source-specific join so there is no more state to trace. However, 1088 the path that traffic would use if the RP did perform a source- 1089 specific join can be traced by setting the trace destination to the 1090 RP, the trace source to the traffic source, and the trace group to 0. 1091 This trace Query may be unicasted to the RP. 1093 11.2. Bi-Directional PIM 1095 Bi-directional PIM [10] is a variant of PIM-SM that builds bi- 1096 directional shared trees connecting multicast sources and receivers. 1097 Along the bi-directional shared trees, multicast data is natively 1098 forwarded from sources to the RPA (Rendezvous Point Address) and from 1099 the RPA to receivers without requiring source-specific state. In 1100 contrast to PIM-SM, RP always has the state to trace. 1102 A Designated Forwarder (DF) for a given RPA is in charge of 1103 forwarding downstream traffic onto its link, and forwarding upstream 1104 traffic from its link towards the RPL (Rendezvous Point Link) that 1105 the RPA belongs to. Hence mtrace2 reports DF addresses or RPA along 1106 the path. 1108 11.3. PIM-DM 1110 Routers running PIM Dense Mode do not know the path packets would 1111 take unless traffic is flowing. Without some extra protocol 1112 mechanism, this means that in an environment with multiple possible 1113 paths with branch points on shared media, multicast traceroute can 1114 only trace existing paths, not potential paths. When there are 1115 multiple possible paths but the branch points are not on shared 1116 media, the previous hop router is known, but the last hop router may 1117 not know that it is the appropriate last hop. 1119 When traffic is flowing, PIM Dense Mode routers know whether or not 1120 they are the last-hop forwarder for the link (because they won or 1121 lost an Assert battle) and know who the previous hop is (because it 1122 won an Assert battle). Therefore, multicast traceroute is always 1123 able to follow the proper path when traffic is flowing. 1125 11.4. IGMP/MLD Proxy 1127 When a mtrace2 Query packet reaches an incoming interface of IGMP/MLD 1128 Proxy [11], it put a WRONG_IF (0x01) value in Forwarding Code of 1129 mtrace2 standard response block (as in Section 6.13) and sends the 1130 mtrace2 response back to the Response Address. When a mtrace2 Query 1131 packet reaches an outgoing interface of IGMP/MLD Proxy, it is 1132 forwarded through its incoming interface towards the upstream router. 1134 11.5. AMT 1136 AMT [12] provides the multicast connectivity to the unicast-only 1137 inter-network. To do this, multicast packets being sent to or from a 1138 site are encapsulated in unicast packets. When a mtrace2 Query 1139 packet reaches an AMT Pseudo-Interface of an AMT Gateway, the AMT 1140 Gateway encapsulats it to a particular AMT Relay reachable across the 1141 unicast-only infrastructure. 1143 12. Problem Diagnosis 1145 12.1. Forwarding Inconsistencies 1147 The forwarding error code can tell if a group is unexpectedly pruned 1148 or administratively scoped. 1150 12.2. TTL or Hop Limit Problems 1152 By taking the maximum of hops (from source + forwarding TTL (or hop 1153 limit) threshold) over all hops, it is possible to discover the TTL 1154 or hop limit required for the source to reach the destination. 1156 12.3. Packet loss 1158 By taking two traces, it is possible to find packet loss information 1159 by comparing the difference in input packet counts to the difference 1160 in output packet counts for the specified source-group address pair 1161 at the previous hop. On a point-to-point link, any difference in 1162 these numbers implies packet loss. Since the packet counts may be 1163 changing as the mtrace2 query is propagating, there may be small 1164 errors (off by 1 or 2 or more) in these statistics. However, these 1165 errors will not accumulate if multiple traces are taken to expand the 1166 measurement period. On a shared link, the count of input packets can 1167 be larger than the number of output packets at the previous hop, due 1168 to other routers or hosts on the link injecting packets. This 1169 appears as "negative loss" which may mask real packet loss. 1171 In addition to the counts of input and output packets for all 1172 multicast traffic on the interfaces, the response data includes a 1173 count of the packets forwarded by a node for the specified source- 1174 group pair. Taking the difference in this count between two traces 1175 and then comparing those differences between two hops gives a measure 1176 of packet loss just for traffic from the specified source to the 1177 specified receiver via the specified group. This measure is not 1178 affected by shared links. 1180 On a point-to-point link that is a multicast tunnel, packet loss is 1181 usually due to congestion in unicast routers along the path of that 1182 tunnel. On native multicast links, loss is more likely in the output 1183 queue of one hop, perhaps due to priority dropping, or in the input 1184 queue at the next hop. The counters in the response data do not 1185 allow these cases to be distinguished. Differences in packet counts 1186 between the incoming and outgoing interfaces on one node cannot 1187 generally be used to measure queue overflow in the node. 1189 12.4. Link Utilization 1191 Again, with two traces, you can divide the difference in the input or 1192 output packet counts at some hop by the difference in time stamps 1193 from the same hop to obtain the packet rate over the link. If the 1194 average packet size is known, then the link utilization can also be 1195 estimated to see whether packet loss may be due to the rate limit or 1196 the physical capacity on a particular link being exceeded. 1198 12.5. Time Delay 1200 If the routers have synchronized clocks, it is possible to estimate 1201 propagation and queuing delay from the differences between the 1202 timestamps at successive hops. However, this delay includes control 1203 processing overhead, so is not necessarily indicative of the delay 1204 that data traffic would experience. 1206 13. IANA Considerations 1208 The following new assignments can only be made via a Standards Action 1209 as specified in [5]. 1211 13.1. Forwarding Codes 1213 New Forwarding codes must only be created by an RFC that modifies 1214 this document's Section 10, fully describing the conditions under 1215 which the new forwarding code is used. The IANA may act as a central 1216 repository so that there is a single place to look up forwarding 1217 codes and the document in which they are defined. 1219 13.2. UDP Destination Port and IPv6 Address 1221 The IANA should allocate UDP destination port for multicast 1222 traceroute version 2 upon publication of the first RFC. 1224 14. Security Considerations 1226 14.1. Topology Discovery 1228 Mtrace2 can be used to discover any actively-used topology. If your 1229 network topology is a secret, mtrace2 may be restricted at the border 1230 of your domain, using the ADMIN_PROHIB forwarding code. 1232 14.2. Traffic Rates 1234 Mtrace2 can be used to discover what sources are sending to what 1235 groups and at what rates. If this information is a secret, mtrace2 1236 may be restricted at the border of your domain, using the 1237 ADMIN_PROHIB forwarding code. 1239 14.3. Unicast Replies 1241 The "Response address" field may be used to send a single packet (the 1242 mtrace2 Reply packet) to an arbitrary unicast address. It is 1243 possible to use this facility as a packet amplifier, as a small 1244 multicast traceroute Query may turn into a large Reply packet. 1246 15. Acknowledgements 1248 This specification started largely as a transcription of Van 1249 Jacobson's slides from the 30th IETF, and the implementation in 1250 mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve 1251 Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original 1252 multicast traceroute client, mtrace (version 1), has been implemented 1253 by Ajit Thyagarajan, Steve Casner and Bill Fenner. 1255 The idea of unicasting a multicast traceroute Query to the 1256 destination of the trace with Router Alert set is due to Tony 1257 Ballardie. The idea of the "S" bit to allow statistics for a source 1258 subnet is due to Tom Pusateri. 1260 For the mtrace version 2 specification, extensive comments were 1261 received from Yiqun Cai, Liu Hui, Bharat Joshi, Shinsuke Suzuki, 1262 Achmad Husni Thamrin, and Cao Wei. 1264 16. References 1266 16.1. Normative References 1268 [1] Bradner, S., "Key words for use in RFCs to indicate requirement 1269 levels", RFC 2119, March 1997. 1271 [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) 1272 Specification", RFC 2460, December 1998. 1274 [3] Hinden, R. and S. Deering, "IP Version 6 Addressing 1275 Architecture", RFC 2373, July 1998. 1277 [4] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 1278 Thyagarajan, "Internet Group Management Protocol, Version 3", 1279 RFC 3376, October 2002. 1281 [5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA 1282 Considerations Section in RFCs", RFC 2434, October 1998. 1284 [6] Braden, B., Borman, D., and C. Partridge, "Computing the 1285 Internet Checksum", RFC 1071, September 1988. 1287 [7] Katz, D., "IP Router Alert Option", RFC 2113, February 1997. 1289 [8] Partridge, C. and A. Jackson, "IPv6 Router Alert Option", 1290 RFC 2711, October 1999. 1292 [9] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 1293 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 1294 Protocol Specification (Revised)", RFC 4601, August 2006. 1296 [10] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 1297 "Bidirectional Protocol Independent Multicast (BIDIR-PIM)", 1298 RFC 5015, October 2007. 1300 [11] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet 1301 Group Management Protocol (IGMP) / Multicast Listener Discovery 1302 (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")", 1303 RFC 4605, August 2006. 1305 [12] Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and T. 1306 Pusateri, "Automatic IP Multicast Without Explicit Tunnels 1307 (AMT)", draft-ietf-mboned-auto-multicast-08.txt (work in 1308 progress), October 2007. 1310 16.2. Informative References 1312 [13] Draves, R. and D. Thaler, "Default Router Preferences and More- 1313 Specific Routes", RFC 4191, November 2005. 1315 [14] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB", 1316 RFC 2863, June 2000. 1318 [15] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast MIB", 1319 RFC 5132, December 2007. 1321 Authors' Addresses 1323 Hitoshi Asaeda 1324 Keio University 1325 Graduate School of Media and Governance 1326 Fujisawa, Kanagawa 252-8520 1327 Japan 1329 Email: asaeda@wide.ad.jp 1330 URI: http://www.sfc.wide.ad.jp/~asaeda/ 1332 Tatuya Jinmei 1333 Internet Systems Consortium 1334 Redwood City, CA 94063 1335 US 1337 Email: Jinmei_Tatuya@isc.org 1339 William C. Fenner 1340 Arastra, Inc. 1341 Menlo Park, CA 94025 1342 US 1344 Email: fenner@fenron.com 1346 Stephen L. Casner 1347 Packet Design, Inc. 1348 Palo Alto, CA 94304 1349 US 1351 Email: casner@packetdesign.com 1353 Full Copyright Statement 1355 Copyright (C) The IETF Trust (2008). 1357 This document is subject to the rights, licenses and restrictions 1358 contained in BCP 78, and except as set forth therein, the authors 1359 retain all their rights. 1361 This document and the information contained herein are provided on an 1362 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 1363 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 1364 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 1365 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 1366 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 1367 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 1369 Intellectual Property 1371 The IETF takes no position regarding the validity or scope of any 1372 Intellectual Property Rights or other rights that might be claimed to 1373 pertain to the implementation or use of the technology described in 1374 this document or the extent to which any license under such rights 1375 might or might not be available; nor does it represent that it has 1376 made any independent effort to identify any such rights. 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