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Lindem 6 Expires: February 6, 2017 Cisco Systems 7 August 5, 2016 9 OSPF Two-part Metric 10 draft-ietf-ospf-two-part-metric-06.txt 12 Abstract 14 This document specifies an optional extension to the OSPF protocol, 15 to represent the metric on a multi-access network as two parts: the 16 metric from a router to the network, and the metric from the network 17 to the router. The router to router metric would be the sum of the 18 two. This document updates RFC 2328 and RFC 5340. 20 Requirements Language 22 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 23 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 24 document are to be interpreted as described in [RFC2119]. 26 Status of This Memo 28 This Internet-Draft is submitted in full conformance with the 29 provisions of BCP 78 and BCP 79. 31 Internet-Drafts are working documents of the Internet Engineering 32 Task Force (IETF). Note that other groups may also distribute 33 working documents as Internet-Drafts. The list of current Internet- 34 Drafts is at http://datatracker.ietf.org/drafts/current/. 36 Internet-Drafts are draft documents valid for a maximum of six months 37 and may be updated, replaced, or obsoleted by other documents at any 38 time. It is inappropriate to use Internet-Drafts as reference 39 material or to cite them other than as "work in progress." 41 This Internet-Draft will expire on February 6, 2017. 43 Copyright Notice 45 Copyright (c) 2016 IETF Trust and the persons identified as the 46 document authors. All rights reserved. 48 This document is subject to BCP 78 and the IETF Trust's Legal 49 Provisions Relating to IETF Documents 50 (http://trustee.ietf.org/license-info) in effect on the date of 51 publication of this document. Please review these documents 52 carefully, as they describe your rights and restrictions with respect 53 to this document. Code Components extracted from this document must 54 include Simplified BSD License text as described in Section 4.e of 55 the Trust Legal Provisions and are provided without warranty as 56 described in the Simplified BSD License. 58 This document may contain material from IETF Documents or IETF 59 Contributions published or made publicly available before November 60 10, 2008. The person(s) controlling the copyright in some of this 61 material may not have granted the IETF Trust the right to allow 62 modifications of such material outside the IETF Standards Process. 63 Without obtaining an adequate license from the person(s) controlling 64 the copyright in such materials, this document may not be modified 65 outside the IETF Standards Process, and derivative works of it may 66 not be created outside the IETF Standards Process, except to format 67 it for publication as an RFC or to translate it into languages other 68 than English. 70 Table of Contents 72 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 73 2. Proposed Enhancement . . . . . . . . . . . . . . . . . . . . 3 74 3. Speficications . . . . . . . . . . . . . . . . . . . . . . . 4 75 3.1. Router Interface Parameters . . . . . . . . . . . . . . . 4 76 3.2. Advertising Network-to-Router Metric in OSPFv2 . . . . . 4 77 3.3. Advertising Network-to-Router Metric in OSPFv3 . . . . . 5 78 3.4. Advertising Network-to-Router TE Metric . . . . . . . . . 5 79 3.5. OSPF Stub Router Behavior . . . . . . . . . . . . . . . . 5 80 3.6. SPF Calculation . . . . . . . . . . . . . . . . . . . . . 6 81 3.7. Backward Compatibility . . . . . . . . . . . . . . . . . 6 82 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 83 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 84 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 85 6.1. Normative References . . . . . . . . . . . . . . . . . . 7 86 6.2. Informative References . . . . . . . . . . . . . . . . . 8 87 Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 8 88 Appendix B. Contributors' Addreses . . . . . . . . . . . . . . . 9 89 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 91 1. Introduction 93 With Open Shortest Path First (OSPF, [RFC2328], [RFC5340]) protocol, 94 for a broadcast network, a Network-LSA is advertised to list all 95 routers on the network, and each router on the network includes a 96 link in its Router-LSA to describe its connection to the network. 97 The link in the Router-LSA includes a metric but the listed routers 98 in the Network LSA do not include a metric. This is based on the 99 assumption that from a particular router, all others on the same 100 network can be reached with the same metric. 102 With some broadcast networks, different routers can be reached with 103 different metrics. [RFC6845] extends the OSPF protocol with a hybrid 104 interface type for that kind of broadcast network, where no Network 105 LSA is advertised and Router-LSAs simply include p2p links to all 106 routers on the same network with individual metrics. Broadcast 107 capability is still utilized to optimize database synchronization and 108 adjacency maintenance. 110 That works well for broadcast networks where the metric between 111 different pair of routers are really independent. For example, VPLS 112 networks. 114 With certain types of broadcast networks, further optimization can be 115 made to reduce the size of the Router-LSAs and number of updates. 117 Consider a satellite radio network with fixed and mobile ground 118 terminals. All communication goes through the satellite. When the 119 mobile terminals move about, their communication capability may 120 change. When OSPF runs over the radio network (routers being or in 121 tandem with the terminals), [RFC6845] hybrid interface can be used, 122 but with the following drawbacks. 124 Consider that one terminal/router moves into an area where its 125 communication capability degrades significantly. Through the radio 126 control protocol, all other routers determine that the metric to this 127 particular router changed and they all need to update their Router- 128 LSAs accordingly. The router in question also determines that its 129 metric to reach all others also changed and it also needs to update 130 its Router-LSA. Consider that there could be many terminals and many 131 of them can be moving fast and frequently, the number/frequency of 132 updates of those large Router-LSAs could inhibit network scaling. 134 2. Proposed Enhancement 136 Notice that in the above scenario, when one terminal's communication 137 capability changes, its metric to all other terminals and the metric 138 from all other terminals to it will all change in a similar fashion. 139 Given this, the above problem can be easily addressed by breaking the 140 metric into two parts: the metric to the satellite and the metric 141 from the satellite. The metric from terminal R1 to R2 would be the 142 sum of the metric from R1 to the satellite and the metric from the 143 satellite to R2. 145 Now instead of using the [RFC6845] hybrid interface type, the network 146 is just treated as a regular broadcast network. A router on the 147 network no longer lists individual metrics to each neighbor in its 148 Router-LSA. Instead, each router advertises the metric from the 149 network to itself in addition to the normal metric for the network. 150 With the normal Router-to-Network and additional Network-to-Router 151 metrics advertised for each router, individual router-to-router 152 metric can be calculated. 154 With the proposed enhancement, the size of Router-LSA will be 155 significantly reduced. In addition, when a router's communication 156 capability changes, only that router needs to update its Router-LSA. 158 Note that while the example uses the satellite as the relay point at 159 the radio level (layer-2), at layer-3, the satellite does not 160 participate in packet forwarding. In fact, the satellite does not 161 need to be running any layer-3 protocol. Therefore for generality, 162 the metric is abstracted as to/from the "network" rather that 163 specifically to/from the "satellite". 165 3. Speficications 167 The following protocol specifications are added to or modified from 168 the base OSPF protocol. If an area contains one or more two-part 169 metric networks, then all routers in the area must support the 170 extensions specified herein. This is ensured by procedures described 171 in Section 3.7. 173 3.1. Router Interface Parameters 175 The "Router interface parameters" have the following additions: 177 o Two-part metric: TRUE if the interface connects to a multi-access 178 network that uses two-part metric. All routers connected to the 179 same network SHOULD have the same configuration for their 180 corresponding interfaces. 182 o Interface input cost: Link state metric from the two-part-metric 183 network to this router. Defaulted to "Interface output cost" but 184 not valid for normal networks using a single metric. May be 185 configured or dynamically adjusted to a value different from the 186 "Interface output cost". 188 3.2. Advertising Network-to-Router Metric in OSPFv2 190 For OSPFv2, the Network-to-Router metric is encoded in an OSPF 191 Extended Link TLV Sub-TLV [RFC7684], defined in this document as the 192 Network-to-Router Metric Sub-TLV. The type of the Sub-TLV is TBD. 194 The length of the Sub-TLV is 4 (for the value part only). The value 195 part of the Sub-TLV is defined as follows: 197 0 1 2 3 198 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 1 199 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 200 | MT | 0 | MT metric | 201 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 203 Multiple such Sub-TLVs can exist in a single OSPF Extended Link TLV, 204 one for each topology [RFC4915]. The OSPF Extended Link TLV 205 identifies the transit link to the network, and is part of an OSPFv2 206 Extended-Link Opaque LSA. The Sub-TLV MUST ONLY appear in Extended- 207 Link TLVs for Link Type 2 (link to transit network), and MUST be 208 ignored if received for other link types. 210 3.3. Advertising Network-to-Router Metric in OSPFv3 212 For OSPFv3, the same Network-to-Router Metric Sub-TLV definition is 213 used, though it is part of the Router-Link TLV of E-Router-LSA 214 [I-D.ietf-ospf-ospfv3-lsa-extend]. Currently OSPFv3 Multi-Toplogy is 215 not defined so the only valid value for the MT field is 0 and only 216 one such Sub-TLV SHOULD be included in the Router-Link TLV. Received 217 Sub-TLVs with non-zero MT field MUST be ignored. 219 Similarly, the Sub-TLV MUST ONLY appear in Router-Link TLVs for Link 220 Type 2 (connection to a transit network) and MUST be ignored if 221 received for other link types. 223 3.4. Advertising Network-to-Router TE Metric 225 A Traffic Engineering Network-to-Router Metric Sub-TLV is defined, 226 similar to the Traffic Engineering Metric Sub-TLV defined in 227 Section 2.5.5 of [RFC3630]. The only difference is the TLV type, 228 which is TBD. The Sub-TLV MUST only appear in type 2 Link TLVs 229 (Multi-access) of Traffic Engineer LSAs (OSPF2) or Intra-Area-TE-LSAs 230 (OSPFv3) [RFC5329], and MUST appear at most once in one such Link 231 TLV. 233 3.5. OSPF Stub Router Behavior 235 When an OSPF router with interfaces including two-part metric is 236 advertising itself as a stub router [RFC6987], only the Router-to- 237 Network metric in the stub router's OSPF Router-LSA links is set to 238 the MaxLinkMetric. This is fully backward compatible and will result 239 in the same behavior as [RFC6987]. 241 3.6. SPF Calculation 243 During the first stage of shortest-path tree calculation for an area, 244 when a vertex V corresponding to a Network-LSA is added to the 245 shortest-path tree and its adjacent vertex W (joined by a link in V's 246 corresponding Network LSA), the cost from V to W, which is W's 247 network-to-router cost, is determined as follows: 249 o For OSPFv2, if vertex W has a corresponding Extended-Link Opaque 250 LSA with an Extended Link TLV for the link from W to V, and the 251 Extended Link TLV has a Network-to-Router Metric Sub-TLV for the 252 corresponding topology, then the cost from V to W is the metric in 253 the Sub-TLV. Otherwise, the cost is 0. 255 o For OSPFv3, if vertex W has a corresponding E-Router-LSA with a 256 Router-Link TLV for the link from W to V, and the Router-Link TLV 257 has a Network-to-Router Metric Sub-TLV, then the cost from V to W 258 is the metric in the Sub-TLV. If not, the cost is 0. 260 3.7. Backward Compatibility 262 Due to the change of procedures in the SPF calculation, all routers 263 in an area that includes one or more two-part metric networks must 264 support the changes specified in this document. To ensure that, if 265 an area is provisioned to support two-part metric networks, all 266 routers supporting this capability must advertise a Router 267 Information (RI) LSA with a Router Functional Capabilities TLV 268 [RFC7770] that includes the following Router Functional Capability 269 Bit: 271 Bit Capabilities 273 0 OSPF Two-part Metric [TPM] 275 Upon detecting the presence of a reachable Router-LSA without a 276 companion RI LSA that has the bit set, all routers MUST recalculate 277 routes w/o considering any network-to-router costs. 279 4. IANA Considerations 281 This document requests the following IANA assignments: 283 o A new bit in Registry for OSPF Router Informational Capability 284 Bits, to indicate the capability of supporting two-part metric. 286 o A new Sub-TLV type in OSPF Extended Link TLV Sub-TLV registry, for 287 the Network-to-Router Metric Sub-TLV. 289 o A new Sub-TLV type in OSPFv3 Extended-LSA Sub-TLV registry, for 290 the Network-to-Router Metric Sub-TLV. 292 o A new Sub-TLV type in Types for sub-TLVs of TE Link TLV (Value 2) 293 registry, for the Network-to-Router TE Metric Sub-TLV. 295 5. Security Considerations 297 This document does not introduce new security risks. 299 6. References 301 6.1. Normative References 303 [I-D.ietf-ospf-ospfv3-lsa-extend] 304 Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3 305 LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-10 306 (work in progress), May 2016. 308 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 309 Requirement Levels", BCP 14, RFC 2119, 310 DOI 10.17487/RFC2119, March 1997, 311 . 313 [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 314 DOI 10.17487/RFC2328, April 1998, 315 . 317 [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering 318 (TE) Extensions to OSPF Version 2", RFC 3630, 319 DOI 10.17487/RFC3630, September 2003, 320 . 322 [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. 323 Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", 324 RFC 4915, DOI 10.17487/RFC4915, June 2007, 325 . 327 [RFC5329] Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed., 328 "Traffic Engineering Extensions to OSPF Version 3", 329 RFC 5329, DOI 10.17487/RFC5329, September 2008, 330 . 332 [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF 333 for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008, 334 . 336 [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., 337 Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute 338 Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 339 2015, . 341 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and 342 S. Shaffer, "Extensions to OSPF for Advertising Optional 343 Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, 344 February 2016, . 346 6.2. Informative References 348 [RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast 349 and Point-to-Multipoint Interface Type", RFC 6845, 350 DOI 10.17487/RFC6845, January 2013, 351 . 353 [RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D. 354 McPherson, "OSPF Stub Router Advertisement", RFC 6987, 355 DOI 10.17487/RFC6987, September 2013, 356 . 358 Appendix A. Acknowledgements 360 The authors would like to thank Abhay Roy, Hannes Gredler, Peter 361 Psenak and Eric Wu for their comments and suggestions. 363 The RFC text was produced using Marshall Rose's xml2rfc tool. 365 Appendix B. Contributors' Addreses 367 David Dubois 368 General Dynamics C4S 369 400 John Quincy Adams Road 370 Taunton, MA 02780 372 EMail: dave.dubois@gd-ms.com 374 Vibhor Julka 375 L3 Communications, Linkabit 376 9890 Towne Centre Drive 377 San Diego, CA 92121 379 EMail: vjulka1@yahoo.com 381 Tom McMillan 382 L3 Communications, Linkabit 383 9890 Towne Centre Drive 384 San Diego, CA 92121 386 EMail: tom.mcmillan@l-3com.com 388 Authors' Addresses 390 Zhaohui Zhang 391 Juniper Networks, Inc. 392 10 Technology Park Drive 393 Westford, MA 01886 395 Email: zzhang@juniper.net 397 Lili Wang 398 Juniper Networks, Inc. 399 10 Technology Park Drive 400 Westford, MA 01886 402 Email: liliw@juniper.net 403 Acee Lindem 404 Cisco Systems 405 301 Midenhall Way 406 Cary, NC 27513 408 Email: acee@cisco.com