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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 1 Network Working Group Naiming Shen, Ed (Redback Networks) 2 Internet Draft Alex Zinin, Ed (Alcatel) 3 Expiration Date: January 2005 4 July 2004 6 Point-to-point operation over LAN 7 in link-state routing protocols 9 draft-ietf-isis-igp-p2p-over-lan-04.txt 11 Status of this Memo 13 By submitting this Internet-Draft, I certify that any applicable 14 patent or other IPR claims of which I am aware have been disclosed, 15 or will be disclosed, and any of which I become aware will be 16 disclosed, in accordance with RFC 3668. 18 Internet-Drafts are working documents of the Internet Engineering 19 Task Force (IETF), its areas, and its working groups. Note that 20 other groups may also distribute working documents as 21 Internet-Drafts. 23 Internet-Drafts are draft documents valid for a maximum of six 24 months and may be updated, replaced, or obsoleted by other 25 documents at any time. It is inappropriate to use Internet- 26 Drafts as reference material or to cite them other than as 27 "work in progress." 29 The list of current Internet-Drafts can be accessed at 30 http://www.ietf.org/1id-abstracts.html 32 The list of Internet-Draft Shadow Directories can be accessed at 33 http://www.ietf.org/shadow.html 35 Abstract 37 The two predominant circuit types used by link state routing 38 protocols are point-to-point and broadcast. It is important to 39 identify the correct circuit type when forming adjacencies, 40 flooding link state database packets, and representing the circuit 41 topologically. This document describes a simple mechanism to treat 42 the broadcast network as a point-to-point connection from the 43 standpoint of IP routing. 45 Contributors 47 The following individuals are the authers that contributed to the 48 contents of this document. 50 Acee Lindem 51 Redback Networks 52 102 Carric Bend Court 53 Cary, NC 27519 USA 54 acee@redback.com 56 Jenny Yuan 57 Redback Networks 58 350 Holger Way 59 San Jose, CA, 95134 USA 60 jenny@redback.com 62 Russ White 63 Cisco Systems, Inc. 64 7025 Kit Creek Rd. 65 Research Triangle Park, NC 27709 66 e-mail: riw@cisco.com 68 Stefano Previdi 69 Cisco Systems, Inc. 70 De Kleetlaan 6A 71 1831 Diegem - Belgium 72 email: sprevidi@cisco.com 74 1. Introduction 76 Point-to-point and broadcast are the two predominant circuit 77 types used by link state routing protocols such as ISIS [ref1] 78 [ref2] and OSPF [ref3, ref5]. They are treated differently with 79 respect to establishing neighbor adjacencies, flooding link-state 80 information, representation of the topology, SPF calculation and 81 protocol packets. The most important differences are that broadcast 82 circuits utilize the concept of a designated router and are 83 represented topologically as virtual nodes in the network topology 84 graph. 86 Compared with broadcast circuits, point-to-point circuits 87 afford more straightforward IGP operation. There is no designated 88 router involved and there is no representation of the pseudo-node 89 or network LSA in the link state database. For ISIS, there also is 90 no periodic database synchronization. Conversely, if there are more 91 than two routers on the LAN media, the traditional view of the 92 broadcast circuit will reduce the routing information in the network. 94 When there are only two routers on the LAN, it makes more sense to 95 treat the connection between the two routers as a point-to-point 96 circuit. This document describes the mechanism to allow link state 97 routing protocols to operate using point-to-point connections over 98 a LAN under this condition. Some implications related to forwarding 99 IP packets on this type of circuit are also discussed. We will refer 100 to this as a p2p-over-lan circuit in this document. 102 2. Motivation 104 Even though a broadcast circuit is meant to handle more than two 105 devices, there are cases where only two routers are connected 106 over either the physical or logical LAN segment: 108 1. The media itself is being used for point-to-point 109 operation between two routers. This is mainly for 110 long-haul operation. 111 2. There are only two routers on the physical LAN. 112 3. There are only two routers on a virtual LAN (vLAN). 114 In any of the above cases, the link state routing protocols will 115 normally still treat the media as a broadcast circuit. Hence, they 116 will have the overhead involved with protocol LAN operation without 117 the benefits of reducing routing information and optimized flooding. 119 Being able to treat a LAN as a point-to-point circuit provides the 120 benefit of reduction in the amount of information routing 121 protocols must carry and manage. DR/DIS election can be omitted. 122 Flooding can be done as in p2p links without the need of using 123 "LSA reflection" by the DR in OSPF or periodic CSNPs in ISIS. 125 Also, if a broadcast segment wired as a point-to-point link 126 can be treated as a point-to-point link, only the connection between 127 the two routers would need to be advertised as a topological entity. 129 Even when there are multiple routers on the LAN an ISP may want 130 to sub-group the routers into multiple vLANs since this allows 131 them to assign different costs to IGP neighbors. When there are 132 only two routers in some of the vLANs, this LAN can be viewed by 133 the IGP as a mesh of point-to-point connections. 135 IP unnumbered configuration is widely used in networks. It enables 136 IP processing on a point-to-point interface without an explicit 137 IP address. The IP unnumbered interface can "borrow" the IP 138 address of another interface on the node. The advantages of 139 unnumbered point-to-point links are obvious in the current IP 140 addressing environment where addresses are a scarce resource. The 141 unnumbered interface can also be applied over p2p-over-lan circuits. 142 Separating the concept of network type from media type will allow 143 LANs, e.g. ethernet, to be unnumbered and realize the IP address 144 space savings. Another advantage is in simpler network management 145 and configuration. In the case of IPv6 network, link-local address 146 used in ISIS [ref4] and OSPFv3 [ref5] serves the same purpose. 148 3. IP multi-access subnets 150 When an IP network includes multi-access segments, each segment is 151 usually assigned a separate subnet and each router connected to it is 152 assigned a distinct IP address within that subnet. The role of the 153 IP address assigned to a multi-access interface can be outlined as 154 follows: 156 1. Source IP address - The interface address can be used by 157 the router as the source IP address in locally originated 158 IP packets destined for that subnet or having a best path 159 next hop on that subnet. 161 2. Destination IP address - The interface address can be used by 162 other devices in the network as a destination address for 163 packets to router applications (examples include telnet, SMTP, 164 TFTP, OSPF, BGP, etc). 166 3. Next-hop identifier - If other routers connected to the same 167 segment need to forward traffic through the router, the 168 corresponding routes in their routing tables will include the 169 router's interface IP address. This address will be used to 170 find the router's MAC address using the ARP protocol. 171 Effectively, the interface IP addresses help other routers 172 find the data-link layer details that are required to specify 173 the destination of the encapsulating data-link frame when it 174 is sent on the segment. 176 The IP addressing scheme includes an option that allows the 177 administrators to not assign any subnets to point-to-point links 178 (links connecting only two devices and using protocols like PPP, SLIP 179 or HDLC for IP encapsulation). This is possible, because the routers 180 do not need next-hop identifiers on point-to-point links (there is 181 only one destination for any transmission), and an interface 182 independent IP address can be used as the source and destination. 183 Using the unnumbered option for a point-to-point link essentially 184 makes it a purely topological entity used only to reach other 185 destinations. 187 4. Point-to-point connection over LAN media 189 The idea is very simple: provide a configuration mechanism to 190 inform the IGP that the circuit is type point-to-point 191 irrespective of the physical media type. For the IGP, this implies 192 that it will send protocol packets with the appropriate 193 point-to-point information and expects to receive protocol packets 194 as they would be received on a point-to-point circuit. Over LAN 195 media, the MAC header must contain the correct multicast MAC address 196 to be received by the other side of the connection. For vLAN 197 environments, the MAC header must also contain the proper vLAN ID. 199 In order to allow LAN links used to connect only two routers to be 200 treated as unnumbered point-to-point interfaces, the MAC address 201 resolution and nexthop IP address issues need to be addressed. 203 4.1 Operation of ISIS 205 This p2p-over-lan circuit extension for ISIS is only concerned 206 in pure IP routing and forwarding operation. 208 Since physically the circuit is a broadcast one, the ISIS protocol 209 packets need to have MAC addresses for this p2p-over-lan circuit. 210 From link layer point of view, those packets are ISIS LAN packets. 211 The Multi-destination address including AllISs, AllL1ISs and AllL2ISs 212 defined in [ref1] can be used for link layer encapsulation, the 213 use of AllISs is recommended. 215 The circuit needs to have IP address(es) and the p2p IIH over this 216 circuit MUST include the IP interface address(es) as defined in 217 [ref2]. The IPv4 address(es) included in the IIHs is either the 218 IP address assigned to the interface in the case of a numbered 219 interface or the interface-independent IP address in the case of 220 an unnumbered interface. The IPv6 addresses are link-local IPv6 221 address(es) [ref4]. 223 4.2 Operation of OSPF and OSPFv3 225 OSPF and OSPFv3 [ref5] routers supporting the capabilities 226 described herein should support an additional interface 227 configuration parameter specifying the interface topology type. 228 For a LAN (i.e., broadcast capable) interface, the interface may 229 be viewed as a point-to-point interface. Both routers on the LAN 230 will simply join the AllSPFRouters multicast group and send all 231 OSPF packets with a destination address of AllSPFRouters. 232 AllSPFRouters is 224.0.0.5 for OSPF and FF02::5 for OSPFv3. 233 This is identical to operation over a physical point-to-point 234 link as described in sections 8.1 and 8.2 of [ref3]. 236 4.3 ARP and ND 238 Unlike normal point-to-point IGP circuit, the IP nexthop for the 239 routes using this p2p-over-lan circuit as an outbound interface is 240 not optional. The IP nexthop address has to be a valid interface 241 or internal address on the adjacent router. This address is used by 242 local router to obtain the MAC address for IP packet forwarding. 243 The ARP process has to be able to resolve the internal IP address 244 used for the unnumbered p2p-over-lan circuits. In IPv6 case, 245 the ND resolves the MAC for the link-local address on the 246 p2p-over-lan circuit, which is part of the IPv6 neighbor 247 discovering process [ref6]. 249 4.4 Other MAC address resolution mechanisms 251 In more general cases while p2p-over-lan circuit is used as an 252 unnumbered link, other MAC address resolution mechanisms are needed 253 for IP packet forwarding. For example, if link-state IGP is not 254 configured over this p2p-over-lan link, or if the mechanism described 255 in section 4.3 is not possible. The following techniques can be used 256 to acquire the MAC address and/or the next-hop IP address of the 257 remote device on an unnumbered point-to-point LAN link. 259 1. Static configuration. A router can be statically configured 260 with the MAC address that should be used as the destination 261 MAC address when sending data out of the interface. 263 2. MAC address gleaning. If a dynamic routing protocol is running 264 between the routers connected to the link, the MAC address of 265 the remote device can be taken from a data-link frame carrying 266 a packet of the corresponding routing protocol. 268 4.5 Detection of mis-configuration 270 With this p2p-over-lan extension, the difference between a LAN and 271 a point-to-point circuit can be made purely by configuration. It is 272 important to implement the mechanisms for early detection of 273 mis-configuration. 275 If the circuit is configured as point-to-point type and receives 276 LAN hello packets, the router MUST discard the incoming packets; If 277 the circuit is a LAN type and receive point-to-point hello packets, 278 it MUST discard the incoming packets. If the system ID or the 279 router ID of incoming hello packet does not match the system ID or 280 the router ID of already established adjacency over this p2p-over-lan 281 circuit, it MUST discard the packet. The implementation should offer 282 logging and debugging information of the above events. 284 5. Compatibility considerations 286 Both routers on a LAN must support the p2p-over-lan extension 287 and both must have the LAN segment configured as a p2p-over-lan 288 circuit for successful operation. Both routers SHOULD support at 289 least one of the above listed methods for mapping ip addresses on 290 the link to MAC address. If a proprietary method of IP address to 291 MAC address resolution is used by one router, both routers must 292 be capable of using the same method. Otherwise, the link should 293 be configured as a standard LAN link, with traditional IGP LAN 294 models used. 296 6. Scalability and deployment considerations 298 While there is advantage to use this extension on the LANs 299 that are connected back-to-back or only contain two routers, 300 however there are tradeoffs when modeling a LAN as multiple vLANs 301 and using this extension since one does sacrifice the inherent 302 scalability benefits of multi-access networks. In general, 303 it will increase the link-state database size, the amount of 304 packets flooded and the route calculation overhead. Network design 305 engineers should carefully balance between the associated 306 overhead. 308 Deployment of the described technique brings noticeable benefits from 309 the perspective of IP address usage, the network management and the 310 router configuration. Note, however, that use of the IP unnumbered 311 option for point-to-point LAN links inherits the same problems as 312 those present for serial links, i.e., not being able to ping or 313 monitor a specific interface between routers. 315 7. Security Considerations 317 This document does not introduce any new security issues to ISIS or 318 OSPF. For ARP to support unnumbered IP interface addresses, it needs 319 to verify the p2p-over-lan circuit type described in this document 320 and to verify the ARP or ND packet source interface address to match 321 the IGP adjacency interface IP address. 323 If one router on a link thinks that a LAN should be either 324 broadcast or p2p-over-lan, and the other router has a different 325 opinion, the adjacencies will never form, as specified in 326 Section 4.5. There are no fallbacks at either end to resolve 327 the situation, except by a manual configuration change. 329 8. Acknowledgments 331 The authors would like to acknowledge the following individuals: 332 (in last name alphabetical order) Pedro Marques, Christian Martin, 333 Danny McPherson, Ajay Patel, Jeff Parker, Tony Przygienda and 334 Alvaro Retana. 336 9. References 338 [ref1] ISO. Information Technology - Telecommunications and 339 Information Exchange between Systems - Intermediate System 340 to Intermediate System Routing Exchange Protocol for 341 Use in Conjunction with the Protocol for Providing the 342 Connectionless-Mode Network Service. ISO, 1990. 344 [ref2] R. Callon. Use of OSI ISIS for Routing in TCP/IP and Dual 345 Environments. INTERNET-RFC, Internet Engineering Task Force, 346 December 1990. 348 [ref3] J. Moy. OSPF Version 2. Technical Report RFC2328 Internet 349 Engineering Task Force, 1998. 351 [ref4] Hopps, C., "Routing IPv6 with IS-IS", 352 draft-ietf-isis-ipv6-05.txt, work in progress. 354 [ref5] Coltun, R., Ferguson, D. and J. Moy, "OSPF for IPv6", 355 RFC 2740, December 1999. 357 [ref6] Narten, T., Nordmark, E. and W. Simpson, "Neighbor Discovery 358 for IP Version 6 (IPv6)", RFC 2461, December 1998. 360 10. Editor Information 362 Naiming Shen 363 Redback Networks 364 350 Holger Way 365 San Jose, CA, 95134 USA 366 naiming@redback.com 368 Alex Zinin 369 Alcatel 370 Sunnyvale, CA, USA 371 e-mail: zinin@psg.com 373 Intellectual Property Considerations 375 The IETF takes no position regarding the validity or scope of any 376 intellectual property or other rights that might be claimed to 377 pertain to the implementation or use of the technology described in 378 this document or the extent to which any license under such rights 379 might or might not be available; neither does it represent that it 380 has made any effort to identify any such rights. Information on the 381 IETF's procedures with respect to rights in standards-track and 382 standards-related documentation can be found in BCP-11. 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This document is subject 398 to the rights, licenses and restrictions contained in BCP 78, and 399 except as set forth therein, the authors retain all their rights. 401 This document and the information contained herein is provided on an 402 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING 403 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING 404 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION 405 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF 406 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 408 -