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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'SA-State-Period' is mentioned on line 191, but not defined == Missing Reference: 'SA-Hold-Down-Period' is mentioned on line 199, but not defined == Missing Reference: 'KeepAlive-Period' is mentioned on line 212, but not defined == Missing Reference: 'ConnectRetry-Period' is mentioned on line 223, but not defined == Missing Reference: 'Hold-Time-Period' is mentioned on line 236, but not defined == Missing Reference: 'MSDP-GRE-ProtocolType' is mentioned on line 894, but not defined == Outdated reference: draft-meyer-gre-update has been published as RFC 2784 ** Obsolete normative reference: RFC 1771 (Obsoleted by RFC 4271) ** Obsolete normative reference: RFC 1825 (Obsoleted by RFC 2401) ** Downref: Normative reference to an Historic RFC: RFC 1828 ** Obsolete normative reference: RFC 2283 (Obsoleted by RFC 2858) ** Obsolete normative reference: RFC 2362 (Obsoleted by RFC 4601, RFC 5059) Summary: 14 errors (**), 0 flaws (~~), 13 warnings (==), 2 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group Dino Farinacci 3 INTERNET DRAFT Procket Networks 4 Yakov Rekhter 5 David Meyer 6 Cisco Systems 7 Peter Lothberg 8 Sprint 9 Hank Kilmer 10 Jeremy Hall 11 UUnet 12 Category Standards Track 13 February, 2000 15 Multicast Source Discovery Protocol (MSDP) 16 18 1. Status of this Memo 20 This document is an Internet-Draft and is in full conformance with 21 all provisions of Section 10 of RFC 2026. 23 Internet Drafts are working documents of the Internet Engineering 24 Task Force (IETF), its areas, and its working groups. Note that other 25 groups may also distribute working documents as Internet-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 2. Abstract 40 The Multicast Source Discovery Protocol, MSDP, describes a mechanism 41 to connect multiple PIM-SM domains together. Each PIM-SM domain uses 42 its own independent RP(s) and does not have to depend on RPs in other 43 domains. 45 3. Copyright Notice 47 Copyright (C) The Internet Society (2000). All Rights Reserved. 49 4. Introduction 51 The Multicast Source Discovery Protocol, MSDP, describes a mechanism 52 to connect multiple PIM-SM domains together. Each PIM-SM domain uses 53 its own independent RP(s) and does not have to depend on RPs in other 54 domains. Advantages of this approach include: 56 o No Third-party resource dependencies on RP 58 PIM-SM domains can rely on their own RPs only. 60 o Receiver only Domains 62 Domains with only receivers get data without globally 63 advertising group membership. 65 o Global Source State 67 Global source state is not required, since a router need not 68 cache Source Active (SA) messages (see below). MSDP is a 69 periodic protocol. 71 The keywords MUST, MUST NOT, MAY, OPTIONAL, REQUIRED, RECOMMENDED, 72 SHALL, SHALL NOT, SHOULD, SHOULD NOT are to be interpreted as defined 73 in RFC 2119 [RFC2119]. 75 5. Overview 77 An RP (or other MSDP SA originator) in a PIM-SM [RFC2362] domain will 78 have a MSDP peering relationship with MSDP peers in another domain. 79 The peering relationship will be made up of a TCP connection in which 80 control information is exchanged. Each domain will have one or more 81 connections to this virtual topology. 83 The purpose of this topology is to have domains discover multicast 84 sources from other domains. If the multicast sources are of interest 85 to a domain which has receivers, the normal source-tree building 86 mechanism in PIM-SM will be used to deliver multicast data over an 87 inter-domain distribution tree. 89 We envision this virtual topology will essentially be congruent to 90 the existing BGP topology used in the unicast-based Internet today. 91 That is, the TCP connections between MSDP peers can be realized by 92 the underlying BGP routing system. 94 6. Procedure 96 A source in a PIM-SM domain originates traffic to a multicast group. 97 The PIM DR which is directly connected to the source sends the data 98 encapsulated in a PIM Register message to the RP in the domain. 100 The RP will construct a "Source-Active" (SA) message and send it to 101 its MSDP peers. The SA message contains the following fields: 103 o Source address of the data source. 104 o Group address the data source sends to. 105 o IP address of the RP. 107 Each MSDP peer receives and forwards the message away from the RP 108 address in a "peer-RPF flooding" fashion. The notion of peer-RPF 109 flooding is with respect to forwarding SA messages. The BGP routing 110 table is examined to determine which peer is the NEXT_HOP towards the 111 originating RP of the SA message. Such a peer is called an "RPF 112 peer". See section 14 below for the details of peer-RPF forwarding. 114 If the MSDP peer receives the SA from a non-RPF peer towards the 115 originating RP, it will drop the message. Otherwise, it forwards the 116 message to all its MSDP peers. 118 The flooding can be further constrained to children of the peer by 119 interrogating BGP reachability information. That is, if a BGP peer 120 advertises a route (back to you) and you are the next to last AS in 121 the AS_PATH, the peer is using you as the NEXT_HOP. This is known in 122 other circles as Split-Horizon with Poison Reverse. An implementation 123 SHOULD NOT forward SA messages (which were originated from the RP 124 address covered by a route) to peers which have not Poison Reversed 125 that route. 127 When an MSDP peer which is also an RP for its own domain receives a 128 new SA message, it determines if it has any group members interested 129 in the group which the SA message describes. That is, the RP checks 130 for a (*,G) entry with a non-empty outgoing interface list; this 131 implies that the domain is interested in the group. In this case, the 132 RP triggers a (S,G) join event towards the data source as if a 133 Join/Prune message was received addressed to the RP itself (See 134 [RFC2362] Section 3.2.2). This sets up a branch of the source-tree to 135 this domain. Subsequent data packets arrive at the RP which are 136 forwarded down the shared-tree inside the domain. If leaf routers 137 choose to join the source-tree they have the option to do so 138 according to existing PIM-SM conventions. Finally, if an RP in a 139 domain receives a PIM Join message for a new group G, and it is 140 caching SAs, then the RP should trigger a (S,G) join event for each 141 SA for that group in its cache. 143 This procedure has been affectionately named flood-and-join because 144 if any RP is not interested in the group, they can ignore the SA 145 message. Otherwise, they join a distribution tree. 147 7. Controlling State 149 While RPs which receive SA messages are not required to keep MSDP 150 (S,G) state, an RP SHOULD cache SA messages by default. The advantage 151 of caching is that newly formed MSDP peers can get MSDP (S,G) state 152 sooner and therefore reduce join latency for new joiners. In 153 addition, caching greatly aids in diagnosis and debugging of various 154 problems. 156 8. Timers 158 The main timers for MSDP are: SA-Advertisement-Timer, SA-Hold-Down- 159 Timer, SA Cache Entry timer, KeepAlive timer, and ConnectRetry and 160 Peer Hold Timer. Each is considered below. 162 8.1. SA-Advertisement-Timer 164 RPs which originate SA messages do it periodically as long as there 165 is data being sent by the source. There is one SA-Advertisement-Timer 166 covering the sources that an RP may advertise. [SA-Advertisement- 167 Period] MUST be 60 seconds. An RP will not send more than one 168 periodic SA message for a given (S,G) within an SA Advertisement 169 interval. Originating periodic SA messages is important so that new 170 receivers who join after a source has been active can get data 171 quickly via the receiver's own RP when it is not caching SA state. 172 Finally, an originating RP SHOULD trigger the transmission of an SA 173 message as soon as it receives data from an internal source for the 174 first time. 176 8.2. SA-Advertisement-Timer Processing 178 An RP starts the SA-Advertisement-Timer when the MSDP process is 179 configured. When the timer expires, an RP advertises any candidate 180 internal sources to its peers and resets the timer to [SA- 181 Advertisement-Period] seconds. The timer is deleted when the MSDP 182 process is deconfigured. Note that a caching implementation may also 183 wish to check the SA-Cache on this timer event. 185 8.3. SA Cache Timeout (SA-State-Timer) 187 Each entry in an SA Cache has an associated SA-State-Timer. A 188 (S,G)-SA-State-Timer is started when an (S,G)-SA message is initially 189 received by a caching MSDP peer. The timer is reset to [SA-State- 190 Period] if another (S,G)-SA message is received before the (S,G)-SA- 191 State-Timer expires. [SA-State-Period] MUST NOT be less than 90 192 seconds. 194 8.4. SA-Hold-Down-Timer 196 A caching MSDP peer SHOULD NOT forward an SA message it has received 197 in during the previous [SA-Hold-Down-Period] seconds. [SA-Hold-Down- 198 Period] SHOULD be set to 30 seconds. The per-SA message timer is set 199 to [SA-Hold-Down-Period] when forwarding an (S,G)-SA message, and a 200 (S,G)-SA message MUST only forwarded when it's associated timer is 201 not running. Finally, the timer is deleted when the (S,G)-SA cache 202 entry is deleted. 204 8.5. KeepAlive Timer 206 The KeepAlive timer is used by the active connect side of the MSDP 207 connection to track the state of the passive-connect side of the 208 connection. In particular, the KeepAlive timer is used to reset the 209 TCP connection when the passive-connect side of the connection goes 210 down. The KeepAlive timer is set to [KeepAlive-Period] when passive- 211 connect peer comes up. [KeepAlive-Period] SHOULD NOT be less that 75 212 seconds. The timer is reset to [KeepAlive-Period] upon receipt of 213 data from peer, and deleted when the timer expires or the passive- 214 connect peer closes the connection. 216 8.6. ConnectRetry Timer 218 The ConnectRetry timer is used by an MSDP peer to transition from 219 INACTIVE to CONNECTING states. There is one timer per peer, and the 220 [ConnectRetry-Period] SHOULD be set to 30 seconds. The timer is 221 initialized to [ConnectRetry-Period] when an MSDP peer's active 222 connect attempt fails. When the timer expires, the peer retries the 223 connection and the timer is reset to [ConnectRetry-Period]. It is 224 deleted if either the connection transitions into ESTABLISHED state 225 or the peer is deconfigured. 227 8.7. Peer Hold Timer 229 If a system does not receive successive KeepAlive messages (or any SA 230 message) within the period specified by the Hold Timer, then a 231 Notification message with Hold Timer Expired Error Code MUST be sent 232 and the MSDP connection MUST be closed. [Hold-Time-Period] MUST be at 233 least three seconds. A suggested value for [Hold-Time-Period] is 90 234 seconds. 236 The Hold Timer is initialized to [Hold-Time-Period] when the peer's 237 transport connection is established, and is reset to [Hold-Time- 238 Period] when either a KeepAlive or any SA message is received. 240 9. Intermediate MSDP Peers 242 Intermediate RPs do not originate periodic SA messages on behalf of 243 sources in other domains. In general, an RP MUST only originate an SA 244 for its own sources. 246 10. SA Filtering and Policy 248 As the number of (S,G) pairs increases in the Internet, an RP may 249 want to filter which sources it describes in SA messages. Also, 250 filtering may be used as a matter of policy which at the same time 251 can reduce state. Only the RP co-located in the same domain as the 252 source can restrict SA messages. Note, however, that MSDP peers in 253 transit domains should not filter SA messages or the flood-and-join 254 model can not guarantee that sources will be known throughout the 255 Internet (i.e., SA filtering by transit domains can cause undesired 256 lack of connectivity). In general, policy should be expressed using 257 MBGP [RFC2283]. This will cause MSDP messages will flow in the 258 desired direction and peer-RPF fail otherwise. An exception occurs at 259 an administrative scope [RFC2365] boundary. In particular, a SA 260 message for a (S,G) MUST NOT be sent to peers which are on the other 261 side of an administrative scope boundary for G. 263 11. SA Requests 265 If an MSDP peer decides to cache SA state, it MAY accept SA-Requests 266 from other MSDP peers. When an MSDP peer receives an SA-Request for a 267 group range, it will respond to the peer with a set of SA entries, in 268 an SA-Response message, for all active sources sending to the group 269 range requested in the SA-Request message. The peer that sends the 270 request will not flood the responding SA-Response message to other 271 peers. See section 17 for discussion of error handling relating to SA 272 requests and responses. 274 12. Encapsulated Data Packets 276 For bursty sources, the RP may encapsulate multicast data from the 277 source. An interested RP may decapsulate the packet, which SHOULD be 278 forwarded as if a PIM register encapsulated packet was received. That 279 is, if packets are already arriving over the interface toward the 280 source, then the packet is dropped. Otherwise, if the outgoing 281 interface list is non-null, the packet is forwarded appropriately. 282 Note that when doing data encapsulation, an implementation MUST bound 283 the time during which packets are encapsulated. 285 This allows for small bursts to be received before the multicast tree 286 is built back toward the source's domain. For example, an 287 implementation SHOULD encapsulate at least the first packet to 288 provide service to bursty sources. 290 13. Other Scenarios 292 MSDP is not limited to deployment across different routing domains. 293 It can be used within a routing domain when it is desired to deploy 294 multiple RPs for the same group ranges. As long as all RPs have a 295 interconnected MSDP topology, each can learn about active sources as 296 well as RPs in other domains. 298 14. MSDP Peer-RPF Forwarding 300 The MSDP Peer-RPF Forwarding rules are used for forwarding SA 301 messages throughout an MSDP enabled internet. Unlike the RPF check 302 used when forwarding data packets, the Peer-RPF check is against the 303 RP address carried in the SA message. 305 14.1. Peer-RPF Forwarding Rules 307 An SA message originated by an MSDP originator R and received by a 308 MSDP router from MSDP peer N is accepted if N is the appropriate RPF 309 neighbor for originator R, and discarded otherwise. 311 The RPF neighbor is chosen using the first of the following rules 312 that matches: 314 (i). R is the RPF neighbor if we have an MSDP peering with R. 316 (ii). The external MBGP neighbor towards which we are 317 poison-reversing the MBGP route towards R is the RPF neighbor 318 if we have an MSDP peering with it. 320 (iii). If we have any MSDP peerings with neighbors in the first 321 AS along the AS_PATH (the AS from which we learned this 322 route), but no external MBGP peerings with them, 323 pick one via a deterministic rule. 325 (vi). The internal MBGP advertiser of the router towards R is 326 the RPF neighbor if we have an MSDP peering with it. 328 (v). If none of the above match, and we have an MSDP 329 default-peer configured, the MSDP default-peer is 330 the RPF neighbor. 332 14.2. MSDP default-peer semantics 334 An MSDP default-peer is much like a default route. It is intended to 335 be used in those cases where a stub network isn't running BGP or 336 MBGP. An MSDP peer configured with a default-peer accepts all SA 337 messages from the default-peer. Note that a router running BGP or 338 MBGP SHOULD NOT allow configuration of default peers, since this 339 allows the possibility for SA looping or black-holes to occur. 341 15. MSDP Connection Establishment 343 MSDP messages will be encapsulated in a TCP connection. An MSDP peer 344 listens for new TCP connections on port 639. One side of the MSDP 345 peering relationship will listen on the well-known port and the other 346 side will do an active connect on the well-known port. The side with 347 the higher peer IP address will do the listen. This connection 348 establishment algorithm avoids call collision. Therefore, there is no 349 need for a call collision procedure. It should be noted, however, 350 that the disadvantage of this approach is that it may result in 351 longer startup times at the passive end. 353 An MSDP peer starts in the INACTIVE state. MSDP peers establish 354 peering sessions according to the following state machine: 356 De-configured or 357 disabled 358 +-------------------------------------------+ 359 | | 360 | | 361 Enable | 362 +-----|--------->+----------+ | 363 | | +->| INACTIVE |----------------+ | 364 | | | +----------+ | | 365 Deconf'ed | | | /|\ /|\ | | Lower Address 366 or | | | | | | | 367 disabled | | | | | \|/ | 368 | | | | | | +-------------+ 369 | | | | | +---------------| CONNECTING | 370 | | | | | Timeout or +-------------+ 371 | | | | | Local Address Change | 372 \|/ \|/ | | | | 373 +----------+ | | | | 374 | DISABLED | | | +---------------------+ | TCP Established 375 +----------+ | | | | 376 /|\ /|\ | | Connection Timeout, | | 377 | | | | Local Address change, | | 378 | | | | Authorization Failure | | 379 | | | | | | 380 | | | | | \|/ 381 | | | | +-------------+ 382 | | Local | | | ESTABLISHED | 383 | | Address | | Higher Address +-------------+ 384 | | Change | \|/ /|\ | 385 | | | +--------+ | | 386 | | +--| LISTEN |--------------------+ | 387 | | +--------+ TCP Accept | 388 | | | | 389 | | | | 390 | +---------------+ | 391 | De-configured or | 392 | disabled | 393 | | 394 +------------------------------------------------------+ 395 De-configured or 396 disabled 398 16. Packet Formats 400 MSDP messages will be encoded in TLV format. If an implementation 401 receives a TLV that has length that is longer than expected, the TLV 402 SHOULD be accepted. Any additional data SHOULD be ignored. 404 16.1. MSDP TLV format: 406 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 1 407 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 408 | Type | Length | Value .... | 409 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 411 Type (8 bits) 412 Describes the format of the Value field. 414 Length (16 bits) 415 Length of Type, Length, and Value fields in octets. The 416 minimum length required is 4 octets. 418 Value (variable length) 419 Format is based on the Type value. See below. The length of 420 the value field is Length field minus 3. All reserved fields 421 in the Value field MUST be transmitted as zeros and ignored on 422 receipt. 424 16.2. Defined TLVs 426 The following TLV Types are defined: 428 Code Type 429 =========================================================== 430 1 IPv4 Source-Active 431 2 IPv4 Source-Active Request 432 3 IPv4 Source-Active Response 433 4 KeepAlive 434 5 Notification 436 Each TLV is described below. 438 16.2.1. IPv4 Source-Active TLV 440 The maximum size SA message that can be sent is 1400 octets. If an 441 MSDP peer needs to originate a message with information greater than 442 1400 octets, it sends successive 1400-octet messages. The 1400 octet 443 size does not include the TCP, IP, layer-2 headers. 445 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 1 446 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 447 | 1 | x + y | Entry Count | 448 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 449 | RP Address | 450 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 451 | Reserved | Sprefix Len | \ 452 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ \ 453 | Group Address | ) z 454 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ / 455 | Source Address | / 456 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 458 Type 459 IPv4 Source-Active TLV is type 1. 461 Length x 462 Is the length of the control information in the message. x is 463 8 octets (for the first two 32-bit quantities) plus 12 times 464 Entry Count octets. 466 Length y 467 If 0, then there is no data encapsulated. Otherwise an IPv4 468 packet follows and y is the length of the total length field 469 of the IPv4 header encapsulated. If there are multiple SA TLVs 470 in a message, and data is also included, y must be 0 in all SA 471 TLVs except the last one. And the last SA TLV must reflect the 472 source and destination addresses in the IP header of the 473 encapsulated data. 475 Entry Count 476 Is the count of z entries (note above) which follow the RP 477 address field. This is so multiple (S,G)s from the same domain 478 can be encoded efficiently for the same RP address. 480 RP Address 481 The address of the RP in the domain the source has become 482 active in. 484 Reserved 485 The Reserved field MUST be transmitted as zeros and ignored 486 by a receiver. 488 Sprefix Len 489 The route prefix length associated with source address. 490 This field MUST be transmitted as 32 (/32). An Invalid 491 Sprefix Len Notification SHOULD be sent upon receipt 492 of any other value. 494 Group Address 495 The group address the active source has sent data to. 497 Source Address 498 The IP address of the active source. 500 Multiple SA TLVs MAY appear in the same message and can be batched 501 for efficiency at the expense of data latency. This would typically 502 occur on intermediate forwarding of SA messages. 504 16.2.2. IPv4 Source-Active Request TLV 506 The Source-Active Request is used to request SA-state from a caching 507 MSDP peer. If an RP in a domain receives a PIM Join message for a 508 group, creates (*,G) state and wants to know all active sources for 509 group G, and it has been configured to peer with an SA-state caching 510 peer, it may send an SA-Request message for the group. 512 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 1 513 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 514 | 2 | 8 | Gprefix Len | 515 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 516 | Group Address Prefix | 517 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 519 Type 520 IPv4 Source-Active Request TLV is type 2. 522 Gprefix Len 523 The route prefix length associated with the group address prefix. 525 Group Address 526 The group address the MSDP peer is requesting. 528 16.2.3. IPv4 Source-Active Response TLV 530 The Source-Active Response is sent in response to a Source-Active 531 Request message. The Source-Active Response message has the same 532 format as a Source-Active message but does not allow encapsulation of 533 multicast data. 535 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 1 536 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 537 | 3 | x | .... | 538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 540 Type 541 IPv4 Source-Active Response TLV is type 3. 543 Length x 544 Is the length of the control information in the message. x is 8 545 octets (for the first two 32-bit quantities) plus 12 times Entry 546 Count octets. 548 16.2.4. KeepAlive TLV 550 A KeepAlive TLV is sent to an MSDP peer if and only if there were no 551 MSDP messages sent to the peer after a period of time. This message 552 is necessary for the active connect side of the MSDP connection. The 553 passive connect side of the connection knows that the connection will 554 be reestablished when a TCP SYN packet is sent from the active 555 connect side. However, the active connect side will not know when the 556 passive connect side goes down. Therefore, the KeepAlive timeout will 557 be used to reset the TCP connection. 559 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 1 560 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 561 | 4 | 3 | 562 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 564 The length of the message is 3 octets which encompasses the one octet 565 Type field and the two octet Length field. 567 16.2.5. Notification TLV 569 A Notification message is sent when an error condition is detected, 570 and has the following form: 572 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 1 573 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 574 | 5 | x + 5 |O| Error Code | 575 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 576 | Error subcode | ... | 577 +-+-+-+-+-+-+-+-+ | 578 | Data | 579 | ... | 580 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 582 Type 583 The Notification TLV is type 5. 585 Length 586 Length is a two octet field with value x + 5, where x is 587 the length of the notification data field. 589 O-bit 590 Open-bit. If clear, the connection will be closed. 592 Error code 593 This 7-bit unsigned integer indicates the type of Notification. 594 The following Error Codes have been defined: 596 Error Code Symbolic Name Reference 598 1 Message Header Error Section 17.1 599 2 SA-Request Error Section 17.2 600 3 SA-Message/SA-Response Error Section 17.3 601 4 Hold Timer Expired Section 17.4 602 5 Finite State Machine Error Section 17.5 603 6 Notification Section 17.6 604 7 Cease Section 17.7 606 Error subcode: 607 This one-octet unsigned integer provides more specific information 608 about the reported error. Each Error Code may have one or more Error 609 Subcodes associated with it. If no appropriate Error Subcode is 610 defined, then a zero (Unspecific) value is used for the Error Subcode 611 field, and the O-bit must be cleared (i.e. the connection will be 612 closed). The used notation in the error description below is: MC = 613 Must Close connection = O-bit clear; CC = Can Close connection = 614 O-bit might be cleared. 616 Message Header Error subcodes: 618 0 - Unspecific (MC) 619 2 - Bad Message Length (MC) 620 3 - Bad Message Type (CC) 622 SA-Request Error subcodes: 624 0 - Unspecific (MC) 625 1 - Does not cache SA (MC) 626 2 - Invalid Group (MC) 628 SA-Message/SA-Response Error subcodes 630 0 - Unspecific (MC) 631 1 - Invalid Entry Count (CC) 632 2 - Invalid RP Address (MC) 633 3 - Invalid Group Address (MC) 634 4 - Invalid Source Address (MC) 635 5 - Invalid Sprefix Length (MC) 636 6 - Looping SA (Self is RP) (MC) 637 7 - Unknown Encapsulation (MC) 638 8 - Administrative Scope Boundary Violated (MC) 640 Hold Timer Expired subcodes (the O-bit is always clear): 642 0 - Unspecific (MC) 644 Finite State Machine Error subcodes: 646 0 - Unspecific (MC) 647 1 - Unexpected Message Type FSM Error (MC) 649 Notification subcodes (the O-bit is always clear): 651 0 - Unspecific (MC) 653 Cease subcodes (the O-bit is always clear): 655 0 - Unspecific (MC) 657 17. MSDP Error Handling 659 This section describes actions to be taken when errors are detected 660 while processing MSDP messages. MSDP Error Handling is similar to 661 that of BGP [RFC1771]. 663 When any of the conditions described here are detected, a 664 Notification message with the indicated Error Code, Error Subcode, 665 and Data fields is sent. In addition, the MSDP connection might be 666 closed. If no Error Subcode is specified, then a zero (Unspecific) 667 must be used. 669 The phrase "the MSDP connection is closed" means that the transport 670 protocol connection has been closed and that all resources for that 671 MSDP connection have been deallocated. 673 17.1. Message Header Error Handling 675 All errors detected while processing the Message Header are indicated 676 by sending the Notification message with Error Code Message Header 677 Error. The Error Subcode describes the specific nature of the error. 678 The Data field contains the erroneous Message (including the message 679 header). 681 If the Length field of the message header is less than 4 or greater 682 than 1400, or the length of a KeepAlive message is not equal to 3, 683 then the Error Subcode is set to Bad Message Length. 685 If the Type field of the message header is not recognized, then the 686 Error Subcode is set to Bad Message Type. 688 17.2. SA-Request Error Handling 690 The SA-Request Error code is used to signal the receipt of a SA 691 request at a non-caching MSDP peer, or at a caching MSDP peer when an 692 invalid group address requested. 694 When a non-caching MSDP peer receives an SA-Request, it returns the 695 following notification: 697 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 1 698 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 699 | 5 | 12 |O| 2 | 700 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 701 | 1 | Reserved | 702 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 703 | Group Address | 704 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 706 If a caching MSDP peer receives a request for an invalid group, it 707 returns the following notification: 709 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 1 710 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 711 | 5 | 12 |O| 2 | 712 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 713 | 2 | Reserved | 714 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 715 | Invalid Group Address | 716 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 718 17.3. SA-Message/SA-Response Error Handling 720 The SA-Message/SA-Response Error code is used to signal the receipt 721 of a erroneous SA Message at an MSDP peer, or the receipt of an SA- 722 Response Message by a peer that did not issue a SA-Request. It has 723 the following form: 725 17.3.1. Invalid Entry Count (IEC) 727 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 1 728 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 729 | 5 | 6 |O| 3 | 730 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 731 | 1 | IEC | 732 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 734 17.3.2. Invalid RP Address 736 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 1 737 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 738 | 5 | 12 |O| 3 | 739 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 740 | 2 | Reserved | 741 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 742 | Invalid RP Address | 743 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 745 17.3.3. Invalid Group Address 747 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 1 748 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 749 | 5 | 12 |O| 3 | 750 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 751 | 3 | Reserved | 752 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 753 | Invalid Group Address | 754 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 756 17.3.4. Invalid Source Address 758 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 1 759 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 760 | 5 | 12 |O| 3 | 761 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 762 | 4 | Reserved | 763 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 764 | Invalid Source Address | 765 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 767 17.3.5. Invalid Sprefix Length (ISL) 769 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 1 770 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 771 | 5 | 6 |O| 3 | 772 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 773 | 5 | ISL | 774 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 776 17.3.6. Looping SAs (Self is RP in received SA) 778 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 1 779 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 780 | 5 | x + 5 |O| 3 | 781 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 782 | 6 | Looping SA Message .... 783 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 785 Length x 786 x is the length of the looping SA message contained in the data 787 field of the Notification message. 789 17.3.7. Unknown Encapsulation 791 This notification is sent on receipt of SA data that is encapsulated 792 in an unknown encapsulation type. See section 18 for known 793 encapsulations. 795 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 1 796 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 797 | 5 | x + 5 |O| 3 | 798 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 799 | 7 | SA Message .... 800 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 802 Length x 803 x is the length of the SA message (which contained data which 804 was encapsulated in some unknown way) that is with contained in the 805 data field of the Notification message. 807 17.3.8. Administrative Scope Boundary Violated 809 This notification is used when an SA message is received for a group 810 G from a peer which is across an administrative scope boundary for G. 812 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 1 813 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 814 | 5 | 16 |O| 3 | 815 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 816 | 8 | Reserved | 817 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 818 | Peer IP Address | 819 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 820 | Group Address | 821 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 823 17.4. Hold Time Expired 825 If a system does not receive successive KEEPALIVE or any SA Message 826 and/or Notification messages within the period specified in the Hold 827 Timer, then the notification message with Hold Timer Expired Error 828 Code must be sent and the MSDP connection closed. 830 17.5. Finite State Machine Error Handling 832 Any error detected by the MSDP Finite State Machine (e.g., receipt of 833 an unexpected event) is indicated by sending the Notification message 834 with Error Code Finite State Machine Error. 836 17.6. Notification Message Error Handling 838 If a node sends a Notification message, and there is an error in that 839 message, and the O-bit of that message is not clear, a Notification 840 with O-bit clear, Error Code of Notification Error, and subcode 841 Unspecific must be sent. In addition, the Data field must include 842 the Notification message that triggered the error. However, if the 843 erroneous Notification message had the O-bit clear, then any error, 844 such as an unrecognized Error Code or Error Subcode, should be 845 noticed, logged locally, and brought to the attention of the 846 administrator of the remote node. 848 17.7. Cease 850 In absence of any fatal errors (that are indicated in this section), 851 an MSDP node may choose at any given time to close its MSDP 852 connection by sending the Notification message with Error Code Cease. 853 However, the Cease Notification message MUST NOT be used when a fatal 854 error indicated by this section does exist. 856 18. SA Data Encapsulation 858 This section describes UDP, GRE, and TCP encapsulation of SA data. 859 Encapsulation type is a configuration option. 861 18.1. UDP Data Encapsulation 863 Data packets MAY be encapsulated in UDP. In this case, the UDP 864 pseudo-header has the following form: 866 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 1 867 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 868 | Source Port | Destination Port | 869 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 870 | Length | Checksum | 871 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 872 | Origin RP Address | 873 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 875 The Source port, Destination Port, Length, and Checksum are used 876 according to RFC 768. Source and Destination ports are known via an 877 implementation-specific method (e.g. per-peer configuration). 879 Checksum 880 The checksum is computed according to RFC 768 [RFC768]. 882 Originating RP Address 883 The Originating RP Address is the address of the RP sending 884 the encapsulated data. 886 18.2. GRE Encapsulation 888 MSDP SA-data MAY be encapsulated in GRE using protocol type [MSDP- 889 GRE-ProtocolType]. The GRE header and payload packet have the 890 following form: 892 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 1 893 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 894 |C| Reserved0 | Ver | [MSDP-GRE-ProtocolType] |\ 895 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ GRE Header 896 | Checksum (optional) | Reserved1 |/ 897 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 898 | Originating RP IPv4 Address |\ 899 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Payload 900 | (S,G) Data Packet .... / 901 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 903 18.2.1. GRE Encapsulation and Path MTU Discovery [RFC1191] 905 Existing implementations of GRE, when using IPv4 as the Delivery 906 Header, do not implement Path MTU discovery and do not set the Don't 907 Fragment bit in the Delivery Header. This can cause large packets to 908 become fragmented within the tunnel and reassembled at the tunnel 909 exit (independent of whether the payload packet is using PMTU). If a 910 tunnel entry point were to use Path MTU discovery, however, that 911 tunnel entry point would also need to relay ICMP unreachable error 912 messages (in particular the "fragmentation needed and DF set" code) 913 back to the originator of the packet, which is not required by the 914 GRE specification [GRE]. Failure to properly relay Path MTU 915 information to an originator can result in the following behavior: 916 the originator sets the don't fragment bit, the packet gets dropped 917 within the tunnel, but since the originator doesn't receive proper 918 feedback, it retransmits with the same PMTU, causing subsequently 919 transmitted packets to be dropped. 921 18.3. TCP Data Encapsulation 923 As discussed earlier, encapsulation of data in SA messages MAY be 924 supported for backwards compatibility with legacy MSDP peers. 926 19. Security Considerations 928 An MSDP implementation MAY use IPsec [RFC1825] or keyed MD5 [RFC1828] 929 to secure control messages. When encapsulating SA data in GRE, 930 security should be relatively similar to security in a normal IPv4 931 network, as routing using GRE follows the same routing that IPv4 uses 932 natively. Route filtering will remain unchanged. However packet 933 filtering at a firewall requires either that a firewall look inside 934 the GRE packet or that the filtering is done on the GRE tunnel 935 endpoints. In those environments in which this is considered to be a 936 security issue it may be desirable to terminate the tunnel at the 937 firewall. 939 20. Acknowledgments 941 The authors would like to thank Bill Nickless, John Meylor, Liming 942 Wei, Manoj Leelanivas, Mark Turner, John Zwiebel, and Cristina 943 Radulescu-Banu for their design feedback and comments. In addition to 944 many other contributions, Tom Pusateri helped to clarify the 945 connection state machine, Dave Thaler helped to clarify the 946 Notification message types, and Bill Fenner helped to clarify the 947 Peer-RPF rules. 949 21. Author's Address: 951 Dino Farinacci 952 Procket Networks 953 3850 No. First St., Ste. C 954 San Jose, CA 95134 955 Email: dino@procket.com 957 Yakov Rehkter 958 Cisco Systems, Inc. 959 170 Tasman Drive 960 San Jose, CA, 95134 961 Email: yakov@cisco.com 963 Peter Lothberg 964 Sprint 965 VARESA0104 966 12502 Sunrise Valley Drive 967 Reston VA, 20196 968 Email: roll@sprint.net 970 Hank Kilmer 971 Email: hank@rem.com 973 Jeremy Hall 974 UUnet Technologies 975 3060 Williams Drive 976 Fairfax, VA 22031 977 Email: jhall@uu.net 979 David Meyer 980 Cisco Systems, Inc. 981 170 Tasman Drive 982 San Jose, CA, 95134 983 Email: dmm@cisco.com 985 22. REFERENCES 987 [GRE] Farinacci, D., et al., "Generic Routing Encapsulation 988 (GRE)", draft-meyer-gre-update-03.txt, January, 989 2000. Work in Progress. 991 [RFC768] Postel, J. "User Datagram Protocol", RFC 768, August, 992 1980. 994 [RFC1191] Mogul, J., and S. Deering, "Path MTU Discovery", 995 RFC 1191, November 1990. 997 [RFC1771] Rekhter, Y., and T. Li, "A Border Gateway Protocol 4 998 (BGP-4)", RFC 1771, March 1995. 1000 [RFC1825] Atkinson, R., "Security Architecture for the Internet 1001 Protocol", RFC 1825, August, 1995. 1003 [RFC1828] P. Metzger and W. Simpson, "IP Authentication using 1004 Keyed MD5", RFC 1828, August, 1995. 1006 [RFC2119] S. Bradner, "Key words for use in RFCs to Indicate 1007 Requirement Levels", RFC 2119, March, 1997. 1009 [RFC2283] Bates, T., Chandra, R., Katz, D., and Y. Rekhter., 1010 "Multiprotocol Extensions for BGP-4", RFC 2283, 1011 February 1998. 1013 [RFC2362] Estrin D., et al., "Protocol Independent Multicast - 1014 Sparse Mode (PIM-SM): Protocol Specification", RFC 1015 2362, June 1998. 1017 [RFC2365] Meyer, D. "Administratively Scoped IP Multicast", RFC 1018 2365, July, 1998.