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Trotter 3 Internet Draft Agilent Technologies 4 Document: draft-ietf-bmwg-fib-term-01.txt March 2001 5 Category: Informational 7 Terminology for Forwarding Information Base (FIB) based Router 8 Performance 10 Status of this Memo 12 This document is an Internet-Draft and is in full conformance with 13 all provisions of Section 10 of RFC2026 [1]. 15 Internet-Drafts are working documents of the Internet Engineering 16 Task Force (IETF), its areas, and its working groups. Note that 17 other groups may also distribute working documents as Internet- 18 Drafts. 20 Internet-Drafts are draft documents valid for a maximum of six 21 months and may be updated, replaced, or obsoleted by other documents 22 at any time. It is inappropriate to use Internet- Drafts as 23 reference material or to cite them other than as "work in progress." 25 The list of current Internet-Drafts can be accessed at 26 http://www.ietf.org/ietf/1id-abstracts.txt. 28 The list of Internet-Draft Shadow Directories can be accessed at 29 http://www.ietf.org/shadow.html. 31 1. Introduction 33 This document defines terms that are to be used in a methodology 34 that determines the IP packet forwarding performance of IP routers 35 as a function of the forwarding information base installed within 36 the router. 38 This document is restricted to IPv4 routers. 40 The objective of this methodology is to evaluate the performance 41 levels of IP routers as forwarding information bases continue to 42 grow in size and complexity of structure. 44 This methodology utilizes the packet forwarding performance 45 measurements described in [2]; reference will also be made to the 46 associated terminology document [3] for these terms. 48 2. Overview 50 In order to measure the forwarding information base-based router 51 performance, different forwarding information bases (5.3) are 52 installed in the router. The two key elements describing the FIB 53 are the FIB size (5.5) and FIB prefix distribution (5.6). As FIB 54 sizes increase, and as FIB prefix distributions tend towards longer 55 Terminology for FIB based Router Performance July, 2000 57 network prefixes (5.1), then it will take more time to match the 58 destination address within an IP packet and its corresponding entry 59 within the FIB. The FIB-dependent throughput, latency and frame 60 loss rate (6.3, 6.4, 6.5), measured with fully meshed traffic flows 61 (Error! Reference source not found.), will reflect the change in 62 performance of the router. Tests may need to be performed up to the 63 maximum FIB size (6.1). 65 When configuring the router for these measurements, the routes need 66 to be manually entered into the router, or advertised via a routing 67 protocol. It may take some period of time (the FIB learning time 68 (6.2)) before the router learns all the routes. 70 When routes are advertised into the router, the routes should be 71 advertised in such a way so that route aggregation (5.10) does not 72 occur. Also, the effect of a per-interface FIB cache (5.9) needs to 73 be taken into account. 75 3. Existing Definitions 77 [3] should be consulted before attempting to make use of this 78 document. [2] contains discussions of a number of terms relevant to 79 the benchmarking of network interconnect devices and should also be 80 consulted. 82 4. Definition Format 84 The definition format is the equivalent to that defined in [3], and 85 is repeated here for convenience: 87 X.x Term to be defined. (e.g., Latency) 89 Definition: 90 The specific definition for the term. 92 Discussion: 93 A brief discussion about the term, it's application and any 94 restrictions on measurement procedures. 96 Measurement units: 97 The units used to report measurements of this term, if 98 applicable. 100 Issues: 101 List of issues or conditions that effect this term. 103 See Also: 104 List of other terms that are relevant to the discussion of 105 this term. 107 5. Definitions - parameters 108 Terminology for FIB based Router Performance July, 2000 110 This section defines parameters that would dictate the execution of 111 methodology to determine the FIB based forwarding performance of a 112 router. 113 5.1 Network Prefix 115 Definition: 116 See section 2.2.5, "Addressing Architecture", in [4]. 118 A network prefix refers to the high-order 'n' bits of an IP 119 address, identifying a particular network within which an IP 120 host is located. 122 Discussion: 123 Network prefixes are represented as a 32 bit IP address with 124 a mask indicating the number of bits representing the network 125 prefix. I.e. 141.184.128 /17 indicates that the network 126 prefix is 17 bits long. 128 Measurement units: 129 131 Issues: 133 See Also: 134 Network Prefix Length (5.2) 136 5.2 Network Prefix Length 138 Definition: 139 The number of bits used to define the network prefix. 140 Network prefixes, using CIDR terminology, are typically 141 referred to as 15.35.128.0 /17, indicating that the network 142 prefix is 17 bits long. 144 Discussion: 146 Measurement units: 147 bits 149 Issues: 151 See Also: 152 network prefix (5.1) 153 forwarding information base prefix distribution (5.6) 155 5.3 Forwarding Information Base (FIB) 157 Definition: 158 As according to the definition in [4]: 160 "The table containing the information necessary to forward IP 161 Datagrams, in this document, is called the Forwarding 162 Information Base. At minimum, this contains the interface 163 Terminology for FIB based Router Performance July, 2000 165 identifier and next hop information for each reachable 166 destination network prefix." 168 A forwarding information base consists of [FIB size (6.1)] 169 FIB entries (5.4). 171 Discussion: 172 The forwarding information base describes a database indexing 173 network prefixes versus router port identifiers. 175 The forwarding information base is distinct from the "routing 176 table" (or, the Routing Information Base), which holds all 177 routing information received from routing peers. 179 The forwarding information base contains unique paths only 180 (i.e. does not contain secondary paths). 182 Measurement units: 183 185 Issues: 187 See Also: 188 forwarding information base entry (5.4) 189 forwarding information base size (5.5) 190 forwarding information base prefix distribution (5.6) 191 maximum forwarding information base size (6.1) 193 5.4 Forwarding Information Base Entry 195 Definition: 196 A single entry within a forwarding information base, 197 consisting of a network prefix,a router port identifier and 198 next hop information. This is an entry that the router can 199 and does use to forward packets. 201 Discussion: 202 See (5.3). 204 Measurement units: 205 207 Issues: 209 See Also: 210 forwarding information base (5.3) 211 forwarding information base size (5.5) 212 forwarding information base prefix distribution (5.6) 213 maximum forwarding information base size (6.1) 215 5.5 Forwarding Information Base Size 217 Definition: 219 Terminology for FIB based Router Performance July, 2000 221 Refers to the number of forwarding information base entries 222 within a forwarding information base. 224 Discussion: 225 The number of entries within a forwarding information base is 226 one of the key elements that may influence the forwarding 227 performance of a router. Generally, the more entries within 228 the forwarding information base, the longer it could take to 229 find the longest matching network prefix within the 230 forwarding information base. 232 Measurement units: 233 Number of routes 235 Issues: 237 See Also: 238 forwarding information base (5.3) 239 forwarding information base entry (5.4) 240 forwarding information base prefix distribution (5.6) 241 maximum forwarding information base size (6.1) 243 5.6 Longest Length Prefix Match Algorithm 245 Definition: 246 An algorithm that a router uses to quickly match destination 247 addresses within received IP packets to exit interfaces on 248 the router. 250 Discussion: 252 Measurement Units: 253 255 Issues: 257 See Also: 259 5.7 Forwarding Information Base Prefix Distribution 261 Definition: 262 The distribution of network prefix lengths within the 263 forwarding information base. 265 Discussion: 266 Network prefixes within the forwarding information base could 267 be all of a single network prefix length, but, more 268 realistically, the network prefix lengths will be distributed 269 across some range. 271 Individual performance measurements will be made against FIBs 272 populated with the same network prefix length, as well as 273 Terminology for FIB based Router Performance July, 2000 275 against FIBs with some distribution of network prefix 276 lengths. 278 The distribution of network prefix lengths may have an impact 279 on the forwarding performance of a router. The longer the 280 network prefix length, the longer it will take for a router 281 to perform the longest length prefix match algorithm, and 282 potentially the lower the performance of the router. 284 Measurement units: 285 The forwarding information base prefix distribution is 286 expressed by a list of network prefix lengths and the 287 percentage of entries within the forwarding information base 288 with a particular network prefix length. For example, a 289 forwarding information base prefix distribution is 290 represented as: 292 {[/16, 100], [/20, 360], [/24, 540]} 294 This indicates that 100 of the entries within the forwarding 295 information base have a 16 bit network prefix length, 360 296 have a 20 bit network prefix length, and 540 have a 24 bit 297 network prefix length. 299 Issues: 301 See Also: 302 forwarding information base (5.3) 303 forwarding information base entry (5.4) 304 forwarding information base size (5.5) 305 maximum forwarding information base size (6.1) 307 5.8 Per-Interface or Per-Card Forwarding Information Base 309 Definition: 310 A complete copy of the forwarding information base, installed 311 on a router's card or individual physical interface to speed 312 the destination address to network prefix lookup process. 314 Discussion: 315 Router manufacturers have developed many optimizations for 316 routers, of which one optimization is to copy the forwarding 317 information base to every interface or interface card on the 318 router. By doing this, destination address / network prefix 319 lookups can be performed on the interface or card, unloading 320 a router's CPU. 322 Measurement units: 323 325 Issues: 327 See Also: 329 Terminology for FIB based Router Performance July, 2000 331 forwarding information base (5.3) 332 per-interface forwarding information base cache (5.9) 334 5.9 Per-Interface Forwarding Information Base Cache 336 Definition: 337 A subset of a forwarding information base, installed on a 338 router's interface card to speed the destination address / 339 network prefix lookup process. 341 Discussion: 342 Prior to installing a complete copy of the forwarding 343 information base on each interface of a router, a popular 344 technique for speeding destination address lookups is to 345 install a cache of frequently used routes on a router's 346 interface. 348 The most frequently used routes are placed in the forwarding 349 information base cache. IP packets whose destination address 350 does not match a network prefix within the per-interface 351 forwarding information base cache are forwarded to a router's 352 central processor for lookup in the complete forwarding 353 information base. 355 The implication for benchmarking the performance of a router 356 as a function of the forwarding information base is 357 significant. IP packets whose destination address matches an 358 entry within the per-interface forwarding information base 359 cache could be forwarded more quickly than packets whose 360 destination address does not match an entry within the per- 361 interface forwarding information base cache. 363 To create useful benchmarks, the role of a per-interface 364 forwarding cache needs to be considered. The nature of 365 benchmarking tests to measure the impact of the forwarding 366 performance of a router requires that the destination 367 addresses within IP packets transmitted into the router be 368 distributed amongst the total set of network prefixes 369 advertised into the router. This negates the role of a per- 370 interface forwarding information base cache, but serves to 371 stress the forwarding information base-based packet 372 forwarding performance of the router. 374 Measurement units: 375 377 Issues: 379 See Also: 380 forwarding information base (5.3) 381 per-interface forwarding information base (5.8) 382 Terminology for FIB based Router Performance July, 2000 384 5.10 Route Aggregation 386 Definition: 387 The ability of a router to collapse many forwarding 388 information base entries into a single entry. 390 Discussion: 391 A router may aggregate routes in a forwarding information 392 base into a single entry to conserve space. 394 When advertising routes into a router to perform benchmarking 395 tests as a function of the forwarding information base 396 installed within the router, it is necessary to ensure that a 397 router does not aggregate routes. 399 Thus, when routes are advertised to the router or installed 400 statically, care must be taken to ensure that the router does 401 not aggregate routes. 403 For example, if advertising a set of /24 network prefixes 404 into a particular port on the router, 256 consecutive /24 405 routes, sharing a common leading 16 bits, should not be 406 advertised on a single port. If this is done, then the 407 router will install a single entry within the forwarding 408 information base indicating that all networks matching a 409 particular /16 network prefix are accessible through one 410 particular entry. 412 Route aggregation on a router can be turned off, but routes 413 should still be advertised into the router in such a manner 414 as to avoid route aggregation. 416 Measurement units: 417 419 Issues: 421 See Also: 423 6. Definitions - metrics 425 This section defines the metrics, or results, that would 426 characterized the FIB based forwarding performance of a router. 428 6.1 Maximum Forwarding Information Base Size 430 Definition: 431 The maximum number of forwarding information base entries 432 that can be supported within the forwarding information base. 433 The Maximum Forwarding Information Base Size is the size over 434 which all entries can and are used to forward traffic. 436 Discussion: 438 Terminology for FIB based Router Performance July, 2000 440 It is useful to know the maximum forwarding information base 441 size for a router as it will be an indicator of the ability 442 of the router to function within the given application space, 443 and whether the router will be able to handle projected 444 network growth. 446 As a benchmarking value, it is necessary to discover this 447 value so that performance measurements can be made up to the 448 maximum possible forwarding information base size. 450 Measurement units: 451 Number of routes 453 Issues: 454 Could this value vary with the forwarding information base 455 prefix distribution? 457 See Also: 458 forwarding information base (5.3) 459 forwarding information base entry (5.4) 460 forwarding information base size (5.5) 461 forwarding information base prefix distribution (5.6) 463 6.2 Forwarding Information Base Learning Time 465 Definition: 466 The time a router takes to process received routing messages, 467 and to construct (and, possibly to distribute amongst the 468 interface cards in the router) the forwarding information 469 base. This is measured from the time at which a router is 470 presented with the first routing message, through to when it 471 can forward packets using any entry in the forwarding 472 information base. 474 Discussion: 475 It takes time for a router to construct its forwarding 476 information base. A router needs to process received routing 477 packets, build the routing information database, select the 478 best paths, build the forwarding information base and then 479 possibly distribute the forwarding information base or a 480 subset thereof to the interface cards. This entire process 481 can take several minutes with very large forwarding 482 information bases. 484 When performing benchmarking tests that take the forwarding 485 information base into account, time must be allocated for the 486 router to process the routing information and to install the 487 complete forwarding information base within itself, before 488 performance measurements are made. 490 Measurement units: 491 Prefixes per second. 493 Terminology for FIB based Router Performance July, 2000 495 Issues: 497 See Also: 498 forwarding information base (5.3) 500 6.3 Forwarding Information Base-dependent Throughput 502 Definition: 503 Throughput, as defined in [3], used in a context where the 504 forwarding information base influences the throughput. 506 Discussion: 507 This definition for FIB-dependent throughput is added to 508 distinguish the context of this measurement from that defined 509 in [3]. 511 Measurement units: 512 See [3]. 514 Issues: 516 See Also: 517 forwarding information base-dependent latency (6.4) 518 forwarding information base-dependent frame loss rate (6.5) 520 6.4 Forwarding Information Base-dependent Latency 522 Definition: 523 Latency, as defined in [3], used in a context where the 524 forwarding information base influences the throughput. 526 Discussion: 527 This definition for FIB-dependent latency is added to 528 distinguish the context of this measurement from that defined 529 in [3]. 531 Measurement units: 532 See [3]. 534 Issues: 536 See Also: 537 forwarding information base-dependent throughput (6.3) 538 forwarding information base-dependent frame loss rate (6.5) 540 6.5 Forwarding Information Base-dependent Frame Loss Rate 542 Definition: 543 Frame Loss Rate, as defined in [3], used in a context where 544 the forwarding information base influences the throughput. 546 Discussion: 548 Terminology for FIB based Router Performance July, 2000 550 This definition for FIB-dependent frame loss rate is added to 551 distinguish the context of this measurement from that defined 552 in [3]. 554 Measurement units: 555 See [3]. 557 Issues: 559 See Also: 560 forwarding information base-dependent throughput (6.3) 561 forwarding information base-dependent latency (6.4) 563 7. Security Considerations 565 As this document is solely for the purpose of providing metric 566 methodology and describes neither a protocol nor a protocols 567 implementation, there are no security considerations associated with 568 this document. 570 8. References 572 1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 573 9, RFC 2026, October 1996. 574 2 Bradner, S., McQuaid, J., "Benchmarking Methodology for Network 575 Interconnect Devices", RFC 2544, March 1999 576 3 Bradner, S., "Benchmarking Terminology for Network 577 Interconnection Devices", RFC 1242, July 1991 578 4 Baker, F., "Requirements for IP Version 4 Routers", RFC 1812, 579 June 1995 581 9. Acknowledgments 583 10. Author's Addresses 585 Guy Trotter 586 Agilent Technologies (Canada) Inc. 587 #2500 4710 Kingsway 588 Burnaby, British Columbia 589 Canada 590 V5H 4M2 591 Phone: +1 604 454 3516 592 Email: Guy_Trotter@agilent.com 594 Full Copyright Statement 596 "Copyright (C) The Internet Society (2000). All Rights Reserved. 598 This document and translations of it may be copied and furnished to 599 others, and derivative works that comment on or otherwise explain it 600 or assist in its implementation may be prepared, copied, published 601 Terminology for FIB based Router Performance July, 2000 603 and distributed, in whole or in part, without restriction of any 604 kind, provided that the above copyright notice and this paragraph 605 are included on all such copies and derivative works. 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