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Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 Working Group U. Chunduri 3 Internet-Draft W. Lu 4 Intended status: Standards Track A. Tian 5 Expires: April 25, 2013 Ericsson Inc. 6 N. Shen 7 Cisco Systems, Inc. 8 October 22, 2012 10 IS-IS Extended Sequence number TLV 11 draft-chunduri-isis-extended-sequence-no-tlv-03 13 Abstract 15 This document defines Extended Sequence number TLV to protect 16 Intermediate System to Intermediate System (IS-IS) PDUs from replay 17 attacks. 19 Status of this Memo 21 This Internet-Draft is submitted in full conformance with the 22 provisions of BCP 78 and BCP 79. 24 Internet-Drafts are working documents of the Internet Engineering 25 Task Force (IETF). Note that other groups may also distribute 26 working documents as Internet-Drafts. The list of current Internet- 27 Drafts is at http://datatracker.ietf.org/drafts/current/. 29 Internet-Drafts are draft documents valid for a maximum of six months 30 and may be updated, replaced, or obsoleted by other documents at any 31 time. It is inappropriate to use Internet-Drafts as reference 32 material or to cite them other than as "work in progress." 34 This Internet-Draft will expire on April 25, 2013. 36 Copyright Notice 38 Copyright (c) 2012 IETF Trust and the persons identified as the 39 document authors. All rights reserved. 41 This document is subject to BCP 78 and the IETF Trust's Legal 42 Provisions Relating to IETF Documents 43 (http://trustee.ietf.org/license-info) in effect on the date of 44 publication of this document. Please review these documents 45 carefully, as they describe your rights and restrictions with respect 46 to this document. Code Components extracted from this document must 47 include Simplified BSD License text as described in Section 4.e of 48 the Trust Legal Provisions and are provided without warranty as 49 described in the Simplified BSD License. 51 Table of Contents 53 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 54 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 55 1.2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . 4 56 2. Replay attacks and Impact on IS-IS networks . . . . . . . . . 4 57 2.1. Impact of Replays . . . . . . . . . . . . . . . . . . . . 4 58 3. Extended Sequence Number TLV . . . . . . . . . . . . . . . . . 5 59 3.1. Sequence Number Wrap . . . . . . . . . . . . . . . . . . . 6 60 4. Mechanism and Packet Encoding . . . . . . . . . . . . . . . . 6 61 4.1. IIHs . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 62 4.2. SNPs . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 63 4.2.1. CSNPs . . . . . . . . . . . . . . . . . . . . . . . . 7 64 4.2.2. PSNPs . . . . . . . . . . . . . . . . . . . . . . . . 7 65 4.3. LSPs . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 66 5. Backward Compatibility and Deployment . . . . . . . . . . . . 8 67 5.1. IIH and SNPs . . . . . . . . . . . . . . . . . . . . . . . 8 68 5.2. LSPs . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 69 5.3. Operational Consideration . . . . . . . . . . . . . . . . 9 70 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 71 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 72 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 73 9. Appendix A . . . . . . . . . . . . . . . . . . . . . . . . . . 10 74 9.1. Appendix A.1 . . . . . . . . . . . . . . . . . . . . . . . 10 75 9.2. Appendix A.2 . . . . . . . . . . . . . . . . . . . . . . . 10 76 10. Appendix B . . . . . . . . . . . . . . . . . . . . . . . . . . 11 77 10.1. Operational/Implementation consideration . . . . . . . . . 11 78 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 79 11.1. Normative References . . . . . . . . . . . . . . . . . . . 11 80 11.2. Informative References . . . . . . . . . . . . . . . . . . 11 81 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 83 1. Introduction 85 With the rapid development of new data center infrastructures, due to 86 its flexibility and scalability attributes, IS-IS has been adopted 87 widely in various L2 and L3 routing deployment of the data centers 88 for critical business operations. At the meantime the SDN-enabled 89 networks even though put more power to Internet applications and also 90 make network management easier, it does raise the security 91 requirement of network routing infrastructure to another level. 93 This document defines Extended Sequence number (ESN) TLV to protect 94 Intermediate System to Intermediate System (IS-IS) PDUs from replay 95 attacks. 97 A replayed IS-IS PDU can potentially cause many problems in the IS-IS 98 networks ranging from bouncing adjacencies to black hole or even some 99 form of Denial of Service (DoS) attacks as explained in Section 2. 100 This problem is also discussed in security consideration section, in 101 the context of cryptographic authentication work as described in 102 [RFC5304] and in [RFC5310]. 104 Currently, there is no mechanism to protect IS-IS HELLO PDUs (IIHs) 105 and Sequence number PDUs (SNPs) from the replay attacks. However, 106 Link State PDUs (LSPs) have sequence number in the LSP header as 107 defined in [RFC1195], with which it can effectively mitigate the 108 intra-session replay attacks. But, LSPs are still susceptible to 109 inter-session replay attacks. 111 The new ESN TLV defined here thwart these threats and can be deployed 112 with authentication mechanism as specified in [RFC5304] and in 113 [RFC5310] for a more secure network. 115 Replay attacks can be effectively mitigated by deploying a group key 116 management protocol (being developed as defined in [I-D.yeung-g- 117 ikev2] and [I-D.hartman-karp-mrkmp]) with a frequent key change 118 policy. Currently, there is no such mechanism defined for IS-IS. 119 Even if such a mechanism is defined, usage of this TLV can be helpful 120 to avoid replays before the keys are changed. 122 Also, it is believed, even when such key management system is 123 deployed, there always will be some manual key based systems that co- 124 exist with KMP (Key Management Protocol) based systems. The ESN TLV 125 defined in this document is more helpful for such deployments. 127 1.1. Requirements Language 129 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 130 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 131 document are to be interpreted as described in RFC 2119 [RFC2119]. 133 1.2. Acronyms 135 CSNP - Complete Sequence Number PDU 137 ESN - Extended Sequence Number 139 IIH - IS-IS Hello PDU 141 KMP - Key Management Protocol (auto key management) 143 LSP - IS-IS Link State PDU 145 MKM - Manual Key management Protocols 147 PDU - Protocol Data Unit 149 PSNP - Partial Sequence Number PDU 151 SNP - Sequence Number PDU 153 2. Replay attacks and Impact on IS-IS networks 155 This section explains the replay attacks and the applicability of the 156 same for IS-IS networks. Replaying a captured protocol packet to 157 cause damage is a common threat for any protocol. Securing the 158 packet with cryptographic authentication information alone can not 159 mitigate this threat completely. This has been described in detail 160 in "Replay Attacks" section of KARP IS-IS gap analysis document 161 [I-D.chunduri-karp-is-is-gap-analysis]. 163 2.1. Impact of Replays 165 At the time of adjacency bring up an IS sends IIH packet with empty 166 neighbor list (TLV 6) and with or with out the authentication 167 information as per provisioned authentication mechanism. If this 168 packet is replayed later on the broadcast network all ISes in the 169 broadcast network can bounce the adjacency to create a huge churn in 170 the network. 172 Today Link State PDUs (LSPs) have intra-session replay protection as 173 LSP header contains 32-bit sequence number which is verified for 174 every received PDU against the local LSP database. But, if the key 175 is not changed, an adversary can cause an inter-session replay attack 176 by replaying a old LSP with higher sequence number and fewer prefixes 177 or fewer adjacencies. This forces the receiver to accept and remove 178 the routes from the routing table, which eventually causes traffic 179 disruption to those prefixes. The more common pre-conditions for 180 inter-session replay attacks with LSPs and the current in-built 181 recovery mechanism, have been discussed in details in KARP IS-IS gap 182 analysis document [I-D.chunduri-karp-is-is-gap-analysis]. 184 In broadcast networks a replayed Complete Sequence Number PDU (CSNP) 185 can force the receiver to request Partial Sequence Number PDU (PSNP) 186 in the network and similarly, a replayed PSNP can cause unnecessary 187 LSP flood in the network. 189 Please refer KARP IS-IS gap analysis document for further details. 191 3. Extended Sequence Number TLV 193 The Extended Sequence Number (ESN) TLV is composed of 1 octet for the 194 Type, 1 octet that specifies the number of bytes in the Value field 195 and an 8 or 12 byte Value field. 197 x CODE - TBD. 199 x LENGTH - total length of the value field, which is 12 bytes for 200 IIH, SNP PDUs and 8 bytes for LSPs. 202 x Value - 64-bit Extended Session Sequence Number (ESSN), which is 203 present for all IS-IS PDUs followed 32 bit monotonically increasing 204 per Packet Sequence Number (PSN). PSN is not required for LSPs. 206 0 1 2 3 207 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 1 208 +-+-+-+-+-+-+-+-+ 209 | Type | 210 +-+-+-+-+-+-+-+-+ 211 | Length | 212 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 213 | Extended Session Sequence Number (High Order 32 Bits) | 214 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 215 | Extended Session Sequence Number (Low Order 32 Bits) | 216 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 217 | (optional) Packet Sequence Number (32 Bits) | 218 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 220 Figure 1: Extended Sequence Number (ESN) TLV 222 The Extended Sequence Number (ESN) TLV Type is TBD. Please refer to 223 IANA Considerations, in Section 6 for more details. Length indicates 224 the length of the value field; which is 12 bytes for IIH and SNP PDUs 225 and 8 bytes for LSPs. 227 In order to provide protection against both inter-session and intra- 228 session replay attacks, the IS-IS Extended Session Sequence Number 229 (ESSN) is defined a 64-bits value; the value MUST contain ever 230 increasing number in all IS-IS PDUs including LSPs whenever it is 231 changed due any situation as specified in Section 3.1. 233 The 32-bit Packet Sequence Number (PSN) MUST be set and increase 234 monotonically for IIH or SNP PDUs sent by IS-IS node. Upon 235 reception, the Packet Sequence number MUST be greater than the last 236 sequence number in the IIH or SNP PDUs accepted from the sending 237 IS-IS node. Otherwise, the IIH or SNP PDU is considered as replayed 238 PDU and dropped. 240 As LSPs contain 32-bit sequence number field already in the LSP 241 header, Packet Sequence Number in the ESN TLV MUST be omitted by 242 setting the length field to 8 bytes and implementations continue to 243 refer the header sequence number for all encoding and validation 244 purposes. 246 The ESN TLV defined here is optional. The ESN TLV MAY present in any 247 IS-IS PDU. If present and authentication is in use this TLV MUST be 248 included as part of the authentication data to calculate the digest. 249 A sender MUST only transmit a single ESN TLV in a IS-IS PDU. 251 3.1. Sequence Number Wrap 253 If the 32-bit Packet Sequence Number in ESN TLV and for LSPs the 32- 254 bit header sequence number wraps; or session is refreshed; or even 255 for the cold restarts the 64-bit ESSN value MUST be set higher than 256 the previous value. IS-IS implementations MAY use guidelines 257 provided in Section 9 for accomplishing this. 259 4. Mechanism and Packet Encoding 261 The ESN TLV defined in this document is optional and the encoding and 262 decoding of this TLV in each IS-IS PDU is as detailed below. Also 263 refer, when to ignore processing of the ESN TLV as described in 264 Section 5 for appropriate operation in the face of legacy node(s) in 265 the network with out having this capability. 267 4.1. IIHs 269 The IIH ESN TLV information is maintained per IS-IS interface and per 270 level. For a broadcast interface, it can have two sets of ESN TLV 271 information, if the circuit belongs to both level-1 and level-2. For 272 point-to-point (P2P) interface, only one ESN TLV information is 273 needed. This TLV information can be maintained as part of the 274 adjacency state. 276 While transmitting, the 64-bit ESSN MUST always be started with a non 277 zero number and MAY use the guidelines as specified in Section 9 to 278 encode this 64-bit value. The 32-bit PSN starts from 1 and increases 279 monotonically for every subsequent PDU. 281 While receiving, the 64-bit ESSN MUST always be either same or higher 282 than the stored value in the adjacency state. Similarly, the 32-bit 283 PSN MUST be higher than the stored value in the adjacency state. If 284 the PDU is accepted then the adjacency state should be updated with 285 the last received IIH PDU's ESN TLV information. 287 For an adjacency refresh or the 32-bit PSN wrap the associated higher 288 order 64-bit ESSN MUST always be higher than the previous value and 289 the lower order 32-bit packet sequence number starts all over again. 291 4.2. SNPs 293 4.2.1. CSNPs 295 In broadcast networks, only Designated Intermediate System (DIS) CSNP 296 ESN TLV information is maintained per adjacency (per level) similar 297 to IIH ESN TLV information. The procedure for encoding, verification 298 and sequence number wrap scenarios are similar as explained in 299 Section 4.1, except separate DIS ESN TLV information should be used. 300 In case of DIS change all adjacencies in the broadcast network MUST 301 reflect new DIS's CSNP ESN TLV information in the adjacency and 302 should be used for encoding/verification. 304 In P2P networks, CSNP ESN TLV information is maintained per adjacency 305 similar to IIH ESN TLV information. The procedure for encoding, 306 verification and sequence number wrap scenarios are similar as 307 explained in Section 4.1, except separate CSNP ESN TLV information 308 should be used. 310 4.2.2. PSNPs 312 In both broadcast and P2P networks, PSNP ESN TLV information is 313 maintained per adjacency (per level) similar to IIH ESN TLV 314 information. The procedure for encoding, verification and sequence 315 number wrap scenarios are similar as explained in Section 4.1, except 316 separate PSNP ESN TLV information should be used. 318 4.3. LSPs 320 For LSPs, while originating, the 64-bit ESSN MUST always be started 321 with a non zero number and MAY use the guidelines as specified in 322 Section 9 for encoding this value. 324 While receiving, the 64-bit Extended Sequence Number MUST always be 325 either same or higher than the stored value in the LSP database. 326 This document does not specify any changes for the existing LSP 327 header 32-bit sequence number validation mechanism. 329 5. Backward Compatibility and Deployment 331 The implementation and deployment of the ESN TLV can be done to 332 support backward compatibility and gradual deployment in the network 333 without requiring a flag day. The deployment can be done for IS-IS 334 links only, or for both IS-IS links and nodes in the networks. This 335 feature can also be deployed for the links in a certain area of the 336 network where the maximum security mechanism is needed, or it can be 337 deployed for the entire network. 339 The implementation SHOULD allow the configuration of ESN TLV feature 340 on each IS-IS link level and on IS-IS node level with area/level 341 scope. The implementation SHOULD also allow operators to control the 342 configuration of 'send' and/or 'verify' the feature of IS-IS PDUs for 343 the links and for the node. In this document, the 'send' operation 344 is to include the ESN TLV in it's own IS-IS PDUs; and the 'verify' 345 operation is to process the ESN TLV in the receiving IS-IS PDUs from 346 neighbors. 348 5.1. IIH and SNPs 350 On the link level, ESN TLV involves the IIH PDUs and SNPs (both CSNP 351 and PSNP). When the router software is upgraded to include this 352 feature, the network operators can configure the IS-IS to 'send' the 353 ESN TLV in it's IIH PDUs and SNPs for those IS-IS interfaces on the 354 IS-IS area or level. When all the routers attached to the link or 355 links have been upgraded with this feature, network operators can 356 start to configure 'verify' on the IS-IS interfaces for all the 357 routers sharing the same link(s). This way deployment can be done in 358 per link basis in the network. Please further refer Section 5.3 for 359 note on operational considerations at the time of 'verify' operation 360 in the network. The operators may decide to only apply ESN TLV 361 feature on some of the links in the network, or only on their multi- 362 access media links. 364 5.2. LSPs 366 On the node level with an area or level scope, ESN TLV involves the 367 IS-IS LSPs. This feature has to be done for the entire IS-IS area or 368 levels with the same flooding domain. The deployment and upgrade of 369 software to support ESN TLV can be gradual and from node to node. 370 When a node is upgraded to support this feature, the operators can 371 configure the node level 'send' in the desired area/level(s) to 372 include the ESN TLV in it's own LSPs. No 'verify' is enabled until 373 all the routers in the entire IS-IS area/level or entire network is 374 upgraded. Then the operators can configure the 'verify' for the 375 IS-IS node level from node to node. Please further refer Section 5.3 376 for note on operational considerations at the time of 'verify' 377 operation in the network. When all the nodes performs the 'verify' 378 of ESN TLVs, the node level ESN TLV feature is supported fully in the 379 network. 381 5.3. Operational Consideration 383 In the face of an adversary doing an active attack, it is possible to 384 have inconsistent data view in the network, if there is a 385 considerable delay in enabling ESN TLV 'verify' operation from first 386 node to the last node in the network. This can happen primarily 387 because, replay PDUs can potentially be accepted by the nodes where 388 'verify' operation is still not provisioned at the time of the 389 attack. To minimize such a window it is recommended that 390 provisioning of 'verify' SHOULD be done in a timely fashion by the 391 network operators. 393 6. IANA Considerations 395 This document requests that IANA allocate from the IS-IS TLV 396 Codepoints Registry a new TLV, referred to as the "Extended Sequence 397 Number" TLV, with the following attributes: IIH = y, LSP = y, SNP = 398 y, Purge = y. 400 7. Security Considerations 402 This document describes a mechanism to the replay attack threat as 403 discussed in the Security Considerations section of [RFC5304] and in 404 [RFC5310]. This document does not introduce any new security 405 concerns to IS-IS or any other specifications referenced in this 406 document. 408 8. Acknowledgements 410 The authors of this document do not make any claims on the 411 originality of the ideas described. Authors are thankful for the 412 review and the valuable feedback provided by Acee Lindem, Joel 413 Halpern and Les Ginsberg. 415 9. Appendix A 417 IS-IS nodes implementing this specification SHOULD use available 418 mechanisms to preserve the 64-bit Extended Session Sequence Number's 419 strictly increasing property, when ever it is changed for the 420 deployed life of the IS-IS node (including cold restarts). 422 This Appendix provides only guidelines for achieving the same and 423 implementations can resort to any similar method as far as strictly 424 increasing property of the 64-bit ESSN in ESN TLV is maintained. 426 9.1. Appendix A.1 428 One mechanism for accomplishing this is by encoding 64-bit ESSN as 429 system time represented in 64-bit unsigned integer value. This MAY 430 be similar to the system timestamp encoding for NTP long format as 431 defined in Appendix A.4 of [RFC5905]. New current time MAY be used 432 when the IS-IS node loses its sequence number state including in 433 Packet Sequence Number wrap scenarios. 435 Implementations MUST make sure while encoding the 64-bit ESN value 436 with current system time, it should not default to any previous value 437 or some default node time of the system; especially after cold 438 restarts or any other similar events. In general system time must be 439 preserved across cold restarts in order for this mechanism to be 440 feasible. One example of such implementation is to use a battery 441 backed real-time clock (RTC). 443 9.2. Appendix A.2 445 One other mechanism for accomplishing this would be similar to the 446 one as specified in [I-D.ietf-ospf-security-extension-manual-keying], 447 to use the 64-bit ESSN as a wrap/boot count stored in non-volatile 448 storage. This value is incremented anytime the IS-IS node loses its 449 sequence number state including in Packet Sequence Number wrap 450 scenarios. 452 The drawback of this approach per Section 6 of [I-D.ietf-ospf- 453 security-extension-manual-keying], if used is applicable here. The 454 only drawback is, it requires the IS-IS implementation to be able to 455 save its boot count in non-volatile storage. If the non-volatile 456 storage is ever repaired or upgraded such that the contents are lost, 457 keys MUST be changed to prevent replay attacks. 459 10. Appendix B 461 10.1. Operational/Implementation consideration 463 Since the ESN is maintained per interface, per level and per PDU 464 type, this scheme can be useful for monitoring the health of the 465 IS-IS adjacency. A Packet Sequence Number skip on IIH can be 466 recorded by the neighbors which can be used later to correlate with 467 adjacency state changes over the interface. For instance in a multi- 468 access media, all the neighbors have the skips from the same IIH 469 sender or only one neighbor has the Packet Sequence Number skips can 470 indicate completely different issues on the network. 472 11. References 474 11.1. Normative References 476 [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and 477 dual environments", RFC 1195, December 1990. 479 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 480 Requirement Levels", BCP 14, RFC 2119, March 1997. 482 [RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network 483 Time Protocol Version 4: Protocol and Algorithms 484 Specification", RFC 5905, June 2010. 486 11.2. Informative References 488 [I-D.chunduri-karp-is-is-gap-analysis] 489 Chunduri, U., Tian, A., and W. Lu, "KARP IS-IS security 490 gap analysis", draft-chunduri-karp-is-is-gap-analysis-01 491 (work in progress), March 2012. 493 [I-D.hartman-karp-mrkmp] 494 Hartman, S., Zhang, D., and G. Lebovitz, "Multicast Router 495 Key Management Protocol (MaRK)", 496 draft-hartman-karp-mrkmp-05 (work in progress), 497 September 2012. 499 [I-D.ietf-karp-threats-reqs] 500 Lebovitz, G. and M. Bhatia, "Keying and Authentication for 501 Routing Protocols (KARP) Overview, Threats, and 502 Requirements", draft-ietf-karp-threats-reqs-05 (work in 503 progress), May 2012. 505 [I-D.ietf-ospf-security-extension-manual-keying] 506 Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, 507 "Security Extension for OSPFv2 when using Manual Key 508 Management", 509 draft-ietf-ospf-security-extension-manual-keying-02 (work 510 in progress), April 2012. 512 [I-D.weis-gdoi-mac-tek] 513 Weis, B. and S. Rowles, "GDOI Generic Message 514 Authentication Code Policy", draft-weis-gdoi-mac-tek-03 515 (work in progress), September 2011. 517 [RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic 518 Authentication", RFC 5304, October 2008. 520 [RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R., 521 and M. Fanto, "IS-IS Generic Cryptographic 522 Authentication", RFC 5310, February 2009. 524 [RFC6518] Lebovitz, G. and M. Bhatia, "Keying and Authentication for 525 Routing Protocols (KARP) Design Guidelines", RFC 6518, 526 February 2012. 528 Authors' Addresses 530 Uma Chunduri 531 Ericsson Inc. 532 300 Holger Way, 533 San Jose, California 95134 534 USA 536 Phone: 408 750-5678 537 Email: uma.chunduri@ericsson.com 539 Wenhu Lu 540 Ericsson Inc. 541 300 Holger Way, 542 San Jose, California 95134 543 USA 545 Email: wenhu.lu@ericsson.com 546 Albert Tian 547 Ericsson Inc. 548 300 Holger Way, 549 San Jose, California 95134 550 USA 552 Phone: 408 750-5210 553 Email: albert.tian@ericsson.com 555 Naiming Shen 556 Cisco Systems, Inc. 557 225 West Tasman Drive, 558 San Jose, California 95134 559 USA 561 Email: naiming@cisco.com