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All references will be assumed normative when checking for downward references. ** There are 11 instances of too long lines in the document, the longest one being 3 characters in excess of 72. == There are 2 instances of lines with multicast IPv4 addresses in the document. If these are generic example addresses, they should be changed to use the 233.252.0.x range defined in RFC 5771 Miscellaneous warnings: ---------------------------------------------------------------------------- == 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 ARP messages with its physical MAC address for the IP address it owns, it should only send ARP messages that include Virtual MAC addresses. 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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) == Missing Reference: 'RFC 2119' is mentioned on line 141, but not defined == Unused Reference: 'RFC2119' is defined on line 1165, but no explicit reference was found in the text ** Obsolete normative reference: RFC 1826 (ref. 'AUTH') (Obsoleted by RFC 2402) ** Obsolete normative reference: RFC 1541 (ref. 'DHCP') (Obsoleted by RFC 2131) -- Possible downref: Non-RFC (?) normative reference: ref. 'HMAC' -- Possible downref: Non-RFC (?) normative reference: ref. 'HSRP' -- Possible downref: Non-RFC (?) normative reference: ref. 'IPSTB' -- Possible downref: Non-RFC (?) normative reference: ref. 'IPX' ** Obsolete normative reference: RFC 1583 (ref. 'OSPF') (Obsoleted by RFC 2178) ** Downref: Normative reference to an Historic RFC: RFC 1058 (ref. 'RIP') ** Downref: Normative reference to an Historic RFC: RFC 1469 -- Possible downref: Non-RFC (?) normative reference: ref. 'TKARCH' Summary: 13 errors (**), 0 flaws (~~), 5 warnings (==), 7 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 INTERNET-DRAFT S. Knight 2 February 2, 1998 D. Weaver 3 Ascend Communications, Inc. 4 D. Whipple 5 Microsoft, Inc. 6 R. Hinden 7 D. Mitzel 8 P. Hunt 9 Nokia 10 P. Higginson 11 M. Shand 12 Digital Equipment Corp. 13 Acee Lindem 14 IBM Corporation 16 Virtual Router Redundancy Protocol 18 20 Status of this Memo 22 This document is an Internet-Draft. Internet-Drafts are working 23 documents of the Internet Engineering Task Force (IETF), its areas, 24 and its working groups. Note that other groups may also distribute 25 working documents as Internet-Drafts. 27 Internet-Drafts are draft documents valid for a maximum of six months 28 and may be updated, replaced, or obsoleted by other documents at any 29 time. It is inappropriate to use Internet-Drafts as reference 30 material or to cite them other than as "work in progress." 32 To learn the current status of any Internet-Draft, please check the 33 "1id-abstracts.txt" listing contained in the Internet- Drafts Shadow 34 Directories on ds.internic.net (US East Coast), nic.nordu.net 35 (Europe), ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific 36 Rim). 38 This internet draft expires on August 2, 1998. 40 Abstract 42 This memo defines the Virtual Router Redundancy Protocol (VRRP). 43 VRRP specifies an election protocol that dynamically assigns 44 responsibility for a virtual router to one of the VRRP routers on a 45 LAN. The VRRP router controlling the IP address(es) associated with 46 a virtual router is called the Master, and forwards packets sent to 47 these IP addresses. The election process provides dynamic fail over 48 in the forwarding responsibility should the Master become 49 unavailable. This allows any of the virtual router IP addresses on 50 the LAN to be used as the default first hop router by end-hosts. The 51 advantage gained from using VRRP is a higher availability default 52 path without requiring configuration of dynamic routing or router 53 discovery protocols on every end-host. 55 Table of Contents 57 1. Introduction...............................................3 58 2. Required Features..........................................5 59 3. VRRP Overview..............................................6 60 4. Sample Configurations......................................8 61 5. Protocol..................................................10 62 5.1 VRRP Packet Format....................................10 63 5.2 IP Field Descriptions.................................10 64 5.3 VRRP Field Descriptions...............................11 65 6. Protocol State Machine....................................14 66 6.1 Parameters............................................14 67 6.2 Timers................................................15 68 6.3 State Transition Diagram..............................15 69 6.4 State Descriptions....................................15 70 7. Sending and Receiving VRRP Packets........................19 71 7.1 Receiving VRRP Packets................................19 72 7.2 Transmitting Packets..................................19 73 7.3 Virtual MAC Address...................................20 74 8. Operational Issues........................................20 75 8.1 ICMP Redirects........................................20 76 8.2 Host ARP Requests.....................................20 77 8.3 Proxy ARP.............................................21 78 9. Operation over FDDI and Token Ring........................21 79 9.1 Operation over FDDI...................................21 80 9.2 Operation over Token Ring.............................22 81 10. Security Considerations...................................24 82 10.1 No Authentication....................................24 83 10.2 Simple Text Password.................................24 84 10.3 IP Authentication Header.............................25 85 11. Acknowledgments...........................................25 86 12. References................................................26 87 13. Authors' Addresses........................................27 88 14. Changes from Previous Drafts..............................29 90 1. Introduction 92 There are a number of methods that an end-host can use to determine 93 its first hop router towards a particular IP destination. These 94 include running (or snooping) a dynamic routing protocol such as 95 Routing Information Protocol [RIP] or OSPF version 2 [OSPF], running 96 an ICMP router discovery client [DISC] or using a statically 97 configured default route. 99 Running a dynamic routing protocol on every end-host may be 100 infeasible for a number of reasons, including administrative 101 overhead, processing overhead, security issues, or lack of a protocol 102 implementation for some platforms. Neighbor or router discovery 103 protocols may require active participation by all hosts on a network, 104 leading to large timer values to reduce protocol overhead in the face 105 of large numbers of hosts. This can result in a significant delay in 106 the detection of a lost (i.e., dead) neighbor, which may introduce 107 unacceptably long "black hole" periods. 109 The use of a statically configured default route is quite popular; it 110 minimizes configuration and processing overhead on the end-host and 111 is supported by virtually every IP implementation. This mode of 112 operation is likely to persist as dynamic host configuration 113 protocols [DHCP] are deployed, which typically provide configuration 114 for an end-host IP address and default gateway. However, this 115 creates a single point of failure. Loss of the default router 116 results in a catastrophic event, isolating all end-hosts that are 117 unable to detect any alternate path that may be available. 119 The Virtual Router Redundancy Protocol (VRRP) is designed to 120 eliminate the single point of failure inherent in the static default 121 routed environment. VRRP specifies an election protocol that 122 dynamically assigns responsibility for a virtual router to one of the 123 VRRP routers on a LAN. The VRRP router controlling the IP 124 address(es) associated with a virtual router is called the Master, 125 and forwards packets sent to these IP addresses. The election 126 process provides dynamic fail-over in the forwarding responsibility 127 should the Master become unavailable. Any of the virtual router's IP 128 addresses on a LAN can then be used as the default first hop router 129 by end-hosts. The advantage gained from using VRRP is a higher 130 availability default path without requiring configuration of dynamic 131 routing or router discovery protocols on every end-host. 133 VRRP provides a function similar to a Cisco Systems, Inc. proprietary 134 protocol named Hot Standby Router Protocol (HSRP) [HSRP] and to a 135 Digital Equipment Corporation, Inc. proprietary protocol named IP 136 Standby Protocol [IPSTB]. 138 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 139 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 140 document are to be interpreted as described in [RFC 2119]. 142 1.1 Scope 144 The remainder of this document describes the features, design goals, 145 and theory of operation of VRRP. The message formats, protocol 146 processing rules and state machine that guarantee convergence to a 147 single Virtual Router Master are presented. Finally, operational 148 issues related to MAC address mapping, handling of ARP requests, 149 generation of ICMP redirect messages, and security issues are 150 addressed. 152 This protocol is intended for use with IPv4 routers only. A separate 153 specification will be produced if it is decided that similar 154 functionality is desirable in an IPv6 environment. 156 1.2 Definitions 158 VRRP Router A router running the Virtual Router Redundancy 159 Protocol. It may participate in one or more 160 virtual routers. 162 Virtual Router An abstract object managed by VRRP that acts 163 as a default router for hosts on a shared LAN. 164 It consists of a Virtual Router Identifier and 165 a set of associated IP address(es) across a 166 common LAN. A VRRP Router may backup one or 167 more virtual routers. 169 IP Address Owner The VRRP router that has the virtual router's 170 IP address(es) as real interface address(es). 171 This is the router that, when up, will respond 172 to packets addressed to one of these IP 173 addresses for ICMP pings, TCP connections, 174 etc. 176 Primary IP Address An IP address selected from the set of real 177 interface addresses. One possible selection 178 algorithm is to always select the first 179 address. VRRP advertisements are always sent 180 using the primary IP address as the source of 181 the IP packet. 183 Virtual Router Master The VRRP router that is assuming the 184 responsibility of forwarding packets sent to 185 the IP address(es) associated with the virtual 186 router, and answering ARP requests for these 187 IP addresses. Note that if the IP address 188 owner is available, then it will always become 189 the Master. 191 Virtual Router Backup The set of VRRP routers available to assume 192 forwarding responsibility for a virtual router 193 should the current Master fail. 195 2.0 Required Features 197 This section outlines the set of features that were considered 198 mandatory and that guided the design of VRRP. 200 2.1 IP Address Backup 202 Backup of IP addresses is the primary function of the Virtual Router 203 Redundancy Protocol. While providing election of a Virtual Router 204 Master and the additional functionality described below, the protocol 205 should strive to: 207 - Minimize the duration of black holes. 208 - Minimize the steady state bandwidth overhead and processing 209 complexity. 210 - Function over a wide variety of multiaccess LAN technologies 211 capable of supporting IP traffic. 212 - Provide for election of multiple virtual routers on a network for 213 load balancing 214 - Support of multiple logical IP subnets on a single LAN segment. 216 2.2 Preferred Path Indication 218 A simple model of Master election among a set of redundant routers is 219 to treat each router with equal preference and claim victory after 220 converging to any router as Master. However, there are likely to be 221 many environments where there is a distinct preference (or range of 222 preferences) among the set of redundant routers. For example, this 223 preference may be based upon access link cost or speed, router 224 performance or reliability, or other policy considerations. The 225 protocol should allow the expression of this relative path preference 226 in an intuitive manner, and guarantee Master convergence to the most 227 preferential router currently available. 229 2.3 Minimization of Unnecessary Service Disruptions 231 Once Master election has been performed then any unnecessary 232 transitions between Master and Backup routers can result in a 233 disruption in service. The protocol should ensure after Master 234 election that no state transition is triggered by any Backup router 235 of equal or lower preference as long as the Master continues to 236 function properly. 238 Some environments may find it beneficial to avoid the state 239 transition triggered when a router becomes available that is more 240 preferential than the current Master. It may be useful to support an 241 override of the immediate convergence to the preferred path. 243 2.4 Extensible Security 245 The virtual router functionality is applicable to a wide range of 246 internetworking environments that may employ different security 247 policies. The protocol should require minimal configuration and 248 overhead in the insecure operation, provide for strong authentication 249 when increased security is required, and allow integration of new 250 security mechanisms without breaking backwards compatible operation. 252 2.5 Efficient Operation over Extended LANs 254 Sending IP packets on a multiaccess LAN requires mapping from an IP 255 address to a MAC address. The use of the virtual router MAC address 256 in an extended LAN employing learning bridges can have a significant 257 effect on the bandwidth overhead of packets sent to the virtual 258 router. If the virtual router MAC address is never used as the 259 source address in a link level frame then the station location is 260 never learned, resulting in flooding of all packets sent to the 261 virtual router. To improve the efficiency in this environment the 262 protocol should: 1) use the virtual router MAC as the source in a 263 packet sent by the Master to trigger station learning; 2) trigger a 264 message immediately after transitioning to Master to update the 265 station learning; and 3) trigger periodic messages from the Master to 266 maintain the station learning cache. 268 3.0 VRRP Overview 270 VRRP specifies an election protocol to provide the virtual router 271 function described earlier. All protocol messaging is performed 272 using IP multicast datagrams, thus the protocol can operate over a 273 variety of multiaccess LAN technologies supporting IP multicast. 275 Each VRRP virtual router has a single well-known MAC address 276 allocated to it. This document currently only details the mapping to 277 networks using the IEEE 802 48-bit MAC address. The virtual router 278 MAC address is used as the source in all periodic VRRP messages sent 279 by the Master router to enable bridge learning in an extended LAN. 281 A virtual router is defined by its virtual router identifier (VRID) 282 and a set of IP addresses. A VRRP router may associate a virtual 283 router with its real addresses on an interface, and may also be 284 configured with additional virtual router mappings and priority for 285 virtual routers it is willing to backup. The mapping between VRID 286 and addresses must be coordinated among all VRRP routers on a LAN. 287 However, there is no restriction against reusing a VRID with a 288 different address mapping on different LANs. The scope of each 289 virtual router is restricted to a single LAN. 291 To minimize network traffic, only the Master for each virtual router 292 sends periodic VRRP Advertisement messages. A Backup router will not 293 attempt to pre-empt the Master unless it has higher priority. This 294 eliminates service disruption unless a more preferred path becomes 295 available. It's also possible to administratively prohibit all pre- 296 emption attempts. The only exception is that a VRRP router will 297 always become Master of any virtual router associated with addresses 298 it owns. If the Master becomes unavailable then the highest priority 299 Backup will transition to Master after a short delay, providing a 300 controlled transition of the virtual router responsibility with 301 minimal service interruption. 303 VRRP defines three types of authentication providing simple 304 deployment in insecure environments, added protection against 305 misconfiguration, and strong sender authentication in security 306 conscious environments. Analysis of the protection provided and 307 vulnerability of each mechanism is deferred to Section 10.0 Security 308 Considerations. In addition new authentication types and data can be 309 defined in the future without affecting the format of the fixed 310 portion of the protocol packet, thus preserving backward compatible 311 operation. 313 The VRRP protocol design provides rapid transition from Backup to 314 Master to minimize service interruption, and incorporates 315 optimizations that reduce protocol complexity while guaranteeing 316 controlled Master transition for typical operational scenarios. The 317 optimizations result in an election protocol with minimal runtime 318 state requirements, minimal active protocol states, and a single 319 message type and sender. The typical operational scenarios are 320 defined to be two redundant routers and/or distinct path preferences 321 among each router. A side effect when these assumptions are violated 322 (i.e., more than two redundant paths all with equal preference) is 323 that duplicate packets may be forwarded for a brief period during 324 Master election. However, the typical scenario assumptions are 325 likely to cover the vast majority of deployments, loss of the Master 326 router is infrequent, and the expected duration in Master election 327 convergence is quite small ( << 1 second ). Thus the VRRP 328 optimizations represent significant simplifications in the protocol 329 design while incurring an insignificant probability of brief network 330 degradation. 332 4. Sample Configurations 334 4.1 Sample Configuration 1 336 The following figure shows a simple network with two VRRP routers 337 implementing one virtual router. Note that this example is provided 338 to help understand the protocol, but is not expected to occur in 339 actual practice. 341 +-----+ +-----+ 342 | MR1 | | BR1 | 343 | | | | 344 | | | | 345 VRID=1 +-----+ +-----+ 346 IP A ---------->* *<--------- IP B 347 | | 348 | | 349 | | 350 ------------------+------------+-----+--------+--------+--------+-- 351 ^ ^ ^ ^ 352 | | | | 353 (IP A) (IP A) (IP A) (IP A) 354 | | | | 355 +--+--+ +--+--+ +--+--+ +--+--+ 356 | H1 | | H2 | | H3 | | H4 | 357 +-----+ +-----+ +--+--+ +--+--+ 359 Legend: 360 ---+---+---+-- = Ethernet, Token Ring, or FDDI 361 H = Host computer 362 MR = Master Router 363 BR = Backup Router 364 * = IP Address 365 (IP) = default router for hosts 367 The above configuration shows a very simple VRRP scenario. In this 368 configuration, the end-hosts install a default route to the IP 369 address of virtual router #1 (IP A) and both routers run VRRP. The 370 router on the left becomes the Master for virtual router #1 (VRID=1) 371 and the router on the right is the Backup for virtual router #1. If 372 the router on the left should fail, the other router will take over 373 virtual router #1 and its IP addresses, and provide uninterrupted 374 service for the hosts. 376 Note that in this example, IP B is not backed up by the router on the 377 left. IP B is only used by the router on the right as its interface 378 address. In order to backup IP B, a second virtual router would have 379 to be configured. This is shown in the next section. 381 4.2 Sample Configuration 2 383 The following figure shows a configuration with two virtual routers 384 with the hosts spitting their traffic between them. This example is 385 expected to be very common in actual practice. 387 +-----+ +-----+ 388 | MR1 | | MR2 | 389 | & | | & | 390 | BR2 | | BR1 | 391 VRID=1 +-----+ +-----+ VRID=2 392 IP A ---------->* *<---------- IP B 393 | | 394 | | 395 | | 396 ------------------+------------+-----+--------+--------+--------+-- 397 ^ ^ ^ ^ 398 | | | | 399 (IP A) (IP A) (IP B) (IP B) 400 | | | | 401 +--+--+ +--+--+ +--+--+ +--+--+ 402 | H1 | | H2 | | H3 | | H4 | 403 +-----+ +-----+ +--+--+ +--+--+ 405 Legend: 406 ---+---+---+-- = Ethernet, Token Ring, or FDDI 407 H = Host computer 408 MR = Master Router 409 BR = Backup Router 410 * = IP Address 411 (IP) = default router for hosts 413 In the above configuration, half of the hosts install a default route 414 to virtual router #1's IP address (IP A), and the other half of the 415 hosts install a default route to virtual router #2's IP address (IP 416 B). This has the effect of load balancing the outgoing traffic, 417 while also providing full redundancy. 419 5.0 Protocol 421 The purpose of the VRRP packet is to communicate to all VRRP routers 422 the priority and the state of the Master router associated with the 423 Virtual Router ID. 425 VRRP packets are sent encapsulated in IP packets. They are sent to 426 the IPv4 multicast address assigned to VRRP. 428 5.1 VRRP Packet Format 430 This section defines the format of the VRRP packet and the relevant 431 fields in the IP header. 433 0 1 2 3 434 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 1 435 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 436 |Version| Type | Virtual Rtr ID| Priority | Count IP Addrs| 437 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 438 | Auth Type | Adver Int | Checksum | 439 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 440 | IP Address (1) | 441 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 442 | . | 443 | . | 444 | . | 445 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 446 | IP Address (n) | 447 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 448 | Authentication Data (1) | 449 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 450 | Authentication Data (2) | 451 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 453 5.2 IP Field Descriptions 455 5.2.1 Source Address 457 The primary IP address of the interface the packet is being sent 458 from. 460 5.2.2 Destination Address 462 The IP multicast address as assigned by the IANA for VRRP is: 464 224.0.0.18 466 This is a link local scope multicast address. Routers MUST NOT 467 forward a datagram with this destination address regardless of its 468 TTL. 470 5.2.3 TTL 472 The TTL MUST be set to 255. A VRRP router receiving a packet with 473 the TTL not equal to 255 MUST discard the packet. 475 5.2.4 Protocol 477 The IP protocol number assigned by the IANA for VRRP is 112 478 (decimal). 480 5.3 VRRP Field Descriptions 482 5.3.1 Version 484 The version field specifies the VRRP protocol version of this packet. 485 This document defines version 2. 487 5.3.2 Type 489 The type field specifies the type of this VRRP packet. The only 490 packet type defined in this version of the protocol is: 492 1 ADVERTISEMENT 494 A packet with unknown type MUST be discarded. 496 5.3.3 Virtual Rtr ID (VRID) 498 The Virtual Router Identifier (VRID) field identifies the virtual 499 router this packet is reporting status for. 501 5.3.4 Priority 503 The priority field specifies the sending VRRP router's priority for 504 the virtual router. Higher values equal higher priority. This field 505 is an 8 bit unsigned integer field. 507 The priority value for the VRRP router that owns the IP address(es) 508 associated with the virtual router MUST be 255 (decimal). 510 VRRP routers backing up a virtual router MUST use priority values 511 between 1-254 (decimal). The default priority value for VRRP routers 512 backing up a virtual router is 100 (decimal). 514 The priority value zero (0) has special meaning indicating that the 515 current Master has stopped participating in VRRP. This is used to 516 trigger Backup routers to quickly transition to Master without having 517 to wait for the current Master to timeout. 519 5.3.5 Count IP Addrs 521 The number of IP addresses contained in this VRRP advertisement. 523 5.3.6 Authentication Type 525 The authentication type field identifies the authentication method 526 being utilized. Authentication type is unique on a per interface 527 basis. The authentication type field is an 8 bit unsigned integer. 528 A packet with unknown authentication type or that does not match the 529 locally configured authentication method MUST be discarded. 531 The authentication methods currently defined are: 533 0 - No Authentication 534 1 - Simple Text Password 535 2 - IP Authentication Header 537 5.3.6.1 No Authentication 539 The use of this authentication type means that VRRP protocol 540 exchanges are not authenticated. The contents of the Authentication 541 Data field should be set to zero on transmission and ignored on 542 reception. 544 5.3.6.2 Simple Text Password 546 The use of this authentication type means that VRRP protocol 547 exchanges are authenticated by a clear text password. The contents 548 of the Authentication Data field should be set to the locally 549 configured password on transmission. There is no default password. 550 The receiver MUST check that the Authentication Data in the packet 551 matches its configured authentication string. Packets that do not 552 match MUST be discarded. 554 5.3.6.3 IP Authentication Header 556 The use of this authentication type means the VRRP protocol exchanges 557 are authenticated using the mechanisms defined by the IP 558 Authentication Header [AUTH] using "The Use of HMAC-MD5-96 within ESP 559 and AH" [HMAC]. Keys may be either configured manually or via a key 560 distribution protocol. 562 If a packet is received that does not pass the authentication check 563 due to a missing authentication header or incorrect message digest, 564 then the packet MUST be discarded. The contents of the 565 Authentication Data field should be set to zero on transmission and 566 ignored on reception. 568 5.3.7 Advertisement Interval (Adver Int) 570 The Advertisement interval indicates the time interval (in seconds) 571 between ADVERTISEMENTS. The default is 1 second. This field is used 572 for troubleshooting misconfigured routers. 574 5.3.8 Checksum 576 The checksum field is used to detect data corruption in the VRRP 577 message. 579 The checksum is the 16-bit one's complement of the one's complement 580 sum of the entire VRRP message starting with the version field. For 581 computing the checksum, the checksum field is set to zero. 583 5.3.9 IP Address(es) 585 One or more IP addresses that are associated with the virtual router. 586 The number of addresses included is specified in the "Count IP Addrs" 587 field. These fields are used for troubleshooting misconfigured 588 routers. 590 5.3.10 Authentication Data 592 The authentication string is currently only utilized for simple text 593 authentication, similar to the simple text authentication found in 594 the Open Shortest Path First routing protocol [OSPF]. It is up to 8 595 characters of plain text. If the configured authentication string is 596 shorter than 8 bytes, the remaining space MUST be zero-filled. Any 597 VRRP packet received with an authentication string that does not 598 match the locally configured authentication string MUST be discarded. 599 The authentication string is unique on a per interface basis. 601 There is no default value for this field. 603 6. Protocol State Machine 605 6.1 Parameters 607 6.1.1 Parameters per Interface 609 Authentication_Type Type of authentication being used. Values 610 are defined in section 5.3.6. 612 Authentication_Data Authentication data specific to the 613 Authentication_Type being used. 615 6.1.2 Parameters per Virtual Router 617 VRID Virtual Router Identifier. Configured item 618 in the range 1-255 (decimal). There is no 619 default. 621 Priority Priority value to be used by this VRRP 622 router in Master election for this virtual 623 router. The value of 255 (decimal) is 624 reserved for the router that owns the IP 625 addresses associated with the virtual 626 router. The value of 0 (zero) is reserved 627 for Master router to indicate it is 628 releasing responsibility for the virtual 629 router. The range 1-254 (decimal) is 630 available for VRRP routers backing up the 631 virtual router. The default value is 100 632 (decimal). 634 IP_Addresses One or more IP addresses associated with 635 this virtual router. Configured item. No 636 default. 638 Advertisement_Interval Time interval between ADVERTISEMENTS 639 (seconds). Default is 1 second. 641 Skew_Time Time to skew Master_Down_Interval in 642 seconds. Calculated as: 644 ( (256 - Priority) / 256 ) 646 Master_Down_Interval Time interval for Backup to declare Master 647 down (seconds). Calculated as: 649 (3 * Advertisement_Interval) + Skew_time 651 Preempt_Mode Controls whether a higher priority Backup 652 router preempts a lower priority Master. 653 Values are True to allow preemption and 654 False to not prohibit preemption. Default 655 is True. 657 Note: Exception is that the router that owns 658 the IP address(es) associated with the 659 virtual router always pre-empts independent 660 of the setting of this flag. 662 6.2 Timers 664 Master_Down_Timer Timer that fires when ADVERTISEMENT has not 665 been heard for Master_Down_Interval. 667 Adver_Timer Timer that fires to trigger sending of 668 ADVERTISEMENT based on 669 Advertisement_Interval. 671 6.3 State Transition Diagram 673 +---------------+ 674 +--------->| |<-------------+ 675 | | Initialize | | 676 | +------| |----------+ | 677 | | +---------------+ | | 678 | | | | 679 | V V | 680 +---------------+ +---------------+ 681 | |---------------------->| | 682 | Master | | Backup | 683 | |<----------------------| | 684 +---------------+ +---------------+ 686 6.4 State Descriptions 688 In the state descriptions below, the state names are identified by 689 {state-name}, and the packets are identified by all upper case 690 characters. 692 A VRRP router implements an instance of the state machine for each 693 virtual router election it is participating in. 695 6.4.1 Initialize 697 The purpose of this state is to wait for a Startup event. If a 698 Startup event is received, then: 700 - If the Priority = 255 (i.e., the router owns the IP address(es) 701 associated with the virtual router) 703 o Send an ADVERTISEMENT 704 o Broadcast a gratuitous ARP request containing the virtual 705 router MAC address for each IP address associated with the 706 virtual router. 707 o Set the Adver_Timer to Advertisement_Interval 708 o Transition to the {Master} state 710 else 712 o Set the Master_Down_Timer to Master_Down_Interval 713 o Transition to the {Backup} state 715 endif 717 6.4.2 Backup 719 The purpose of the {Backup} state is to monitor the availability and 720 state of the Master Router. 722 While in this state, a VRRP router MUST do the following: 724 - MUST NOT respond to ARP requests for the IP address(s) associated 725 with the virtual router. 727 - MUST discard packets with a destination link layer MAC address 728 equal to the virtual router MAC address. 730 - MUST NOT accept packets addressed to the IP address(es) associated 731 with the virtual router. 733 - If a Shutdown event is received, then: 735 o Cancel the Master_Down_Timer 736 o Transition to the {Initialize} state 738 endif 740 - If the Master_Down_Timer fires, then: 742 o Send an ADVERTISEMENT 743 o Broadcast a gratuitous ARP request containing the virtual 744 router MAC address for each IP address associated with the 745 virtual router 746 o Set the Adver_Timer to Advertisement_Interval 747 o Transition to the {Master} state 749 endif 751 - If an ADVERTISEMENT is received, then: 753 If the Priority in the ADVERTISEMENT is Zero, then: 755 o Set the Master_Down_Timer to Skew_Time 757 else: 759 If Preempt_Mode is False, or If the Priority in the 760 ADVERTISEMENT is greater than or equal to the local 761 Priority, then: 763 o Reset the Master_Down_Timer to Master_Down_Interval 765 else: 767 o Discard the ADVERTISEMENT 769 endif 770 endif 771 endif 773 6.4.3 Master 775 While in the {Master} state the router functions as the forwarding 776 router for the IP address(es) associated with the virtual router. 778 While in this state, a VRRP router MUST do the following: 780 - MUST respond to ARP requests for the IP address(es) associated 781 with the virtual router. 783 - MUST forward packets with a destination link layer MAC address 784 equal to the virtual router MAC address. 786 - MUST NOT accept packets addressed to the IP address(es) associated 787 with the virtual router if it is not the IP address owner. 789 - MUST accept packets addressed to the IP address(es) associated 790 with the virtual router if it is the IP address owner. 792 - If a Shutdown event is received, then: 794 o Cancel the Adver_Timer 795 o Send an ADVERTISEMENT with Priority = 0 796 o Transition to the {Initialize} state 798 endif 800 - If the Adver_Timer fires, then: 802 o Send an ADVERTISEMENT 803 o Reset the Adver_Timer to Advertisement_Interval 805 endif 807 - If an ADVERTISEMENT is received, then: 809 If the Priority in the ADVERTISEMENT is Zero, then: 811 o Send an ADVERTISEMENT 812 o Reset the Adver_Timer to Advertisement_Interval 814 else: 816 If the Priority in the ADVERTISEMENT is greater than the 817 local Priority, 818 or 819 If the Priority in the ADVERTISEMENT is equal to the local 820 Priority and the primary IP Address of the sender is greater 821 than the local primary IP Address, then: 823 o Cancel Adver_Timer 824 o Set Master_Down_Timer to Master_Down_Interval 825 o Transition to the {Backup} state 827 else: 829 o Discard ADVERTISEMENT 831 endif 832 endif 833 endif 835 7. Sending and Receiving VRRP Packets 837 7.1 Receiving VRRP Packets 839 Performed the following functions when a VRRP packet is received: 841 - MUST verify that the IP TTL is 255. 842 - MUST verify the VRRP version 843 - MUST verify that the received packet length is greater than or 844 equal to the VRRP header 845 - MUST verify the VRRP checksum 846 - MUST perform authentication specified by Auth Type 848 If any one of the above checks fails, the receiver MUST discard the 849 packet, SHOULD log the event and MAY indicate via network management 850 that an error occurred. 852 - MUST verify that the VRID is valid on the receiving interface 854 If the above check fails, the receiver MUST discard the packet. 856 - MAY verify that the IP address(es) associated with the VRID are 857 valid 859 If the above check fails, the receiver SHOULD log the event and MAY 860 indicate via network management that a misconfiguration was detected. 861 If the packet was not generated by the address owner (Priority does 862 not equal 255 (decimal)), the receiver MUST drop the packet, 863 otherwise continue processing. 865 - MUST verify that the Adver Interval in the packet is the same as 866 the locally configured for this virtual router 868 If the above check fails, the receiver MUST discard the packet, 869 SHOULD log the event and MAY indicate via network management that a 870 misconfiguration was detected. 872 7.2 Transmitting VRRP Packets 874 The following operations MUST be performed when transmitting a VRRP 875 packet. 877 - Fill in the VRRP packet fields with the appropriate virtual 878 router configuration state 879 - Compute the VRRP checksum 880 - Set the source MAC address to Virtual Router MAC Address 881 - Set the source IP address to interface primary IP address 882 - Set the IP protocol to VRRP 883 - Send the VRRP packet to the VRRP IP multicast group 885 Note: VRRP packets are transmitted with the virtual router MAC 886 address as the source MAC address to ensure that learning bridges 887 correctly determine the LAN segment the virtual router is attached 888 to. 890 7.3 Virtual Router MAC Address 892 The virtual router MAC address associated with a virtual router is an 893 IEEE 802 MAC Address in the following format: 895 00-00-5E-00-01-{VRID} (in hex in internet standard bit-order) 897 The first three octets are derived from the IANA's OUI. The next two 898 octets (00-01) indicate the address block assigned to the VRRP 899 protocol. {VRID} is the VRRP Virtual Router Identifier. This 900 mapping provides for up to 255 VRRP routers on a network. 902 8. Operational Issues 904 8.1 ICMP Redirects 906 ICMP Redirects may be used normally when VRRP is running between a 907 group of routers. This allows VRRP to be used in environments where 908 the topology is not symmetric. 910 The IP source address of an ICMP redirect should be the address the 911 end host used when making its next hop routing decision. If a VRRP 912 router is acting as Master for virtual router(s) containing addresses 913 it does not own, then it must determine which virtual router the 914 packet was sent to when selecting the redirect source address. One 915 method to deduce the virtual router used is to examine the 916 destination MAC address in the packet that triggered the redirect. 918 It may be useful to disable Redirects for specific cases where VRRP 919 is being used to load share traffic between a number of routers in a 920 symmetric topology. 922 8.2 Host ARP Requests 924 When a host sends an ARP request for one of the virtual router IP 925 addresses, the Master virtual router MUST respond to the ARP request 926 with the virtual MAC address for the virtual router. The Master 927 virtual router MUST NOT respond with its physical MAC address. This 928 allows the client to always use the same MAC address regardless of 929 the current Master router. 931 When a VRRP router restarts or boots, it SHOULD not send any ARP 932 messages with its physical MAC address for the IP address it owns, it 933 should only send ARP messages that include Virtual MAC addresses. 934 This may entail: 936 - When configuring an interface, VRRP routers should broadcast a 937 gratuitous ARP request containing the virtual router MAC address 938 for each IP address on that interface. 940 - At system boot, when initializing interfaces for VRRP operation; 941 delay gratuitous ARP requests and ARP responses until both the IP 942 address and the virtual router MAC address are configured. 944 8.3 Proxy ARP 946 If Proxy ARP is to be used on a VRRP router, then the VRRP router 947 must advertise the Virtual Router MAC address in the Proxy ARP 948 message. Doing otherwise could cause hosts to learn the real MAC 949 address of the VRRP router. 951 9. Operation over FDDI and Token Ring 953 9.1 Operation over FDDI 955 FDDI interfaces remove from the FDDI ring frames that have a source 956 MAC address matching the device's hardware address. Under some 957 conditions, such as router isolations, ring failures, protocol 958 transitions, etc., VRRP may cause there to be more than one Master 959 router. If a Master router installs the virtual router MAC address 960 as the hardware address on a FDDI device, then other Masters' 961 ADVERTISEMENTS will be removed from the ring during the Master 962 convergence, and convergence will fail. 964 To avoid this an implementation SHOULD configure the virtual router 965 MAC address by adding a unicast MAC filter in the FDDI device, rather 966 than changing its hardware MAC address. This will prevent a Master 967 router from removing any ADVERTISEMENTS it did not originate. 969 9.2 Operation over Token Ring 971 Token ring has several characteristics which make running VRRP 972 difficult. These include: 974 - In order to switch to a new master located on a different bridge 975 token ring segment from the previous master when using source 976 route bridges, a mechanism is required to update cached source 977 route information. 979 - No general multicast mechanism supported across old and new token 980 ring adapter implementations. While many newer token ring adapters 981 support group addresses, token ring functional address support is 982 the only generally available multicast mechanism. Due to the 983 limited number of token ring functional addresses these may 984 collide with other usage of the same token ring functional 985 addresses. 987 Due to these difficulties, the preferred mode of operation over token 988 ring will be to use a token ring functional address for the VRID 989 virtual MAC address. Token ring functional addresses have the two 990 high order bits in the first MAC address octet set to B'1'. They 991 range from 03-00-00-00-00-80 to 03-00-02-00-00-00 (canonical format). 992 However, unlike multicast addresses, there is only one unique 993 functional address per bit position. The functional addresses 994 addresses 03-00-00-10-00-00 through 03-00-02-00-00-00 are reserved 995 by the Token Ring Architecture [TKARCH] for user-defined 996 applications. However, since there are only 12 user-defined token 997 ring functional addresses, there may be other non-IP protocols using 998 the same functional address. Since the Novell IPX [IPX] protocol uses 999 the 03-00-00-10-00-00 functional address, operation of VRRP over 1000 token ring will avoid use of this functional address. In general, 1001 token ring VRRP users will be responsible for resolution of other 1002 user-defined token ring functional address conflicts. 1004 VRIDs are mapped directly to token ring functional addresses. In 1005 order to decrease the likelihood of functional address conflicts, 1006 allocation will begin with the largest functional address. Most non- 1007 IP protocols use the first or first couple user-defined functional 1008 addresses and it is expected that VRRP users will choose VRIDs 1009 sequentially starting with 1. 1011 VRID Token Ring Functional Address 1012 ---- ----------------------------- 1013 1 03-00-02-00-00-00 1014 2 03-00-04-00-00-00 1015 3 03-00-08-00-00-00 1016 4 03-00-10-00-00-00 1017 5 03-00-20-00-00-00 1018 6 03-00-40-00-00-00 1019 7 03-00-80-00-00-00 1020 8 03-00-00-01-00-00 1021 9 03-00-00-02-00-00 1022 10 03-00-00-04-00-00 1023 11 03-00-00-08-00-00 1025 Or more succinctly, octets 3 and 4 of the functional address are 1026 equal to (0x4000 >> (VRID - 1)) in non-canonical format. 1028 Since a functional address cannot be used used as a MAC level source 1029 address, the real MAC address is used as the MAC source address in 1030 VRRP advertisements. This is not a problem for bridges since packets 1031 addressed to functional addresses will be sent on the spanning-tree 1032 explorer path [802.1D]. 1034 The functional address mode of operation MUST be implemented by 1035 routers supporting VRRP on token ring. 1037 Additionally, routers MAY support unicast mode of operation to take 1038 advantage of newer token ring adapter implementations which support 1039 non-promiscuous reception for multiple unicast MAC addresses and to 1040 avoid both the multicast traffic and usage conflicts associated with 1041 the use of token ring functional addresses. Unicast mode uses the 1042 same mapping of VRIDs to virtual MAC addresses as Ethernet. However, 1043 one important difference exists. ARP request/reply packets contain 1044 the virtual MAC address as the source MAC address. The reason for 1045 this is that some token ring driver implementations keep a cache of 1046 MAC address/source routing information independent of the ARP cache. 1047 Hence, these implementations need have to receive a packet with the 1048 virtual MAC address as the source address in order to transmit to 1049 that MAC address in a source-route bridged network. 1051 Unicast mode on token ring has one limitation which should be 1052 considered. If there are VRID routers on different source-route 1053 bridge segments and there are host implementations which keep their 1054 source-route information in the ARP cache and do not listen to 1055 gratuitous ARPs, these hosts will not update their ARP source-route 1056 information correctly when a switch-over occurs. The only possible 1057 solution is to put all routers with the same VRID on the same source- 1058 bridge segment and use techniques to prevent that bridge segment from 1059 being a single point of failure. These techniques are beyond the 1060 scope this document. 1062 For both the multicast and unicast mode of operation, VRRP 1063 advertisements sent to 224.0.0.18 should be encapsulated as described 1064 in [RFC1469]. 1066 10. Security Considerations 1068 VRRP is designed for a range of internetworking environments that may 1069 employ different security policies. The protocol includes several 1070 authentication methods ranging from no authentication, simple clear 1071 text passwords, and strong authentication using IP Authentication 1072 with MD5 HMAC. The details on each approach including possible 1073 attacks and recommended environments follows. 1075 Independent of any authentication type VRRP includes a mechanism 1076 (setting TTL=255, checking on receipt) that protects against VRRP 1077 packets being injected from another remote network. This limits most 1078 vulnerabilities to local attacks. 1080 10.1 No Authentication 1082 The use of this authentication type means that VRRP protocol 1083 exchanges are not authenticated. This type of authentication SHOULD 1084 only be used in environments were there is minimal security risk and 1085 little chance for configuration errors (e.g., two VRRP routers on a 1086 LAN). 1088 10.2 Simple Text Password 1090 The use of this authentication type means that VRRP protocol 1091 exchanges are authenticated by a simple clear text password. 1093 This type of authentication is useful to protect against accidental 1094 misconfiguration of routers on a LAN. It protects against routers 1095 inadvertently backing up another router. A new router must first be 1096 configured with the correct password before it can run VRRP with 1097 another router. This type of authentication does not protect against 1098 hostile attacks where the password can be learned by a node snooping 1099 VRRP packets on the LAN. The Simple Text Authentication combined 1100 with the TTL check makes it difficult for a VRRP packet to be sent 1101 from another LAN to disrupt VRRP operation. 1103 This type of authentication is RECOMMENDED when there is minimal risk 1104 of nodes on a LAN actively disrupting VRRP operation. 1106 10.3 IP Authentication Header 1108 The use of this authentication type means the VRRP protocol exchanges 1109 are authenticated using the mechanisms defined by the IP 1110 Authentication Header [AUTH] using "The Use of HMAC-MD5-96 within ESP 1111 and AH", [HMAC]. This provides strong protection against 1112 configuration errors, replay attacks, and packet 1113 corruption/modification. 1115 This type of authentication is RECOMMENDED when there is limited 1116 control over the administration of nodes on a LAN. While this type 1117 of authentication does protect the operation of VRRP, there are other 1118 types of attacks that may be employed on shared media links (e.g., 1119 generation of bogus ARP replies) which are independent from VRRP and 1120 are not protected. 1122 11. Acknowledgments 1124 The authors would like to thank Glen Zorn, and Michael Lane, Clark 1125 Bremer, Hal Peterson, Tony Li, Barbara Denny, Joel Halpern, and Steve 1126 Bellovin for their comments and suggestions. 1128 12. References 1130 [802.1D] International Standard ISO/IEC 10038: 1993, ANSI/IEEE Std 1131 802.1D, 1993 edition. 1133 [AUTH] Atkinson, R., "IP Authentication Header", RFC-1826, August 1134 1995. 1136 [DISC] Deering, S., "ICMP Router Discovery Messages", RFC-1256, 1137 September 1991. 1139 [DHCP] Droms, R., "Dynamic Host Configuration Protocol", RFC-1541, 1140 October 1993. 1142 [HMAC] Madson, C., R. Glenn, "The Use of HMAC-MD5-96 within ESP 1143 and AH", Internet Draft, , July 1997. 1146 [HSRP] Li, T., B. Cole, P. Morton, D. Li, "Hot Standby Router 1147 Protocol (HSRP)", Internet Draft, , 1148 October 1997. 1150 [IPSTB] Higginson, P., M. Shand, "Development of Router Clusters to 1151 Provide Fast Failover in IP Networks", Digital Technical 1152 Journal, Volume 9 Number 3, Winter 1997. 1154 [IPX] Novell Incorporated., "IPX Router Specification", Version 1155 1.10, October 1992. 1157 [OSPF] Moy, J., "OSPF version 2", RFC-1583, July 1997. 1159 [RIP] Hedrick, C., "Routing Information Protocol" , RFC-1058, 1160 June 1988. 1162 [RFC1469] Pusateri, T., "IP over Token Ring LANs", RFC 1469, June 1163 1993. 1165 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 1166 Requirement Levels", RFC-2119, BCP14, March 1997. 1168 [TKARCH] IBM Token-Ring Network, Architecture Reference, Publication 1169 SC30-3374-02, Third Edition, (September, 1989). 1171 13. Author's Addresses 1173 Steven Knight Phone: +1 612 943-8990 1174 Ascend Communications EMail: Steven.Knight@ascend.com 1175 High Performance Network Division 1176 10250 Valley View Road, Suite 113 1177 Eden Prairie, MN USA 55344 1178 USA 1180 Douglas Weaver Phone: +1 612 943-8990 1181 Ascend Communications EMail: Doug.Weaver@ascend.com 1182 High Performance Network Division 1183 10250 Valley View Road, Suite 113 1184 Eden Prairie, MN USA 55344 1185 USA 1187 David Whipple Phone: +1 206 703-3876 1188 Microsoft Corporation EMail: dwhipple@microsoft.com 1189 One Microsoft Way 1190 Redmond, WA USA 98052-6399 1191 USA 1193 Robert Hinden Phone: +1 408 990-2004 1194 Nokia EMail: hinden@ipsilon.com 1195 232 Java Drive 1196 Sunnyvale, CA 94089 1197 USA 1199 Danny Mitzel Phone: +1 408 990-2037 1200 Nokia EMail: mitzel@ipsilon.com 1201 232 Java Drive 1202 Sunnyvale, CA 94089 1203 USA 1205 Peter Hunt Phone: +1 408 990-2093 1206 Nokia EMail: hunt@ipsilon.com 1207 232 Java Drive 1208 Sunnyvale, CA 94089 1209 USA 1211 P. Higginson Phone: +44 118 920 6293 1212 Digital Equipment Corp. EMail: higginson@mail.dec.com 1213 Digital Park 1214 Imperial Way 1215 Reading 1216 Berkshire 1217 RG2 0TE 1218 UK 1219 M. Shand Phone: +44 118 920 4424 1220 Digital Equipment Corp. EMail: shand@mail.dec.com 1221 Digital Park 1222 Imperial Way 1223 Reading 1224 Berkshire 1225 RG2 0TE 1226 UK 1228 Acee Lindem Phone: 1-919-254-1805 1229 IBM Corporation E-Mail: acee@raleigh.ibm.com 1230 P.O. Box 12195 1231 Research Triangle Park, NC 27709 1232 USA 1234 14. Changes from Previous Drafts 1236 Changes from 1238 - Added IANA assignment for MAC prefix. 1239 - Clarified examples and definitions. 1240 - Updated reference to Digital IP Standby protocol. 1242 Changes from 1244 - Added IANA assignments for protocol and multicast address. MAC 1245 prefix still needed. 1246 - Added Token Ring specific procedures supplied by Acee Lindem and 1247 added him as an author. 1248 - Tightened up terminology and definitions and made appropriate 1249 changes in the text. 1251 Changes from 1253 - Updated text and references to point to "The Use of HMAC-MD5-96 1254 within ESP and AH" that is the correct reference for the use of 1255 IPSEC AH with MD5. 1257 Changes from 1259 Major change to use real IP addresses instead of virtual IP 1260 addresses. Changes include: 1262 - Updated version number to 2. 1263 - Modified packet header 1264 - New terminology (removed cluster, virtual IP address, etc., added 1265 VRID, associated IP address(es), etc.). 1266 - Special case of priority = 255 for router owning VRID and 1267 associated IP address(es). 1268 - Reworked examples. 1269 - Rewrote introductory and overview sections. 1270 - Added rules for redirects and ARP. 1271 - Added sending gratuitous ARP request when transitioning to Master. 1273 Changes from 1275 - Added Preempt_Mode to allow user control over preemption 1276 independent of configured priorities. 1277 - Rewrote authentication section and expanded security 1278 considerations. 1279 - Expanded State Description section and removed State Table which 1280 become redundant and impossible to edit. 1281 - Changed authentication to be on a per interface basis (not per 1282 cluster). 1283 - Clarified text on disabling ICMP Redirects. 1284 - Added text on FDDI and Token Ring issues. 1285 - Added HSRP acknowledgment. 1286 - Rewrote Introduction, Required Features, and VRRP Overview 1287 sections. 1288 - Many small text clarifications. 1290 Changes from 1292 - Changed default behavior to stay with current master when 1293 priorities are equal. This behavior can be changed by configuring 1294 explicit priorities. 1295 - Changed Master state behavior to not send Advertisements when 1296 receiving Advertisement with lower priority. Change reduces worst 1297 case election message overhead to "n", where "n" is number of 1298 configured equal priority VRRP routers. 1299 - Added Skew_Time parameter and changed receiving advertisement with 1300 zero priority behavior to cause resulting advertisement sent to be 1301 skewed by priority. 1302 - Changed sending behavior to send VRRP packets with VMAC as source 1303 MAC and added text describing why this is important for bridged 1304 environments. 1305 - Changed definition of VMAC to be in IANA assigned unicast MAC 1306 block. 1307 - Added Advertisement Interval to VRRP header. 1308 - Added text regarding ICMP Redirects, Proxy ARP, and network 1309 management issues. 1310 - Various small text clarifications.