idnits 2.17.1 draft-ietf-mboned-mtrace-v2-01.txt: Checking boilerplate required by RFC 5378 and the IETF Trust (see https://trustee.ietf.org/license-info): ---------------------------------------------------------------------------- ** It looks like you're using RFC 3978 boilerplate. You should update this to the boilerplate described in the IETF Trust License Policy document (see https://trustee.ietf.org/license-info), which is required now. -- Found old boilerplate from RFC 3978, Section 5.1 on line 20. -- Found old boilerplate from RFC 3978, Section 5.5, updated by RFC 4748 on line 1326. -- Found old boilerplate from RFC 3979, Section 5, paragraph 1 on line 1337. -- Found old boilerplate from RFC 3979, Section 5, paragraph 2 on line 1344. -- Found old boilerplate from RFC 3979, Section 5, paragraph 3 on line 1350. Checking nits according to https://www.ietf.org/id-info/1id-guidelines.txt: ---------------------------------------------------------------------------- No issues found here. Checking nits according to https://www.ietf.org/id-info/checklist : ---------------------------------------------------------------------------- == There are 7 instances of lines with non-RFC2606-compliant FQDNs in the document. == There are 1 instance of lines with multicast IPv4 addresses in the document. If these are generic example addresses, they should be changed to use the 233.252.0.x range defined in RFC 5771 Miscellaneous warnings: ---------------------------------------------------------------------------- == The copyright year in the IETF Trust Copyright Line does not match the current year == The document seems to lack the recommended RFC 2119 boilerplate, even if it appears to use RFC 2119 keywords -- however, there's a paragraph with a matching beginning. Boilerplate error? (The document does seem to have the reference to RFC 2119 which the ID-Checklist requires). -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (July 4, 2008) is 5768 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Unused Reference: '2' is defined on line 1230, but no explicit reference was found in the text == Unused Reference: '7' is defined on line 1248, but no explicit reference was found in the text ** Obsolete normative reference: RFC 2460 (ref. '2') (Obsoleted by RFC 8200) ** Obsolete normative reference: RFC 2373 (ref. '3') (Obsoleted by RFC 3513) ** Obsolete normative reference: RFC 2434 (ref. '5') (Obsoleted by RFC 5226) == Outdated reference: A later version (-07) exists of draft-ietf-mboned-ip-mcast-mib-05 -- Obsolete informational reference (is this intentional?): RFC 4601 (ref. '12') (Obsoleted by RFC 7761) == Outdated reference: A later version (-18) exists of draft-ietf-mboned-auto-multicast-08 Summary: 4 errors (**), 0 flaws (~~), 8 warnings (==), 8 comments (--). 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: January 5, 2009 ISC 6 W. Fenner 7 Arastra, Inc. 8 S. Casner 9 Packet Design, Inc. 10 July 4, 2008 12 Mtrace Version 2: Traceroute Facility for IP Multicast 13 draft-ietf-mboned-mtrace-v2-01 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 January 5, 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 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. Resp TTL/HopLim: 8 bits . . . . . . . . . . . . . . . . . 10 63 5.7. Query ID: 24 bits . . . . . . . . . . . . . . . . . . . . 10 64 6. IPv4 Mtrace2 Response Data . . . . . . . . . . . . . . . . . . 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 Response Data . . . . . . . . . . . . . . . . . . 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 . . . . 18 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. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 19 94 8.1. Traceroute Query . . . . . . . . . . . . . . . . . . . . . 19 95 8.1.1. Packet Verification . . . . . . . . . . . . . . . . . 19 96 8.1.2. Normal Processing . . . . . . . . . . . . . . . . . . 19 97 8.2. Mtrace2 Request . . . . . . . . . . . . . . . . . . . . . 19 98 8.2.1. Packet Verification . . . . . . . . . . . . . . . . . 20 99 8.2.2. Normal Processing . . . . . . . . . . . . . . . . . . 20 100 8.3. Mtrace2 Response . . . . . . . . . . . . . . . . . . . . . 21 101 8.4. Forwarding Mtrace2 Requests . . . . . . . . . . . . . . . 21 102 8.5. Sending Mtrace2 Responses . . . . . . . . . . . . . . . . 22 103 8.5.1. Destination Address . . . . . . . . . . . . . . . . . 22 104 8.5.2. TTL and Hop Limit . . . . . . . . . . . . . . . . . . 22 105 8.5.3. Source Address . . . . . . . . . . . . . . . . . . . . 22 106 8.5.4. Sourcing Multicast Responses . . . . . . . . . . . . . 22 107 8.6. Hiding Information . . . . . . . . . . . . . . . . . . . . 22 108 9. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 23 109 9.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 23 110 9.2. Determining the Path . . . . . . . . . . . . . . . . . . . 23 111 9.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 23 112 9.4. Last Hop Router . . . . . . . . . . . . . . . . . . . . . 23 113 9.5. First Hop Router . . . . . . . . . . . . . . . . . . . . . 24 114 9.6. Broken Intermediate Router . . . . . . . . . . . . . . . . 24 115 9.7. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 24 116 9.7.1. Arriving at source . . . . . . . . . . . . . . . . . . 24 117 9.7.2. Fatal error . . . . . . . . . . . . . . . . . . . . . 25 118 9.7.3. No previous hop . . . . . . . . . . . . . . . . . . . 25 119 9.7.4. Traceroute shorter than requested . . . . . . . . . . 25 120 9.8. Continuing after an error . . . . . . . . . . . . . . . . 25 121 10. Protocol-Specific Considerations . . . . . . . . . . . . . . . 26 122 10.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 26 123 10.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . . 26 124 10.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . . 26 125 10.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . 26 126 10.5. AMT . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 127 11. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 28 128 11.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . . 28 129 11.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 28 130 11.3. Packet loss . . . . . . . . . . . . . . . . . . . . . . . 28 131 11.4. Link Utilization . . . . . . . . . . . . . . . . . . . . . 29 132 11.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . . 29 133 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 30 134 12.1. Forwarding Codes . . . . . . . . . . . . . . . . . . . . . 30 135 12.2. UDP Destination Port and IPv6 Address . . . . . . . . . . 30 136 13. Security Considerations . . . . . . . . . . . . . . . . . . . 31 137 13.1. Topology Discovery . . . . . . . . . . . . . . . . . . . . 31 138 13.2. Traffic Rates . . . . . . . . . . . . . . . . . . . . . . 31 139 13.3. Unicast Replies . . . . . . . . . . . . . . . . . . . . . 31 140 14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 32 141 15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33 142 15.1. Normative References . . . . . . . . . . . . . . . . . . . 33 143 15.2. Informative References . . . . . . . . . . . . . . . . . . 33 144 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 35 145 Intellectual Property and Copyright Statements . . . . . . . . . . 36 147 1. Introduction 149 The unicast "traceroute" program allows the tracing of a path from 150 one machine to another. The key mechanism for unicast traceroute is 151 the ICMP TTL exceeded message, which is specifically precluded as a 152 response to multicast packets. On the other hand, the multicast 153 traceroute facility allows the tracing of an IP multicast routing 154 paths. In this document, we specify the multicast "traceroute" 155 facility to be implemented in multicast routers and accessed by 156 diagnostic programs. The multicast traceroute described in this 157 document named as mtrace version 2 or mtrace2 provides additional 158 information about packet rates and losses that the unicast traceroute 159 cannot, and generally requires fewer packets to be sent. 161 o. To be able to trace the path that a packet would take from some 162 source to some destination. 164 o. To be able to isolate packet loss problems (e.g., congestion). 166 o. To be able to isolate configuration problems (e.g., TTL 167 threshold). 169 o. To minimize packets sent (e.g. no flooding, no implosion). 171 This document supports both IPv4 and IPv6 multicast traceroute 172 facility. The protocol design, concept, and program behavior are 173 same between IPv4 and IPv6 mtrace2. While the original IPv4 174 multicast traceroute, mtrace, the query and response messages are 175 implemented as IGMP messages [4], all mtrace2 messages are carried on 176 UDP. The packet formats of IPv4 and IPv6 mtrace2 are different 177 because of the different address families, but the syntax is similar. 179 2. Terminology 181 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL 182 NOT","SHOULD", "SHOULD NOT", "RECOMMENDED","MAY", and "OPTIONAL" in 183 this document are to be interpreted as described in RFC 2119 [1]. 185 Since multicast traceroutes flow in the opposite direction to the 186 data flow, we refer to "upstream" and "downstream" with respect to 187 data, unless explicitly specified. 189 Incoming interface: 190 The interface on which traffic is expected from the specified source 191 and group. 193 Outgoing interface: 194 The interface on which traffic is forwarded from the specified source 195 and group toward the destination. It is the interface on which the 196 multicast traceroute Request was received. 198 Previous-hop router: 199 The router that is on the link attached to the Incoming Interface and 200 is responsible for forwarding traffic for the specified source and 201 group. 203 Group state: 204 It is the state in which a shared-tree protocol (e.g., PIM-SM [12]) 205 running on a router chooses the previous-hop router toward the core 206 router or Rendezvous Point (RP) as its parent router. In this state, 207 source-specific state is not available for the corresponding 208 multicast address on the router. 210 Source-specific state: 211 It is the state in which a routing protocol running on a router 212 chooses the path that would be followed for a source-specific join. 214 ALL-[protocol]-ROUTERS.MCAST.NET: 215 It is a dedicated multicast address for a multicast router to 216 communicate with other routers that are working with the same routing 217 protocol. For instance,the address of ALL-PIM-ROUTERS.MCAST.NET is 218 '224.0.0.13' for IPv4 and 'ff02::d' for IPv6. 220 3. Overview 222 Given a multicast distribution tree, tracing from a source to a 223 multicast destination is hard, since you don't know down which branch 224 of the multicast tree the destination lies. This means that you have 225 to flood the whole tree to find the path from one source to one 226 destination. However, walking up the tree from destination to source 227 is easy, as most existing multicast routing protocols know the 228 previous hop for each source. Tracing from destination to source can 229 involve only routers on the direct path. 231 The party requesting the traceroute (which need be neither the source 232 nor the destination) sends a traceroute Query packet to the last-hop 233 multicast router for the given destination. The last-hop router 234 turns the Query into a Request packet by adding a response data block 235 containing its interface addresses and packet statistics, and then 236 forwards the Request packet via unicast to the router that it 237 believes is the proper previous hop for the given source and group. 238 Each hop adds its response data to the end of the Request packet, 239 then unicast forwards it to the previous hop. The first hop router 240 (the router that believes that packets from the source originate on 241 one of its directly connected networks) changes the packet type to 242 indicate a Response packet and sends the completed response to the 243 response destination address. The response may be returned before 244 reaching the first hop router if a fatal error condition such as "no 245 route" is encountered along the path. 247 Multicast traceroute uses any information available to it in the 248 router to attempt to determine a previous hop to forward the trace 249 towards. Multicast routing protocols vary in the type and amount of 250 state they keep; multicast traceroute endeavors to work with all of 251 them by using whatever is available. For example, if a PIM-SM router 252 is on the (*,G) tree, it chooses the parent towards the RP as the 253 previous hop. In these cases, no source/group-specific state is 254 available, but the path may still be traced. 256 4. Packet Formats 258 Mtrace2 message is encoded in TLV format. If an implementation 259 receives a TLV whose length exceeds the TLV length specified in the 260 Length field, the TLV SHOULD be accepted but any additional data 261 SHOULD be ignored. 263 4.1. Mtrace2 TLV format 265 0 1 2 3 266 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 1 267 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 268 | Type | Length | Value .... | 269 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 271 Type (8 bits) 273 Length (16 bits) 275 Value (variable length) 277 4.2. Defined TLVs 279 The following TLV Types are defined: 281 Code Type 282 ====== ============================ 283 1 Mtrace2 Query 284 2 Mtrace2 Response 286 The type field is defined to be "0x1" for traceroute queries and 287 requests. The type field is changed to "0x2" when the packet is 288 completed and sent as a response from the first hop router to the 289 querier. Two codes are required so that multicast routers won't 290 attempt to process a completed response in those cases where the 291 initial query was issued from a router or the response is sent via 292 multicast. 294 5. Mtrace2 Header 296 The mtrace2 message is carried as a UDP packet. The UDP source port 297 is uniquely selected by the local host operating system. The UDP 298 destination port is the IANA reserved mtrace2 port number (see 299 Section 12). The UDP checksum MUST be valid in mtrace2 control 300 messages. 302 The mtrace2 includes the common packet header as follows. The header 303 is only filled in by the originator of the traceroute Query; 304 intermediate routers MUST NOT modify any of the fields. 306 0 1 2 3 307 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 1 308 +-+-+-+-+-+-+-+-+ 309 | # hops | 310 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 311 | | 312 | Multicast Address | 313 | | 314 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 315 | | 316 | Source Address | 317 | | 318 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 319 | | 320 | Destination Address | 321 | | 322 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 323 | | 324 | Response Address | 325 | | 326 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 327 |Resp TTL/HopLim| Query ID | 328 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 330 Figure 1 332 5.1. # hops: 8 bits 334 This field specifies the maximum number of hops that the requester 335 wants to trace. If there is some error condition in the middle of 336 the path that keeps the traceroute request from reaching the first- 337 hop router, this field can be used to perform an expanding-ring 338 search to trace the path to just before the problem. 340 5.2. Multicast Address 342 This field specifies the 32 bits length IPv4 or 128 bits length IPv6 343 multicast address to be traced, or is filled with "all 1" in case of 344 IPv4 or with the unspecified address (::) in case of IPv6 if no 345 source-specific information is desired. Note that non-group-specific 346 traceroutes may not be possible with certain multicast routing 347 protocols. 349 5.3. Source Address 351 This field specifies the 32 bits length IPv4 or 128 bits length IPv6 352 address of the multicast source for the path being traced, or is 353 filled with "all 1" in case of IPv4 or with the unspecified address 354 (::) in case of IPv6 if no source-specific information is desired. 355 Note that non-source-specific traceroutes may not be possible with 356 certain multicast routing protocols. 358 5.4. Destination Address 360 This field specifies the 32 bits length IPv4 or 128 bits length IPv6 361 address of the multicast receiver for the path being traced. The 362 trace starts at this destination and proceeds toward the traffic 363 source. 365 5.5. Response Address 367 This field specifies 32 bits length IPv4 or 128 bits length IPv6 368 address to which the completed traceroute response packet gets sent. 369 It can be a unicast address or a multicast address, as explained in 370 Section 8.2 372 5.6. Resp TTL/HopLim: 8 bits 374 This field specifies the TTL or Hop Limit at which to multicast the 375 response, if the response address is a multicast address. 377 5.7. Query ID: 24 bits 379 This field is used as a unique identifier for this traceroute request 380 so that duplicate or delayed responses may be detected and to 381 minimize collisions when a multicast response address is used. 383 6. IPv4 Mtrace2 Response Data 385 Each intermediate IPv4 router in a trace path appends "response data" 386 to the forwarded trace packet. The response data looks as follows. 388 0 1 2 3 389 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 1 390 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 391 | Query Arrival Time | 392 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 393 | Incoming Interface Address | 394 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 395 | Outgoing Interface Address | 396 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 397 | Previous-Hop Router Address | 398 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 399 | | 400 . Input packet count on incoming interface . 401 | | 402 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 403 | | 404 . Output packet count on outgoing interface . 405 | | 406 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 407 | | 408 . Total number of packets for this source-group pair . 409 | | 410 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 411 | | |M| | | | 412 | Rtg Protocol | Fwd TTL |B|S| Src Mask |Forwarding Code| 413 | | |Z| | | | 414 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 416 6.1. Query Arrival Time: 32 bits 418 The Query Arrival Time is a 32-bit NTP timestamp specifying the 419 arrival time of the traceroute request packet at this router. The 420 32-bit form of an NTP timestamp consists of the middle 32 bits of the 421 full 64-bit form; that is, the low 16 bits of the integer part and 422 the high 16 bits of the fractional part. 424 The following formula converts from a UNIX timeval to a 32-bit NTP 425 timestamp: 427 query_arrival_time 428 = (tv.tv_sec + 32384) << 16 + ((tv.tv_usec << 10) / 15625) 430 The constant 32384 is the number of seconds from Jan 1, 1900 to Jan 431 1, 1970 truncated to 16 bits. ((tv.tv_usec << 10) / 15625) is a 432 reduction of ((tv.tv_usec / 100000000) << 16). 434 6.2. Incoming Interface Address: 32 bits 436 This field specifies the address of the interface on which packets 437 from this source and group are expected to arrive, or 0 if unknown. 439 6.3. Outgoing Interface Address: 32 bits 441 This field specifies the address of the interface on which packets 442 from this source and group flow to the specified destination, or 0 if 443 unknown. 445 6.4. Previous-Hop Router Address: 32 bits 447 This field specifies the router from which this router expects 448 packets from this source. This may be a multicast group (e.g. ALL- 449 [protocol]-ROUTERS.MCAST.NET) if the previous hop is not known 450 because of the workings of the multicast routing protocol. However, 451 it should be 0 if the incoming interface address is unknown. 453 6.5. Input packet count on incoming interface: 64 bits 455 This field contains the number of multicast packets received for all 456 groups and sources on the incoming interface, or "all 1" if no count 457 can be reported. This counter may have the same value as 458 ifHCInMulticastPkts from the IF-MIB [10] for this interface. 460 6.6. Output packet count on incoming interface: 64 bits 462 This field contains the number of multicast packets that have been 463 transmitted or queued for transmission for all groups and sources on 464 the outgoing interface, or "all 1" if no count can be reported. This 465 counter may have the same value as ifHCOutMulticastPkts from the IF- 466 MIB for this interface. 468 6.7. Total number of packets for this source-group pair: 64 bits 470 This field counts the number of packets from the specified source 471 forwarded by this router to the specified group, or "all 1" if no 472 count can be reported. If the S bit is set, the count is for the 473 source network, as specified by the Src Mask field. If the S bit is 474 set and the Src Mask field is 63, indicating no source-specific 475 state, the count is for all sources sending to this group. This 476 counter should have the same value as ipMcastRoutePkts from the 477 IPMROUTE-STD-MIB [11] for this forwarding entry. 479 6.8. Rtg Protocol: 8 bits 481 This field describes the routing protocol in use between this router 482 and the previous-hop router. Specified values include: 484 0 Unknown 485 1 PIM 486 2 PIM using special routing table 487 3 PIM using a static route 488 4 PIM using MBGP route 489 5 PIM using state created by Assert processing 490 6 Bi-directional PIM 491 7 IGMP/MLD proxy 492 8 AMT Relay 493 9 AMT Gateway 495 6.9. Fwd TTL: 8 bits 497 This field contains the TTL that a packet is required to have before 498 it will be forwarded over the outgoing interface. 500 6.10. MBZ: 1 bit 502 Must be zeroed on transmission and ignored on reception. 504 6.11. S: 1 bit 506 This S bit indicates that the packet count for the source-group pair 507 is for the source network, as determined by masking the source 508 address with the Src Mask field. 510 6.12. Src Mask: 6 bits 512 This field contains the number of 1's in the netmask this router has 513 for the source (i.e. a value of 24 means the netmask is 0xffffff00). 514 If the router is forwarding solely on group state, this field is set 515 to 63 (0x3f). 517 6.13. Forwarding Code: 8 bits 519 This field contains a forwarding information/error code. Section 8.2 520 explains how and when the forwarding code is filled. Defined values 521 are as follows; 523 Value Name Description 525 ----- -------------- ------------------------------------------- 526 0x00 NO_ERROR No error 528 0x01 WRONG_IF Mtrace2 request arrived on an interface 529 to which this router would not forward for 530 this source,group,destination. 532 0x02 PRUNE_SENT This router has sent a prune upstream which 533 applies to the source and group in the 534 traceroute request. 536 0x03 PRUNE_RCVD This router has stopped forwarding for this 537 source and group in response to a request 538 from the next hop router. 540 0x04 SCOPED The group is subject to administrative 541 scoping at this hop. 543 0x05 NO_ROUTE This router has no route for the source or 544 group and no way to determine a potential 545 route. 547 0x06 WRONG_LAST_HOP This router is not the proper last-hop 548 router. 550 0x07 NOT_FORWARDING This router is not forwarding this source, 551 group out the outgoing interface for an 552 unspecified reason. 554 0x08 REACHED_RP Reached Rendezvous Point or Core 556 0x09 RPF_IF Mtrace2 request arrived on the expected 557 RPF interface for this source and group. 559 0x0A NO_MULTICAST Mtrace2 request arrived on an interface 560 which is not enabled for multicast. 562 0x0B INFO_HIDDEN One or more hops have been hidden from this 563 trace. 565 0x81 NO_SPACE There was not enough room to insert another 566 response data block in the packet. 568 0x82 OLD_ROUTER The previous-hop router does not understand 569 traceroute requests. 571 0x83 ADMIN_PROHIB Mtrace2 is administratively prohibited. 573 Note that if a router discovers there is not enough room in a packet 574 to insert its response, it puts the 0x81 error code in the previous 575 router's Forwarding Code field, overwriting any error the previous 576 router placed there. A multicast traceroute client, upon receiving 577 this error, MAY restart the trace at the last hop listed in the 578 packet. 580 The 0x80 bit of the Forwarding Code is used to indicate a fatal 581 error. A fatal error is one where the router may know the previous 582 hop but cannot forward the message to it. 584 7. IPv6 Mtrace2 Response Data 586 Each intermediate IPv6 router in a trace path appends "response data" 587 to the forwarded trace packet. The response data looks as follows. 589 0 1 2 3 590 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 1 591 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 592 | Query Arrival Time | 593 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 594 | Incoming Interface ID | 595 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 596 | Outgoing Interface ID | 597 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 598 | | 599 * Local Address * 600 | | 601 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 602 | | 603 * Remote Address * 604 | | 605 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 606 | | 607 . Input packet count on incoming interface . 608 | | 609 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 610 | | 611 . Output packet count on outgoing interface . 612 | | 613 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 614 | | 615 . Total number of packets for this source-group pair . 616 | | 617 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 618 | Rtg Protocol | MBZ |S|Src Prefix Len |Forwarding Code| 619 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 621 7.1. Query Arrival Time: 32 bits 623 Same definition described in Section 6.1 625 7.2. Incoming Interface ID: 32 bits 627 This field specifies the interface ID on which packets from this 628 source and group are expected to arrive, or 0 if unknown. This ID 629 should be the value taken from InterfaceIndex of the IF-MIB [10] for 630 this interface. This field is carried in network byte order. 632 7.3. Outgoing Interface ID: 32 bits 634 This field specifies the interface ID on which packets from this 635 source and group flow to the specified destination, or 0 if unknown. 636 This ID should be the value taken from InterfaceIndex of the IF-MIB 637 for this interface. This field is carried in network byte order. 639 7.4. Local Address 641 This field specifies a global IPv6 address that uniquely identifies 642 the router. A unique local unicast address [6] SHOULD NOT be used 643 unless the node is only assigned link-local and unique local 644 addresses. [TBD: What if the node is only assigned link-local 645 addresses? It should be very unlikely case, but is possible even for 646 a properly working router.] 648 Note that since interface indices used in the Incoming and Outgoing 649 Interface ID fields are node-local information, a global identifier 650 is needed to specify the router. 652 7.5. Remote Address 654 This field specifies the address of the previous-hop router, which, 655 in most cases, is a link-local unicast address for the queried source 656 and destination addresses. 658 Although a link-local address does not have enough information to 659 identify a node, it is possible to detect the previous-hop router 660 with the assistance of Incoming Interface ID and the current router 661 address (i.e., Local Address). 663 This may be a multicast group (e.g., ALL-[protocol]- 664 ROUTERS.MCAST.NET) if the previous hop is not known because of the 665 workings of the multicast routing protocol. However, it should be 666 the unspecified address (::) if the incoming interface address is 667 unknown. 669 7.6. Input packet count on incoming interface 671 Same definition described in Section 6.5 673 7.7. Output packet count on incoming interface 675 Same definition described in Section 6.6 677 7.8. Total number of packets for this source-group pair 679 This field counts the number of packets from the specified source 680 forwarded by this router to the specified group, or "all 1" if no 681 count can be reported. If the S bit is set, the count is for the 682 source network, as specified by the Src Prefix Len field. If the S 683 bit is set and the Src Prefix Len field is 255, indicating no source- 684 specific state, the count is for all sources sending to this group. 685 This counter should have the same value as ipMcastRoutePkts from the 686 IPMROUTE-STD-MIB for this forwarding entry. 688 7.9. Rtg Protocol: 8 bits 690 Same definition described in Section 6.8 692 7.10. MBZ: 7 bits 694 Must be zeroed on transmission and ignored on reception. 696 7.11. S: 1 bit 698 This S bit indicates that the packet count for the source-group pair 699 is for the source network, as determined by masking the source 700 address with the Src Prefix Len field. 702 7.12. Src Prefix Len: 8 bits 704 This field contains the prefix length this router has for the source. 705 If the router is forwarding solely on group state, this field is set 706 to 255 (0xff) 708 7.13. Forwarding Code: 8 bits 710 Same definition described in Section 6.13 712 8. Router Behavior 714 All of these actions are performed in addition to (NOT instead of) 715 forwarding the packet, if applicable. E.g. a multicast packet that 716 has TTL or the hop limit remaining MUST be forwarded normally, as 717 MUST a unicast packet that has TTL or the hop limit remaining and is 718 not addressed to this router. 720 8.1. Traceroute Query 722 An mtrace2 Query message is a traceroute message with no response 723 blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 mtrace2. 725 8.1.1. Packet Verification 727 Upon receiving an mtrace2 Query message, a router must examine the 728 Query to see if it is the proper last-hop router for the destination 729 address in the packet. It is the proper last-hop router if it has a 730 multicast-capable interface on the same subnet as the Destination 731 Address and is the router that would forward traffic from the given 732 (S,G) onto that subnet. 734 If the router determines that it is not the proper last-hop router, 735 or it cannot make that determination, it does one of two things 736 depending if the Query was received via multicast or unicast. If the 737 Query was received via multicast, then it MUST be silently dropped. 738 If it was received via unicast, a forwarding code of WRONG_LAST_HOP 739 is noted and processing continues as in Section 8.2 741 Duplicate Query messages as identified by the tuple (IP Source, Query 742 ID) SHOULD be ignored. This MAY be implemented using a simple 1-back 743 cache (i.e. remembering the IP source and Query ID of the previous 744 Query message that was processed, and ignoring future messages with 745 the same IP Source and Query ID). Duplicate Request messages MUST 746 NOT be ignored in this manner. 748 8.1.2. Normal Processing 750 When a router receives an mtrace2 Query and it determines that it is 751 the proper last-hop router, it treats it like an mtrace2 Request and 752 performs the steps listed in Section 8.2 754 8.2. Mtrace2 Request 756 An mtrace2 Request is a traceroute message with some number of 757 response blocks filled in, and uses TLV type 0x1 for IPv4 and IPv6 758 mtrace2. Routers can tell the difference between Queries and 759 Requests by checking the length of the packet. 761 8.2.1. Packet Verification 763 If the mtrace2 Request is not addressed to this router, or if the 764 Request is addressed to a multicast group which is not a link-scoped 765 group (i.e. 224/24 for IPv4, FFx2::/16 [3] for IPv6), it MUST be 766 silently ignored. 768 8.2.2. Normal Processing 770 When a router receives an mtrace2 Request, it performs the following 771 steps. Note that it is possible to have multiple situations covered 772 by the Forwarding Codes. The first one encountered is the one that 773 is reported, i.e. all "note forwarding code N" should be interpreted 774 as "if forwarding code is not already set, set forwarding code to N". 776 1. If there is room in the current buffer (or the router can 777 efficiently allocate more space to use), insert a new response 778 block into the packet and fill in the Query Arrival Time, 779 Outgoing Interface Address (for IPv4 mtrace2) or Outgoing 780 Interface ID (for IPv6 mtrace2), Output Packet Count, and Fwd 781 TTL (for IPv4 mtrace2). If there was no room, fill in the 782 response code "NO_SPACE" in the *previous* hop's response block, 783 and forward the packet to the requester as described in 784 Section 8.4. 786 2. Attempt to determine the forwarding information for the source 787 and group specified, using the same mechanisms as would be used 788 when a packet is received from the source destined for the 789 group. State need not be instantiated, it can be "phantom" 790 state created only for the purpose of the trace. 792 If using a shared-tree protocol and there is no source-specific 793 state, or if the source is specified as "all 1", group state 794 should be used. If there is no group state or the group is 795 specified as 0, potential source state (i.e. the path that would 796 be followed for a source-specific Join) should be used. If this 797 router is the Core or RP and no source-specific information is 798 available, note an error code of REACHED_RP. 800 3. If no forwarding information can be determined, the router notes 801 an error code of NO_ROUTE, sets the remaining fields that have 802 not yet been filled in to zero, and then forwards the packet to 803 the requester as described in Section 8.4. 805 4. Fill in the Incoming Interface Address, Previous-Hop Router 806 Address, Input Packet Count, Total Number of Packets, Routing 807 Protocol, S, and Src Mask from the forwarding information that 808 was determined. 810 5. If traceroute is administratively prohibited or the previous hop 811 router does not understand traceroute requests, note the 812 appropriate forwarding code (ADMIN_PROHIB or OLD_ROUTER). If 813 traceroute is administratively prohibited and any of the fields 814 as filled in step 4 are considered private information, zero out 815 the applicable fields. Then the packet is forwarded to the 816 requester as described in Section 8.4. 818 6. If the reception interface is not enabled for multicast, note 819 forwarding code NO_MULTICAST. If the reception interface is the 820 interface from which the router would expect data to arrive from 821 the source, note forwarding code RPF_IF. Otherwise, if the 822 reception interface is not one to which the router would forward 823 data from the source to the group, a forwarding code of WRONG_IF 824 is noted. 826 7. If the group is subject to administrative scoping on either the 827 Outgoing or Incoming interfaces, a forwarding code of SCOPED is 828 noted. 830 8. If this router is the Rendezvous Point or Core for the group, a 831 forwarding code of REACHED_RP is noted. 833 9. If this router has sent a prune upstream which applies to the 834 source and group in the traceroute Request, it notes forwarding 835 code PRUNE_SENT. If the router has stopped forwarding 836 downstream in response to a prune sent by the next hop router, 837 it notes forwarding code PRUNE_RCVD. If the router should 838 normally forward traffic for this source and group downstream 839 but is not, it notes forwarding code NOT_FORWARDING. 841 10. The packet is then sent on to the previous hop or the requester 842 as described in Section 8.4. 844 8.3. Mtrace2 Response 846 A router must forward all mtrace2 response packets normally, with no 847 special processing. If a router has initiated an mtrace2 with a 848 Query or Request message, it may listen for Responses to that 849 traceroute but MUST still forward them as well. 851 8.4. Forwarding Mtrace2 Requests 853 If the Previous-hop router is known for this request, the packet is 854 sent to that router. If the Incoming Interface is known but the 855 Previous-hop router is not known, the packet is sent to an 856 appropriate multicast address on the Incoming Interface. The 857 appropriate multicast address may depend on the routing protocol in 858 use, MUST be a link-scoped group (i.e. 224/24 for IPv4, FF02::/16 for 859 IPv6), MUST NOT be ALL-SYSTEMS.MCAST.NET (224.0.0.1) for IPv4 and All 860 Nodes Address (FF02::1) for IPv6, and MAY be ALL-ROUTERS.MCAST.NET 861 (224.0.0.2) for IPv4 or All Routers Address (FF02::2) for IPv6 if the 862 routing protocol in use does not define a more appropriate group. 863 Otherwise, it is sent to the Response Address in the header, as 864 described in Section 8.5. 866 8.5. Sending Mtrace2 Responses 868 8.5.1. Destination Address 870 An mtrace2 response must be sent to the Response Address in the 871 traceroute header. 873 8.5.2. TTL and Hop Limit 875 If the Response Address is unicast, the router inserts its normal 876 unicast TTL or hop limit in the IP header. If the Response Address 877 is multicast, the router copies the Response TTL or hop limit from 878 the traceroute header into the IP header. 880 8.5.3. Source Address 882 If the Response Address is unicast, the router may use any of its 883 interface addresses as the source address. Since some multicast 884 routing protocols forward based on source address, if the Response 885 Address is multicast, the router MUST use an address that is known in 886 the multicast routing topology if it can make that determination. 888 8.5.4. Sourcing Multicast Responses 890 When a router sources a multicast response, the response packet MUST 891 be sent on a single interface, then forwarded as if it were received 892 on that interface. It MUST NOT source the response packet 893 individually on each interface, in order to avoid duplicate packets. 895 8.6. Hiding Information 897 Information about a domain's topology and connectivity may be hidden 898 from multicast traceroute requests. The exact mechanism is not 899 specified here; however, the INFO_HIDDEN forwarding code may be used 900 to note that, for example, the incoming interface address and packet 901 count are for the entrance to the domain and the outgoing interface 902 address and packet count are the exit from the domain. The source- 903 group packet count may be from either router or not specified (all 904 1). 906 9. Client Behavior 908 9.1. Sending Mtrace2 Query 910 When the destination of the mtrace2 is the machine running the 911 client, the mtrace2 Query packet can be sent to the ALL- 912 ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All Routers Address 913 (FF02::2) for IPv6. This will ensure that the packet is received by 914 the last-hop router on the subnet. Otherwise, if the proper last-hop 915 router is known for the mtrace2 destination, the Query could be 916 unicasted to that router. Otherwise, the Query packet should be 917 multicasted to the group being queried; if the destination of the 918 mtrace2 is a member of the group, this will get the Query to the 919 proper last-hop router. In this final case, the packet should 920 contain the Router Alert option [8][9], to make sure that routers 921 that are not members of the multicast group notice the packet. 923 See also Section 9.4 on determining the last-hop router. 925 9.2. Determining the Path 927 The client could send a small number of initial query messages with a 928 large "# hops" field, in order to try to trace the full path. If 929 this attempt fails, one strategy is to perform a linear search (as 930 the traditional unicast traceroute program does); set the "# hops" 931 field to 1 and try to get a response, then 2, and so on. If no 932 response is received at a certain hop, the hop count can continue 933 past the non-responding hop, in the hopes that further hops may 934 respond. These attempts should continue until a user-defined timeout 935 has occurred. 937 See also Section 9.5 and Section 9.6 on receiving the results of a 938 trace. 940 9.3. Collecting Statistics 942 After a client has determined that it has traced the whole path or as 943 much as it can expect to (see Section 9.7), it might collect 944 statistics by waiting a short time and performing a second trace. If 945 the path is the same in the two traces, statistics can be displayed 946 as described in Section 11.3 and Section 11.4. 948 9.4. Last Hop Router 950 The mtrace2 querier may not know which is the last hop router, or 951 that router may be behind a firewall that blocks unicast packets but 952 passes multicast packets. In these cases, the mtrace2 request should 953 be multicasted to ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All 954 Routers Address (FF02::2) for IPv6. All routers except the correct 955 last hop router should ignore any mtrace2 request received via 956 multicast. Mtrace2 requests which are multicasted to the group being 957 traced must include the Router Alert option[8][9]. 959 Another alternative is to unicast to the trace destination. Mtrace2 960 requests which are unicasted to the trace destination must include 961 the Router Alert option, in order that the last-hop router is aware 962 of the packet. 964 9.5. First Hop Router 966 The mtrace2 querier may not be unicast reachable from the first hop 967 router. In this case, the querier should set the traceroute response 968 address to a multicast address, and should set the response TTL (or 969 hop limit) to a value sufficient for the response from the first hop 970 router to reach the querier. It may be appropriate to start with a 971 small TTL and increase in subsequent attempts until a sufficient TTL 972 is reached, up to an appropriate maximum (such as 192). 974 The IANA has assigned 224.0.1.32, MTRACE.MCAST.NET as the default 975 multicast group for IPv4 mtrace2 responses, and will assign 976 MTRACE2_IPV6RESPADDR (TBD (see Section 12)) for IPv6 mtrace2 977 responses. Other groups may be used if needed, e.g. when using 978 mtrace2 to diagnose problems with the IANA-assigned group. 980 9.6. Broken Intermediate Router 982 A broken intermediate router might simply not understand traceroute 983 packets, and drop them. The querier would then get no response at 984 all from its traceroute requests. It should then perform a hop-by- 985 hop search by setting the number of responses field until it gets a 986 response (both linear and binary search are options, but binary is 987 likely to be slower because a failure requires waiting for a 988 timeout). 990 9.7. Mtrace2 Termination 992 When performing an expanding hop-by-hop trace, it is necessary to 993 determine when to stop expanding. 995 9.7.1. Arriving at source 997 A trace can be determined to have arrived at the source if the 998 Incoming Interface of the last router in the trace is non-zero, but 999 the Previous Hop router is zero. 1001 9.7.2. Fatal error 1003 A trace has encountered a fatal error if the last Forwarding Error in 1004 the trace has the 0x80 bit set. 1006 9.7.3. No previous hop 1008 A trace can not continue if the last Previous Hop in the trace is set 1009 to 0. 1011 9.7.4. Traceroute shorter than requested 1013 If the trace that is returned is shorter than requested (i.e. the 1014 number of Response blocks is smaller than the "# hops" field), the 1015 trace encountered an error and could not continue. 1017 9.8. Continuing after an error 1019 When the NO_SPACE error occurs, the client might try to continue the 1020 trace by starting it at the last hop in the trace. It can do this by 1021 unicasting to this router's outgoing interface address, keeping all 1022 fields the same. If this results in a single hop and a "WRONG_IF" 1023 error, the client may try setting the trace destination to the same 1024 outgoing interface address. 1026 If a trace times out, it is likely to be because a router in the 1027 middle of the path does not support multicast traceroute. That 1028 router's address will be in the Previous Hop field of the last entry 1029 in the last response packet received. A client may be able to 1030 determine (via mrinfo or SNMP [6][11]) a list of neighbors of the 1031 non-responding router. If desired, each of those neighbors could be 1032 probed to determine the remainder of the path. Unfortunately, this 1033 heuristic may end up with multiple paths, since there is no way of 1034 knowing what the non-responding router's algorithm for choosing a 1035 previous-hop router is. However, if all paths but one flow back 1036 towards the non-responding router, it is possible to be sure that 1037 this is the correct path. 1039 10. Protocol-Specific Considerations 1041 10.1. PIM-SM 1043 When a multicast traceroute reaches a PIM-SM RP and the RP does not 1044 forward the trace on, it means that the RP has not performed a 1045 source-specific join so there is no more state to trace. However, 1046 the path that traffic would use if the RP did perform a source- 1047 specific join can be traced by setting the trace destination to the 1048 RP, the trace source to the traffic source, and the trace group to 0. 1049 This trace Query may be unicasted to the RP. 1051 10.2. Bi-Directional PIM 1053 Bi-directional PIM [13] is a variant of PIM-SM that builds bi- 1054 directional shared trees connecting multicast sources and receivers. 1055 Along the bi-directional shared trees, multicast data is natively 1056 forwarded from sources to the RPA (Rendezvous Point Address) and from 1057 the RPA to receivers without requiring source-specific state. In 1058 contrast to PIM-SM, RP always has the state to trace. 1060 A Designated Forwarder (DF) for a given RPA is in charge of 1061 forwarding downstream traffic onto its link, and forwarding upstream 1062 traffic from its link towards the RPL (Rendezvous Point Link) that 1063 the RPA belongs to. Hence mtrace2 reports DF addresses or RPA along 1064 the path. 1066 10.3. PIM-DM 1068 Routers running PIM Dense Mode do not know the path packets would 1069 take unless traffic is flowing. Without some extra protocol 1070 mechanism, this means that in an environment with multiple possible 1071 paths with branch points on shared media, multicast traceroute can 1072 only trace existing paths, not potential paths. When there are 1073 multiple possible paths but the branch points are not on shared 1074 media, the previous hop router is known, but the last hop router may 1075 not know that it is the appropriate last hop. 1077 When traffic is flowing, PIM Dense Mode routers know whether or not 1078 they are the last-hop forwarder for the link (because they won or 1079 lost an Assert battle) and know who the previous hop is (because it 1080 won an Assert battle). Therefore, multicast traceroute is always 1081 able to follow the proper path when traffic is flowing. 1083 10.4. IGMP/MLD Proxy 1085 When a mtrace2 Query packet reaches an incoming interface of IGMP/MLD 1086 Proxy [14], it must be simply discarded. When a mtrace2 Query packet 1087 reaches an outgoing interface of IGMP/MLD Proxy, it is forwarded 1088 through its incoming interface towards the upstream router. 1090 10.5. AMT 1092 AMT [15] provides the multicast connectivity to the unicast-only 1093 inter-network. To do this, multicast packets being sent to or from a 1094 site are encapsulated in unicast packets. When a mtrace2 Query 1095 packet reaches an AMT Pseudo-Interface of an AMT Gateway, the AMT 1096 Gateway encapsulats it to a particular AMT Relay reachable across the 1097 unicast-only infrastructure. 1099 11. Problem Diagnosis 1101 11.1. Forwarding Inconsistencies 1103 The forwarding error code can tell if a group is unexpectedly pruned 1104 or administratively scoped. 1106 11.2. TTL or Hop Limit Problems 1108 By taking the maximum of hops (from source + forwarding TTL (or hop 1109 limit) threshold) over all hops, you can discover the TTL or hop 1110 limit required for the source to reach the destination. 1112 11.3. Packet loss 1114 By taking two traces, you can find packet loss information by 1115 comparing the difference in input packet counts to the difference in 1116 output packet counts for the specified source-group address pair at 1117 the previous hop. On a point-to-point link, any difference in these 1118 numbers implies packet loss. Since the packet counts may be changing 1119 as the mtrace2 query is propagating, there may be small errors (off 1120 by 1 or 2 or more) in these statistics. However, these errors will 1121 not accumulate if multiple traces are taken to expand the measurement 1122 period. On a shared link, the count of input packets can be larger 1123 than the number of output packets at the previous hop, due to other 1124 routers or hosts on the link injecting packets. This appears as 1125 "negative loss" which may mask real packet loss. 1127 In addition to the counts of input and output packets for all 1128 multicast traffic on the interfaces, the response data includes a 1129 count of the packets forwarded by a node for the specified source- 1130 group pair. Taking the difference in this count between two traces 1131 and then comparing those differences between two hops gives a measure 1132 of packet loss just for traffic from the specified source to the 1133 specified receiver via the specified group. This measure is not 1134 affected by shared links. 1136 On a point-to-point link that is a multicast tunnel, packet loss is 1137 usually due to congestion in unicast routers along the path of that 1138 tunnel. On native multicast links, loss is more likely in the output 1139 queue of one hop, perhaps due to priority dropping, or in the input 1140 queue at the next hop. The counters in the response data do not 1141 allow these cases to be distinguished. Differences in packet counts 1142 between the incoming and outgoing interfaces on one node cannot 1143 generally be used to measure queue overflow in the node. 1145 11.4. Link Utilization 1147 Again, with two traces, you can divide the difference in the input or 1148 output packet counts at some hop by the difference in time stamps 1149 from the same hop to obtain the packet rate over the link. If the 1150 average packet size is known, then the link utilization can also be 1151 estimated to see whether packet loss may be due to the rate limit or 1152 the physical capacity on a particular link being exceeded. 1154 11.5. Time Delay 1156 If the routers have synchronized clocks, it is possible to estimate 1157 propagation and queuing delay from the differences between the 1158 timestamps at successive hops. However, this delay includes control 1159 processing overhead, so is not necessarily indicative of the delay 1160 that data traffic would experience. 1162 12. IANA Considerations 1164 The following new assignments can only be made via a Standards Action 1165 as specified in [5]. 1167 12.1. Forwarding Codes 1169 New Forwarding codes must only be created by an RFC that modifies 1170 this document's Section 9, fully describing the conditions under 1171 which the new forwarding code is used. The IANA may act as a central 1172 repository so that there is a single place to look up forwarding 1173 codes and the document in which they are defined. 1175 12.2. UDP Destination Port and IPv6 Address 1177 The IANA should allocate UDP destination port for multicast 1178 traceroute version 2 upon publication of the first RFC. 1179 Additionally, the well-known multicast address (MTRACE2_IPV6RESPADDR) 1180 intended for default use by IPv6 multicast traceroute should be 1181 registered and defined by the first RFC published. 1183 13. Security Considerations 1185 13.1. Topology Discovery 1187 Mtrace2 can be used to discover any actively-used topology. If your 1188 network topology is a secret, mtrace2 may be restricted at the border 1189 of your domain, using the ADMIN_PROHIB forwarding code. 1191 13.2. Traffic Rates 1193 Mtrace2 can be used to discover what sources are sending to what 1194 groups and at what rates. If this information is a secret, mtrace2 1195 may be restricted at the border of your domain, using the 1196 ADMIN_PROHIB forwarding code. 1198 13.3. Unicast Replies 1200 The "Response address" field may be used to send a single packet (the 1201 traceroute Reply packet) to an arbitrary unicast address. It is 1202 possible to use this facility as a packet amplifier, as a small 1203 multicast traceroute Query may turn into a large Reply packet. 1205 14. Acknowledgements 1207 This specification started largely as a transcription of Van 1208 Jacobson's slides from the 30th IETF, and the implementation in 1209 mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve 1210 Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original 1211 multicast traceroute client, mtrace (version 1), has been implemented 1212 by Ajit Thyagarajan, Steve Casner and Bill Fenner. 1214 The idea of unicasting a multicast traceroute Query to the 1215 destination of the trace with Router Alert set is due to Tony 1216 Ballardie. The idea of the "S" bit to allow statistics for a source 1217 subnet is due to Tom Pusateri. 1219 For the mtrace version 2 specification, extensive comments were 1220 received from Yiqun Cai, Liu Hui, Bharat Joshi, Shinsuke Suzuki, and 1221 Cao Wei. 1223 15. References 1225 15.1. Normative References 1227 [1] Bradner, S., "Key words for use in RFCs to indicate requirement 1228 levels", RFC 2119, March 1997. 1230 [2] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) 1231 Specification", RFC 2460, December 1998. 1233 [3] Hinden, R. and S. Deering, "IP Version 6 Addressing 1234 Architecture", RFC 2373, July 1998. 1236 [4] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 1237 Thyagarajan, "Internet Group Management Protocol, Version 3", 1238 RFC 3376, October 2002. 1240 [5] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA 1241 Considerations Section in RFCs", RFC 2434, October 1998. 1243 15.2. Informative References 1245 [6] Draves, R. and D. Thaler, "Default Router Preferences and More- 1246 Specific Routes", RFC 4191, November 2005. 1248 [7] Braden, B., Borman, D., and C. Partridge, "Computing the 1249 Internet Checksum", RFC 1071, September 1988. 1251 [8] Katz, D., "IP Router Alert Option", RFC 2113, February 1997. 1253 [9] Partridge, C. and A. Jackson, "IPv6 Router Alert Option", 1254 RFC 2711, October 1999. 1256 [10] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB", 1257 RFC 2863, June 2000. 1259 [11] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast MIB", 1260 draft-ietf-mboned-ip-mcast-mib-05.txt (work in progress), 1261 March 2007. 1263 [12] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 1264 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 1265 Protocol Specification (Revised)", RFC 4601, August 2006. 1267 [13] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 1268 "Bidirectional Protocol Independent Multicast (BIDIR-PIM)", 1269 RFC 5015, October 2007. 1271 [14] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet 1272 Group Management Protocol (IGMP) / Multicast Listener Discovery 1273 (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")", 1274 RFC 4605, August 2006. 1276 [15] Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and T. 1277 Pusateri, "Automatic IP Multicast Without Explicit Tunnels 1278 (AMT)", draft-ietf-mboned-auto-multicast-08.txt (work in 1279 progress), October 2007. 1281 Authors' Addresses 1283 Hitoshi Asaeda 1284 Keio University 1285 Graduate School of Media and Governance 1286 Fujisawa, Kanagawa 252-8520 1287 Japan 1289 Email: asaeda@wide.ad.jp 1291 Tatuya Jinmei 1292 Internet Systems Consortium 1293 Redwood City, CA 94063 1294 US 1296 Email: Jinmei_Tatuya@isc.org 1298 William C. Fenner 1299 Arastra, Inc. 1300 Menlo Park, CA 94025 1301 US 1303 Email: fenner@fenron.com 1305 Stephen L. Casner 1306 Packet Design, Inc. 1307 Palo Alto, CA 94304 1308 US 1310 Email: casner@packetdesign.com 1312 Full Copyright Statement 1314 Copyright (C) The IETF Trust (2008). 1316 This document is subject to the rights, licenses and restrictions 1317 contained in BCP 78, and except as set forth therein, the authors 1318 retain all their rights. 1320 This document and the information contained herein are provided on an 1321 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS 1322 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND 1323 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 1324 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 1325 THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 1326 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 1328 Intellectual Property 1330 The IETF takes no position regarding the validity or scope of any 1331 Intellectual Property Rights or other rights that might be claimed to 1332 pertain to the implementation or use of the technology described in 1333 this document or the extent to which any license under such rights 1334 might or might not be available; nor does it represent that it has 1335 made any independent effort to identify any such rights. Information 1336 on the procedures with respect to rights in RFC documents can be 1337 found in BCP 78 and BCP 79. 1339 Copies of IPR disclosures made to the IETF Secretariat and any 1340 assurances of licenses to be made available, or the result of an 1341 attempt made to obtain a general license or permission for the use of 1342 such proprietary rights by implementers or users of this 1343 specification can be obtained from the IETF on-line IPR repository at 1344 http://www.ietf.org/ipr. 1346 The IETF invites any interested party to bring to its attention any 1347 copyrights, patents or patent applications, or other proprietary 1348 rights that may cover technology that may be required to implement 1349 this standard. Please address the information to the IETF at 1350 ietf-ipr@ietf.org.