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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 (May 20, 2003) is 7639 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 1118, but no explicit reference was found in the text == Unused Reference: 'OSPF' is defined on line 1136, but no explicit reference was found in the text == Unused Reference: 'RIP' is defined on line 1138, but no explicit reference was found in the text -- Possible downref: Non-RFC (?) normative reference: ref. 'ADD-ARH' ** 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: 10 errors (**), 0 flaws (~~), 9 warnings (==), 5 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 INTERNET-DRAFT R. Hinden/Nokia 2 May 20, 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 November 20, 2003. 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 it's 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 spitting 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 MAY indicate via network management 788 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 MAY 794 indicate via network management that a misconfiguration was detected. 795 If the packet was not generated by the address owner (Priority does 796 not equal 255 (decimal)), the receiver MUST drop the packet, 797 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 MAY indicate via network management that a 804 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-00-01-{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 (00-01) indicate the address block assigned to the VRRP 833 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. 855 The IPv6 source address of an ICMPv6 redirect should be the address 856 the end host used when making its next hop routing decision. If a 857 VRRP router is acting as Master for virtual router(s) containing 858 addresses it does not own, then it must determine which virtual 859 router the packet was sent to when selecting the redirect source 860 address. One method to deduce the virtual router used is to examine 861 the destination MAC address in the packet that triggered the 862 redirect. 864 It may be useful to disable Redirects for specific cases where VRRP 865 is being used to load share traffic between a number of routers in a 866 symmetric topology. 868 8.2 ND Neighbor Solicitation 870 When a host sends an ND Neighbor Solicitation message for the virtual 871 router IPv6 address, the Master virtual router MUST respond to the ND 872 Neighbor Solicitation message with the virtual MAC address for the 873 virtual router. The Master virtual router MUST NOT respond with its 874 physical MAC address. This allows the client to always use the same 875 MAC address regardless of the current Master router. 877 When a Master virtual routers sends an ND Neighbor Solicitation 878 message for a hosts IPv6 address, the Master virtual router MUST 879 include the virtual MAC address for the virtual router if it sends a 880 source link-layer address option in the neighbor solicitation 881 message. It MUST NOT use its physical MAC address in the source 882 link-layer address option. 884 When a VRRP router restarts or boots, it SHOULD not send any ND 885 messages with its physical MAC address for the IPv6 address it owns, 886 it should only send ND messages that include Virtual MAC addresses. 887 This may entail: 889 - When configuring an interface, VRRP routers should send an 890 unsolicitated ND Neighbor Advertisement message containing the 891 virtual router MAC address for the IPv6 address on that interface. 893 - At system boot, when initializing interfaces for VRRP operation; 894 delay all ND Router and Neighbor Advertisements and Solicitation 895 messages until both the IPv6 address and the virtual router MAC 896 address are configured. 898 8.3 Potential Forwarding Loop 900 A VRRP router SHOULD not forward packets addressed to the IPv6 901 Address it becomes Master for if it is not the owner. Forwarding 902 these packets would result in unnecessary traffic. Also in the case 903 of LANs that receive packets they transmit (e.g., token ring) this 904 can result in a forwarding loop that is only terminated when the IPv6 905 TTL expires. 907 One such mechanism for VRRP routers is to add/delete a reject host 908 route for each adopted IPv6 address when transitioning to/from MASTER 909 state. 911 9. Operation over FDDI, Token Ring, and ATM LANE 913 9.1 Operation over FDDI 915 FDDI interfaces remove from the FDDI ring frames that have a source 916 MAC address matching the device's hardware address. Under some 917 conditions, such as router isolations, ring failures, protocol 918 transitions, etc., VRRP may cause there to be more than one Master 919 router. If a Master router installs the virtual router MAC address 920 as the hardware address on a FDDI device, then other Masters' 921 ADVERTISEMENTS will be removed from the ring during the Master 922 convergence, and convergence will fail. 924 To avoid this an implementation SHOULD configure the virtual router 925 MAC address by adding a unicast MAC filter in the FDDI device, rather 926 than changing its hardware MAC address. This will prevent a Master 927 router from removing any ADVERTISEMENTS it did not originate. 929 9.2 Operation over Token Ring 931 Token ring has several characteristics that make running VRRP 932 difficult. These include: 934 - In order to switch to a new master located on a different bridge 935 token ring segment from the previous master when using source 936 route bridges, a mechanism is required to update cached source 937 route information. 939 - No general multicast mechanism supported across old and new token 940 ring adapter implementations. While many newer token ring adapters 941 support group addresses, token ring functional address support is 942 the only generally available multicast mechanism. Due to the 943 limited number of token ring functional addresses these may 944 collide with other usage of the same token ring functional 945 addresses. 947 Due to these difficulties, the preferred mode of operation over token 948 ring will be to use a token ring functional address for the VRID 949 virtual MAC address. Token ring functional addresses have the two 950 high order bits in the first MAC address octet set to B'1'. They 951 range from 03-00-00-00-00-80 to 03-00-02-00-00-00 (canonical format). 952 However, unlike multicast addresses, there is only one unique 953 functional address per bit position. The functional addresses 954 addresses 03-00-00-10-00-00 through 03-00-02-00-00-00 are reserved 955 by the Token Ring Architecture [TKARCH] for user-defined 956 applications. However, since there are only 12 user-defined token 957 ring functional addresses, there may be other non-IP protocols using 958 the same functional address. Since the Novell IPX [IPX] protocol uses 959 the 03-00-00-10-00-00 functional address, operation of VRRP over 960 token ring will avoid use of this functional address. In general, 961 token ring VRRP users will be responsible for resolution of other 962 user-defined token ring functional address conflicts. 964 VRIDs are mapped directly to token ring functional addresses. In 965 order to decrease the likelihood of functional address conflicts, 966 allocation will begin with the largest functional address. Most non- 967 IP protocols use the first or first couple user-defined functional 968 addresses and it is expected that VRRP users will choose VRIDs 969 sequentially starting with 1. 971 VRID Token Ring Functional Address 972 ---- ----------------------------- 973 1 03-00-02-00-00-00 974 2 03-00-04-00-00-00 975 3 03-00-08-00-00-00 976 4 03-00-10-00-00-00 977 5 03-00-20-00-00-00 978 6 03-00-40-00-00-00 979 7 03-00-80-00-00-00 980 8 03-00-00-01-00-00 981 9 03-00-00-02-00-00 982 10 03-00-00-04-00-00 983 11 03-00-00-08-00-00 985 Or more succinctly, octets 3 and 4 of the functional address are 986 equal to (0x4000 >> (VRID - 1)) in non-canonical format. 988 Since a functional address cannot be used used as a MAC level source 989 address, the real MAC address is used as the MAC source address in 990 VRRP advertisements. This is not a problem for bridges since packets 991 addressed to functional addresses will be sent on the spanning-tree 992 explorer path [802.1D]. 994 The functional address mode of operation MUST be implemented by 995 routers supporting VRRP on token ring. 997 Additionally, routers MAY support unicast mode of operation to take 998 advantage of newer token ring adapter implementations that support 999 non-promiscuous reception for multiple unicast MAC addresses and to 1000 avoid both the multicast traffic and usage conflicts associated with 1001 the use of token ring functional addresses. Unicast mode uses the 1002 same mapping of VRIDs to virtual MAC addresses as Ethernet. However, 1003 one important difference exists. ND request/reply packets contain the 1004 virtual MAC address as the source MAC address. The reason for this is 1005 that some token ring driver implementations keep a cache of MAC 1006 address/source routing information independent of the ND cache. 1007 Hence, these implementations need have to receive a packet with the 1008 virtual MAC address as the source address in order to transmit to 1009 that MAC address in a source-route bridged network. 1011 Unicast mode on token ring has one limitation that should be 1012 considered. If there are VRID routers on different source-route 1013 bridge segments and there are host implementations that keep their 1014 source-route information in the ND cache and do not listen to 1015 gratuitous NDs, these hosts will not update their ND source-route 1016 information correctly when a switch-over occurs. The only possible 1017 solution is to put all routers with the same VRID on the same source- 1018 bridge segment and use techniques to prevent that bridge segment from 1019 being a single point of failure. These techniques are beyond the 1020 scope this document. 1022 For both the multicast and unicast mode of operation, VRRP 1023 advertisements sent to 224.0.0.18 should be encapsulated as described 1024 in [RFC1469]. 1026 9.3 Operation over ATM LANE 1028 Operation of VRRP over ATM LANE on routers with ATM LANE interfaces 1029 and/or routers behind proxy LEC's are beyond the scope of this 1030 document. 1032 10. Security Considerations 1034 VRRP for IPv6 does not include any type of authentication. Earlier 1035 versions of VRRP for IPv4 specification included several types of 1036 authentication ranging from none to strong [VRRP-V4]. 1038 Operational experience and further analysis determined that these did 1039 not provide any real measure of security and do to the nature of the 1040 VRRP protocol they did not prevent incorrectly configured or hostile 1041 routers from becoming VRRP masters. In general on LANs any device on 1042 the LAN has the ability to disrupt all communication. For example 1043 although securing VRRP prevents unauthorized machines from taking 1044 part in the election protocol, it does not protect hosts on the 1045 network from being deceived. A gratuitous ND reply from what 1046 purports to be the virtual router's IPv6 address can redirect traffic 1047 to an unauthorized machine. Similarly, individual connections can be 1048 diverted by means of forged ICMPv6 Redirect messages. Consequentially 1049 it was determined it was better to remove the additional 1050 authentication methods in this specification of the VRRP protocol as 1051 it did not provide the authentication originally intended. 1053 VRRP includes a mechanism (setting TTL=255, checking on receipt) that 1054 protects against VRRP packets being injected from another remote 1055 network. This limits most vulnerabilities to local attacks. 1057 VRRP does not provide any confidentiality. Confidentiality is not 1058 necessary for the correct operation of VRRP and there is no 1059 information in the VRRP messages that must be kept secret from other 1060 nodes on the LAN. 1062 11. Acknowledgments 1064 This specification is based on RFC2238. The authors of RFC2238 are 1065 S. Knight, D. Weaver, D. Whipple, R. Hinden, D. Mitzel, P. Hunt, P. 1066 Higginson, M. Shand, and A. Lindem. 1068 The author of this document would also like to thank Erik Nordmark, 1069 Thomas Narten, and Steve Deering for their his helpful suggestions. 1071 12. IANA Considerations 1073 VRRP for IPv6 needs an IPv6 link-local scope multicast address 1074 assigned by the IANA for this specification. The IPv6 multicast 1075 address should be of the following form: 1077 FF02:0:0:0:0:0:XXXX:XXXX 1079 The values assigned address should be entered into section 5.2.2. 1081 A convenient assignment of this link-local scope multicast would be: 1083 FF02:0:0:0:0:0:0:12 1085 as this would be consistent with the IPv4 assignment for VRRP. 1087 13. Normative References 1089 [802.1D] International Standard ISO/IEC 10038: 1993, ANSI/IEEE Std 1090 802.1D, 1993 edition. 1092 [ADD-ARH] Hinden, R., S. Deering, "IP Version 6 Addressing 1093 Architecture", Internet Draft, , October 2002. 1096 [CKSM] Braden, R., D. Borman, C. Partridge, "Computing the 1097 Internet Checksum", RFC1071, September 1988. 1099 [ICMPv6] Conta, A., S. Deering, "Internet Control Message Protocol 1100 (ICMPv6) for the Internet Protocol Version 6 (IPv6)", 1101 RFC2463, December 1998. 1103 [IPv6] Deering, S., R. Hinden, "Internet Protocol, Version 6 1104 (IPv6) Specification", RFC2460, December 1998. 1106 [IPX] Novell Incorporated., "IPX Router Specification", Version 1107 1.10, October 1992. 1109 [ND] Narten, T., E. Nordmark, W. Simpson, "Neighbor Discovery 1110 for IP Version 6 (IPv6)", RFC2461, December 1998. 1112 [RFC1469] Pusateri, T., "IP Multicast over Token Ring Local Area 1113 Networks", RFC1469, June 1993. 1115 [RFC2026] Bradner, S., "The Internet Standards Process -- Revision 1116 3", RFC2026, BCP00009, October 1996. 1118 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1119 Requirement Levels", RFC2119, BCP0014, March 1997. 1121 [TKARCH] IBM Token-Ring Network, Architecture Reference, Publication 1122 SC30-3374-02, Third Edition, (September, 1989). 1124 [VRRP-V4] Knight, S., et. al., "Virtual Router Redundancy Protocol", 1125 RFC2338, April 1998. 1127 14. Informative References 1129 [HSRP] Li, T., B. Cole, P. Morton, D. Li, "Cisco Hot Standby 1130 Router Protocol (HSRP)", RFC2281, March 1998. 1132 [IPSTB] Higginson, P., M. Shand, "Development of Router Clusters to 1133 Provide Fast Failover in IP Networks", Digital Technical 1134 Journal, Volume 9 Number 3, Winter 1997. 1136 [OSPF] Moy, J., "OSPF version 2", RFC2328, STD0054, April 1998. 1138 [RIP] Malkin, G., "RIP Version 2", RFC2453, STD0056, November 1139 1998. 1141 15. Author's Address 1143 Robert Hinden 1144 Nokia 1145 313 Fairchild Drive 1146 Mountain View, CA 94043 1147 USA 1149 Phone: +1 650 625-2004 1150 EMail: hinden@iprg.nokia.com 1152 16. Changes from RFC2338 1154 - Removed different authentication methods, header fields, and 1155 updated the security considerations section. 1156 - General rewrite to change protocol to provide virtual router 1157 functionality from IPv4 to IPv6. Specific changes include: 1158 o Increment VRRP version to 3. 1159 o Change packet format to support an 128-bit IPv6 address. 1160 o Change to only support one router address (instead of multiple 1161 addresses). This included removing address count field from 1162 header. 1163 o Rewrote text to specify IPv6 Neighbor Discovery mechanisms 1164 instead of ARP. 1165 o Changed state machine actions to use Neighbor Discovery 1166 mechanisms. This includes sending unsolicited Neighbor 1167 Advertisements, Receiving Neighbor Solicitations, joining the 1168 appropriate solicited node multicast group, sending Router 1169 Advertisements, and receiving Router Solicitations. 1170 - Revised the section 4 examples text with a clearer description of 1171 mapping of IPv6 address owner, priorities, etc. 1172 - Clarify the section 7.1 text describing address list validation. 1174 - Corrected text in Preempt_Mode definition. 1175 - Changed authentication to be per Virtual Router instead of per 1176 Interface. 1177 - Added new subsection (9.3) stating that VRRP over ATM LANE is 1178 beyond the scope of this document. 1179 - Clarified text describing received packet length check. 1180 - Clarified text describing received authentication check. 1181 - Clarified text describing VRID verification check. 1182 - Added new subsection (8.4) describing need to not forward packets 1183 for adopted IPv6 addresses. 1184 - Added clarification to the security considerations section. 1185 - Added reference for computing the internet checksum. 1186 - Updated references and author information. 1187 - Removed IPR section as no IPR claims have been made against this 1188 draft.