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If these are generic example addresses, they should be changed to use the 233.252.0.x range defined in RFC 5771 == There are 1 instance of lines with non-RFC3849-compliant IPv6 addresses in the document. If these are example addresses, they should be changed. Miscellaneous warnings: ---------------------------------------------------------------------------- == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: When a VRRP router restarts or boots, it SHOULD not send any ND messages with its physical MAC address for the IPv6 address it owns, it should only send ND messages that include Virtual MAC addresses. This may entail: == Using lowercase 'not' together with uppercase 'MUST', 'SHALL', 'SHOULD', or 'RECOMMENDED' is not an accepted usage according to RFC 2119. Please use uppercase 'NOT' together with RFC 2119 keywords (if that is what you mean). Found 'SHOULD not' in this paragraph: A VRRP router SHOULD not forward packets addressed to the IPv6 Address it becomes Master for if it is not the owner. Forwarding these packets would result in unnecessary traffic. Also in the case of LANs that receive packets they transmit (e.g., token ring) this can result in a forwarding loop that is only terminated when the IPv6 TTL expires. -- The document seems to lack a disclaimer for pre-RFC5378 work, but may have content which was first submitted before 10 November 2008. If you have contacted all the original authors and they are all willing to grant the BCP78 rights to the IETF Trust, then this is fine, and you can ignore this comment. If not, you may need to add the pre-RFC5378 disclaimer. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (June 29, 2003) is 7606 days in the past. Is this intentional? Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFC 2119' is mentioned on line 133, but not defined == Unused Reference: 'RFC2119' is defined on line 1124, but no explicit reference was found in the text == Unused Reference: 'OSPF' is defined on line 1142, but no explicit reference was found in the text == Unused Reference: 'RIP' is defined on line 1144, but no explicit reference was found in the text ** Obsolete normative reference: RFC 3513 (ref. 'ADD-ARH') (Obsoleted by RFC 4291) ** Downref: Normative reference to an Informational RFC: RFC 1071 (ref. 'CKSM') ** Obsolete normative reference: RFC 2463 (ref. 'ICMPv6') (Obsoleted by RFC 4443) ** Obsolete normative reference: RFC 2460 (ref. 'IPv6') (Obsoleted by RFC 8200) -- Possible downref: Non-RFC (?) normative reference: ref. 'IPX' ** Obsolete normative reference: RFC 2461 (ref. 'ND') (Obsoleted by RFC 4861) ** Downref: Normative reference to an Historic RFC: RFC 1469 -- Possible downref: Non-RFC (?) normative reference: ref. 'TKARCH' ** Obsolete normative reference: RFC 2338 (ref. 'VRRP-V4') (Obsoleted by RFC 3768) Summary: 11 errors (**), 0 flaws (~~), 9 warnings (==), 4 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 INTERNET-DRAFT R. Hinden/Nokia 2 June 29, 2003 4 Virtual Router Redundancy Protocol for IPv6 6 8 Status of this Memo 10 This document is an Internet-Draft and is in full conformance with 11 all provisions of Section 10 of [RFC2026]. 13 Internet-Drafts are working documents of the Internet Engineering 14 Task Force (IETF), its areas, and its working groups. Note that 15 other groups may also distribute working documents as Internet- 16 Drafts. 18 Internet-Drafts are draft documents valid for a maximum of six months 19 and may be updated, replaced, or obsoleted by other documents at any 20 time. It is inappropriate to use Internet-Drafts as reference 21 material or to cite them other than as "work in progress." 23 To view the list Internet-Draft Shadow Directories, see 24 http://www.ietf.org/shadow.html. 26 This internet draft expires on January 4, 2004. 28 Abstract 30 This memo defines the Virtual Router Redundancy Protocol (VRRP) for 31 IPv6. It is version three (3) of the protocol. It is based on the 32 original version of VRRP (version 2) for IPv4 that is defined in 33 RFC2338. 35 VRRP specifies an election protocol that dynamically assigns 36 responsibility for a virtual router to one of the VRRP routers on a 37 LAN. The VRRP router controlling the IP address associated with a 38 virtual router is called the Master, and forwards packets sent to 39 this IP address. The election process provides dynamic fail over in 40 the forwarding responsibility should the Master become unavailable. 41 The advantage gained from using VRRP for IPv6 is a quicker switch 42 over to back up routers than can be obtained with standard IPv6 43 Neighbor Discovery [ND] mechanisms. 45 Table of Contents 47 1. Introduction................................................3 48 2. Required Features...........................................5 49 3. VRRP Overview...............................................6 50 4. Sample Configurations.......................................8 51 5. Protocol...................................................10 52 5.1 VRRP Packet Format....................................10 53 5.2 IP Field Descriptions.................................10 54 5.3 VRRP Field Descriptions...............................11 55 6. Protocol State Machine....................................13 56 6.1 Parameters per Virtual Router.........................13 57 6.2 Timers................................................14 58 6.3 State Transition Diagram..............................14 59 6.4 State Descriptions....................................14 60 7. Sending and Receiving VRRP Packets........................18 61 7.1 Receiving VRRP Packets................................18 62 7.2 Transmitting Packets..................................18 63 7.3 Virtual MAC Address...................................19 64 7.4 IPv6 Interface Identifiers............................19 65 8. Operational Issues........................................20 66 8.1 ICMPv6 Redirects......................................20 67 8.2 ND Neighbor Solicitation..............................20 68 8.3 Potential Forwarding Loop.............................21 69 9. Operation over FDDI, Token Ring, and ATM LANE.............21 70 9.1 Operation over FDDI...................................21 71 9.2 Operation over Token Ring.............................21 72 9.3 Operation over ATM LANE...............................23 73 10. Security Considerations...................................24 74 11. Acknowledgments...........................................24 75 12. IANA Considerations.......................................24 76 13. Normative References......................................25 77 14. Informative References....................................26 78 15. Authors' Address..........................................26 79 16. Changes from RFC2338......................................26 81 1. Introduction 83 IPv6 hosts on a LAN will usually learn about one or more default 84 routers by receiving Router Advertisements sent using the IPv6 85 Neighbor Discovery protocol [ND]. The Router Advertisements are 86 multicast periodically at a rate that the hosts will learn about the 87 default routers in a few minutes. They are not sent frequently enough 88 to rely on the absence of the router advertisement to detect router 89 failures. 91 Neighbor Discovery (ND) includes a mechanism called Neighbor 92 Unreachability Detection to detect the failure of a neighbor node 93 (router or host) or the forwarding path to a neighbor. This is done 94 by sending unicast ND Neighbor Solicitation messages to the neighbor 95 node. To reduce the overhead of sending Neighbor Solicitations, they 96 are only sent to neighbors to which the node is actively sending 97 traffic and only after there has been no positive indication that the 98 router is up for a period of time. Using the default parameters in 99 ND, it will take a host about 38 seconds to learn that a router is 100 unreachable before it will switch to another default router. This 101 delay would be very noticeable to users and cause some transport 102 protocol implementations to timeout. 104 While the ND unreachability detection could be speeded up by changing 105 the parameters to be more aggressive (note that the current lower 106 limit for this is 5 seconds), this would have the downside of 107 significantly increasing the overhead of ND traffic. Especially when 108 there are many hosts all trying to determine the reachability of a 109 one of more routers. 111 The Virtual Router Redundancy Protocol for IPv6 provides a much 112 faster switch over to an alternate default router than can be 113 obtained using standard ND procedures. Using VRRP a backup router 114 can take over for a failed default router in around three seconds 115 (using VRRP default parameters). This is done with out any 116 interaction with the hosts and a minimum amount of VRRP traffic. 118 VRRP specifies an election protocol that dynamically assigns 119 responsibility for a virtual router to one of the VRRP routers on a 120 LAN. The VRRP router controlling the IP address associated with a 121 virtual router is called the Master, and forwards packets sent to 122 this IP address. The election process provides dynamic fail over in 123 the forwarding responsibility should the Master become unavailable. 125 VRRP provides a function similar to a Cisco Systems, Inc. proprietary 126 protocol named Hot Standby Router Protocol (HSRP) [HSRP] and to a 127 Digital Equipment Corporation, Inc. proprietary protocol named IP 128 Standby Protocol [IPSTB]. 130 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 131 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 132 document are to be interpreted as described in [RFC 2119]. 134 The IESG/IETF take no position regarding the validity or scope of any 135 intellectual property right or other rights that might be claimed to 136 pertain to the implementation or use of the technology, or the extent 137 to which any license under such rights might or might not be 138 available. See the IETF IPR web page at http://www.ietf.org/ipr.html 139 for additional information. 141 1.1 Scope 143 The remainder of this document describes the features, design goals, 144 and theory of operation of VRRP for IPv6. The message formats, 145 protocol processing rules and state machine that guarantee 146 convergence to a single Virtual Router Master are presented. 147 Finally, operational issues related to MAC address mapping, handling 148 of Neighbor Discovery requests, generation of ICMPv6 redirect 149 messages, and security issues are addressed. 151 This protocol is intended for use with IPv6 routers only. VRRP for 152 IPv4 is defined in [VRRP-V4]. 154 1.2 Definitions 156 VRRP Router A router running the Virtual Router Redundancy 157 Protocol. It may participate in one or more 158 virtual routers. 160 Virtual Router An abstract object managed by VRRP that acts 161 as a default router for hosts on a shared LAN. 162 It consists of a Virtual Router Identifier and 163 an IPv6 address across a common LAN. A VRRP 164 Router may backup one or more virtual routers. 166 IPv6 Address Owner The VRRP router that has the virtual router's 167 IPv6 address as real interface address. This 168 is the router that, when up, will respond to 169 packets addressed to the IPv6 addresses for 170 ICMPv6 pings, TCP connections, etc. 172 Virtual Router Master The VRRP router that is assuming the 173 responsibility of forwarding packets sent to 174 the IPv6 address associated with the virtual 175 router, and answering ND requests for this 176 IPv6 address. Note that if the IPv6 address 177 owner is available, then it will always become 178 the Master. 180 Virtual Router Backup The set of VRRP routers available to assume 181 forwarding responsibility for a virtual router 182 should the current Master fail. 184 2.0 Required Features 186 This section outlines the set of features that were considered 187 mandatory and that guided the design of VRRP. 189 2.1 IPv6 Address Backup 191 Backup of an IPv6 address is the primary function of the Virtual 192 Router Redundancy Protocol. While providing election of a Virtual 193 Router Master and the additional functionality described below, the 194 protocol should strive to: 196 - Minimize the duration of black holes. 197 - Minimize the steady state bandwidth overhead and processing 198 complexity. 199 - Function over a wide variety of multiaccess LAN technologies 200 capable of supporting IPv6 traffic. 201 - Provide for election of multiple virtual routers on a network for 202 load balancing 203 - Support of multiple logical IPv6 subnets on a single LAN segment. 205 2.2 Preferred Path Indication 207 A simple model of Master election among a set of redundant routers is 208 to treat each router with equal preference and claim victory after 209 converging to any router as Master. However, there are likely to be 210 many environments where there is a distinct preference (or range of 211 preferences) among the set of redundant routers. For example, this 212 preference may be based upon access link cost or speed, router 213 performance or reliability, or other policy considerations. The 214 protocol should allow the expression of this relative path preference 215 in an intuitive manner, and guarantee Master convergence to the most 216 preferential router currently available. 218 2.3 Minimization of Unnecessary Service Disruptions 220 Once Master election has been performed then any unnecessary 221 transitions between Master and Backup routers can result in a 222 disruption in service. The protocol should ensure after Master 223 election that no state transition is triggered by any Backup router 224 of equal or lower preference as long as the Master continues to 225 function properly. 227 Some environments may find it beneficial to avoid the state 228 transition triggered when a router becomes available that is more 229 preferential than the current Master. It may be useful to support an 230 override of the immediate convergence to the preferred path. 232 2.4 Efficient Operation over Extended LANs 234 Sending IPv6 packets on a multiaccess LAN requires mapping from an 235 IPv6 address to a MAC address. The use of the virtual router MAC 236 address in an extended LAN employing learning bridges can have a 237 significant effect on the bandwidth overhead of packets sent to the 238 virtual router. If the virtual router MAC address is never used as 239 the source address in a link level frame then the station location is 240 never learned, resulting in flooding of all packets sent to the 241 virtual router. To improve the efficiency in this environment the 242 protocol should: 1) use the virtual router MAC as the source in a 243 packet sent by the Master to trigger station learning; 2) trigger a 244 message immediately after transitioning to Master to update the 245 station learning; and 3) trigger periodic messages from the Master to 246 maintain the station learning cache. 248 3.0 VRRP Overview 250 VRRP specifies an election protocol to provide the virtual router 251 function described earlier. All protocol messaging is performed 252 using IPv6 multicast datagrams, thus the protocol can operate over a 253 variety of multiaccess LAN technologies supporting IPv6 multicast. 254 Each VRRP virtual router has a single well-known MAC address 255 allocated to it. This document currently only details the mapping to 256 networks using the IEEE 802 48-bit MAC address. The virtual router 257 MAC address is used as the source in all periodic VRRP messages sent 258 by the Master router to enable bridge learning in an extended LAN. 260 A virtual router is defined by its virtual router identifier (VRID) 261 and an IPv6 address. A VRRP router may associate a virtual router 262 with its real address on an interface, and may also be configured 263 with additional virtual router mappings and priority for virtual 264 routers it is willing to backup. The mapping between VRID and its 265 IPv6 address must be coordinated among all VRRP routers on a LAN. 266 However, there is no restriction against reusing a VRID with a 267 different address mapping on different LANs. The scope of each 268 virtual router is restricted to a single LAN. 270 To minimize network traffic, only the Master for each virtual router 271 sends periodic VRRP Advertisement messages. A Backup router will not 272 attempt to preempt the Master unless it has higher priority. This 273 eliminates service disruption unless a more preferred path becomes 274 available. It's also possible to administratively prohibit all 275 preemption attempts. The only exception is that a VRRP router will 276 always become Master of any virtual router associated with address it 277 owns. If the Master becomes unavailable then the highest priority 278 Backup will transition to Master after a short delay, providing a 279 controlled transition of the virtual router responsibility with 280 minimal service interruption. 282 The VRRP protocol design provides rapid transition from Backup to 283 Master to minimize service interruption, and incorporates 284 optimizations that reduce protocol complexity while guaranteeing 285 controlled Master transition for typical operational scenarios. The 286 optimizations result in an election protocol with minimal runtime 287 state requirements, minimal active protocol states, and a single 288 message type and sender. The typical operational scenarios are 289 defined to be two redundant routers and/or distinct path preferences 290 among each router. A side effect when these assumptions are violated 291 (i.e., more than two redundant paths all with equal preference) is 292 that duplicate packets may be forwarded for a brief period during 293 Master election. However, the typical scenario assumptions are 294 likely to cover the vast majority of deployments, loss of the Master 295 router is infrequent, and the expected duration in Master election 296 convergence is quite small ( << 1 second ). Thus the VRRP 297 optimizations represent significant simplifications in the protocol 298 design while incurring an insignificant probability of brief network 299 degradation. 301 4. Sample Configurations 303 4.1 Sample Configuration 1 305 The following figure shows a simple network with two VRRP routers 306 implementing one virtual router. Note that this example is provided 307 to help understand the protocol, but is not expected to occur in 308 actual practice. 310 +-----------+ +-----------+ 311 | Rtr1 | | Rtr2 | 312 |(MR VRID=1)| |(BR VRID=1)| 313 | | | | 314 VRID=1 +-----------+ +-----------+ 315 IPv6 A -------->* *<--------- IPv6 B 316 | | 317 | | 318 ------------------+------------+-----+--------+--------+--------+-- 319 ^ ^ ^ ^ 320 | | | | 321 (IPv6 A) (IPv6 A) (IPv6 A) (IPv6 A) 322 | | | | 323 +--+--+ +--+--+ +--+--+ +--+--+ 324 | H1 | | H2 | | H3 | | H4 | 325 +-----+ +-----+ +--+--+ +--+--+ 326 Legend: 327 ---+---+---+-- = Ethernet, Token Ring, or FDDI 328 H = Host computer 329 MR = Master Router 330 BR = Backup Router 331 * = IPv6 Address 332 (IPv6) = default router for hosts 334 Eliminating all mention of VRRP (VRID=1) from the figure above leaves 335 it as a typical IPv6 deployment. Each router has a link-local IPv6 336 address on the LAN interface (Rtr1 is assigned IPv6 Link-Local A and 337 Rtr2 is assigned IPv6 Link-Local B), and each host learns a default 338 route from Router Advertisements through one of the routers (in this 339 example they all use Rtr1's IPv6 Link-Local A). 341 Moving to the VRRP environment, each router has the exact same Link- 342 Local IPv6 address. Rtr1 is said to be the IPv6 address owner of 343 IPv6 A, and Rtr2 is the IPv6 address owner of IPv6 B. A virtual 344 router is then defined by associating a unique identifier (the 345 virtual router ID) with the address owned by a router. Finally, the 346 VRRP protocol manages virtual router fail over to a backup router. 348 The example above shows a virtual router configured to cover the IPv6 349 address owned by Rtr1 (VRID=1,IPv6_Address=A). When VRRP is enabled 350 on Rtr1 for VRID=1 it will assert itself as Master, with 351 priority=255, since it is the IPv6 address owner for the virtual 352 router IPv6 address. When VRRP is enabled on Rtr2 for VRID=1 it will 353 transition to Backup, with priority=100, since it is not the IPv6 354 address owner. If Rtr1 should fail then the VRRP protocol will 355 transition Rtr2 to Master, temporarily taking over forwarding 356 responsibility for IPv6 A to provide uninterrupted service to the 357 hosts. 359 Note that in this example IPv6 B is not backed up, it is only used by 360 Rtr2 as its interface address. In order to backup IPv6 B, a second 361 virtual router must be configured. This is shown in the next 362 section. 364 4.2 Sample Configuration 2 366 The following figure shows a configuration with two virtual routers 367 with the hosts splitting their traffic between them. This example is 368 expected to be common in actual practice. 370 +-----------+ +-----------+ 371 | Rtr1 | | Rtr2 | 372 |(MR VRID=1)| |(BR VRID=1)| 373 |(BR VRID=2)| |(MR VRID=2)| 374 VRID=1 +-----------+ +-----------+ VRID=2 375 IPv6 A -------->* *<---------- IPv6 B 376 | | 377 | | 378 ------------------+------------+-----+--------+--------+--------+-- 379 ^ ^ ^ ^ 380 | | | | 381 (IPv6 A) (IPv6 A) (IPv6 B) (IPv6 B) 382 | | | | 383 +--+--+ +--+--+ +--+--+ +--+--+ 384 | H1 | | H2 | | H3 | | H4 | 385 +-----+ +-----+ +--+--+ +--+--+ 386 Legend: 387 ---+---+---+-- = Ethernet, Token Ring, or FDDI 388 H = Host computer 389 MR = Master Router 390 BR = Backup Router 391 * = IPv6 Address 392 (IPv6) = default router for hosts 394 In the example above, half of the hosts have learned a default route 395 through Rtr1's IPv6 A and half are using Rtr2's IPv6 B. The 396 configuration of virtual router VRID=1 is exactly the same as in the 397 first example (see section 4.1), and a second virtual router has been 398 added to cover the IPv6 address owned by Rtr2 (VRID=2, 399 IPv6_Address=B). In this case Rtr2 will assert itself as Master for 400 VRID=2 while Rtr1 will act as a backup. This scenario demonstrates a 401 deployment providing load splitting when both routers are available 402 while providing full redundancy for robustness. 404 5.0 Protocol 406 The purpose of the VRRP packet is to communicate to all VRRP routers 407 the priority and the state of the Master router associated with the 408 Virtual Router ID. 410 VRRP packets are sent encapsulated in IPv6 packets. They are sent to 411 the IPv6 multicast address assigned to VRRP. 413 5.1 VRRP Packet Format 415 This section defines the format of the VRRP packet and the relevant 416 fields in the IPv6 header. 418 0 1 2 3 419 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 1 420 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 421 |Version| Type | Virtual Rtr ID| Priority | (reserved) | 422 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 423 | (reserved) | Adver Int | Checksum | 424 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 425 | | 426 + + 427 | | 428 + IPv6 Address + 429 | | 430 + + 431 | | 432 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 434 5.2 IPv6 Field Descriptions 436 5.2.1 Source Address 438 The IPv6 link-local address of the interface the packet is being sent 439 from. 441 5.2.2 Destination Address 443 The IPv6 multicast address as assigned by the IANA for VRRP is: 445 FF02:0:0:0:0:0:XXXX:XXXX 447 This is a link-local scope multicast address. Routers MUST NOT 448 forward a datagram with this destination address regardless of its 449 Hop Limit. 451 5.2.3 Hop Limit 453 The Hop Limit MUST be set to 255. A VRRP router receiving a packet 454 with the Hop Limit not equal to 255 MUST discard the packet. 456 5.2.4 Next Header 458 The IPv6 Next Header protocol assigned by the IANA for VRRP is 112 459 (decimal). 461 5.3 VRRP Field Descriptions 463 5.3.1 Version 465 The version field specifies the VRRP protocol version of this packet. 466 This document defines version 3. 468 5.3.2 Type 470 The type field specifies the type of this VRRP packet. The only 471 packet type defined in this version of the protocol is: 473 1 ADVERTISEMENT 475 A packet with unknown type MUST be discarded. 477 5.3.3 Virtual Rtr ID (VRID) 479 The Virtual Router Identifier (VRID) field identifies the virtual 480 router this packet is reporting status for. 482 5.3.4 Priority 484 The priority field specifies the sending VRRP router's priority for 485 the virtual router. Higher values equal higher priority. This field 486 is an 8 bit unsigned integer field. 488 The priority value for the VRRP router that owns the IPv6 address 489 associated with the virtual router MUST be 255 (decimal). 491 VRRP routers backing up a virtual router MUST use priority values 492 between 1-254 (decimal). The default priority value for VRRP routers 493 backing up a virtual router is 100 (decimal). 495 The priority value zero (0) has special meaning indicating that the 496 current Master has stopped participating in VRRP. This is used to 497 trigger Backup routers to quickly transition to Master without having 498 to wait for the current Master to timeout. 500 5.3.5 Reserved 502 This field MUST be set to zero on transmission and ignored on 503 reception. 505 5.3.5 Reserved 507 This field MUST be set to zero on transmission and ignored on 508 reception. 510 5.3.6 Advertisement Interval (Adver Int) 512 The Advertisement interval indicates the time interval (in seconds) 513 between ADVERTISEMENTS. The default is 1 second. This field is used 514 for troubleshooting misconfigured routers. 516 5.3.7 Checksum 518 The checksum field is used to detect data corruption in the VRRP 519 message. 521 The checksum is the 16-bit one's complement of the one's complement 522 sum of the entire VRRP message starting with the version field and a 523 "pseudo-header" as defined in section 8.1 of RFC2460 [IPv6]. The 524 next header field in the "pseudo-header" should be set to 112 525 (decimal) for VRRP. For computing the checksum, the checksum field 526 is set to zero. See RFC1071 for more detail [CKSM]. 528 5.3.8 IPv6 Address 530 The IPv6 link-local address associated with the virtual router. 532 6. Protocol State Machine 534 6.1 Parameters per Virtual Router 536 VRID Virtual Router Identifier. Configured item 537 in the range 1-255 (decimal). There is no 538 default. 540 Priority Priority value to be used by this VRRP 541 router in Master election for this virtual 542 router. The value of 255 (decimal) is 543 reserved for the router that owns the IPv6 544 address associated with the virtual router. 545 The value of 0 (zero) is reserved for Master 546 router to indicate it is releasing 547 responsibility for the virtual router. The 548 range 1-254 (decimal) is available for VRRP 549 routers backing up the virtual router. The 550 default value is 100 (decimal). 552 IPv6_Address The IPv6 link-local address associated with 553 this virtual router. Configured item. No 554 default. 556 Advertisement_Interval Time interval between ADVERTISEMENTS 557 (seconds). Default is 1 second. 559 Skew_Time Time to skew Master_Down_Interval in 560 seconds. Calculated as: 562 ( (256 - Priority) / 256 ) 564 Master_Down_Interval Time interval for Backup to declare Master 565 down (seconds). Calculated as: 567 (3 * Advertisement_Interval) + Skew_time 569 Preempt_Mode Controls whether a higher priority Backup 570 router preempts a lower priority Master. 571 Values are True to allow preemption and 572 False to prohibit preemption. Default is 573 True. 575 Note: Exception is that the router that owns 576 the IPv6 address associated with the virtual 577 router always preempts independent of the 578 setting of this flag. 580 6.2 Timers 582 Master_Down_Timer Timer that fires when ADVERTISEMENT has not 583 been heard for Master_Down_Interval. 585 Adver_Timer Timer that fires to trigger sending of 586 ADVERTISEMENT based on 587 Advertisement_Interval. 589 6.3 State Transition Diagram 591 +---------------+ 592 +--------->| |<-------------+ 593 | | Initialize | | 594 | +------| |----------+ | 595 | | +---------------+ | | 596 | | | | 597 | V V | 598 +---------------+ +---------------+ 599 | |---------------------->| | 600 | Master | | Backup | 601 | |<----------------------| | 602 +---------------+ +---------------+ 604 6.4 State Descriptions 606 In the state descriptions below, the state names are identified by 607 {state-name}, and the packets are identified by all upper case 608 characters. 610 A VRRP router implements an instance of the state machine for each 611 virtual router election it is participating in. 613 6.4.1 Initialize 615 The purpose of this state is to wait for a Startup event. If a 616 Startup event is received, then: 618 - If the Priority = 255 (i.e., the router owns the IPv6 address 619 associated with the virtual router) 621 o Send an ADVERTISEMENT 622 o Send an unsolicited ND Neighbor Advertisement with the Router 623 Flag (R) set, the Solicited Flag (S) unset, the Override flag 624 (O) set, the Target Address set to the IPv6 link-local address 625 of the Virtual Router, and the Target Link Layer address set to 626 the virtual router MAC address. 627 o Set the Adver_Timer to Advertisement_Interval 628 o Transition to the {Master} state 630 else 632 o Set the Master_Down_Timer to Master_Down_Interval 633 o Transition to the {Backup} state 635 endif 637 6.4.2 Backup 639 The purpose of the {Backup} state is to monitor the availability and 640 state of the Master Router. 642 While in this state, a VRRP router MUST do the following: 644 - MUST NOT respond to ND Neighbor Solicitation messages for the IPv6 645 address associated with the virtual router. 647 - MUST NOT send ND Router Advertisement messages for the virtual 648 router. 650 - MUST discard packets with a destination link layer MAC address 651 equal to the virtual router MAC address. 653 - MUST NOT accept packets addressed to the IPv6 address associated 654 with the virtual router. 656 - If a Shutdown event is received, then: 658 o Cancel the Master_Down_Timer 659 o Transition to the {Initialize} state 661 endif 663 - If the Master_Down_Timer fires, then: 665 o Send an ADVERTISEMENT 666 o Compute and join the Solicited-Node multicast address [ADD-ARH] 667 for the link-local IPv6 address of the Virtual Router. 668 o Send an unsolicited ND Neighbor Advertisement with the Router 669 Flag (R) set, the Solicited Flag (S) unset, the Override flag 670 (O) set, the Target Address set to the IPv6 link-local address 671 of the Virtual Router, and the Target Link Layer address set to 672 the virtual router MAC address. 674 o Set the Adver_Timer to Advertisement_Interval 675 o Transition to the {Master} state 677 endif 679 - If an ADVERTISEMENT is received, then: 681 If the Priority in the ADVERTISEMENT is Zero, then: 683 o Set the Master_Down_Timer to Skew_Time 685 else: 687 If Preempt_Mode is False, or If the Priority in the 688 ADVERTISEMENT is greater than or equal to the local 689 Priority, then: 691 o Reset the Master_Down_Timer to Master_Down_Interval 693 else: 695 o Discard the ADVERTISEMENT 697 endif 698 endif 699 endif 701 6.4.3 Master 703 While in the {Master} state the router functions as the forwarding 704 router for the IPv6 address associated with the virtual router. 706 While in this state, a VRRP router MUST do the following: 708 - MUST be a member of the Solicited-Node multicast address for the 709 IPv6 link-local address associated with the virtual router. 711 - MUST respond to ND Neighbor Solicitation message for the IPv6 712 address associated with the virtual router. 714 - MUST send ND Router Advertisements for the virtual router. 716 - MUST respond to ND Router Solicitation message for the virtual 717 router. 719 - MUST forward packets with a destination link layer MAC address 720 equal to the virtual router MAC address. 722 - MUST NOT accept packets addressed to the IPv6 address associated 723 with the virtual router if it is not the IPv6 address owner. 725 - MUST accept packets addressed to the IPv6 address associated with 726 the virtual router if it is the IPv6 address owner. 728 - If a Shutdown event is received, then: 730 o Cancel the Adver_Timer 731 o Send an ADVERTISEMENT with Priority = 0 732 o Transition to the {Initialize} state 734 endif 736 - If the Adver_Timer fires, then: 738 o Send an ADVERTISEMENT 739 o Reset the Adver_Timer to Advertisement_Interval 741 endif 743 - If an ADVERTISEMENT is received, then: 745 If the Priority in the ADVERTISEMENT is Zero, then: 747 o Send an ADVERTISEMENT 748 o Reset the Adver_Timer to Advertisement_Interval 750 else: 752 If the Priority in the ADVERTISEMENT is greater than the 753 local Priority, 754 or 755 If the Priority in the ADVERTISEMENT is equal to the local 756 Priority and the IPv6 Address of the sender is greater than 757 the local IPv6 Address, then: 759 o Cancel Adver_Timer 760 o Set Master_Down_Timer to Master_Down_Interval 761 o Transition to the {Backup} state 763 else: 765 o Discard ADVERTISEMENT 767 endif 768 endif 769 endif 771 7. Sending and Receiving VRRP Packets 773 7.1 Receiving VRRP Packets 775 Performed the following functions when a VRRP packet is received: 777 - MUST verify that the IPv6 Hop Limit is 255. 778 - MUST verify the VRRP version is 3 779 - MUST verify that the received packet contains the complete VRRP 780 packet (including fixed fields, and IPv6 Address. 781 - MUST verify the VRRP checksum 782 - MUST verify that the VRID is configured on the receiving 783 interface and the local router is not the IPv6 Address owner 784 (Priority equals 255 (decimal)). 786 If any one of the above checks fails, the receiver MUST discard the 787 packet, SHOULD log the event and SHOULD indicate via network 788 management that an error occurred. 790 - MAY verify that the IPv6 Address matches the IPv6_Address 791 configured for the VRID. 793 If the above check fails, the receiver SHOULD log the event and 794 SHOULD indicate via network management that a misconfiguration was 795 detected. If the packet was not generated by the address owner 796 (Priority does not equal 255 (decimal)), the receiver MUST drop the 797 packet, otherwise continue processing. 799 - MUST verify that the Adver Interval in the packet is the same as 800 the locally configured for this virtual router 802 If the above check fails, the receiver MUST discard the packet, 803 SHOULD log the event and SHOULD indicate via network management that 804 a misconfiguration was detected. 806 7.2 Transmitting VRRP Packets 808 The following operations MUST be performed when transmitting a VRRP 809 packet. 811 - Fill in the VRRP packet fields with the appropriate virtual 812 router configuration state 813 - Compute the VRRP checksum 814 - Set the source MAC address to Virtual Router MAC Address 815 - Set the source IPv6 address to interface link-local IPv6 address 816 - Set the IPv6 protocol to VRRP 817 - Send the VRRP packet to the VRRP IP multicast group 819 Note: VRRP packets are transmitted with the virtual router MAC 820 address as the source MAC address to ensure that learning bridges 821 correctly determine the LAN segment the virtual router is attached 822 to. 824 7.3 Virtual Router MAC Address 826 The virtual router MAC address associated with a virtual router is an 827 IEEE 802 MAC Address in the following format: 829 00-00-5E-00-02-{VRID} (in hex in internet standard bit-order) 831 The first three octets are derived from the IANA's OUI. The next two 832 octets (00-02) indicate the address block assigned to the VRRP for 833 IPv6 protocol. {VRID} is the VRRP Virtual Router Identifier. This 834 mapping provides for up to 255 VRRP routers on a network. 836 7.4 IPv6 Interface Identifiers 838 IPv6 Routers running VRRP MUST create their Interface Identifiers in 839 the normal manner (e.g., RFC2464 "Transmission of IPv6 Packets over 840 Ethernet"). They MUST NOT use the Virtual Router MAC address to 841 create the Modified EUI-64 identifiers. 843 This VRRP specification describes how to advertise and resolve the 844 VRRP routers IPv6 link local address into the Virtual Router MAC 845 address. 847 8. Operational Issues 849 8.1 ICMPv6 Redirects 851 ICMPv6 Redirects may be used normally when VRRP is running between a 852 group of routers [ICMPv6]. This allows VRRP to be used in 853 environments where the topology is not symmetric (e.g., the VRRP 854 routers do not connect to the same destinations). 856 The IPv6 source address of an ICMPv6 redirect should be the address 857 the end host used when making its next hop routing decision. If a 858 VRRP router is acting as Master for virtual router(s) containing 859 addresses it does not own, then it must determine which virtual 860 router the packet was sent to when selecting the redirect source 861 address. One method to deduce the virtual router used is to examine 862 the destination MAC address in the packet that triggered the 863 redirect. 865 8.2 ND Neighbor Solicitation 867 When a host sends an ND Neighbor Solicitation message for the virtual 868 router IPv6 address, the Master virtual router MUST respond to the ND 869 Neighbor Solicitation message with the virtual MAC address for the 870 virtual router. The Master virtual router MUST NOT respond with its 871 physical MAC address. This allows the client to always use the same 872 MAC address regardless of the current Master router. 874 When a Master virtual router sends an ND Neighbor Solicitation 875 message for a host's IPv6 address, the Master virtual router MUST 876 include the virtual MAC address for the virtual router if it sends a 877 source link-layer address option in the neighbor solicitation 878 message. It MUST NOT use its physical MAC address in the source 879 link-layer address option. 881 When a VRRP router restarts or boots, it SHOULD not send any ND 882 messages with its physical MAC address for the IPv6 address it owns, 883 it should only send ND messages that include Virtual MAC addresses. 884 This may entail: 886 - When configuring an interface, VRRP routers should send an 887 unsolicitated ND Neighbor Advertisement message containing the 888 virtual router MAC address for the IPv6 address on that interface. 890 - At system boot, when initializing interfaces for VRRP operation; 891 delay all ND Router and Neighbor Advertisements and Solicitation 892 messages until both the IPv6 address and the virtual router MAC 893 address are configured. 895 8.3 Potential Forwarding Loop 897 A VRRP router SHOULD not forward packets addressed to the IPv6 898 Address it becomes Master for if it is not the owner. Forwarding 899 these packets would result in unnecessary traffic. Also in the case 900 of LANs that receive packets they transmit (e.g., token ring) this 901 can result in a forwarding loop that is only terminated when the IPv6 902 TTL expires. 904 One such mechanism for VRRP routers is to add/delete a reject host 905 route for each adopted IPv6 address when transitioning to/from MASTER 906 state. 908 9. Operation over FDDI, Token Ring, and ATM LANE 910 9.1 Operation over FDDI 912 FDDI interfaces remove from the FDDI ring frames that have a source 913 MAC address matching the device's hardware address. Under some 914 conditions, such as router isolations, ring failures, protocol 915 transitions, etc., VRRP may cause there to be more than one Master 916 router. If a Master router installs the virtual router MAC address 917 as the hardware address on a FDDI device, then other Masters' 918 ADVERTISEMENTS will be removed from the ring during the Master 919 convergence, and convergence will fail. 921 To avoid this an implementation SHOULD configure the virtual router 922 MAC address by adding a unicast MAC filter in the FDDI device, rather 923 than changing its hardware MAC address. This will prevent a Master 924 router from removing any ADVERTISEMENTS it did not originate. 926 9.2 Operation over Token Ring 928 Token ring has several characteristics that make running VRRP 929 difficult. These include: 931 - In order to switch to a new master located on a different bridge 932 token ring segment from the previous master when using source 933 route bridges, a mechanism is required to update cached source 934 route information. 936 - No general multicast mechanism supported across old and new token 937 ring adapter implementations. While many newer token ring adapters 938 support group addresses, token ring functional address support is 939 the only generally available multicast mechanism. Due to the 940 limited number of token ring functional addresses these may 941 collide with other usage of the same token ring functional 942 addresses. 944 Due to these difficulties, the preferred mode of operation over token 945 ring will be to use a token ring functional address for the VRID 946 virtual MAC address. Token ring functional addresses have the two 947 high order bits in the first MAC address octet set to B'1'. They 948 range from 03-00-00-00-00-80 to 03-00-02-00-00-00 (canonical format). 949 However, unlike multicast addresses, there is only one unique 950 functional address per bit position. The functional addresses 951 addresses 03-00-00-10-00-00 through 03-00-02-00-00-00 are reserved 952 by the Token Ring Architecture [TKARCH] for user-defined 953 applications. However, since there are only 12 user-defined token 954 ring functional addresses, there may be other non-IP protocols using 955 the same functional address. Since the Novell IPX [IPX] protocol uses 956 the 03-00-00-10-00-00 functional address, operation of VRRP over 957 token ring will avoid use of this functional address. In general, 958 token ring VRRP users will be responsible for resolution of other 959 user-defined token ring functional address conflicts. 961 VRIDs are mapped directly to token ring functional addresses. In 962 order to decrease the likelihood of functional address conflicts, 963 allocation will begin with the largest functional address. Most non- 964 IP protocols use the first or first couple user-defined functional 965 addresses and it is expected that VRRP users will choose VRIDs 966 sequentially starting with 1. 968 VRID Token Ring Functional Address 969 ---- ----------------------------- 970 1 03-00-02-00-00-00 971 2 03-00-04-00-00-00 972 3 03-00-08-00-00-00 973 4 03-00-10-00-00-00 974 5 03-00-20-00-00-00 975 6 03-00-40-00-00-00 976 7 03-00-80-00-00-00 977 8 03-00-00-01-00-00 978 9 03-00-00-02-00-00 979 10 03-00-00-04-00-00 980 11 03-00-00-08-00-00 982 Or more succinctly, octets 3 and 4 of the functional address are 983 equal to (0x4000 >> (VRID - 1)) in non-canonical format. 985 Since a functional address cannot be used used as a MAC level source 986 address, the real MAC address is used as the MAC source address in 987 VRRP advertisements. This is not a problem for bridges since packets 988 addressed to functional addresses will be sent on the spanning-tree 989 explorer path [802.1D]. 991 The functional address mode of operation MUST be implemented by 992 routers supporting VRRP on token ring. 994 Additionally, routers MAY support unicast mode of operation to take 995 advantage of newer token ring adapter implementations that support 996 non-promiscuous reception for multiple unicast MAC addresses and to 997 avoid both the multicast traffic and usage conflicts associated with 998 the use of token ring functional addresses. Unicast mode uses the 999 same mapping of VRIDs to virtual MAC addresses as Ethernet. However, 1000 one important difference exists. ND request/reply packets contain the 1001 virtual MAC address as the source MAC address. The reason for this is 1002 that some token ring driver implementations keep a cache of MAC 1003 address/source routing information independent of the ND cache. 1004 Hence, these implementations need have to receive a packet with the 1005 virtual MAC address as the source address in order to transmit to 1006 that MAC address in a source-route bridged network. 1008 Unicast mode on token ring has one limitation that should be 1009 considered. If there are VRID routers on different source-route 1010 bridge segments and there are host implementations that keep their 1011 source-route information in the ND cache and do not listen to 1012 gratuitous NDs, these hosts will not update their ND source-route 1013 information correctly when a switch-over occurs. The only possible 1014 solution is to put all routers with the same VRID on the same source- 1015 bridge segment and use techniques to prevent that bridge segment from 1016 being a single point of failure. These techniques are beyond the 1017 scope this document. 1019 For both the multicast and unicast mode of operation, VRRP 1020 advertisements sent to 224.0.0.18 should be encapsulated as described 1021 in [RFC1469]. 1023 9.3 Operation over ATM LANE 1025 Operation of VRRP over ATM LANE on routers with ATM LANE interfaces 1026 and/or routers behind proxy LEC's are beyond the scope of this 1027 document. 1029 10. Security Considerations 1031 VRRP for IPv6 does not include any type of authentication. Earlier 1032 versions of VRRP for IPv4 specification included several types of 1033 authentication ranging from none to strong [VRRP-V4]. 1035 Operational experience and further analysis determined that these did 1036 not provide any real measure of security and do to the nature of the 1037 VRRP protocol they did not prevent incorrectly configured or hostile 1038 routers from becoming VRRP masters. In general on LANs any device on 1039 the LAN has the ability to disrupt all communication. For example 1040 although securing VRRP prevents unauthorized machines from taking 1041 part in the election protocol, it does not protect hosts on the 1042 network from being deceived. A gratuitous ND reply from what 1043 purports to be the virtual router's IPv6 address can redirect traffic 1044 to an unauthorized machine. Similarly, individual connections can be 1045 diverted by means of forged ICMPv6 Redirect messages. Consequentially 1046 it was determined it was better to remove the additional 1047 authentication methods in this specification of the VRRP protocol as 1048 it did not provide the authentication originally intended. 1050 VRRP includes a mechanism (setting TTL=255, checking on receipt) that 1051 protects against VRRP packets being injected from another remote 1052 network. This limits most vulnerabilities to local attacks. 1054 VRRP does not provide any confidentiality. Confidentiality is not 1055 necessary for the correct operation of VRRP and there is no 1056 information in the VRRP messages that must be kept secret from other 1057 nodes on the LAN. 1059 11. Acknowledgments 1061 This specification is based on RFC2238. The authors of RFC2238 are 1062 S. Knight, D. Weaver, D. Whipple, R. Hinden, D. Mitzel, P. Hunt, P. 1063 Higginson, M. Shand, and A. Lindem. 1065 The author of this document would also like to thank Erik Nordmark, 1066 Thomas Narten, Steve Deering, Radia Perlman, and Danny Mitzel for 1067 their helpful suggestions. 1069 12. IANA Considerations 1071 VRRP for IPv6 needs an IPv6 link-local scope multicast address 1072 assigned by the IANA for this specification. The IPv6 multicast 1073 address should be of the following form: 1075 FF02:0:0:0:0:0:XXXX:XXXX 1077 The values assigned address should be entered into section 5.2.2. 1079 A convenient assignment of this link-local scope multicast would be: 1081 FF02:0:0:0:0:0:0:12 1083 as this would be consistent with the IPv4 assignment for VRRP. 1085 The IANA should also reserve a block of IANA Ethernet unicast 1086 addresses from: 1088 00-00-5E-00-02-00 to 00-00-5E-00-02-FF in hex 1090 for VRRP for IPv6. Similar assignments are documented in: 1092 http://www.iana.org/assignments/ethernet-numbers 1094 13. Normative References 1096 [802.1D] International Standard ISO/IEC 10038: 1993, ANSI/IEEE Std 1097 802.1D, 1993 edition. 1099 [ADD-ARH] Hinden, R., S. Deering, "IP Version 6 Addressing 1100 Architecture", RFC3513, April 2003. 1102 [CKSM] Braden, R., D. Borman, C. Partridge, "Computing the 1103 Internet Checksum", RFC1071, September 1988. 1105 [ICMPv6] Conta, A., S. Deering, "Internet Control Message Protocol 1106 (ICMPv6) for the Internet Protocol Version 6 (IPv6)", 1107 RFC2463, December 1998. 1109 [IPv6] Deering, S., R. Hinden, "Internet Protocol, Version 6 1110 (IPv6) Specification", RFC2460, December 1998. 1112 [IPX] Novell Incorporated., "IPX Router Specification", Version 1113 1.10, October 1992. 1115 [ND] Narten, T., E. Nordmark, W. Simpson, "Neighbor Discovery 1116 for IP Version 6 (IPv6)", RFC2461, December 1998. 1118 [RFC1469] Pusateri, T., "IP Multicast over Token Ring Local Area 1119 Networks", RFC1469, June 1993. 1121 [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 1122 3", RFC2026, BCP00009, October 1996. 1124 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1125 Requirement Levels", RFC2119, BCP0014, March 1997. 1127 [TKARCH] IBM Token-Ring Network, Architecture Reference, Publication 1128 SC30-3374-02, Third Edition, (September, 1989). 1130 [VRRP-V4] Knight, S., et. al., "Virtual Router Redundancy Protocol", 1131 RFC2338, April 1998. 1133 14. Informative References 1135 [HSRP] Li, T., B. Cole, P. Morton, D. Li, "Cisco Hot Standby 1136 Router Protocol (HSRP)", RFC2281, March 1998. 1138 [IPSTB] Higginson, P., M. Shand, "Development of Router Clusters to 1139 Provide Fast Failover in IP Networks", Digital Technical 1140 Journal, Volume 9 Number 3, Winter 1997. 1142 [OSPF] Moy, J., "OSPF version 2", RFC2328, STD0054, April 1998. 1144 [RIP] Malkin, G., "RIP Version 2", RFC2453, STD0056, November 1145 1998. 1147 15. Author's Address 1149 Robert Hinden 1150 Nokia 1151 313 Fairchild Drive 1152 Mountain View, CA 94043 1153 USA 1155 Phone: +1 650 625-2004 1156 EMail: hinden@iprg.nokia.com 1158 16. Changes from RFC2338 1160 - Changed VMAC assignements to a separate block of IANA Ethernet 1161 addresses and added this to the IANA considerations section. 1162 - Removed different authentication methods, header fields, and 1163 updated the security considerations section. 1164 - General rewrite to change protocol to provide virtual router 1165 functionality from IPv4 to IPv6. Specific changes include: 1166 o Increment VRRP version to 3. 1167 o Change packet format to support an 128-bit IPv6 address. 1168 o Change to only support one router address (instead of multiple 1169 addresses). This included removing address count field from 1170 header. 1171 o Rewrote text to specify IPv6 Neighbor Discovery mechanisms 1172 instead of ARP. 1174 o Changed state machine actions to use Neighbor Discovery 1175 mechanisms. This includes sending unsolicited Neighbor 1176 Advertisements, Receiving Neighbor Solicitations, joining the 1177 appropriate solicited node multicast group, sending Router 1178 Advertisements, and receiving Router Solicitations. 1179 - Revised the section 4 examples text with a clearer description of 1180 mapping of IPv6 address owner, priorities, etc. 1181 - Clarify the section 7.1 text describing address list validation. 1182 - Corrected text in Preempt_Mode definition. 1183 - Changed authentication to be per Virtual Router instead of per 1184 Interface. 1185 - Added new subsection (9.3) stating that VRRP over ATM LANE is 1186 beyond the scope of this document. 1187 - Clarified text describing received packet length check. 1188 - Clarified text describing received authentication check. 1189 - Clarified text describing VRID verification check. 1190 - Added new subsection (8.4) describing need to not forward packets 1191 for adopted IPv6 addresses. 1192 - Added clarification to the security considerations section. 1193 - Added reference for computing the internet checksum. 1194 - Updated references and author information. 1195 - Removed IPR section as no IPR claims have been made against this 1196 draft.