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The disclaimer is usually necessary only for documents that revise or obsolete older RFCs, and that take significant amounts of text from those RFCs. If you can contact all authors of the source material and they are willing to grant the BCP78 rights to the IETF Trust, you can and should remove the disclaimer. Otherwise, the disclaimer is needed and you can ignore this comment. (See the Legal Provisions document at https://trustee.ietf.org/license-info for more information.) -- The document date (March 28, 2011) is 4779 days in the past. Is this intentional? Checking references for intended status: Informational ---------------------------------------------------------------------------- No issues found here. Summary: 0 errors (**), 0 flaws (~~), 2 warnings (==), 1 comment (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Network Working Group J. Wu 3 Internet-Draft J. Bi 4 Intended status: Informational Tsinghua Univ. 5 Expires: September 29, 2011 M. Bagnulo 6 UC3M 7 F. Baker 8 Cisco 9 C. Vogt, Ed. 10 Ericsson 11 March 28, 2011 13 Source Address Validation Improvement Framework 14 draft-ietf-savi-framework-04 16 Abstract 18 The Source Address Validation Improvement method was developed to 19 complement ingress filtering with finer-grained, standardized IP 20 source address validation. This document describes and motivates the 21 design of the SAVI method. 23 Status of this Memo 25 This Internet-Draft is submitted in full conformance with the 26 provisions of BCP 78 and BCP 79. 28 Internet-Drafts are working documents of the Internet Engineering 29 Task Force (IETF). Note that other groups may also distribute 30 working documents as Internet-Drafts. The list of current Internet- 31 Drafts is at http://datatracker.ietf.org/drafts/current/. 33 Internet-Drafts are draft documents valid for a maximum of six months 34 and may be updated, replaced, or obsoleted by other documents at any 35 time. It is inappropriate to use Internet-Drafts as reference 36 material or to cite them other than as "work in progress." 38 This Internet-Draft will expire on September 29, 2011. 40 Copyright Notice 42 Copyright (c) 2011 IETF Trust and the persons identified as the 43 document authors. All rights reserved. 45 This document is subject to BCP 78 and the IETF Trust's Legal 46 Provisions Relating to IETF Documents 47 (http://trustee.ietf.org/license-info) in effect on the date of 48 publication of this document. Please review these documents 49 carefully, as they describe your rights and restrictions with respect 50 to this document. Code Components extracted from this document must 51 include Simplified BSD License text as described in Section 4.e of 52 the Trust Legal Provisions and are provided without warranty as 53 described in the Simplified BSD License. 55 This document may contain material from IETF Documents or IETF 56 Contributions published or made publicly available before November 57 10, 2008. The person(s) controlling the copyright in some of this 58 material may not have granted the IETF Trust the right to allow 59 modifications of such material outside the IETF Standards Process. 60 Without obtaining an adequate license from the person(s) controlling 61 the copyright in such materials, this document may not be modified 62 outside the IETF Standards Process, and derivative works of it may 63 not be created outside the IETF Standards Process, except to format 64 it for publication as an RFC or to translate it into languages other 65 than English. 67 Table of Contents 69 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 70 2. Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 71 3. Deployment Options . . . . . . . . . . . . . . . . . . . . . . 6 72 4. Scalability Optimizations . . . . . . . . . . . . . . . . . . 8 73 5. Reliability Optimizations . . . . . . . . . . . . . . . . . . 10 74 6. Mix Scenario . . . . . . . . . . . . . . . . . . . . . . . . . 10 75 7. Prefix Configuration . . . . . . . . . . . . . . . . . . . . . 11 76 8. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . 12 77 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 78 10. Security Considerations . . . . . . . . . . . . . . . . . . . 12 79 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 80 11.1. Informative References . . . . . . . . . . . . . . . . . 12 81 11.2. Normative References . . . . . . . . . . . . . . . . . . 13 82 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13 84 1. Introduction 86 Since IP source addresses are used by hosts and network entities to 87 determine the origin of a packet and as a destination for return 88 data, spoofing of IP source addresses can enable impersonation, 89 concealment, and malicious traffic redirection. Unfortunately, the 90 Internet architecture does not prevent IP source address spoofing 91 [draft-ietf-savi-threat-scope]. Since the IP source address of a 92 packet generally takes no role in forwarding the packet, it can be 93 selected arbitrarily by the sending host without jeopardizing packet 94 delivery. Extra methods are necessary for IP source address 95 validation, to augment packet forwarding with an explicit check of 96 whether a given packet's IP source address is legitimate. 98 IP source address validation can happen at different granularity: 99 Ingress filtering [BCP38], a widely deployed standard for IP source 100 address validation, functions at the coarse granularity of networks. 101 It verifies that the prefix of an IP source address routes to the 102 network from which the packet was received. An advantage of ingress 103 filtering is simplicity: the decision of whether to accept or to 104 reject an IP source address can be made solely based on the 105 information available from routing protocols. However, the 106 simplicity comes at the cost of not being able to validate IP source 107 addresses at a finer granularity, due to the aggregated nature of the 108 information available from routing protocols. Finer-grained IP 109 source address validation would be helpful to enable IP-source- 110 address-based authentication, authorization, and host localization, 111 as well as to efficiently identify misbehaving hosts. Partial 112 solutions [BA2007] exist for finer-grained IP source address 113 validation, but are proprietary and hence often unsuitable for 114 corporate procurement. 116 The Source Address Validation Improvement method was developed to 117 complement ingress filtering with standardized IP source address 118 validation at the maximally fine granularity of individual IP 119 addresses: It prevents hosts attached to the same link from spoofing 120 each other's IP addresses. To facilitate deployment in networks of 121 various kinds, the SAVI method was designed to be modular and 122 extensible. This document describes and motivates the design of the 123 SAVI method. 125 2. Model 127 To enable network operators to deploy fine-grained IP source address 128 validation without a dependency on supportive functionality on hosts, 129 the SAVI method was designed to be purely network-based. A SAVI 130 instance is located on the path of hosts' packets, enforcing the 131 hosts' use of legitimate IP source addresses according to the 132 following three-step model: 134 1. Identify which IP source addresses are legitimate for a host, 135 based on monitoring packets exchanged by the host. 137 2. Bind a legitimate IP address to a link layer property of the 138 host's network attachment. This property, called a "binding 139 anchor", must be verifiable in every packet that the host sends, 140 and harder to spoof than the host's IP source address itself. 142 3. Enforce that the IP source addresses in packets match the binding 143 anchors to which they were bound. 145 This model allows a SAVI instance to be located anywhere on the link 146 to which the hosts attach, hence enabling different locations for a 147 SAVI instance. One way to locate a SAVI instance is in the hosts' 148 default router. IP source addresses are then validated in packets 149 traversing the default router, yet the IP source addresses in packets 150 exchanged locally on the link may bypass validation. Another way to 151 locate a SAVI instance is in a switch between the hosts and their 152 default router. Thus, packets may undergo IP source address 153 validation even if exchanged locally on the link. 155 The closer a SAVI instance is located to the hosts, the more 156 effective the SAVI method is. This is because each of the three 157 steps of the SAVI model can best be accomplished in a position close 158 to the host: 160 o Identifying a host's legitimate IP source addresses is most 161 efficient close to the host, because the likelihood that the 162 host's packets bypass a SAVI instance, and hence cannot be 163 monitored, increases with the distance between the SAVI instance 164 and the host. 166 o Selecting a binding anchor for a host's IP source address is 167 easiest close to the host, because many link layer properties are 168 unique for a given host only on a link segment directly attaching 169 to the host. 171 o Enforcing a host's use of a legitimate IP source address is most 172 reliable when pursued close to the host, because the likelihood 173 that the host's packets bypass a SAVI instance, and hence do not 174 undergo IP source address validation, increases with the distance 175 between the SAVI instance and the host. 177 The preferred location of SAVI instances is therefore close to hosts, 178 such as in switches that directly attach to the hosts whose IP source 179 addresses are being validated. 181 To make SAVI of better applicability, to handle the scenarios in 182 which hosts are not directly attached is of value. For example, a 183 SAVI instance is attached by a legacy switch which is attached by 184 hosts. However, to take such scenario into consideration requires 185 support in the bind-and-identify model. Considering two scenarios: 187 o A legacy switch to which hosts are attaching uses two trunked 188 ports to connect to SAVI switch. 190 o STP runs among switches, and a link failure happens. 192 Both scenarios require more specified design to build correct 193 binding. Thus, for each SAVI solution, the applicability must be 194 specified explicitly. 196 Besides, in the case of legacy switches, the security level is lower, 197 as there is no full protection for the hosts connected to the legacy 198 server. 200 3. Deployment Options 202 The model of the SAVI method, as explained in Section 2, is 203 deployment-specific in two ways: 205 o The identification of legitimate IP source addresses is dependent 206 on the IP address assignment method in use on a link, since it is 207 through assignment that a host becomes the legitimate user of an 208 IP source address. 210 o Binding anchors are dependent on the technology used to build the 211 link on which they are used, as binding anchors are link layer 212 properties of a host's network attachment. 214 To facilitate the deployment of the SAVI method in networks of 215 various kinds, the SAVI method is designed to support different IP 216 address assignment methods, and to function with different binding 217 anchors. Naturally, both the IP address assignment methods in use on 218 a link and the available binding anchors have an impact on the 219 functioning and the strength of IP source address validation. The 220 following two sub-sections explain this impact, and describe how the 221 SAVI method accommodates this. 223 3.1. IP Address Assignment Methods 225 Since the SAVI method traces IP address assignment packets, it 226 necessarily needs to incorporate logic that is specific to particular 227 IP address assignment methods. However, developing SAVI method 228 variants for each IP address assignment method is alone not 229 sufficient, since multiple IP address assignment methods may co-exist 230 on a given link. The SAVI method hence comes in multiple variants: 231 for links with Stateless Address Autoconfiguration [rfc4862], for 232 links with DHCP [rfc2131][rfc3315], for links with Secure Neighbor 233 Discovery [rfc3971], for links with IKEv2 [rfc5996] [rfc5739] 234 [rfc5026] and for links that use any combination of IP address 235 assignment methods. 237 The reason to develop SAVI method variants for each single IP address 238 configuration method, in addition to the variant that handles all IP 239 address assignment methods, is to minimize the complexity of the 240 common case: many link deployments today either are constrained to a 241 single IP address assignment methods or, equivalently from the 242 perspective of the SAVI method, separate IP address assignment 243 methods into different IP address prefixes. The SAVI method for such 244 links can be simpler than the SAVI method for links with multiple IP 245 address assignment methods per IP address prefix. 247 3.2. Binding Anchors 249 The SAVI method supports a range of binding anchors: 251 o The IEEE extended unique identifier, EUI-48 or EUI-64, of a host's 252 interface. 254 o The port on an Ethernet switch to which a host attaches. 256 o The security association between a host and the base station on 257 wireless links. 259 o The combination of a host interface's link-layer address and a 260 customer relationship in cable modem networks. 262 o An ATM virtual channel, a PPPoE session identifier, or an L2TP 263 session identifier in a DSL network. 265 o A tunnel that connects to a single host, such as an IP-in-IP 266 tunnel, a GRE tunnel, or an MPLS label-switched path. 268 The various binding anchors differ significantly in the security they 269 provide. IEEE extended unique identifiers, for example, fail to 270 render a secure binding anchor because they can be spoofed with 271 little effort. And switch ports alone may be insufficient because 272 they may connect to more than a single host, such as in the case of 273 concatenated switches. 275 Given this diversity in the security provided, one could define a set 276 of possible binding anchors, and leave it up to the administrator to 277 choose one or more of them. Such a selection of binding anchors 278 would, of course, have to be accompanied by an explanation of the 279 pros and cons of the different binding anchors. In addition, SAVI 280 devices may have a default binding anchor depending on the lower 281 layers. Such a default could be to use switch ports when available, 282 and MAC addresses otherwise. Or to use MAC addresses, and switch 283 ports in addition if available. 285 4. Scalability Optimizations 287 The preference to locate a SAVI instance close to hosts implies that 288 multiple SAVI instances must be able to co-exist in order to support 289 large links. Although the model of the SAVI method is independent of 290 the number of SAVI instances per link, co-existence of multiple SAVI 291 instances without further measures can lead to higher-than-necessary 292 memory requirements: since a SAVI instance creates bindings for the 293 IP source addresses of all hosts on a link, bindings are replicated 294 if multiple SAVI instances co-exist on the link. High memory 295 requirements, in turn, increase the cost of a SAVI instance. This is 296 problematic in particular for SAVI instances that are located on a 297 switch, since it may significantly increase the cost of such a 298 switch. 300 To reduce memory requirements for SAVI instances that are located on 301 a switch, the SAVI method enables the suppression of binding 302 replication on links with multiple SAVI instances. This requires 303 manual disabling of IP source address validation on switch ports that 304 connect to other switches running a SAVI instance. Each SAVI 305 instance is then responsible for validating IP source addresses only 306 on those ports to which hosts attach either directly, or via switches 307 without a SAVI instance. On ports towards other switches running a 308 SAVI instance, IP source addresses are not validated. The switches 309 running SAVI instances thus form a "protection perimeter". The IP 310 source addresses in packets passing the protection perimeter are 311 validated by the ingress SAVI instance, but no further validation 312 takes place as long as the packets remain within, or leave the 313 protection perimeter. 315 .............. 316 protection perimeter --> : +--------+ : 317 +---+ +---+ : | SAVI | : 318 | A | | B | <-- hosts : | switch | : 319 +---+ +---+ : +--------+ : 320 ...|......|.............................: | : 321 : +--------+ +--------+ +--------+ : 322 : | SAVI |----------| legacy | | SAVI | : 323 : | switch | | switch |----------| switch | : 324 : +--------+ +--------+ +--------+ : 325 : | ...............................|........: 326 : +--------+ : +--------+ 327 : | SAVI | : | legacy | 328 : | switch | : | switch | 329 : +--------+ : +--------+ 330 :............: | | 331 +---+ +---+ 332 hosts --> | C | | D | 333 +---+ +---+ 335 Figure 1: Protection perimeter concept 337 Figure 1 illustrates the concept of the protection perimeter. The 338 figure shows a link with six switches, of which four, denoted "SAVI 339 switch", run a SAVI instance. The protection perimeter created by 340 the four SAVI instances is shown as a dotted line in the figure. IP 341 source address validation is enabled on all switch ports on the 342 protection perimeter, and it is disabled on all other switch ports. 343 Four hosts, denoted A through D in the figure, attach to the 344 protection perimeter. 346 In the example of figure Figure 1, the protection perimeter 347 encompasses one of the legacy switches, located in the middle of the 348 depicted link topology. This enables a single, unpartitioned 349 protection perimeter. A single protection perimeter minimizes memory 350 requirements for the SAVI instances because every binding is kept 351 only once, namely, by the SAVI instance that attaches to the host 352 being validated. Excluding the legacy switch from the protection 353 perimeter would result in two smaller protection perimeters to the 354 left and to the right of the depicted link topology. The memory 355 requirements for the SAVI instances would then be higher: since IP 356 source address validation would be activated on the two ports 357 connecting to the legacy switch, the SAVI instances adjacent to the 358 legacy switch would replicate all bindings from the respectively 359 other protection perimeter. The reason why it is possible to include 360 the legacy switch in the protection perimeter is because the depicted 361 link topology guarantees that packets cannot enter the protection 362 perimeter via this legacy switch. Without this guarantee, the legacy 363 switch would have to be excluded from the protection perimeter in 364 order to ensure that packets entering the protection perimeter 365 undergo IP source address validation. 367 5. Reliability Optimizations 369 The explicit storage of legitimate IP addresses in the form of 370 bindings implies that failure to create a binding, or the premature 371 removal of bindings, can lead to loss of legitimate packets. There 372 are three situations in which this can happen: 374 o Legitimate IP address configuration packets, which should trigger 375 the creation of a binding in a SAVI instance, are lost before 376 reaching the SAVI instance. 378 o A SAVI instance loses a binding, for example, due to a restart. 380 o The link topology changes, resulting in hosts to communicate 381 through SAVI instances that do not have a binding for those hosts' 382 IP addresses. 384 To limit the disruption that missing bindings for legitimate IP 385 addresses can have, the SAVI method includes a mechanism for reactive 386 binding creation based on regular packets. This mechanism 387 supplements the proactive binding creation based on IP address 388 configuration packets. Reactive binding creation occurs when a SAVI 389 instances recognizes excessive drops of regular packets originating 390 from the same IP address. The SAVI instance then verifies whether 391 said IP address is unique on the link. How the verification is 392 carried out depends on the IP address configuration method that the 393 SAVI instance supports: the SAVI method variant for Stateless 394 Address Autoconfiguration and for Secure Neighbor Discovery verifies 395 an IP address through the Duplicate Address Detection procedure. The 396 SAVI method variant for DHCP verifies an IP address through a DHCP 397 Lease Query message exchange with the DHCP server. If verification 398 indicates that the IP address is unique on the link, the SAVI 399 instance creates a binding for the IP address. Otherwise, no binding 400 is created, and packets sent from the IP address continue to be 401 dropped. 403 6. Mix Scenario 405 While multiple assignment methods can be used on the same link, the 406 SAVI device may have to deal with a mix of binding discovery methods. 407 If the address prefix used for each assignment method is different, 408 mix scenario can handle the same as scenario with only one assignment 409 method. If different address assignment methods are used to assign 410 addresses from the same prefix, additional considerations are needed 411 because one binding mechanism may create a binding violating an 412 existing binding from another binding mechanism, e.g., binding from 413 SAVI-FCFS [savi-fcfs] may violate binding from SAVI-DHCP [savi-dhcp]. 414 Thus, the collision between different SAVI mechanisms in mix scenario 415 must be handled in case more than one address assignment method is 416 used to assign addresses from the same prefix. 418 Prioritization relationship between different address assignment 419 methods is used as the basis to solve possible collisions. Current 420 standard documents of address assignment methods have implied the 421 prioritization relationship in general cases. However, considering 422 in some scenarios, default prioritization level may not be quite 423 suitable. Configurable prioritization level should be supported in a 424 document of SAVI solution for the mix scenario. 426 7. Prefix Configuration 428 Before setting up a host-level granularity binding, it is important 429 to configure correct prefixes on the SAVI device. This document 430 suggests set 3 prefix configuration mechanisms at SAVI device: 432 o Manually Prefix Configuration: The allowed prefix scope of IPv4 433 Addresses, IPv6 static addresses, IPv6 addresses assigned by 434 SLAAC, and IPv6 addresses assigned by DHCPv6 can be set manually 435 at SAVI device. FE80::/64 is always a feasible prefix in IPv6. 437 o Prefix Configuration by RA Snooping: The allowed prefix scope of 438 IPv6 static addresses and IPv6 addresses assigned by SLAAC can be 439 set at SAVI device through snooping RA message at SAVI device. 440 FE80::/64 is always a feasible prefix in IPv6. 442 o Prefix Configuration by DHCP-PD Snooping: The allowed prefix 443 scope of IPv6 static addresses, IPv6 addresses assigned by SLAAC, 444 and IPv6 addresses assigned by DHCPv6 can be set through snooping 445 DHCP-PD message at SAVI device. FE80::/64 is always a feasible 446 prefix in IPv6. 448 If some of the prefix scopes is set to have non prefix, it implies 449 corresponding address assignment method is not allowed in the 450 network. 452 There is no need to explicitly present these prefix scopes, but these 453 restrictions should be used as premier check in binding set up. 455 8. Acknowledgment 457 The author would like to thank the SAVI working group for a thorough 458 technical discussion on the design and the framework of the SAVI 459 method, as captured in this document, in particular Erik Nordmark, 460 Guang Yao, Eric Levy-Abegnoli, and Alberto Garcia. Thanks also to 461 Torben Melsen for reviewing this document. 463 This document was generated using the xml2rfc tool. 465 9. IANA Considerations 467 This memo asks the IANA for no new parameters. 469 Note to RFC Editor: This section will have served its purpose if it 470 correctly tells IANA that no new assignments or registries are 471 required, or if those assignments or registries are created during 472 the RFC publication process. From the authors' perspective, it may 473 therefore be removed upon publication as an RFC at the RFC Editor's 474 discretion. 476 10. Security Considerations 478 This document only discusses the possible methods to mitigrate the 479 usage of forged IP address, but doesn't propose a mechanism that 480 provides strong security for IP address. If binding anchor is not 481 exclusive for each user, or is without strong security, addresses can 482 still be forged. Besides, the binding may not accord with the 483 address management requirement, which can be more specified for each 484 client. However, given no new protocol is introduced, the 485 improvements are still acceptable. If there is requirement the usage 486 of IP address must be of strong security, the only way is using 487 cryptographic based authentication. 489 11. References 491 11.1. Informative References 493 [BA2007] Baker, F., "Cisco IP Version 4 Source Guard", IETF 494 Internet draft (work in progress), November 2007. 496 [BCP38] Paul, P. and D. Senie, "Network Ingress Filtering: 497 Defeating Denial of Service Attacks which employ IP Source 498 Address Spoofing", RFC 2827, BCP 38, May 2000. 500 11.2. Normative References 502 [draft-ietf-savi-threat-scope] 503 McPherson, D., Baker, F., and J. Halpern, "SAVI Threat 504 Scope", draft-ietf-savi-threat-scope-04 (work in 505 progress), March 2011. 507 [rfc2131] Droms, R., "Dynamic Host Configuration Protocol", 508 RFC 2131, March 1997. 510 [rfc3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C., 511 and M. Carney, "Dynamic Host Configuration Protocol for 512 IPv6 (DHCPv6)", RFC 3315, July 2003. 514 [rfc3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure 515 Neighbor Discovery (SEND)", RFC 3971, March 2005. 517 [rfc4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless 518 Address Autoconfiguration", RFC 4862, September 2007. 520 [rfc5026] Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6 521 Bootstrapping in Split Scenario", RFC 5026, October 2007. 523 [rfc5739] Eronen, P., Laganier, J., and C. Madson, "IPv6 524 Configuration in Internet Key Exchange Protocol Version 2 525 (IKEv2)", RFC 5739, February 2010. 527 [rfc5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen, 528 "Internet Key Exchange Protocol Version 2 (IKEv2)", 529 RFC 5996, September 2010. 531 [savi-dhcp] 532 Bi, J., Wu, J., Yao, G., and F. Baker, "SAVI Solution for 533 DHCP", draft-ietf-savi-dhcp-07 (work in progress), 534 November 2010. 536 [savi-fcfs] 537 Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS- 538 SAVI: First-Come First-Serve Source-Address Validation for 539 Locally Assigned Addresses", draft-ietf-savi-fcfs-05 (work 540 in progress), October 2010. 542 Authors' Addresses 544 Jianping Wu 545 Tsinghua University 546 Computer Science, Tsinghua University 547 Beijing 100084 548 China 550 Email: jianping@cernet.edu.cn 552 Jun Bi 553 Tsinghua University 554 Network Research Center, Tsinghua University 555 Beijing 100084 556 China 558 Email: junbi@tsinghua.edu.cn 560 Marcelo Bagnulo 561 Universidad Carlos III de Madrid 562 Avenida de la Universidad 30 563 Leganes, Madrid 28911 564 Spain 566 Email: marcelo@it.uc3m.es 568 Fred Baker 569 Cisco Systems 570 Santa Barbara, CA 93117 571 United States 573 Email: fred@cisco.com 575 Christian Vogt (editor) 576 Ericsson 577 200 Holger Way 578 San Jose, CA 95134 579 United States 581 Email: christian.vogt@ericsson.com