IP Security Protocol Working Group A. Huttunen (IPSEC) F-Secure Corporation Internet-Draft B. Swander Expires: November 3, 2004 Microsoft V. Volpe Cisco Systems L. DiBurro Nortel Networks M. Stenberg May 5, 2004 UDP Encapsulation of IPsec ESP Packets draft-ietf-ipsec-udp-encaps-09.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on November 3, 2004. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. Abstract This protocol specification defines methods to encapsulate and decapsulate IP Encapsulating Security Payload (ESP) packets inside UDP packets for the purpose of traversing Network Address Translators. ESP encapsulation as defined in this document is capable of being used in both IPv4 and IPv6 scenarios. The encapsulation is used whenever negotiated using Internet Key Exchange (IKE). Huttunen, et al. Expires November 3, 2004 [Page 1] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1 UDP-encapsulated ESP Header Format . . . . . . . . . . . . 4 2.2 IKE Header Format for Port 4500 . . . . . . . . . . . . . 4 2.3 NAT-keepalive Packet Format . . . . . . . . . . . . . . . 5 3. Encapsulation and Decapsulation Procedures . . . . . . . . . . 6 3.1 Auxiliary Procedures . . . . . . . . . . . . . . . . . . . 6 3.1.1 Tunnel Mode Decapsulation NAT Procedure . . . . . . . 6 3.1.2 Transport Mode Decapsulation NAT Procedure . . . . . . 6 3.2 Transport Mode ESP Encapsulation . . . . . . . . . . . . . 7 3.3 Transport Mode ESP Decapsulation . . . . . . . . . . . . . 7 3.4 Tunnel Mode ESP Encapsulation . . . . . . . . . . . . . . 8 3.5 Tunnel Mode ESP Decapsulation . . . . . . . . . . . . . . 8 4. NAT Keepalive Procedure . . . . . . . . . . . . . . . . . . . 9 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 5.1 Tunnel Mode Conflict . . . . . . . . . . . . . . . . . . . 10 5.2 Transport Mode Conflict . . . . . . . . . . . . . . . . . 10 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13 7. IAB Considerations . . . . . . . . . . . . . . . . . . . . . . 14 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 9.1 Normative references . . . . . . . . . . . . . . . . . . . . 16 9.2 Non-normative references . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 17 A. Clarification of potential NAT multiple client solutions . . . 18 Intellectual Property and Copyright Statements . . . . . . . . 20 Huttunen, et al. Expires November 3, 2004 [Page 2] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 1. Introduction This protocol specification defines methods to encapsulate and decapsulate ESP packets inside UDP packets for the purpose of traversing NATs (see [RFC 3715] section 2.2, case i). The UDP port numbers are the same as used by IKE traffic, as defined in [NAT-T-IKE]. The sharing of the port numbers for both IKE and UDP encapsulated ESP traffic was selected because it offers better scaling (only one NAT mapping in the NAT, no need to send separate IKE keepalives), easier configuration (only one port to be configured in firewalls), and easier implementation. It is up to the need of the clients whether transport mode or tunnel mode is to be supported (see [RFC 3715] Section 3 criteria "Telecommuter scenario"). L2TP/IPsec clients MUST support the modes as defined in [RFC 3193]. IPsec tunnel mode clients MUST support tunnel mode. An IKE implementation supporting this protocol specification MUST NOT use the ESP SPI field zero for ESP packets. This ensures that IKE packets and ESP packets can be distinguished from each other. UDP encapsulation of ESP packets as defined in this document is written in terms of IPv4 headers. There is no technical reason why an IPv6 header could not be used as the outer header and/or as the inner header. Because the protection of the outer IP addresses in IPsec AH is inheritly incompatible with NAT, the IPsec AH was left out of the scope of this protocol specification. This protocol also assumes that IKE (IKEv1 [RFC2401] or IKEv2 [IKEv2]) is used to negotiate the IPsec SAs, manual keying is not supported. Huttunen, et al. Expires November 3, 2004 [Page 3] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 2. Packet Formats 2.1 UDP-encapsulated ESP Header Format 0 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Destination Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | ESP header [RFC 2406] | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The UDP header is a standard [RFC 768] header, where o Source Port and Destination Port MUST be the same as used by IKE traffic. o IPv4 UDP Checksum SHOULD be transmitted as a zero value. o Receivers MUST NOT depend upon the UDP checksum being a zero value. The SPI field in the ESP header MUST NOT be zero. 2.2 IKE Header Format for Port 4500 0 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Destination Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Non-ESP Marker | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IKE header [RFC 2409] | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The UDP header is a standard [RFC 768] header, and is used as defined in [NAT-T-IKE]. This document does not set any new requirements for the checksum handling of an IKE packet. Non-ESP Marker is 4 bytes of zero aligning with the SPI field of an ESP packet. Huttunen, et al. Expires November 3, 2004 [Page 4] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 2.3 NAT-keepalive Packet Format 0 1 2 3 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Port | Destination Port | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 0xFF | +-+-+-+-+-+-+-+-+ The UDP header is a standard [RFC 768] header, where o Source Port and Destination Port MUST be the same as used by UDP-ESP encapsulation of Section 2.1 o IPv4 UDP Checksum SHOULD be transmitted as a zero value. o Receivers MUST NOT depend upon the UDP checksum being a zero value. The sender MUST use a one octet long payload with the value 0xFF. The receiver SHOULD ignore a received NAT-keepalive packet. Huttunen, et al. Expires November 3, 2004 [Page 5] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 3. Encapsulation and Decapsulation Procedures 3.1 Auxiliary Procedures 3.1.1 Tunnel Mode Decapsulation NAT Procedure When a tunnel mode has been used to transmit packets (see [RFC 3715] Section 3 criteria "Mode support" and "Telecommuter scenario"), the inner IP header can contain addresses that are not suitable for the current network. This procedure defines how these addresses are to be converted to suitable addresses for the current network. Depending on local policy, one of the following MUST be done: 1. If a valid source IP address space has been defined in the policy for the encapsulated packets from the peer, check that the source IP address of the inner packet is valid according to the policy. 2. If an address has been assigned for the remote peer, check that the source IP address used in the inner packet is the same as the IP address assigned. 3. NAT is performed for the packet, making it suitable for transport in the local network. 3.1.2 Transport Mode Decapsulation NAT Procedure When a transport mode has been used to transmit packets, contained TCP or UDP headers will contain incorrect checksums due to the change of parts of the IP header during transit. This procedure defines how to fix these checksums (see [RFC 3715] Section 2.1, case b). Depending on local policy, one of the following MUST be done: 1. If the protocol header after the ESP header is a TCP/UDP header and the peer's real source and destination IP address have been received according to [NAT-T-IKE], incrementally recompute the TCP/UDP checksum: * subtract the IP source address in the received packet from the checksum * add the real IP source address received via IKE to the checksum (obtained from the NAT-OA) * subtract the IP destination address in the received packet from the checksum * add the real IP destination address received via IKE to the checksum (obtained from the NAT-OA) Note: if received and real address are the same for a given address, say the source address, the operations cancel and don't need to be performed. 2. If the protocol header after the ESP header is a TCP/UDP header, recompute the checksum field in the TCP/UDP header. Huttunen, et al. Expires November 3, 2004 [Page 6] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 3. If the protocol header after the ESP header is an UDP header, zero the checksum field in the UDP header. If the protocol header after the ESP header is a TCP header, and there is an option to flag to the stack that TCP checksum does not need to be computed, then that flag MAY be used. This SHOULD only be done for transport mode, and if the packet is integrity protected. Tunnel mode TCP checksums MUST be verified. [This is not a violation to the spirit of section 4.2.2.7 in RFC 1122 because a checksum is being generated by the sender, and verified by the receiver. That checksum is the integrity over the packet performed by IPsec.] In addition an implementation MAY fix any contained protocols that have been broken by NAT (see [RFC 3715] Section 2.1 case g). 3.2 Transport Mode ESP Encapsulation BEFORE APPLYING ESP/UDP ---------------------------- IPv4 |orig IP hdr | | | |(any options)| TCP | Data | ---------------------------- AFTER APPLYING ESP/UDP ------------------------------------------------------- IPv4 |orig IP hdr | UDP | ESP | | | ESP | ESP| |(any options)| Hdr | Hdr | TCP | Data | Trailer |Auth| ------------------------------------------------------- |<----- encrypted ---->| |<------ authenticated ----->| 1. Ordinary ESP encapsulation procedure is used. 2. A properly formatted UDP header is inserted where shown. 3. The Total Length, Protocol and Header Checksum (for IPv4) fields in the IP header are edited to match the resulting IP packet. 3.3 Transport Mode ESP Decapsulation 1. The UDP header is removed from the packet. 2. The Total Length, Protocol and Header Checksum (for IPv4) fields in the new IP header are edited to match the resulting IP packet. 3. Ordinary ESP decapsulation procedure is used. 4. Transport mode decapsulation NAT procedure is used. Huttunen, et al. Expires November 3, 2004 [Page 7] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 3.4 Tunnel Mode ESP Encapsulation BEFORE APPLYING ESP/UDP ---------------------------- IPv4 |orig IP hdr | | | |(any options)| TCP | Data | ---------------------------- AFTER APPLYING ESP/UDP -------------------------------------------------------------- IPv4 |new h.| UDP | ESP |orig IP hdr | | | ESP | ESP| |(opts)| Hdr | Hdr |(any options)| TCP | Data | Trailer |Auth| -------------------------------------------------------------- |<------------ encrypted ----------->| |<------------- authenticated ------------>| 1. Ordinary ESP encapsulation procedure is used. 2. A properly formatted UDP header is inserted where shown. 3. The Total Length, Protocol and Header Checksum (for IPv4) fields in the new IP header are edited to match the resulting IP packet. 3.5 Tunnel Mode ESP Decapsulation 1. The UDP header is removed from the packet. 2. The Total Length, Protocol and Header Checksum (for IPv4) fields in the new IP header are edited to match the resulting IP packet. 3. Ordinary ESP decapsulation procedure is used. 4. Tunnel mode decapsulation NAT procedure is used. Huttunen, et al. Expires November 3, 2004 [Page 8] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 4. NAT Keepalive Procedure The sole purpose of sending NAT-keepalive packets is to keep NAT mappings alive for the duration of a connection between the peers (see [RFC 3715] Section 2.2 case j). Reception of NAT-keepalive packets MUST NOT be used to detect liveness of a connection. A peer MAY send a NAT-keepalive packet if there exists one or more phase I or phase II SAs between the peers, or such an SA has existed at most N minutes earlier. N is a locally configurable parameter with a default value of 5 minutes. A peer SHOULD send a NAT-keepalive packet if a need to send such packets is detected according to [NAT-T-IKE] and if no other packet to the peer has been sent in M seconds. M is a locally configurable parameter with a default value of 20 seconds. Huttunen, et al. Expires November 3, 2004 [Page 9] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 5. Security Considerations 5.1 Tunnel Mode Conflict Implementors are warned that it is possible for remote peers to negotiate entries that overlap in a SGW (security gateway), an issue affecting tunnel mode (see [RFC 3715] Section 2.1 case e). +----+ \ / | |-------------|----\ +----+ / \ \ Ari's NAT 1 \ Laptop \ 10.1.2.3 \ +----+ \ / \ +----+ +----+ | |-------------|----------+------| |----------| | +----+ / \ +----+ +----+ Bob's NAT 2 SGW Suzy's Laptop Server 10.1.2.3 Because SGW will now see two possible SAs that lead to 10.1.2.3, it can become confused where to send packets coming from Suzy's server. Implementators MUST devise ways of preventing such a thing from occurring. It is RECOMMENDED that SGW either assign locally unique IP addresses to Ari's and Bob's Laptop using a protocol such as DHCP over IPsec, or uses NAT to change Ari's and Bob's Laptop source IP addresses to such locally unique addresses before sending packets forward to Suzy's Server (this covers "Scaling" criteria of section 3 in [RFC 3715]). Please see Appendix A 5.2 Transport Mode Conflict Another similar issue may occur in transport mode, with 2 clients, Ari and Bob, behind the same NAT talking securely to the same server (see [RFC 3715] Section 2.1 case e). Cliff wants to talk in the clear to the same server. Huttunen, et al. Expires November 3, 2004 [Page 10] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 +----+ | | +----+ \ Ari's \ Laptop \ 10.1.2.3 \ +----+ \ / +----+ | |-----+-----------------| | +----+ / \ +----+ Bob's NAT Server Laptop / 10.1.2.4 / / +----+ / | |/ +----+ Cliff's Laptop 10.1.2.5 Now, transport SAs on the server will look like: To Ari: Server to NAT, , UDP encap <4500, Y> To Bob: Server to NAT, , UDP encap <4500, Z> Cliff's traffic is in the clear, so there is no SA. is the protocol and port information. The UDP encap ports are the ports used in UDP encapsulated ESP format of Section 2.1. Y,Z are the dynamic ports assigned by the NAT during the IKE negotiation. So IKE traffic from Ari's laptop goes out on UDP <4500,4500>. It reaches the server as UDP , where Y is the dynamically assigned port. If the overlaps , then simple filter lookups may not be sufficient to determine which SA needs to be used to send traffic. Implementations MUST handle this situation, either by disallowing conflicting connections, or by other means. Assume now that Cliff wants to connect to the server in the clear. This is going to be difficult to configure since the server already has a policy from Server to the NAT's external address, for securing . For totally non-overlapping traffic descriptions, this is possible. Sample server policy could be: Huttunen, et al. Expires November 3, 2004 [Page 11] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 To Ari: Server to NAT, All UDP, secure To Bob: Server to NAT, All TCP, secure To Cliff: Server to NAT, ALL ICMP, clear text Note, this policy also lets Ari and Bob send cleartext ICMP to the server. The server sees all clients behind the NAT as the same IP address, so setting up different policies for the same traffic descriptor is in principle impossible. A problematic example configuration on the server is: Server to NAT, TCP, secure (for Ari and Bob) Server to NAT, TCP, clear (for Cliff) The problem is that the server cannot enforce his policy, since it is possible that misbehaving Bob sends traffic in the clear. This is indistinguishable from Cliff sending traffic in the clear. So it is impossible to guarantee security from some clients behind a NAT, and also allow clear text from different clients behind the SAME NAT. If the server's security policy allows, however, it can do best effort security: if the client from behind the NAT initiates security, his connection will be secured. If he sends in the clear, the server will still accept that clear text. So, for security guarantees, the above problematic scenario MUST NOT be allowed on servers. For best effort security, this scenario MAY be used. Please see Appendix A Huttunen, et al. Expires November 3, 2004 [Page 12] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 6. IANA Considerations No IANA assignments are needed. Huttunen, et al. Expires November 3, 2004 [Page 13] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 7. IAB Considerations The UNSAF [RFC 3424] questions are addressed by the IPsec-NAT compatibility requirements document [RFC 3715]. Huttunen, et al. Expires November 3, 2004 [Page 14] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 8. Acknowledgments Thanks to Tero Kivinen and William Dixon who contributed actively to this document. Thanks to Joern Sierwald, Tamir Zegman, Tatu Ylonen and Santeri Paavolainen who contributed to the early drafts about NAT traversal. Huttunen, et al. Expires November 3, 2004 [Page 15] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 9. References 9.1 Normative references [RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768, August 1980. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2406] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload (ESP)", RFC 2406, November 1998. [RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)", RFC 2409, November 1998. [I-D.ietf-ipsec-nat-t-ike] Kivinen, T., "Negotiation of NAT-Traversal in the IKE", draft-ietf-ipsec-nat-t-ike-08 (work in progress), February 2004. 9.2 Non-normative references [RFC1122] Braden, R., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, October 1989. [RFC3193] Patel, B., Aboba, B., Dixon, W., Zorn, G. and S. Booth, "Securing L2TP using IPsec", RFC 3193, November 2001. [RFC3424] Daigle, L. and IAB, "IAB Considerations for UNilateral Self-Address Fixing (UNSAF) Across Network Address Translation", RFC 3424, November 2002. [RFC3715] Aboba, B. and W. Dixon, "IPsec-Network Address Translation (NAT) Compatibility Requirements", RFC 3715, March 2004. [I-D.ietf-ipsec-ikev2] Kaufman, C., "Internet Key Exchange (IKEv2) Protocol", draft-ietf-ipsec-ikev2-13 (work in progress), March 2004. Huttunen, et al. Expires November 3, 2004 [Page 16] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 Authors' Addresses Ari Huttunen F-Secure Corporation Tammasaarenkatu 7 HELSINKI FIN-00181 FI EMail: Ari.Huttunen@F-Secure.com Brian Swander Microsoft One Microsoft Way Redmond, WA 98052 US EMail: briansw@microsoft.com Victor Volpe Cisco Systems 124 Grove Street Suite 205 Franklin, MA 02038 US EMail: vvolpe@cisco.com Larry DiBurro Nortel Networks 80 Central Street Boxborough, MA 01719 US EMail: ldiburro@nortelnetworks.com Markus Stenberg FI EMail: markus.stenberg@iki.fi Huttunen, et al. Expires November 3, 2004 [Page 17] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 Appendix A. Clarification of potential NAT multiple client solutions This appendix provides clarification about potential solutions to the problem of multiple clients behind the same NAT simultaneously connecting to the same destination IP address. Section 5.1 and Section 5.2 say that you MUST avoid this problem. As this isn't a wire protocol matter, but a local implementation matter, specification of the mechanisms do not belong in the protocol specification itself. They are instead listed in this appendix. Choosing an option will likely depend on the scenarios for which you use/support IPsec NAT-T. This list is not meant to be exhaustive, so other solutions may exist. We first describe the generic choices that solve the problem for all upper layer protocols. Generic choices for ESP transport mode: Tr1) Implement a built-in NAT (network address translation) above IPsec decapsulation. Tr2) Implement a built-in NAPT (network address port translation) above IPsec decapsulation. Tr3) An initiator may decide not to request transport mode once NAT is detected and instead request a tunnel mode SA. This may be a retry after transport mode is denied by the responder, or it may be the initiator's choice to propose a tunnel SA initially. This is no more difficult than knowing whether to propose transport mode or tunnel mode without NAT. If for some reason the responder prefers or requires tunnel mode for NAT traversal, it must reject the quick mode SA proposal for transport mode. Generic choises for ESP tunnel mode: Tn1) Same as Tr1. Tn2) Same as Tr2. Tn3) This option is possible if an initiator is capable of being assigned an address through it's tunnel SA with the responder using DHCP. The initiator may initially request an internal address via the DHCP-IPsec method, regardless of whether it knows it is behind a NAT. Or it may re-initiate an IKE quick mode negotiation for DHCP tunnel SA after the responder fails the quick mode SA transport mode proposal, either when NAT-OA payload is sent or because it discovers from NAT-D the initiator is behind a NAT and it's local configuration/policy will only accept connecting through NAT when Huttunen, et al. Expires November 3, 2004 [Page 18] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 being assigned an address through DHCP-IPsec. There are also implementation choices offereing limited interoperability. Implementors should specify what applications or protocols should work using their NAT-T solution if these options are selected. Note that neither Tr4 nor Tn4, as described below, are expected to work with TCP traffic. Limited interoperability choices for ESP transport mode: Tr4) Implement upper layer protocol awareness of the inbound & outbound IPsec SA so that it doesn't use the source IP and the source port as the session identifier. (E.g. L2TP session ID mapped to the IPsec SA pair which doesn't use the UDP source port or the source IP address for peer uniqueness.) Tr5) Implement application integration with IKE initiation such that it can rebind to a different source port if the IKE quick mode SA proposal is rejected by the responder, then repropose the new QM selector. Limited interoperability choices for ESP tunnel mode: Tn4) Same as Tr4. Huttunen, et al. Expires November 3, 2004 [Page 19] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. 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The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assignees. Huttunen, et al. Expires November 3, 2004 [Page 20] Internet-Draft UDP Encapsulation of IPsec ESP Packets May 2004 This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Huttunen, et al. Expires November 3, 2004 [Page 21] --