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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 MBONED Working Group H. Asaeda 3 Internet-Draft NICT 4 Intended status: Standards Track W. Lee, Ed. 5 Expires: April 25, 2013 Juniper Networks, Inc. 6 October 22, 2012 8 Mtrace Version 2: Traceroute Facility for IP Multicast 9 draft-ietf-mboned-mtrace-v2-09 11 Abstract 13 This document describes the IP multicast traceroute facility, named 14 Mtrace version 2 (Mtrace2). Unlike unicast traceroute, Mtrace2 15 requires special implementations on the part of routers. This 16 specification describes the required functionality in multicast 17 routers, as well as how an Mtrace2 client invokes a query and 18 receives a reply. 20 Status of this Memo 22 This Internet-Draft is submitted in full conformance with the 23 provisions of BCP 78 and BCP 79. 25 Internet-Drafts are working documents of the Internet Engineering 26 Task Force (IETF). Note that other groups may also distribute 27 working documents as Internet-Drafts. The list of current Internet- 28 Drafts is at http://datatracker.ietf.org/drafts/current/. 30 Internet-Drafts are draft documents valid for a maximum of six months 31 and may be updated, replaced, or obsoleted by other documents at any 32 time. It is inappropriate to use Internet-Drafts as reference 33 material or to cite them other than as "work in progress." 35 This Internet-Draft will expire on April 25, 2013. 37 Copyright Notice 39 Copyright (c) 2012 IETF Trust and the persons identified as the 40 document authors. All rights reserved. 42 This document is subject to BCP 78 and the IETF Trust's Legal 43 Provisions Relating to IETF Documents 44 (http://trustee.ietf.org/license-info) in effect on the date of 45 publication of this document. Please review these documents 46 carefully, as they describe your rights and restrictions with respect 47 to this document. Code Components extracted from this document must 48 include Simplified BSD License text as described in Section 4.e of 49 the Trust Legal Provisions and are provided without warranty as 50 described in the Simplified BSD License. 52 Table of Contents 54 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 55 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6 56 2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 6 57 3. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 7 58 3.1. Mtrace2 TLV format . . . . . . . . . . . . . . . . . . . . 8 59 3.2. Defined TLVs . . . . . . . . . . . . . . . . . . . . . . . 8 60 3.2.1. Mtrace2 Query . . . . . . . . . . . . . . . . . . . . 9 61 3.2.2. Mtrace2 Extended Query Block . . . . . . . . . . . . . 10 62 3.2.3. Mtrace2 Request . . . . . . . . . . . . . . . . . . . 11 63 3.2.4. Mtrace2 Reply . . . . . . . . . . . . . . . . . . . . 11 64 3.2.5. IPv4 Mtrace2 Standard Response Block . . . . . . . . . 12 65 3.2.6. IPv6 Mtrace2 Standard Response Block . . . . . . . . . 16 66 3.2.7. Mtrace2 Augmented Response Block . . . . . . . . . . . 19 67 4. Router Behavior . . . . . . . . . . . . . . . . . . . . . . . 20 68 4.1. Receiving Mtrace2 Query . . . . . . . . . . . . . . . . . 20 69 4.1.1. Query Packet Verification . . . . . . . . . . . . . . 20 70 4.1.2. Query Normal Processing . . . . . . . . . . . . . . . 21 71 4.2. Receiving Mtrace2 Request . . . . . . . . . . . . . . . . 21 72 4.2.1. Request Packet Verification . . . . . . . . . . . . . 21 73 4.2.2. Request Normal Processing . . . . . . . . . . . . . . 22 74 4.3. Forwarding Mtrace2 Request . . . . . . . . . . . . . . . . 23 75 4.3.1. Destination Address . . . . . . . . . . . . . . . . . 24 76 4.3.2. Source Address . . . . . . . . . . . . . . . . . . . . 24 77 4.3.3. Appending Standard Response Block . . . . . . . . . . 24 78 4.4. Sending Mtrace2 Reply . . . . . . . . . . . . . . . . . . 24 79 4.4.1. Destination Address . . . . . . . . . . . . . . . . . 25 80 4.4.2. Source Address . . . . . . . . . . . . . . . . . . . . 25 81 4.4.3. Appending Standard Response Block . . . . . . . . . . 25 82 4.5. Proxying Mtrace2 Query . . . . . . . . . . . . . . . . . . 25 83 4.6. Hiding Information . . . . . . . . . . . . . . . . . . . . 26 84 5. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 26 85 5.1. Sending Mtrace2 Query . . . . . . . . . . . . . . . . . . 26 86 5.1.1. Destination Address . . . . . . . . . . . . . . . . . 26 87 5.1.2. Source Address . . . . . . . . . . . . . . . . . . . . 26 88 5.2. Determining the Path . . . . . . . . . . . . . . . . . . . 26 89 5.3. Collecting Statistics . . . . . . . . . . . . . . . . . . 27 90 5.4. Last Hop Router (LHR) . . . . . . . . . . . . . . . . . . 27 91 5.5. First Hop Router (FHR) . . . . . . . . . . . . . . . . . . 27 92 5.6. Broken Intermediate Router . . . . . . . . . . . . . . . . 27 93 5.7. Non-Supported Router . . . . . . . . . . . . . . . . . . . 28 94 5.8. Mtrace2 Termination . . . . . . . . . . . . . . . . . . . 28 95 5.8.1. Arriving at Source . . . . . . . . . . . . . . . . . . 28 96 5.8.2. Fatal Error . . . . . . . . . . . . . . . . . . . . . 28 97 5.8.3. No Upstream Router . . . . . . . . . . . . . . . . . . 28 98 5.8.4. Reply Timeout . . . . . . . . . . . . . . . . . . . . 28 99 5.9. Continuing after an Error . . . . . . . . . . . . . . . . 28 100 6. Protocol-Specific Considerations . . . . . . . . . . . . . . . 29 101 6.1. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 29 102 6.2. Bi-Directional PIM . . . . . . . . . . . . . . . . . . . . 29 103 6.3. PIM-DM . . . . . . . . . . . . . . . . . . . . . . . . . . 30 104 6.4. IGMP/MLD Proxy . . . . . . . . . . . . . . . . . . . . . . 30 105 7. Problem Diagnosis . . . . . . . . . . . . . . . . . . . . . . 30 106 7.1. Forwarding Inconsistencies . . . . . . . . . . . . . . . . 30 107 7.2. TTL or Hop Limit Problems . . . . . . . . . . . . . . . . 30 108 7.3. Packet Loss . . . . . . . . . . . . . . . . . . . . . . . 30 109 7.4. Link Utilization . . . . . . . . . . . . . . . . . . . . . 31 110 7.5. Time Delay . . . . . . . . . . . . . . . . . . . . . . . . 31 111 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 32 112 8.1. Forwarding Codes . . . . . . . . . . . . . . . . . . . . . 32 113 8.2. UDP Destination Port . . . . . . . . . . . . . . . . . . . 32 114 9. Security Considerations . . . . . . . . . . . . . . . . . . . 32 115 9.1. Addresses in Mtrace2 Header . . . . . . . . . . . . . . . 32 116 9.2. Topology Discovery . . . . . . . . . . . . . . . . . . . . 32 117 9.3. Characteristics of Multicast Channel . . . . . . . . . . . 32 118 9.4. Limiting Query/Request Rates . . . . . . . . . . . . . . . 33 119 9.5. Limiting Reply Rates . . . . . . . . . . . . . . . . . . . 33 120 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 33 121 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 33 122 11.1. Normative References . . . . . . . . . . . . . . . . . . . 33 123 11.2. Informative References . . . . . . . . . . . . . . . . . . 34 124 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 34 126 1. Introduction 128 Given a multicast distribution tree, tracing from a multicast source 129 to a receiver is difficult, since we do not know which branch of the 130 multicast tree the receiver lies. This means that we have to flood 131 the whole tree to find the path from a source to a receiver. On the 132 other hand, walking up the tree from a receiver to a source is easy, 133 as most existing multicast routing protocols know the upstream router 134 for each source. Tracing from a receiver to a source can involve 135 only the routers on the direct path. 137 This document specifies the multicast traceroute facility named 138 Mtrace version 2 or Mtrace2 which allows the tracing of an IP 139 multicast routing path. Mtrace2 is usually initiated from a Mtrace2 140 client towards a specified source, or a Rendezvous Point (RP) if no 141 source address is specified. RP is a special router where the source 142 and receiver meet in PIM-SM [1]. Moreover, Mtrace2 provides 143 additional information such as the packet rates and losses, as well 144 as other diagnosis information. Especially, Mtrace2 can be used for 145 the following purposes: 147 o To trace the path that a packet would take from a source to a 148 receiver. 150 o To isolate packet loss problems (e.g., congestion). 152 o To isolate configuration problems (e.g., TTL threshold). 154 Figure 1 shows a typical case on how Mtrace2 is used. FHR represents 155 the first-hop router, LHR represents the last-hop router, and the 156 arrow lines represent the Mtrace2 messages that are sent from one 157 node to another. The numbers before the Mtrace2 messages represent 158 the sequence of the messages that would happen. Source, Receiver and 159 Mtrace2 client are typically a host on the Internet. 161 2. Request 2. Request 162 +----+ +----+ 163 | | | | 164 v | v | 165 +--------+ +-----+ +-----+ +----------+ 166 | Source |----| FHR |----- The Internet -----| LHR |----| Receiver | 167 +--------+ +-----+ | +-----+ +----------+ 168 \ | ^ 169 \ | / 170 \ | / 171 \ | / 172 3. Reply \ | / 1. Query 173 \ | / 174 \ | / 175 \ +---------+ / 176 v | Mtrace2 |/ 177 | client | 178 +---------+ 180 Figure 1 182 When an Mtrace2 client initiates a multicast trace anywhere on the 183 Internet, it sends an Mtrace2 Query packet to the LHR for a multicast 184 group and a source address. The LHR turns the Query packet into a 185 Request, appends a standard response block containing its interface 186 addresses and packet statistics to the Request packet, then forwards 187 the packet towards the source. The Request packet is either 188 unicasted to its upstream router towards the source, or multicasted 189 to the group if the upsteam router's IP address is not known. In a 190 similar fashion, each router along the path to the source appends a 191 standard response block to the end of the Request packet before 192 forwarding it to its upstream router. When the FHR receives the 193 Request packet, it appends its own standard response block, turns the 194 Request packet into a Reply, and unicasts the Reply back to the 195 Mtrace2 client. 197 The Mtrace2 Reply may be returned before reaching the FHR if it 198 reaches the RP first, or a fatal error condition such as "no route" 199 is encountered along the path, or the hop count is exceeded. 201 The Mtrace2 client waits for the Mtrace2 Reply message and displays 202 the results. When not receiving an Mtrace2 Reply message due to 203 network congestion, a broken router (see Section 5.6), or a non- 204 responding router (see Section 5.7), the Mtrace2 client may resend 205 another Mtrace2 Query with a lower hop count (see Section 3.2.1), and 206 repeat the process until it receives an Mtrace2 Reply message. The 207 details are Mtrace2 client specific, and it is outside the scope of 208 this document. 210 Note that when a router's control plane and forwarding plane are out 211 of sync, the Mtrace2 Requests might be forwarded based on the control 212 states instead. In which case, the traced path might not represent 213 the real path the data packets would follow. 215 Mtrace2 supports both IPv4 and IPv6. Unlike the previous version of 216 Mtrace, which implements its query and response as IGMP messages [8], 217 all Mtrace2 messages are UDP-based. Although the packet formats of 218 IPv4 and IPv6 Mtrace2 are different because of the address families, 219 the syntax between them is similar. 221 2. Terminology 223 In this document, the key words "MUST", "MUST NOT", "REQUIRED", 224 "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", 225 and "OPTIONAL" are to be interpreted as described in RFC 2119 [2], 226 and indicate requirement levels for compliant Mtrace2 227 implementations. 229 2.1. Definitions 231 Since Mtrace2 Queries and Requests flow in the opposite direction to 232 the data flow, we refer to "upstream" and "downstream" with respect 233 to data, unless explicitly specified. 235 Incoming interface 236 The interface on which data is expected to arrive from the 237 specified source and group. 239 Outgoing interface 240 The interface to which data from the source or RP is expected to 241 transmit for the specified source and group. It is also the 242 interface on which the Mtrace2 Request will be received. 244 Upstream router 245 The router, connecting to the Incoming interface of the current 246 router, which is responsible for forwarding data for the specified 247 source and group to the current router. 249 First-hop router (FHR) 250 The router that is directly connected to the source the Mtrace2 251 Query specifies. 253 Last-hop router (LHR) 254 The router that is directly connected to the receivers. It is 255 also the router that receives the Mtrace2 Query from an Mtrace2 256 client. 258 Group state 259 It is the state a shared-tree protocol, such as PIM-SM [1], uses 260 to choose the upstream router towards the RP for the specified 261 group. In this state, source-specific state is not available for 262 the corresponding group address on the router. 264 Source-specific state 265 It is the state that is used to choose the path towards the source 266 for the specified source and group. 268 ALL-[protocol]-ROUTERS.MCAST.NET 269 It is a link-local multicast address for multicast routers to 270 communicate with their adjacent routers that are running the same 271 routing protocol. For instance, the address of ALL-PIM- 272 ROUTERS.MCAST.NET [1] is '224.0.0.13' for IPv4 and 'ff02::d' for 273 IPv6. 275 3. Packet Formats 277 This section describes the details of the packet formats for Mtrace2 278 messages. 280 All Mtrace2 messages are encoded in TLV format (see Section 3.1). If 281 an implementation receives an unknown TLV, it SHOULD ignored and 282 silently discarded the unknown TLV. If the length of a TLV exceeds 283 the length specified in the TLV, the TLV SHOULD be accepted; however, 284 any additional data after the TLV SHOULD be ignored. 286 All Mtrace2 messages are UDP packets. For IPv4, Mtrace2 Query and 287 Request messages MUST NOT be fragmented. For IPv6, the packet size 288 for the Mtrace2 messages MUST NOT exceed 1280 bytes, which is the 289 smallest MTU for an IPv6 interface [3]. The source port is uniquely 290 selected by the local host operating system. The destination port is 291 the IANA reserved Mtrace2 port number (see Section 8). All Mtrace2 292 messages MUST have a valid UDP checksum. 294 Additionally, Mtrace2 supports both IPv4 and IPv6, but not mixed. 295 For example, if an Mtrace2 Query or Reply message arrives in as an 296 IPv4 packet, all addresses specified in the Mtrace2 messages MUST be 297 IPv4 as well. Same rule applies to IPv6 Mtrace2 messages. 299 3.1. Mtrace2 TLV format 301 0 1 2 3 302 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 1 303 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 304 | Type | Length | Value .... | 305 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 307 Type: 8 bits 309 Describes the format of the Value field. For all the available 310 types, please see Section 3.2 312 Length: 16 bits 314 Length of Type, Length, and Value fields in octets. Minimum 315 length required is 6 octets. The maximum TLV length is not 316 defined; however the entired Mtrace2 packet length should not 317 exceeed the available MTU. 319 Value: variable length 321 The format is based on the Type value. The length of the value 322 field is Length field minus 3. All reserved fields in the Value 323 field MUST be transmitted as zeros and ignored on receipt. 325 3.2. Defined TLVs 327 The following TLV Types are defined: 329 Code Type 330 ==== ================================ 331 0x01 Mtrace2 Query 332 0x02 Mtrace2 Request 333 0x03 Mtrace2 Reply 334 0x04 Mtrace2 Standard Response Block 335 0x05 Mtrace2 Augmented Response Block 336 0x06 Mtrace2 Extended Query Block 338 Each Mtrace2 message MUST begin with either a Query, Request or Reply 339 TLV. The first TLV determines the type of each Mtrace2 message. 340 Following this TLV, there can be a sequence of optional Extended 341 Query Blocks. In the case of the Request and Reply message, it is 342 then followed by a sequence of Standard Response Blocks, each from a 343 multicast router on the path towards the source or the RP. In the 344 case more information is needed, a Standard Response Block can be 345 followed by one or multiple Augmented Response Blocks. 347 We will describe each message type in details in the next few 348 sections. 350 3.2.1. Mtrace2 Query 352 An Mtrace2 query is usually originated by an Mtrace2 client which 353 sends an Mtrace2 Query message to the LHR. When tracing towards the 354 source or the RP, the intermediate routers MUST NOT modify the Query 355 message except the Type field. 357 An Mtrace2 Query message is shown as follows: 359 0 1 2 3 360 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 1 361 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 362 | Type | Length | # Hops | 363 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 364 | | 365 | Multicast Address | 366 | | 367 +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 368 | | 369 | Source Address | 370 | | 371 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 372 | | 373 | Mtrace2 Client Address | 374 | | 375 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 376 | Query ID | Client Port # | 377 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 379 Figure 2 381 # Hops: 8 bits 382 This field specifies the maximum number of hops that the Mtrace2 383 client wants to trace. If there are some error conditions in the 384 middle of the path that prevent an Mtrace2 Reply from being 385 received by the client, the client MAY issues another Mtrace2 386 Query with the lower number of hops until it receives a Reply from 387 the FHR. 389 Multicast Address: 32 bits or 128 bits 390 This field specifies an IPv4 or IPv6 address, which can be either: 392 m-1: a multicast group address to be traced; or, 394 m-2: all 1's in case of IPv4 or the unspecified address (::) in 395 case of IPv6 if no group-specific information is desired. 397 Source Address: 32 bits or 128 bits 398 This field specifies an IPv4 or IPv6 address, which can be either: 400 s-1: an unicast address of the source to be traced; or, 402 s-2: all 1's in case of IPv4 or the unspecified address (::) in 403 case of IPv6 if no source-specific information is desired. 404 For example, the client is tracing a (*,g) group state. 406 Note that it is invalid to have a source-group combination of 407 (s-2, m-2). If a router receives such combination in an Mtrace2 408 Query, it MUST silently discard the Query. 410 Mtrace2 Client Address: 32 bits or 128 bits 411 This field specifies the Mtrace2 client's IPv4 address or IPv6 412 global address. This address MUST be a valid unicast address, and 413 therefore, MUST NOT be all 1's or an unspecified address. The 414 Mtrace2 Reply will be sent to this address. 416 Query ID: 16 bits 417 This field is used as a unique identifier for this Mtrace2 Query 418 so that duplicate or delayed Reply messages may be detected. 420 Client Port #: 16 bits 421 This field specifies the destination UDP port number for receiving 422 the Mtrace2 Reply packet. 424 3.2.2. Mtrace2 Extended Query Block 426 There may be a sequence of optional Extended Query Blocks that follow 427 an Mtrace2 Query to further specify any information needed for the 428 Query. For example, an Mtrace2 client might be interested in tracing 429 the path the specified source and group would take based on a certain 430 topology. In which case, the client can pass in the multi-topology 431 ID as the Value for an Extended Query Type (see below). The Extended 432 Query Type is extensible and the behavior of the new types will be 433 addressed by seperate documents. 435 The Mtrace2 Extended Query Block is formatted as follows: 437 0 1 2 3 438 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 1 439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 440 | Type | Length | MBZ |T| 441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 442 | Extended Query Type | Value .... | 443 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 445 MBZ: 7 bits 446 This field must be zeroed on transmission and ignored on 447 reception. 449 T-bit (Transitive Attribute): 1 bit 450 If the TLV type is unrecognized by the receiving router, then this 451 TLV is either discarded or forwarded along with the Query, 452 depending on the value of this bit. If this bit is set, then the 453 router MUST forward this TLV. If this bit is clear, the router 454 MUST send an mtrace2 Reply with an UNKNOWN_QUERY error. 456 Extended Query Type: 16 bits 457 This field specifies the type of the Extended Query Block. 459 Value: 16 bits 460 This field specifies the value of this Extended Query. 462 3.2.3. Mtrace2 Request 464 The format of an Mtrace2 Request message is similar to an Mtrace2 465 Query except the Type field is 0x02. 467 When a LHR receives an Mtrace2 Query message, it would turn the Query 468 into a Request by changing the Type field of the Query from 0x01 to 469 0x02. The LHR would then append an Mtrace2 Standard Response Block 470 (see Section 3.2.5) of its own to the Request message before sending 471 it upstream. The upstream routers would do the same without changing 472 the Type field until one of them is ready to send a Reply. 474 3.2.4. Mtrace2 Reply 476 The format of an Mtrace2 Reply message is similar to an Mtrace2 Query 477 except the Type field is 0x03. 479 When a FHR or a RP receives an Mtrace2 Request message which is 480 destined to itself, it would append an Mtrace2 Standard Response 481 Block (see Section 3.2.5) of its own to the Request message. Next, 482 it would turn the Request message into a Reply by changing the Type 483 field of the Request from 0x02 to 0x03. The Reply message would then 484 be unicated to the Mtrace2 client specified in the Mtrace2 Client 485 Address field. 487 There are a number of cases an intermediate router might return a 488 Reply before a Request reaches the FHR or the RP. See Section 4.1.1, 489 Section 4.2.2, Section 4.3.3, and Section 4.5 for more details. 491 3.2.5. IPv4 Mtrace2 Standard Response Block 493 This section describes the message format of an IPv4 Mtrace2 Standard 494 Response Block. The Type field is 0x04. 496 0 1 2 3 497 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 1 498 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 499 | Type | Length | MBZ | 500 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 501 | Query Arrival Time | 502 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 503 | Incoming Interface Address | 504 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 505 | Outgoing Interface Address | 506 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 507 | Upstream Router Address | 508 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 509 | | 510 . Input packet count on incoming interface . 511 | | 512 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 513 | | 514 . Output packet count on outgoing interface . 515 | | 516 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 517 | | 518 . Total number of packets for this source-group pair . 519 | | 520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 521 | Rtg Protocol | Multicast Rtg Protocol | 522 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 523 | Fwd TTL | MBZ |S| Src Mask |Forwarding Code| 524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 526 MBZ: 8 bits 527 This field must be zeroed on transmission and ignored on 528 reception. 530 Query Arrival Time: 32 bits 531 The Query Arrival Time is a 32-bit NTP timestamp specifying the 532 arrival time of the Mtrace2 Query or Request packet at this 533 router. The 32-bit form of an NTP timestamp consists of the 534 middle 32 bits of the full 64-bit form; that is, the low 16 bits 535 of the integer part and the high 16 bits of the fractional part. 537 The following formula converts from a UNIX timeval to a 32-bit NTP 538 timestamp: 540 query_arrival_time 541 = (tv.tv_sec + 32384) << 16 + ((tv.tv_usec << 10) / 15625) 543 The constant 32384 is the number of seconds from Jan 1, 1900 to 544 Jan 1, 1970 truncated to 16 bits. ((tv.tv_usec << 10) / 15625) is 545 a reduction of ((tv.tv_usec / 100000000) << 16). 547 Note that Mtrace2 does not require all the routers on the path to 548 have synchronized clocks in order to measure one-way latency. 550 Additionally, Query Arrival Time is useful for measuring the 551 packet rate. For example, suppose that a client issues two 552 queries, and the corresponding requests R1 and R2 arrive at router 553 X at time T1 and T2, then the client would be able to compute the 554 packet rate on router X by using the packet count information 555 stored in the R1 and R2, and the time T1 and T2. 557 Incoming Interface Address: 32 bits 558 This field specifies the address of the interface on which packets 559 from the source or the RP are expected to arrive, or 0 if unknown 560 or unnumbered. 562 Outgoing Interface Address: 32 bits 563 This field specifies the address of the interface on which packets 564 from the source or the RP are expected to transmit towards the 565 receiver, or 0 if unknown or unnumbered. This is also the address 566 of the interface on which the Mtrace2 Query or Request arrives. 568 Upstream Router Address: 32 bits 569 This field specifies the address of the upstream router from which 570 this router expects packets from this source. This may be a 571 multicast group (e.g. ALL-[protocol]-ROUTERS.MCAST.NET) if the 572 upstream router is not known because of the workings of the 573 multicast routing protocol. However, it should be 0 if the 574 incoming interface address is unknown or unnumbered. 576 Input packet count on incoming interface: 64 bits 577 This field contains the number of multicast packets received for 578 all groups and sources on the incoming interface, or all 1's if no 579 count can be reported. This counter may have the same value as 580 ifHCInMulticastPkts from the IF-MIB [9] for this interface. 582 Output packet count on outgoing interface: 64 bit 583 This field contains the number of multicast packets that have been 584 transmitted or queued for transmission for all groups and sources 585 on the outgoing interface, or all 1's if no count can be reported. 586 This counter may have the same value as ifHCOutMulticastPkts from 587 the IF-MIB [9] for this interface. 589 Total number of packets for this source-group pair: 64 bits 590 This field counts the number of packets from the specified source 591 forwarded by the router to the specified group, or all 1's if no 592 count can be reported. If the S bit is set (see below), the count 593 is for the source network, as specified by the Src Mask field (see 594 below). If the S bit is set and the Src Mask field is 63, 595 indicating no source-specific state, the count is for all sources 596 sending to this group. This counter should have the same value as 597 ipMcastRoutePkts from the IPMROUTE-STD-MIB [10] for this 598 forwarding entry. 600 Rtg Protocol: 16 bits 601 This field describes the unicast routing protocol running between 602 this router and the upstream router, and it is used to determine 603 the RPF interface for the specified source or RP. This value 604 should have the same value as ipMcastRouteRtProtocol from the 605 IPMROUTE-STD-MIB [10] for this entry. If the router is not able 606 to obtain this value, all 0's must be specified. 608 Multicast Rtg Protocol: 16 bits 609 This field describes the multicast routing protocol in use between 610 the router and the upstream router. This value should have the 611 same value as ipMcastRouteProtocol from the IPMROUTE-STD-MIB [10] 612 for this entry. If the router cannot obtain this value, all 0's 613 must be specified. 615 Fwd TTL: 8 bits 616 This field contains the TTL in which an Mtrace2 Request packet can 617 be forwarded towards the source or the RP. 619 S: 1 bit 620 If this bit is set, it indicates that the packet count for the 621 source-group pair is for the source network, as determined by 622 masking the source address with the Src Mask field. 624 Src Mask: 7 bits 625 This field contains the number of 1's in the netmask the router 626 has for the source (i.e. a value of 24 means the netmask is 627 0xffffff00). If the router is forwarding solely on group state, 628 this field is set to 127 (0x7f). 630 Forwarding Code: 8 bits 631 This field contains a forwarding information/error code. 632 Section 4.1 and Section 4.2 will explain how and when the 633 Forwarding Code is filled. Defined values are as follows: 635 Value Name Description 636 ----- -------------- ---------------------------------------------- 637 0x00 NO_ERROR No error 638 0x01 WRONG_IF Mtrace2 Request arrived on an interface 639 to which this router would not forward for 640 the specified group towards the source or RP. 641 0x02 PRUNE_SENT This router has sent a prune upstream which 642 applies to the source and group in the 643 Mtrace2 Request. 644 0x03 PRUNE_RCVD This router has stopped forwarding for this 645 source and group in response to a request 646 from the downstream router. 647 0x04 SCOPED The group is subject to administrative 648 scoping at this router. 649 0x05 NO_ROUTE This router has no route for the source or 650 group and no way to determine a potential 651 route. 652 0x06 WRONG_LAST_HOP This router is not the proper LHR. 653 0x07 NOT_FORWARDING This router is not forwarding this source and 654 group out the outgoing interface for an 655 unspecified reason. 656 0x08 REACHED_RP Reached the Rendezvous Point. 657 0x09 RPF_IF Mtrace2 Request arrived on the expected 658 RPF interface for this source and group. 659 0x0A NO_MULTICAST Mtrace2 Request arrived on an interface 660 which is not enabled for multicast. 661 0x0B INFO_HIDDEN One or more hops have been hidden from this 662 trace. 663 0x0C REACHED_GW Mtrace2 Request arrived on a gateway (e.g., 664 a NAT or firewall) that hides the 665 information between this router and the 666 Mtrace2 client. 667 0x0D UNKNOWN_QUERY A non-transitive Extended Query Type was 668 received by a router which does not support 669 the type. 670 0x80 FATAL_ERROR A fatal error is one where the router may 671 know the upstream router but cannot forward 672 the message to it. 673 0x81 NO_SPACE There was not enough room to insert another 674 Standard Response Block in the packet. 675 0x83 ADMIN_PROHIB Mtrace2 is administratively prohibited. 677 3.2.6. IPv6 Mtrace2 Standard Response Block 679 This section describes the message format of an IPv6 Mtrace2 Standard 680 Response Block. The Type field is also 0x04. 682 0 1 2 3 683 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 1 684 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 685 | Type | Length | MBZ | 686 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 687 | Query Arrival Time | 688 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 689 | Incoming Interface ID | 690 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 691 | Outgoing Interface ID | 692 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 693 | | 694 * Local Address * 695 | | 696 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 697 | | 698 * Remote Address * 699 | | 700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 701 | | 702 . Input packet count on incoming interface . 703 | | 704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 705 | | 706 . Output packet count on outgoing interface . 707 | | 708 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 709 | | 710 . Total number of packets for this source-group pair . 711 | | 712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 713 | Rtg Protocol | Multicast Rtg Protocol | 714 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 715 | MBZ 2 |S|Src Prefix Len |Forwarding Code| 716 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 718 MBZ: 8 bits 719 This field must be zeroed on transmission and ignored on 720 reception. 722 Query Arrival Time: 32 bits 723 Same definition as in IPv4. 725 Incoming Interface ID: 32 bits 726 This field specifies the interface ID on which packets from the 727 source or RP are expected to arrive, or 0 if unknown. This ID 728 should be the value taken from InterfaceIndex of the IF-MIB [9] 729 for this interface. 731 Outgoing Interface ID: 32 bits 732 This field specifies the interface ID to which packets from the 733 source or RP are expected to transmit, or 0 if unknown. This ID 734 should be the value taken from InterfaceIndex of the IF-MIB [9] 735 for this interface 737 Local Address: 128 bits 738 This field specifies a global IPv6 address that uniquely 739 identifies the router. An unique local unicast address [11] 740 SHOULD NOT be used unless the router is only assigned link-local 741 and unique local addresses. If the router is only assigned link- 742 local addresses, its link-local address can be specified in this 743 field. 745 Remote Address: 128 bits 746 This field specifies the address of the upstream router, which, in 747 most cases, is a link-local unicast address for the upstream 748 router. 750 Although a link-local address does not have enough information to 751 identify a node, it is possible to detect the upstream router with 752 the assistance of Incoming Interface ID and the current router 753 address (i.e., Local Address). 755 Note that this may be a multicast group (e.g., ALL-[protocol]- 756 ROUTERS.MCAST.NET) if the upstream router is not known because of 757 the workings of a multicast routing protocol. However, it should 758 be the unspecified address (::) if the incoming interface address 759 is unknown. 761 Input packet count on incoming interface: 64 bits 762 Same definition as in IPv4. 764 Output packet count on outgoing interface: 64 bits 765 Same definition as in IPv4. 767 Total number of packets for this source-group pair: 64 bits 768 Same definition as in IPv4, except if the S bit is set (see 769 below), the count is for the source network, as specified by the 770 Src Prefix Len field. If the S bit is set and the Src Prefix Len 771 field is 255, indicating no source-specific state, the count is 772 for all sources sending to this group. This counter should have 773 the same value as ipMcastRoutePkts from the IPMROUTE-STD-MIB [10] 774 for this forwarding entry. 776 Rtg Protocol: 16 bits 777 Same definition as in IPv4. 779 Multicast Rtg Protocol: 16 bits 780 Same definition as in IPv4. 782 MBZ 2: 15 bits 783 This field must be zeroed on transmission and ignored on 784 reception. 786 S: 1 bit 787 Same definition as in IPv4, except the Src Prefix Len field is 788 used to mask the source address. 790 Src Prefix Len: 8 bits 791 This field contains the prefix length this router has for the 792 source. If the router is forwarding solely on group state, this 793 field is set to 255 (0xff). 795 Forwarding Code: 8 bits 796 Same definition as in IPv4. 798 3.2.7. Mtrace2 Augmented Response Block 800 In addition to the Standard Response Block, a multicast router on the 801 traced path can optionally add one or multiple Augmented Response 802 Blocks before sending the Request to its upstream router. 804 The Augmented Response Block is flexible for various purposes such as 805 providing diagnosis information (see Section 7) and protocol 806 verification. It's Type field is 0x05, and its format is as follows: 808 0 1 2 3 809 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 1 810 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 811 | Type | Length | MBZ | 812 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 813 | Augmented Response Type | Value .... | 814 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 816 MBZ: 8 bits 817 This field must be zeroed on transmission and ignored on 818 reception. 820 Augmented Response Type: 16 bits 821 This field specifies the type of various responses from a 822 multicast router that might need to communicate back to the 823 Mtrace2 client as well as the multicast routers on the traced 824 path. 826 The Augmented Response Type is defined as follows: 828 Code Type 829 ==== =============================================== 830 0x01 # of the returned Standard Response Blocks 832 When the NO_SPACE error occurs on a router, the router should send 833 the original Mtrace2 Request received from the downstream router 834 as a Reply back to the Mtrace2 client, and continue with a new 835 Mtrace2 Request. In the new Request, the router would add a 836 Standard Response Block followed by an Augmented Response Block 837 with 0x01 as the Augmented Response Type, and the number of the 838 returned Mtrace2 Standard Response Blocks as the Value. 840 Each upstream router would recognize the total number of hops the 841 Request has been traced so far by adding this number and the 842 number of the Standard Response Block in the current Request 843 message. 845 This document only defines one Augmented Response Type in the 846 Augmented Response Block. The description on how to provide 847 diagnosis information using the Augmented Response Block is out of 848 the scope of this document, and will be addressed in separate 849 documents. 851 Value: variable length 852 The format is based on the Augmented Response Type value. The 853 length of the value field is Length field minus 6. 855 4. Router Behavior 857 This section describes the router behavior in the context of Mtrace2 858 in details. 860 4.1. Receiving Mtrace2 Query 862 An Mtrace2 Query message is an Mtrace2 message with no response 863 blocks filled in, and uses TLV type of 0x01. 865 4.1.1. Query Packet Verification 867 Upon receiving an Mtrace2 Query message, a router MUST examine 868 whether the Multicast Address and the Source Address are a valid 869 combination as specified in Section 3.2.1, and whether the Mtrace2 870 Client Address is a valid IP unicast address. If either one is 871 invalid, the Query MUST be silently ignored. 873 Mtrace2 supports non-local client to the LHR. It is up to the 874 implementation to filter out such queries. 876 In the case when it is a local client, the router must then examine 877 the Query to see if it is the proper LHR for the destination address 878 in the packet. It is the proper LHR if it has a multicast-capable 879 interface on the same subnet as the Mtrace2 Client Address and is the 880 router that would forward traffic from the given (S,G) or (*,G) onto 881 that subnet. 883 If the router determines that it is not the proper LHR, or it cannot 884 make that determination, it does one of two things depending on 885 whether the Query was received via multicast or unicast. If the 886 Query was received via multicast, then it MUST be silently discarded. 887 If it was received via unicast, the router turns the Query into a 888 Reply message by changing the TLV type to 0x03 and appending a 889 Standard Response Block with a Forwarding Code of WRONG_LAST_HOP. 890 The rest of the fields in the Standard Response Block MUST be zeroed. 891 The router then sends the Reply message to the Mtrace2 Client Address 892 on the Client Port # as specified in the Mtrace2 Query. 894 Duplicate Query messages as identified by the tuple (Mtrace2 Client 895 Address, Query ID) SHOULD be ignored. This MAY be implemented using 896 a cache of previously processed queries keyed by the Mtrace2 Client 897 Address and Query ID pair. The duration of the cached entries is 898 implementation specific. Duplicate Request messages MUST NOT be 899 ignored in this manner. 901 4.1.2. Query Normal Processing 903 When a router receives an Mtrace2 Query and it determines that it is 904 the proper LHR, it turns the Query to a Request by changing the TLV 905 type from 0x01 to 0x02, and performs the steps listed in Section 4.2. 907 4.2. Receiving Mtrace2 Request 909 An Mtrace2 Request is an Mtrace2 message that uses TLV type of 0x02. 910 With the exception of the LHR, whose Request was just converted from 911 a Query, each Request received by a router should have at least one 912 Standard Response Block filled in. 914 4.2.1. Request Packet Verification 916 If the Mtrace2 Request does not come from an adjacent router, or if 917 the Request is not addressed to this router, or if the Request is 918 addressed to a multicast group which is not a link-scoped group (i.e. 920 224/24 for IPv4, FFx2::/16 [4] for IPv6), it MUST be silently 921 ignored. GTSM [12] SHOULD be used by the router to determine whether 922 the router is adjacent or not. 924 If the sum of the number of the Standard Response Blocks in the 925 received Mtrace2 Request and the value of the Augmented Response Type 926 of 0x01, if any, is equal or more than the # Hops in the Mtrace2 927 Request, it MUST be silently ignored. 929 4.2.2. Request Normal Processing 931 When a router receives an Mtrace2 Request message, it performs the 932 following steps. Note that it is possible to have multiple 933 situations covered by the Forwarding Codes. The first one 934 encountered is the one that is reported, i.e. all "note Forwarding 935 Code N" should be interpreted as "if Forwarding Code is not already 936 set, set Forwarding Code to N". 938 1. Prepare a Standard Response Block to be appended to the packet 939 and fill in the Query Arrival Time, Outgoing Interface Address 940 (for IPv4) or Outgoing Interface ID (for IPv6), Output Packet 941 Count, and Fwd TTL (for IPv4). Note that the Outgoing Interface 942 is the one on which the Mtrace2 Request message arrives. 944 2. Attempt to determine the forwarding information for the 945 specified source and group, using the same mechanisms as would 946 be used when a packet is received from the source destined for 947 the group. A state need not be instantiated, it can be a 948 "phantom" state created only for the purpose of the trace, such 949 as "dry-run." 951 If using a shared-tree protocol and there is no source-specific 952 state, or if no source-specific information is desired (i.e., 953 all 1's for IPv4 or unspecified address (::) for IPv6), group 954 state should be used. If there is no group state or no group- 955 specific information is desired, potential source state (i.e., 956 the path that would be followed for a source-specific Join) 957 should be used. 959 3. If no forwarding information can be determined, the router notes 960 a Forwarding Code of NO_ROUTE, sets the remaining fields that 961 have not yet been filled in to zero, and then sends an Mtrace2 962 Reply back to the Mtrace2 client. 964 4. Fill in the Incoming Interface Address, Upstream Router Address, 965 Input Packet Count, Total Number of Packets, Routing Protocol, 966 S, and Src Mask (or Src Prefix Len for IPv6) using the 967 forwarding information determined by the step 2. 969 5. If Mtrace2 is administratively prohibited, note the Forwarding 970 Code of ADMIN_PROHIB. If Mtrace2 is administratively prohibited 971 and any of the fields as filled in the step 4 are considered 972 private information, zero out the applicable fields. 974 6. If the Outgoing interface is not enabled for multicast, note 975 Forwarding Code of NO_MULTICAST. If the Outgoing interface is 976 the interface from which the router would expect data to arrive 977 from the source, note forwarding code RPF_IF. If the Outgoing 978 interface is not one to which the router would forward data from 979 the source or RP to the group, a Forwarding code of WRONG_IF is 980 noted. In the above three cases, the router will return an 981 Mtrace2 Reply and terminate the trace. 983 7. If the group is subject to administrative scoping on either the 984 Outgoing or Incoming interfaces, a Forwarding Code of SCOPED is 985 noted. 987 8. If this router is the RP for the group, note a Forwarding Code 988 of REACHED_RP. The router will send an Mtrace2 Reply and 989 terminate the trace. 991 9. If this router has sent a prune upstream which applies to the 992 source and group in the Mtrace2 Request, it notes Forwarding 993 Code of PRUNE_SENT. If the router has stopped forwarding 994 downstream in response to a prune sent by the downstream router, 995 it notes Forwarding Code of PRUNE_RCVD. If the router should 996 normally forward traffic downstream for this source and group 997 but is not, it notes Forwarding Code of NOT_FORWARDING. 999 10. If this router is a gateway (e.g., a NAT or firewall) that hides 1000 the information between this router and the Mtrace2 client, it 1001 notes Forwarding Code of REACHED_GW. The router continues the 1002 processing as described in Section 4.5. 1004 11. If the total number of the Standard Response Blocks, including 1005 the newly prepared one, and the value of the Augmented Response 1006 Type of 0x01, if any, is less than the # Hops in the Request, 1007 the packet is then forwarded to the upstream router as described 1008 in Section 4.3; otherwise, the packet is sent as an Mtrace2 1009 Reply to the Mtrace2 client as described in Section 4.4. 1011 4.3. Forwarding Mtrace2 Request 1013 This section describes how an Mtrace2 Request should be forwarded. 1015 4.3.1. Destination Address 1017 If the upstream router for the Mtrace2 Request is known for this 1018 request, the Mtrace2 Request is sent to that router. If the Incoming 1019 interface is known but the upstream router is not, the Mtrace2 1020 Request is sent to an appropriate multicast address on the Incoming 1021 interface. The multicast address SHOULD depend on the multicast 1022 routing protocol in use, such as ALL-[protocol]-ROUTERS.MCAST.NET. 1023 It MUST be a link-scoped group (i.e. 224/24 for IPv4, FF02::/16 for 1024 IPv6), and MUST NOT be ALL-SYSTEMS.MCAST.NET (224.0.0.1) for IPv4 and 1025 All Nodes Address (FF02::1) for IPv6. It MAY also be ALL- 1026 ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All Routers Address 1027 (FF02::2) for IPv6 if the routing protocol in use does not define a 1028 more appropriate multicast address. 1030 4.3.2. Source Address 1032 An Mtrace2 Request should be sent with the address of the Incoming 1033 interface. However, if the Incoming interface is unnumbered, the 1034 router can use one of its numbered interface address as the source 1035 address. 1037 4.3.3. Appending Standard Response Block 1039 An Mtrace2 Request MUST be sent upstream towards the source or the RP 1040 after appending a Standard Response Block to the end of the received 1041 Mtrace2 Request. The Standard Response Block includes the multicast 1042 states and statistics information of the router described in 1043 Section 3.2.5. 1045 If appending the Standard Response Block would make the Mtrace2 1046 Request packet longer than the MTU of the Incoming Interface, or, in 1047 the case of IPv6, longer than 1280 bytes, the router MUST change the 1048 Forwarding Code in the last Standard Response Block of the received 1049 Mtrace2 Request into NO_SPACE. The router then turns the Request 1050 into a Reply, and sends the Reply as described in Section 4.4. 1052 The router will continue with a new Request by copying from the old 1053 Request excluding all the response blocks, followed by the previously 1054 prepared Standard Response Block, and an Augmented Response Block 1055 with Augmented Response Type of 0x01 and the number of the returned 1056 Standard Response Blocks as the value. The new Request is then 1057 forwarded upstream. 1059 4.4. Sending Mtrace2 Reply 1061 An Mtrace2 Reply MUST be returned to the client by a router if the 1062 total number of the traced routers is equal to the # Hops in the 1063 Request. The total number of the traced routers is the sum of the 1064 Standard Response Blocks in the Request (including the one just 1065 added) and the number of the returned blocks, if any. 1067 4.4.1. Destination Address 1069 An Mtrace2 Reply MUST be sent to the address specified in the Mtrace2 1070 Client Address field in the Mtrace2 Request. 1072 4.4.2. Source Address 1074 An Mtrace2 Reply SHOULD be sent with the address of the router's 1075 Outgoing interface. However, if the Outgoing interface address is 1076 unnumbered, the router can use one of its numbered interface address 1077 as the source address. 1079 4.4.3. Appending Standard Response Block 1081 An Mtrace2 Reply MUST be sent with the prepared Standard Response 1082 Block appended at the end of the received Mtrace2 Request except in 1083 the case of NO_SPACE forwarding code. 1085 4.5. Proxying Mtrace2 Query 1087 When a gateway (e.g., a NAT or firewall), which needs to block 1088 unicast packets to the Mtrace2 client, or hide information between 1089 the gateway and the Mtrace2 client, receives an Mtrace2 Query from an 1090 adjacent host or Mtrace2 Request from an adjacent router, it appends 1091 a Standard Response Block with REACHED_GW as the Forwarding Code, and 1092 turns the Query or Request as a Reply, and sends the Reply back to 1093 the client. 1095 At the same time, the gateway originates a new Mtrace2 Query message 1096 by copying the original Mtrace2 header (the Query or Request without 1097 any of the response blocks), and makes the changes as follows: 1099 o sets the RPF interface's address as the Mtrace2 Client Address; 1101 o uses its own port number as the Client Port #; and, 1103 o decreases # Hops by the number of the Standard Response Block that 1104 was just returned as a Reply. 1106 The new Mtrace2 Query message is then sent to the upstream router or 1107 to an appropriate multicast address on the RPF interface. 1109 When the gateway receives an Mtrace2 Reply whose Query ID matches the 1110 one in the original Mtrace2 header, it MUST relay the Mtrace2 Reply 1111 back to the Mtrace2 client by replacing the Reply's header with the 1112 original Mtrace2 header. If the gateway does not receive the 1113 corresponding Mtrace2 Reply within the [Mtrace Reply Timeout] period 1114 (see Section 5.8.4), then it silently discards the original Mtrace2 1115 Query or Request message, and terminates the trace. 1117 4.6. Hiding Information 1119 Information about a domain's topology and connectivity may be hidden 1120 from the Mtrace2 Requests. The Forwarding Code of INFO_HIDDEN may be 1121 used to note that. For example, the incoming interface address and 1122 packet count on the ingress router of a domain, and the outgoing 1123 interface address and packet count on the egress router of the domain 1124 can be specified as all 1's. Additionally, the source-group packet 1125 count (see Section 3.2.5 and Section 3.2.6) within the domain may be 1126 all 1's if it is hidden. 1128 5. Client Behavior 1130 This section describes the behavior of an Mtrace2 client in details. 1132 5.1. Sending Mtrace2 Query 1134 An Mtrace2 client initiates an Mtrace2 Query by sending the Query to 1135 the LHR of interest. 1137 5.1.1. Destination Address 1139 If an Mtrace2 client knows the proper LHR, it unicasts an Mtrace2 1140 Query packet to that router; otherwise, it MAY send the Mtrace2 Query 1141 packet to the ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All 1142 Routers Address (FF02::2) for IPv6. This will ensure that the packet 1143 is received by the LHR on the subnet. 1145 See also Section 5.4 on determining the LHR. 1147 5.1.2. Source Address 1149 An Mtrace2 Query MUST be sent with the client's interface address, 1150 which would be the Mtrace2 Client Address. 1152 5.2. Determining the Path 1154 An Mtrace2 client could send an initial Query messages with a large # 1155 Hops, in order to try to trace the full path. If this attempt fails, 1156 one strategy is to perform a linear search (as the traditional 1157 unicast traceroute program does); set the # Hops field to 1 and try 1158 to get a Reply, then 2, and so on. If no Reply is received at a 1159 certain hop, the hop count can continue past the non-responding hop, 1160 in the hopes that further hops may respond. These attempts should 1161 continue until the [Mtrace Reply Timeout] timeout has occurred. 1163 See also Section 5.6 on receiving the results of a trace. 1165 5.3. Collecting Statistics 1167 After a client has determined that it has traced the whole path or as 1168 much as it can expect to (see Section 5.8), it might collect 1169 statistics by waiting a short time and performing a second trace. If 1170 the path is the same in the two traces, statistics can be displayed 1171 as described in Section 7.3 and Section 7.4. 1173 5.4. Last Hop Router (LHR) 1175 The Mtrace2 client may not know which is the last-hop router, or that 1176 router may be behind a firewall that blocks unicast packets but 1177 passes multicast packets. In these cases, the Mtrace2 Request should 1178 be multicasted to ALL-ROUTERS.MCAST.NET (224.0.0.2) for IPv4 or All 1179 Routers Address (FF02::2) for IPv6. All routers except the correct 1180 last-hop router SHOULD ignore any Mtrace2 Request received via 1181 multicast. 1183 5.5. First Hop Router (FHR) 1185 The IANA assigned 224.0.1.32, MTRACE.MCAST.NET as the default 1186 multicast group for old IPv4 mtrace (v1) responses, in order to 1187 support mtrace clients that are not unicast reachable from the first- 1188 hop router. Mtrace2, however, does not require any IPv4/IPv6 1189 multicast addresses for the Mtrace2 Replies. Every Mtrace2 Reply is 1190 sent to the unicast address specified in the Mtrace2 Client Address 1191 field of the Mtrace2 Reply. 1193 5.6. Broken Intermediate Router 1195 A broken intermediate router might simply not understand Mtrace2 1196 packets, and drop them. The Mtrace2 client will get no Reply at all 1197 as a result. It should then perform a hop-by-hop search by setting 1198 the # Hops field until it gets an Mtrace2 Reply. The client may use 1199 linear or binary search; however, the latter is likely to be slower 1200 because a failure requires waiting for the [Mtrace Reply Timeout] 1201 period. 1203 5.7. Non-Supported Router 1205 When a non-supported router receives an Mtrace2 Query or Request 1206 message whose destination address is a multicast address, the router 1207 will silently discard the message. 1209 When the router receives an Mtrace2 Query which is destined to 1210 itself, the router would return an ICMP port unreachable to the 1211 Mtrace2 client. On the other hand, when the router receives an 1212 Mtrace2 Request which is destined to itself, the router would return 1213 an ICMP port unreachable to its adjacent router from which the 1214 Request receives. Therefore, the Mtrace2 client needs to terminate 1215 the trace when the [Mtrace Reply Timeout] timeout has occurred, and 1216 may then issue another Query with a lower number of # Hops. 1218 5.8. Mtrace2 Termination 1220 When performing an expanding hop-by-hop trace, it is necessary to 1221 determine when to stop expanding. 1223 5.8.1. Arriving at Source 1225 A trace can be determined to have arrived at the source if the 1226 Incoming Interface of the last router in the trace is non-zero, but 1227 the Upstream Router is zero. 1229 5.8.2. Fatal Error 1231 A trace has encountered a fatal error if the last Forwarding Error in 1232 the trace has the 0x80 bit set. 1234 5.8.3. No Upstream Router 1236 A trace can not continue if the last Upstream Router in the trace is 1237 set to 0. 1239 5.8.4. Reply Timeout 1241 This document defines the [Mtrace Reply Timeout] value, which is used 1242 to time out an Mtrace2 Reply as seen in Section 4.5, Section 5.2, and 1243 Section 5.7. The default [Mtrace Reply Timeout] value is 10 1244 (seconds), and can be manually changed on the Mtrace2 client and 1245 routers. 1247 5.9. Continuing after an Error 1249 When the NO_SPACE error occurs, as described in Section 4.2, a router 1250 will send back an Mtrace2 Reply to the Mtrace2 client, and continue 1251 with a new Request (see Section 4.3.3). In which case, the Mtrace2 1252 client may receive multiple Mtrace2 Replies from different routers 1253 along the path. When this happens, the client MUST treat them as a 1254 single Mtrace2 Reply message. 1256 If a trace times out, it is very likely that a router in the middle 1257 of the path does not support Mtrace2. That router's address will be 1258 in the Upstream Router field of the last Standard Response Block in 1259 the last received Reply. A client may be able to determine (via 1260 mrinfo or SNMP [11][10]) a list of neighbors of the non-responding 1261 router. If desired, each of those neighbors could be probed to 1262 determine the remainder of the path. Unfortunately, this heuristic 1263 may end up with multiple paths, since there is no way of knowing what 1264 the non-responding router's algorithm for choosing an upstream router 1265 is. However, if all paths but one flow back towards the non- 1266 responding router, it is possible to be sure that this is the correct 1267 path. 1269 6. Protocol-Specific Considerations 1271 This section describes the Mtrace2 behavior with the present of 1272 different multicast protocols. 1274 6.1. PIM-SM 1276 When an Mtrace2 reaches a PIM-SM RP, and the RP does not forward the 1277 trace on, it means that the RP has not performed a source-specific 1278 join so there is no more state to trace. However, the path that 1279 traffic would use if the RP did perform a source-specific join can be 1280 traced by setting the trace destination to the RP, the trace source 1281 to the traffic source, and the trace group to 0. This Mtrace2 Query 1282 may be unicasted to the RP. 1284 6.2. Bi-Directional PIM 1286 Bi-directional PIM [5] is a variant of PIM-SM that builds bi- 1287 directional shared trees connecting multicast sources and receivers. 1288 Along the bi-directional shared trees, multicast data is natively 1289 forwarded from the sources to the Rendezvous Point Link (RPL), and 1290 from which, to receivers without requiring source-specific state. In 1291 contrast to PIM-SM, Bi-directional PIM always has the state to trace. 1293 A Designated Forwarder (DF) for a given Rendezvous Point Address 1294 (RPA) is in charge of forwarding downstream traffic onto its link, 1295 and forwarding upstream traffic from its link towards the RPL that 1296 the RPA belongs to. Hence Mtrace2 Reply reports DF addresses or RPA 1297 along the path. 1299 6.3. PIM-DM 1301 Routers running PIM Dense Mode [13] do not know the path packets 1302 would take unless traffic is flowing. Without some extra protocol 1303 mechanism, this means that in an environment with multiple possible 1304 paths with branch points on shared media, Mtrace2 can only trace 1305 existing paths, not potential paths. When there are multiple 1306 possible paths but the branch points are not on shared media, the 1307 upstream router is known, but the LHR may not know that it is the 1308 appropriate last hop. 1310 When traffic is flowing, PIM Dense Mode routers know whether or not 1311 they are the LHR for the link (because they won or lost an Assert 1312 battle) and know who the upstream router is (because it won an Assert 1313 battle). Therefore, Mtrace2 is always able to follow the proper path 1314 when traffic is flowing. 1316 6.4. IGMP/MLD Proxy 1318 When an IGMP/MLD Proxy [6] receives an Mtrace2 Query packet on an 1319 incoming interface, it notes a WRONG_IF in the Forwarding Code of the 1320 last Standard Response Block (see Section 3.2.5), and sends the 1321 Mtrace2 Reply back to the Mtrace2 client. On the other hand, when an 1322 Mtrace2 Query packet reaches an outgoing interface of the IGMP/MLD 1323 proxy, it is forwarded onto its incoming interface towards the 1324 upstream router. 1326 7. Problem Diagnosis 1328 This section describes different scenarios Mtrace2 can be used to 1329 diagnose the multicast problems. 1331 7.1. Forwarding Inconsistencies 1333 The Forwarding Error code can tell if a group is unexpectedly pruned 1334 or administratively scoped. 1336 7.2. TTL or Hop Limit Problems 1338 By taking the maximum of hops from the source and forwarding TTL 1339 threshold over all hops, it is possible to discover the TTL or hop 1340 limit required for the source to reach the destination. 1342 7.3. Packet Loss 1344 By taking two traces, it is possible to find packet loss information 1345 by comparing the difference in input packet counts to the difference 1346 in output packet counts for the specified source-group address pair 1347 at the previous hop. On a point-to-point link, any difference in 1348 these numbers implies packet loss. Since the packet counts may be 1349 changing as the Mtrace2 Request is propagating, there may be small 1350 errors (off by 1 or 2 or more) in these statistics. However, these 1351 errors will not accumulate if multiple traces are taken to expand the 1352 measurement period. On a shared link, the count of input packets can 1353 be larger than the number of output packets at the previous hop, due 1354 to other routers or hosts on the link injecting packets. This 1355 appears as "negative loss" which may mask real packet loss. 1357 In addition to the counts of input and output packets for all 1358 multicast traffic on the interfaces, the Standard Response Block 1359 includes a count of the packets forwarded by a node for the specified 1360 source-group pair. Taking the difference in this count between two 1361 traces and then comparing those differences between two hops gives a 1362 measure of packet loss just for traffic from the specified source to 1363 the specified receiver via the specified group. This measure is not 1364 affected by shared links. 1366 On a point-to-point link that is a multicast tunnel, packet loss is 1367 usually due to congestion in unicast routers along the path of that 1368 tunnel. On native multicast links, loss is more likely in the output 1369 queue of one hop, perhaps due to priority dropping, or in the input 1370 queue at the next hop. The counters in the Standard Response Block 1371 do not allow these cases to be distinguished. Differences in packet 1372 counts between the incoming and outgoing interfaces on one node 1373 cannot generally be used to measure queue overflow in the node. 1375 7.4. Link Utilization 1377 Again, with two traces, you can divide the difference in the input or 1378 output packet counts at some hop by the difference in time stamps 1379 from the same hop to obtain the packet rate over the link. If the 1380 average packet size is known, then the link utilization can also be 1381 estimated to see whether packet loss may be due to the rate limit or 1382 the physical capacity on a particular link being exceeded. 1384 7.5. Time Delay 1386 If the routers have synchronized clocks, it is possible to estimate 1387 propagation and queuing delay from the differences between the 1388 timestamps at successive hops. However, this delay includes control 1389 processing overhead, so is not necessarily indicative of the delay 1390 that data traffic would experience. 1392 8. IANA Considerations 1394 The following new assignments can only be made via a Standards Action 1395 as specified in [7]. 1397 8.1. Forwarding Codes 1399 New Forwarding Codes must only be created by an RFC that modifies 1400 this document's Section 3.2.5 and Section 3.2.6, fully describing the 1401 conditions under which the new Forwarding Code is used. The IANA may 1402 act as a central repository so that there is a single place to look 1403 up Forwarding Codes and the document in which they are defined. 1405 8.2. UDP Destination Port 1407 The IANA should allocate UDP destination port for Mtrace2 upon 1408 publication of the first RFC. 1410 9. Security Considerations 1412 This section addresses some of the security considerations related to 1413 Mtrace2. 1415 9.1. Addresses in Mtrace2 Header 1417 An Mtrace2 header includes three addresses, source address, multicast 1418 address, and Mtrace2 client address. These addresses MUST be 1419 congruent with the definition defined in Section 3.2.1 and forwarding 1420 Mtrace2 messages having invalid addresses MUST be prohibited. For 1421 instance, if Mtrace2 Client Address specified in an Mtrace header is 1422 a multicast address, then a router that receives the Mtrace2 message 1423 MUST silently discard it. 1425 9.2. Topology Discovery 1427 Mtrace2 can be used to discover any actively-used topology. If your 1428 network topology is a secret, Mtrace2 may be restricted at the border 1429 of your domain, using the ADMIN_PROHIB forwarding code. 1431 9.3. Characteristics of Multicast Channel 1433 Mtrace2 can be used to discover what sources are sending to what 1434 groups and at what rates. If this information is a secret, Mtrace2 1435 may be restricted at the border of your domain, using the 1436 ADMIN_PROHIB forwarding code. 1438 9.4. Limiting Query/Request Rates 1440 A router may limit Mtrace2 Queries and Requests by ignoring some of 1441 the consecutive messages. The router MAY randomly ignore the 1442 received messages to minimize the processing overhead, i.e., to keep 1443 fairness in processing queries, or prevent traffic amplification. 1444 The rate limit is left to the router's implementation. 1446 9.5. Limiting Reply Rates 1448 The proxying and NO_SPACE behaviors may result in one Query returning 1449 multiple Reply messages. In order to prevent abuse, the routers in 1450 the traced MAY need to rate-limit the Replies. The rate limit 1451 function is left to the router's implementation. 1453 10. Acknowledgements 1455 This specification started largely as a transcription of Van 1456 Jacobson's slides from the 30th IETF, and the implementation in 1457 mrouted 3.3 by Ajit Thyagarajan. Van's original slides credit Steve 1458 Casner, Steve Deering, Dino Farinacci and Deb Agrawal. The original 1459 multicast traceroute client, mtrace (version 1), has been implemented 1460 by Ajit Thyagarajan, Steve Casner and Bill Fenner. The idea of the 1461 "S" bit to allow statistics for a source subnet is due to Tom 1462 Pusateri. 1464 For the Mtrace version 2 specification, the authors would like to 1465 give special thanks to Tatsuya Jinmei, Bill Fenner, and Steve Casner. 1466 Also, extensive comments were received from David L. Black, Ronald 1467 Bonica, Yiqun Cai, Liu Hui, Bharat Joshi, Robert W. Kebler, Heidi Ou, 1468 Pekka Savola, Shinsuke Suzuki, Dave Thaler, Achmad Husni Thamrin, and 1469 Cao Wei. 1471 11. References 1473 11.1. Normative References 1475 [1] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas, 1476 "Protocol Independent Multicast - Sparse Mode (PIM-SM): 1477 Protocol Specification (Revised)", RFC 4601, August 2006. 1479 [2] Bradner, S., "Key words for use in RFCs to indicate requirement 1480 levels", RFC 2119, March 1997. 1482 [3] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) 1483 Specification", RFC 2460, December 1998. 1485 [4] Hinden, R. and S. Deering, "IP Version 6 Addressing 1486 Architecture", RFC 4291, February 2006. 1488 [5] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano, 1489 "Bidirectional Protocol Independent Multicast (BIDIR-PIM)", 1490 RFC 5015, October 2007. 1492 [6] Fenner, B., He, H., Haberman, B., and H. Sandick, "Internet 1493 Group Management Protocol (IGMP) / Multicast Listener Discovery 1494 (MLD)-Based Multicast Forwarding ("IGMP/MLD Proxying")", 1495 RFC 4605, August 2006. 1497 [7] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA 1498 Considerations Section in RFCs", RFC 5226, May 2008. 1500 11.2. Informative References 1502 [8] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A. 1503 Thyagarajan, "Internet Group Management Protocol, Version 3", 1504 RFC 3376, October 2002. 1506 [9] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB", 1507 RFC 2863, June 2000. 1509 [10] McWalter, D., Thaler, D., and A. Kessler, "IP Multicast MIB", 1510 RFC 5132, December 2007. 1512 [11] Draves, R. and D. Thaler, "Default Router Preferences and More- 1513 Specific Routes", RFC 4191, November 2005. 1515 [12] Gill, V., Heasley, J., Meyer, D., Savola, P., and C. Pignataro, 1516 "The Generalized TTL Security Mechanism (GTSM)", RFC 5082, 1517 October 2007. 1519 [13] Adams, A., Nicholas, J., and W. Siadak, "Protocol Independent 1520 Multicast - Dense Mode (PIM-DM): Protocol Specification 1521 (Revised)", RFC 3973, January 2005. 1523 Authors' Addresses 1525 Hitoshi Asaeda 1526 National Institute of Information and Communications Technology 1527 4-2-1 Nukui-Kitamachi 1528 Koganei, Tokyo 184-8795 1529 Japan 1531 Email: asaeda@nict.go.jp 1533 WeeSan Lee (editor) 1534 Juniper Networks, Inc. 1535 1194 North Mathilda Avenue 1536 Sunnyvale, CA 94089-1206 1537 US 1539 Email: weesan@juniper.net