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Checking references for intended status: Proposed Standard ---------------------------------------------------------------------------- (See RFCs 3967 and 4897 for information about using normative references to lower-maturity documents in RFCs) -- Looks like a reference, but probably isn't: '16' on line 522 ** Obsolete normative reference: RFC 5077 (Obsoleted by RFC 8446) ** Obsolete normative reference: RFC 5245 (Obsoleted by RFC 8445, RFC 8839) ** Obsolete normative reference: RFC 5389 (Obsoleted by RFC 8489) ** Obsolete normative reference: RFC 5766 (Obsoleted by RFC 8656) -- Obsolete informational reference (is this intentional?): RFC 6982 (Obsoleted by RFC 7942) Summary: 4 errors (**), 0 flaws (~~), 1 warning (==), 3 comments (--). Run idnits with the --verbose option for more detailed information about the items above. -------------------------------------------------------------------------------- 2 TRAM T. Reddy 3 Internet-Draft D. Wing 4 Intended status: Standards Track P. Patil 5 Expires: February 19, 2017 P. Martinsen 6 Cisco 7 August 18, 2016 9 Mobility with TURN 10 draft-ietf-tram-turn-mobility-05 12 Abstract 14 It is desirable to minimize traffic disruption caused by changing IP 15 address during a mobility event. One mechanism to minimize 16 disruption is to expose a shorter network path to the mobility event 17 so only the local network elements are aware of the changed IP 18 address but the remote peer is unaware of the changed IP address. 20 This draft provides such an IP address mobility solution using 21 Traversal Using Relays around NAT (TURN). This is achieved by 22 allowing a client to retain an allocation on the TURN server when the 23 IP address of the client changes. 25 Status of This Memo 27 This Internet-Draft is submitted in full conformance with the 28 provisions of BCP 78 and BCP 79. 30 Internet-Drafts are working documents of the Internet Engineering 31 Task Force (IETF). Note that other groups may also distribute 32 working documents as Internet-Drafts. The list of current Internet- 33 Drafts is at http://datatracker.ietf.org/drafts/current/. 35 Internet-Drafts are draft documents valid for a maximum of six months 36 and may be updated, replaced, or obsoleted by other documents at any 37 time. It is inappropriate to use Internet-Drafts as reference 38 material or to cite them other than as "work in progress." 40 This Internet-Draft will expire on February 19, 2017. 42 Copyright Notice 44 Copyright (c) 2016 IETF Trust and the persons identified as the 45 document authors. All rights reserved. 47 This document is subject to BCP 78 and the IETF Trust's Legal 48 Provisions Relating to IETF Documents 49 (http://trustee.ietf.org/license-info) in effect on the date of 50 publication of this document. Please review these documents 51 carefully, as they describe your rights and restrictions with respect 52 to this document. Code Components extracted from this document must 53 include Simplified BSD License text as described in Section 4.e of 54 the Trust Legal Provisions and are provided without warranty as 55 described in the Simplified BSD License. 57 Table of Contents 59 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 60 2. Notational Conventions . . . . . . . . . . . . . . . . . . . 3 61 3. Mobility using TURN . . . . . . . . . . . . . . . . . . . . . 4 62 3.1. Creating an Allocation . . . . . . . . . . . . . . . . . 5 63 3.1.1. Sending an Allocate Request . . . . . . . . . . . . . 5 64 3.1.2. Receiving an Allocate Request . . . . . . . . . . . . 5 65 3.1.3. Receiving an Allocate Success Response . . . . . . . 6 66 3.1.4. Receiving an Allocate Error Response . . . . . . . . 6 67 3.2. Refreshing an Allocation . . . . . . . . . . . . . . . . 6 68 3.2.1. Sending a Refresh Request . . . . . . . . . . . . . . 6 69 3.2.2. Receiving a Refresh Request . . . . . . . . . . . . . 7 70 3.2.3. Receiving a Refresh Response . . . . . . . . . . . . 8 71 3.3. New STUN Attribute MOBILITY-TICKET . . . . . . . . . . . 8 72 3.4. New STUN Error Response Code . . . . . . . . . . . . . . 8 73 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 74 5. Implementation Status . . . . . . . . . . . . . . . . . . . . 9 75 5.1. open-sys . . . . . . . . . . . . . . . . . . . . . . . . 9 76 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 77 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10 78 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10 79 8.1. Normative References . . . . . . . . . . . . . . . . . . 10 80 8.2. Informative References . . . . . . . . . . . . . . . . . 11 81 Appendix A. Example ticket construction . . . . . . . . . . . . 12 82 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 84 1. Introduction 86 When moving between networks, the endpoint's IP address can change or 87 (due to NAT) the endpoint's public IP address can change. Such a 88 change of IP address breaks upper layer protocols such as TCP and 89 RTP. Various techniques exist to prevent this breakage, all tied to 90 making the endpoint's IP address static (e.g., Mobile IP, Proxy 91 Mobile IP, LISP). Other techniques exist, which make the change in 92 IP address agnostic to the upper layer protocol (e.g., SCTP). The 93 mechanism described in this document are in that last category. 95 A Traversal Using Relays around NAT (TURN) [RFC5766] server relays 96 media packets and is used for a variety of purposes, including 97 overcoming NAT and firewall traversal issues. The existing TURN 98 specification does not permit a TURN client to reuse an allocation 99 across client IP address changes. Due to this, when the IP address 100 of the client changes, the TURN client has to request for a new 101 allocation, create permissions for the remote peer, create channels 102 etc. In addition the client has to re-establish communication with 103 its signaling server, send an updated offer to the remote peer 104 conveying the new relayed candidate address, remote side has to 105 regather all candidates and signal them to the client and then the 106 endpoints have to perform Interactive Connectivity Establishment 107 (ICE) [RFC5245] connectivity checks. If ICE continuous nomination 108 procedure [I-D.uberti-mmusic-nombis] is used then new relayed 109 candidate address would have to be tricked 110 [I-D.ietf-mmusic-trickle-ice] and ICE connectivity checks have to be 111 performed by the endpoints to nominate pairs that will be selected by 112 ICE. 114 This specification describes a mechanism to seamlessly reuse 115 allocations across client IP address changes without any of the 116 hassles described above. A critical benefit of this technique is 117 that the remote peer does not have to support mobility, or deal with 118 any of the address changes. The client, that is subject to IP 119 address changes, does all the work. The mobility technique works 120 across and between network types (e.g., between 3G and wired Internet 121 access), so long as the client can still access the TURN server. The 122 technique should also work seamlessly when (D)TLS is used as a 123 transport protocol for Session Traversal Utilities for NAT (STUN) 124 [RFC5389]. When there is a change in IP address, the client uses 125 (D)TLS Session Resumption without Server-Side State as described in 126 [RFC5077] to resume secure communication with the TURN server, using 127 the changed client IP address. 129 2. Notational Conventions 131 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 132 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 133 document are to be interpreted as described in [RFC2119]. 135 This note uses terminology defined in [RFC5245], and the following 136 additional terminology: 138 Break Before Make: The old communication path is broken ("break") 139 before new communication can be created ("make"). Such changes 140 typically occur because a network is disconnected with a physical 141 cable, turning radio off, or moving out of radio range. 143 Make Before Break: A new communication path is created ("make") 144 before the old communication path is broken ("break"). Such changes 145 typically occur because a network is connected with a physical cable, 146 turning radio on, or moving into radio range. 148 3. Mobility using TURN 150 To achieve mobility, a TURN client should be able to retain an 151 allocation on the TURN server across changes in the client IP address 152 as a consequence of movement to other networks. 154 When the client sends the initial Allocate request to the TURN 155 server, it will include a new STUN attribute MOBILITY-TICKET (with 156 zero length value), which indicates that the client is capable of 157 mobility and desires a ticket. The TURN server provisions a ticket 158 that is sent inside the new STUN attribute MOBILITY-TICKET in the 159 Allocate Success response to the client. The ticket will be used by 160 the client when it wants to refresh the allocation but with a new 161 client IP address and port. This ensures that an allocation can only 162 be refreshed by the same client that allocated relayed transport 163 address. When a client's IP address changes due to mobility, it 164 presents the previously obtained ticket in a Refresh Request to the 165 TURN server. If the ticket is found to be valid, the TURN server 166 will retain the same relayed address/port for the new IP address/port 167 allowing the client to continue using previous channel bindings -- 168 thus, the TURN client does not need to obtain new channel bindings. 169 Any data from external peer will be delivered by the TURN server to 170 this new IP address/port of the client. The TURN client will 171 continue to send application data to its peers using the previously 172 allocated channelBind Requests. 174 TURN TURN Peer 175 client server A 176 |-- Allocate request --------------->| | 177 | + MOBILITY-TICKET (length=0) | | 178 | | | 179 |<--------------- Allocate failure --| | 180 | (401 Unauthorized) | | 181 | | | 182 |-- Allocate request --------------->| | 183 | + MOBILITY-TICKET (length=0) | | 184 | | | 185 |<---------- Allocate success resp --| | 186 | + MOBILITY-TICKET | | 187 ... ... ... 188 (changes IP address) 189 | | | 190 |-- Refresh request ---------------->| | 191 | + MOBILITY-TICKET | | 192 | | | 193 |<----------- Refresh success resp --| | 194 | + MOBILITY-TICKET | | 195 | | | 197 3.1. Creating an Allocation 199 3.1.1. Sending an Allocate Request 201 In addition to the process described in Section 6.1 of [RFC5766], the 202 client includes the MOBILITY-TICKET attribute with length 0. This 203 indicates the client is a mobile node and wants a ticket. 205 3.1.2. Receiving an Allocate Request 207 In addition to the process described in Section 6.2 of [RFC5766], the 208 server does the following: 210 If the MOBILITY-TICKET attribute is included, and has length zero, 211 but TURN session mobility is forbidden by local policy, the server 212 will reject the request with the new Mobility Forbidden error code. 213 If the MOBILITY-TICKET attribute is included and has non-zero length 214 then the server will generate an error response with an error code of 215 400 (Bad Request). Following the rules specified in [RFC5389], if 216 the server does not understand the MOBILITY-TICKET attribute, it 217 ignores the attribute. 219 If the server can successfully process the request and create an 220 allocation, the server replies with a success response that includes 221 a STUN MOBILITY-TICKET attribute. TURN server can store system 222 internal data into the ticket that is encrypted by a key known only 223 to the TURN server and sends the ticket in the STUN MOBILITY-TICKET 224 attribute as part of Allocate success response. An example for 225 ticket construction is discussed in Appendix A .The ticket is opaque 226 to the client, so the structure is not subject to interoperability 227 concerns, and implementations may diverge from this format. The 228 client could be roaming across networks with different path MTU and 229 from one address family to another (e.g. IPv6 to IPv4). The TURN 230 server to support mobility must assume that the path MTU is unknown 231 and use a ticket length in accordance with published guidance on STUN 232 UDP fragmentation (Section 7.1 of [RFC5389]). 234 Note: There is no guarantee that the fields in the ticket are going 235 to be decodable to a client, and therefore attempts by a client to 236 examine the ticket are unlikely to be useful. 238 3.1.3. Receiving an Allocate Success Response 240 In addition to the process described in Section 6.3 of [RFC5766], the 241 client will store the MOBILITY-TICKET attribute, if present, from the 242 response. This attribute will be presented by the client to the 243 server during a subsequent Refresh request to aid mobility. 245 3.1.4. Receiving an Allocate Error Response 247 If the client receives an Allocate error response with error code TBD 248 (Mobility Forbidden), the error is processed as follows: 250 o TBD (Mobility Forbidden): The request is valid, but the server is 251 refusing to perform it, likely due to administrative restrictions. 252 The client considers the current transaction as having failed. The 253 client can notify the user or operator. The client SHOULD NOT retry 254 the same request with this server until it believes the problem has 255 been fixed. 257 All other error responses must be handled as described in [RFC5766]. 259 3.2. Refreshing an Allocation 261 3.2.1. Sending a Refresh Request 263 If a client wants to refresh an existing allocation and update its 264 time-to-expiry or delete an existing allocation, it will send a 265 Refresh Request as described in Section 7.1 of [RFC5766]. If the 266 client wants to retain the existing allocation in case of IP change, 267 it will include the MOBILITY-TICKET attribute received in the 268 Allocate Success response. 270 3.2.2. Receiving a Refresh Request 272 In addition to the process described in Section 7.2 of [RFC5766], the 273 server does the following: 275 If the STUN MOBILITY-TICKET attribute is included in the Refresh 276 Request then the server will not retrieve the 5-tuple from the packet 277 to identify an associated allocation. Instead the TURN server will 278 decrypt the received ticket, verify the ticket's validity and 279 retrieve the 5-tuple allocation using the ticket. If this 5-tuple 280 obtained does not identify an existing allocation then the server 281 MUST reject the request with a 437 (Allocation Mismatch) error. If 282 the ticket is invalid then then server MUST reject the request with a 283 400 (Bad Request) error. 285 If the source IP address and port of the Refresh Request with STUN 286 MOBILITY-TICKET attribute is same as the stored 5-tuple allocation 287 then the TURN server rejects the request with 400 (Bad Request) 288 error. If the source IP address and port of the Refresh Request is 289 different from the stored 5-tuple allocation, the TURN server 290 proceeds with MESSAGE-INTEGRITY validation to identify the that it is 291 the same user which had previously created the TURN allocation. If 292 the above check is not successful then server MUST reject the request 293 with a 441 (Wrong Credentials) error. 295 If all of the above checks pass, the TURN server understands that the 296 client has either moved to a new network and acquired a new IP 297 address (Break Before Make) or is in the process of switching to a 298 new interface (Make Before Break). The source IP address of the 299 request could either be the host transport address or server- 300 reflexive transport address. The server then updates its state data 301 with the new client IP address and port but does not discard the old 302 5-tuple from its state data. TURN server calculates the ticket with 303 the new 5-tuple and sends the new ticket in the STUN MOBILITY-TICKET 304 attribute as part of Refresh Success response. The new ticket sent 305 in the refresh response MUST be different from the old ticket. 307 The TURN server MUST continue receiving and processing data on the 308 old 5-tuple and MUST continue transmitting data on the old-5 tuple 309 until it receives an Send Indication or ChannelData message from the 310 client on the new 5-tuple or an message from the client to close the 311 old connection (e.g., a TLS fatal alert, TCP RST). After receiving 312 any of those messages, a TURN server discards the the old ticket and 313 the old 5-tuple associated with the old ticket from its state data. 314 Data sent by the client to the peer is accepted on the new 5-tuple 315 and data received from the peer is forwarded to the new 5-tuple. If 316 the refresh request containing the MOBILITY-TICKET attribute does not 317 succeed (e.g., packet lost if the request is sent over UDP, or the 318 server being unable to fulfill the request) then the client can 319 continue to exchange data on the old 5-tuple until it receives 320 Refresh success response. 322 The old ticket can only be used for the purposes of retransmission. 323 If the client wants to refresh its allocation with a new server- 324 reflexive transport address, it MUST use the new ticket. If the TURN 325 server has not received a Refresh Request with STUN MOBILITY-TICKET 326 attribute but receives Send indications or ChannelData messages from 327 a client, the TURN server MAY discard or queue those Send indications 328 or ChannelData messages (at its discretion). Thus, it is RECOMMENDED 329 that the client avoid transmitting a Send indication or ChannelData 330 message until it has received an acknowledgement for the Refresh 331 Request with STUN MOBILITY-TICKET attribute. 333 To accommodate for loss of Refresh responses, a server must retain 334 the old STUN MOBILITY-TICKET attribute for a period of at least 30 335 seconds to be able to recognize a retransmission of Refresh request 336 with the old STUN MOBILITY-TICKET attribute from the client. 338 3.2.3. Receiving a Refresh Response 340 In addition to the process described in Section 7.3 of [RFC5766], the 341 client will store the MOBILITY-TICKET attribute, if present, from the 342 response. This attribute will be presented by the client to the 343 server during a subsequent Refresh Request to aid mobility. 345 3.3. New STUN Attribute MOBILITY-TICKET 347 This attribute is used to retain an Allocation on the TURN server. 348 It is exchanged between the client and server to aid mobility. The 349 value of MOBILITY-TICKET is encrypted and is of variable-length. 351 3.4. New STUN Error Response Code 353 This document defines the following new error response code: 355 TBD Mobility Forbidden: Mobility request was valid but cannot be 356 performed due to administrative or similar restrictions. 358 4. IANA Considerations 360 [Note to RFC editor: Please update sections 3.1.4 and 3.4 with the 361 error number.] 363 IANA is requested to add the following attributes to the STUN 364 attribute registry [iana-stun], 365 o MOBILITY-TICKET (0x8030, in the comprehension-optional range) 367 and to add a new STUN error code "Mobility Forbidden" with the value 368 405 to the STUN Error Codes registry [iana-stun]. 370 5. Implementation Status 372 [Note to RFC Editor: Please remove this section and reference to 373 [RFC6982] prior to publication.] 375 This section records the status of known implementations of the 376 protocol defined by this specification at the time of posting of this 377 Internet-Draft, and is based on a proposal described in [RFC6982]. 378 The description of implementations in this section is intended to 379 assist the IETF in its decision processes in progressing drafts to 380 RFCs. Please note that the listing of any individual implementation 381 here does not imply endorsement by the IETF. Furthermore, no effort 382 has been spent to verify the information presented here that was 383 supplied by IETF contributors. This is not intended as, and must not 384 be construed to be, a catalog of available implementations or their 385 features. Readers are advised to note that other implementations may 386 exist. 388 According to [RFC6982], "this will allow reviewers and working groups 389 to assign due consideration to documents that have the benefit of 390 running code, which may serve as evidence of valuable experimentation 391 and feedback that have made the implemented protocols more mature. 392 It is up to the individual working groups to use this information as 393 they see fit". 395 5.1. open-sys 397 Organization: This is a public project, the full list of authors 398 and contributors here: http://turnserver.open-sys.org/downloads/ 399 AUTHORS 401 Description: A mature open-source TURN server specs implementation 402 (RFC 5766, RFC 6062, RFC 6156, etc) designed for high-performance 403 applications, especially geared for WebRTC. 405 Implementation: http://code.google.com/p/rfc5766-turn-server/ 407 Level of maturity: The Mobile ICE feature implementation can be 408 qualified as "production" - it is well tested and fully 409 implemented, but not widely used, yet.. 411 Coverage: Fully implements MICE with TURN protocol. 413 Licensing: BSD: http://turnserver.open-sys.org/downloads/LICENSE 415 Implementation experience: MICE implementation is somewhat 416 challenging for a multi-threaded performance-oriented application 417 (because the mobile ticket information must be shared between the 418 threads) but it is doable. 420 Contact: Oleg Moskalenko . 422 6. Security Considerations 424 TURN server MUST use strong encryption and integrity protection for 425 the ticket to prevent an attacker from using a brute force mechanism 426 to obtain the ticket's contents or refreshing allocations. The 427 ticket MUST be constructed such that it has strong entropy to ensure 428 nothing can be gleaned by looking at the ticket alone. 430 An attacker monitoring the traffic between the TURN client and server 431 can impersonate the client and refresh the allocation using the 432 ticket issued to the client with the attackers IP address and port. 433 This attack can be prevented by using STUN long-term credential 434 mechanism or STUN Extension for Third-Party Authorization [RFC7635] 435 or (D)TLS connection between the TURN client and the TURN server. 436 With any of those three mechanisms, when the server receives Refresh 437 Request with STUN MOBILITY-TICKET attribute from the client it 438 identifies that it is indeed the same client but with a new IP 439 address and port using the ticket it had previously issued to refresh 440 the allocation. 442 Security considerations described in [RFC5766] are also applicable to 443 this mechanism. 445 7. Acknowledgements 447 Thanks to Alfred Heggestad, Lishitao, Sujing Zhou, Martin Thomson, 448 Emil Ivov, Oleg Moskalenko, Dave Waltermire, Pete Resnick, Antoni 449 Przygienda and Brandon Williams for review and comments. 451 8. References 453 8.1. Normative References 455 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate 456 Requirement Levels", BCP 14, RFC 2119, 457 DOI 10.17487/RFC2119, March 1997, 458 . 460 [RFC5077] Salowey, J., Zhou, H., Eronen, P., and H. Tschofenig, 461 "Transport Layer Security (TLS) Session Resumption without 462 Server-Side State", RFC 5077, DOI 10.17487/RFC5077, 463 January 2008, . 465 [RFC5245] Rosenberg, J., "Interactive Connectivity Establishment 466 (ICE): A Protocol for Network Address Translator (NAT) 467 Traversal for Offer/Answer Protocols", RFC 5245, 468 DOI 10.17487/RFC5245, April 2010, 469 . 471 [RFC5389] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing, 472 "Session Traversal Utilities for NAT (STUN)", RFC 5389, 473 DOI 10.17487/RFC5389, October 2008, 474 . 476 [RFC5766] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using 477 Relays around NAT (TURN): Relay Extensions to Session 478 Traversal Utilities for NAT (STUN)", RFC 5766, 479 DOI 10.17487/RFC5766, April 2010, 480 . 482 8.2. Informative References 484 [I-D.ietf-mmusic-trickle-ice] 485 Ivov, E., Rescorla, E., and J. Uberti, "Trickle ICE: 486 Incremental Provisioning of Candidates for the Interactive 487 Connectivity Establishment (ICE) Protocol", draft-ietf- 488 mmusic-trickle-ice-02 (work in progress), January 2015. 490 [I-D.uberti-mmusic-nombis] 491 Uberti, J. and J. Lennox, "Improvements to ICE Candidate 492 Nomination", draft-uberti-mmusic-nombis-00 (work in 493 progress), March 2015. 495 [iana-stun] 496 IANA, , "IANA: STUN Attributes", April 2011, 497 . 500 [RFC6982] Sheffer, Y. and A. Farrel, "Improving Awareness of Running 501 Code: The Implementation Status Section", RFC 6982, 502 DOI 10.17487/RFC6982, July 2013, 503 . 505 [RFC7635] Reddy, T., Patil, P., Ravindranath, R., and J. Uberti, 506 "Session Traversal Utilities for NAT (STUN) Extension for 507 Third-Party Authorization", RFC 7635, 508 DOI 10.17487/RFC7635, August 2015, 509 . 511 Appendix A. Example ticket construction 513 The TURN server uses two different keys: one 128-bit key for Advance 514 Encryption Standard (AES) in Cipher Block Chaining (CBC) mode 515 (AES_128_CBC) and 256-bit key for HMAC-SHA-256-128 for integrity 516 protection. The ticket can be structured as follows: 518 struct { 519 opaque key_name[16]; 520 opaque iv[16]; 521 opaque state<0..2^16-1>; 522 opaque mac[16]; 523 } ticket; 525 Figure 1: Ticket Format 527 Here, key_name serves to identify a particular set of keys used to 528 protect the ticket. It enables the TURN server to easily recognize 529 tickets it has issued. The key_name should be randomly generated to 530 avoid collisions between servers. One possibility is to generate new 531 random keys and key_name every time the server is started. 533 The TURN state information (self-contained or handle) in 534 encrypted_state is encrypted using 128-bit AES in CBC mode with the 535 given IV. The MAC is calculated using HMAC-SHA-256-128 over key_name 536 (16 octets)and IV (16 octets), followed by the length of the 537 encrypted_state field (2 octets) and its contents (variable length). 539 Authors' Addresses 541 Tirumaleswar Reddy 542 Cisco Systems, Inc. 543 Cessna Business Park, Varthur Hobli 544 Sarjapur Marathalli Outer Ring Road 545 Bangalore, Karnataka 560103 546 India 548 Email: tireddy@cisco.com 549 Dan Wing 550 Cisco Systems, Inc. 551 170 West Tasman Drive 552 San Jose, California 95134 553 USA 555 Email: dwing@cisco.com 557 Prashanth Patil 558 Cisco Systems, Inc. 559 Bangalore 560 India 562 Email: praspati@cisco.com 564 Paal-Erik Martinsen 565 Cisco Systems, Inc. 566 Philip Pedersens vei 22 567 Lysaker, Akershus 1325 568 Norway 570 Email: palmarti@cisco.com