Network Working Group Rahul Aggarwal Internet Draft Juniper Networks Expires: July 2004 Christian Jacquenet France Telecom Jeremy De Clercq Alcatel Encapsulating MPLS in IPsec draft-raggarwa-mpls-ipsec-00.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. Copyright Notice Copyright (C) The Internet Society (2004). All Rights Reserved. draft-raggarwa-mpls-ipsec-00.txt [Page 1] Internet Draft draft-raggarwa-mpls-ipsec-00.txt January 2004 Abstract In various applications of MPLS, label stacks with multiple entries are used. In some cases, it is possible to replace the top label of the stack with an IP-based encapsulation, thereby enabling the application to run over networks which do not have MPLS enabled in their core routers. MPLS-in-IP and MPLS-in-GRE encapsulations have already been specified by the MPLS WG. In some cases, in addition to IP and GRE tunnels, it may be desirable to use IPsec for transporting MPLS packets securely over non-MPLS networks, using standard IPsec authentication and/or encryption functions. This draft describes procedures for encapsulating MPLS packets in IPsec. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [KEYWORDS]. 1. Motivation In many applications of MPLS, packets traversing an MPLS backbone carry label stacks with more than one label. [MPLS-IP-GRE] specifies procedures for encapsulating MPLS in IP and MPLS in GRE. This allows the top label to be replaced, without loss of functionality, by an IP header or a GRE header. Hence two LSRs that are adjacent on an LSP can be separated by an IP network, even if the routers on that network do not support MPLS. For instance these two LSRs may have a directed LDP session between them to exchange LDP labels, but may be separated by an IP network, where the routers in the IP network do not support MPLS. In some cases it may be desirable for two such LSRs to use IPsec [IP-SEC-ARCH] to carry MPLS packets securely over the IP network. 1.1. IPsec Authentication and/or Encryption for Security An IPsec security association (SA), enables MPLS packets to be carried securely over non-MPLS networks. An IPsec protected IP/GRE encapsulation replaces the upper MPLS labels, which are required when the backbone network is MPLS. MPLS packets can be protected using standard IPsec authentication and/or encryption functions. The payload of the IPsec encapsulation contains an authenticated and/or encrypted MPLS packet with the inner MPLS label(s). draft-raggarwa-mpls-ipsec-00.txt [Page 2] Internet Draft draft-raggarwa-mpls-ipsec-00.txt January 2004 1.1.1. Protection Against Spoofed Packets The use of IPsec tunnels protects the tunnelled MPLS packets against spoofed packets in a more secure fashion compared to an IP or GRE tunnel. It should be noted that if the upper MPLS labels are replaced with an unsecured IP encapsulation, like GRE or IP, it becomes more difficult to protect the application against spoofed packets. A Service Provider can protect against spoofed MPLS packets by the simple expedient of not accepting MPLS packets from outside its own domain boundaries (or more generally by keeping track of which labels are validly received over which interfaces, and discarding packets which arrive with labels that are not valid for their incoming interfaces). Protection against spoofed IP packets requires having all the boundary routers perform filtering; either filtering out packets from "outside" which are addressed to PE routers, or filtering out packets from "outside" which have source addresses that belong "inside" and filtering on each PE all packets which have source addresses that belong "outside". The maintenance of these filter lists can be management-intensive, and their use at all border routers can affect the performance seen by all traffic entering the Service Provider's network. Furthermore, these filtering techniques may be difficult to apply when the application is being used across multiple providers, because in that case IP datagrams from outside an Service Provider's network can legitimately be addressed to its PE routers. If on the other hand, the upper MPLS labels are replaced by an IPsec encapsulation, protection against spoofed packets does not rely on filtering at the border routers. The ingress PE router may still maintain filtering policies to filter IP datagrams from outside. However such filter lists have to be maintained only on the ingress and are not required on the border routers or the egress PE. The cryptographic authentication features of IPsec [AH, ESP] enable an egress PE to detect and discard tunneled MPLS packets that were not generated by a valid ingress PE for that particular application. Thus protection against spoofing is managed entirely at the ingress and egress PE routers, transparent to the border routers. The tradeoff is the management and performance implications associated with the use of IPsec. 1.1.2. Protection Against Transit Node Misbehavior Cryptographic authentication [AH, ESP] applied by the ingress PE on MPLS packets destined to an egress PE can protect against misrouting occurences or modification of packets by transit nodes. The authentication check at the egress PE will fail if the MPLS packets are forwarded to the incorrect egress PE or are modified in transit. draft-raggarwa-mpls-ipsec-00.txt [Page 3] Internet Draft draft-raggarwa-mpls-ipsec-00.txt January 2004 This will also protect against packet spoofing from within a Service Provider's network. 1.1.3. Encryption of the Application Data If the path followed by the traffic from ingress PE to egress PE contains non-trusted network parts, IPsec data encryption may be used to encrypt the payload [ESP]. This can help in providing privacy for the application data in some cases. 2. Encapsulation of MPLS in IPsec by Ingress PE We describe two possible ways of encapsulating MPLS packets in IPsec. In the first approach an MPLS-in-GRE or MPLS-in-IP [MPLS-IP-GRE] encapsulation is used by the ingress PE to turn the MPLS packet into an IP packet. The IP packet's source IP address is an address of the Ingress PE; the IP packet's destination IP address is an address of the Egress PE. The net effect is to create an IP or GRE tunnel to send the MPLS packet to the egress PE. IPsec tunnel mode is then used to secure these tunnels. Thus the MPLS packet gets sent through an IPsec secured IP or GRE tunnel. The resulting packet has an outer IP header preceding the IPsec header and an inner IP header following the IPsec header. In the second approach an MPLS-in-GRE or MPLS-in-IP [MPLS-IP-GRE] encapsulation is used by the ingress PE to turn the MPLS packet into an IP packet. The IP packet's source IP address is an address of the Ingress PE; the IP packet's destination IP address is an address of the Egress PE. The net effect is to create an IP or GRE tunnel to send the MPLS packet. IPsec transport mode is then used to secure these tunnels. Thus the resulting packet has an outer IP header preceding the IPsec header but does not have an inner IP header. The MPLS label stack follows the IPsec header. In this case the IPsec header needs to set the payload type to MPLS. MPLS in IP payload types defined in [MPLS-IP-GRE] MUST be used for this purpose. The ingress PE needs to have an IPsec security association (SA) with the egress PE router. The traffic type to be protected by the considered SA is MPLS-in-IP/GRE packets with ingress PE/egress PE IP addresses as the IP source/destination addresses. Depending on the application it may be important to set up IPsec SAs dynamically and static keying may not be a viable option. There may be a need for a key distribution infrastructure that supports multiple Service Providers and IKE [IKE] may need to be used to establish the SAs. The identification of whether transport mode or tunnel mode IPsec is used is accomplished via configuration of Ingress and Egress PE or via draft-raggarwa-mpls-ipsec-00.txt [Page 4] Internet Draft draft-raggarwa-mpls-ipsec-00.txt January 2004 dynamic negotiation with e.g. IKE. 3. De-capsulation of MPLS in IPsec by the Egress PE The egress PE will handle the necessary IKE functions, SA and IPsec tunnel maintenance, etc., as well as handle arriving IPsec packets. It will apply the necessary IPsec procedures to arriving IPsec packets. The result of the IPsec 'outbound' processing at the egress PE is the recovering of a contained MPLS-in-IP/GRE packet. With tunnel mode, IPsec will delete one of both IP headers and the result will still contain one IP header. The egress PE will then strip off the encapsulating IP header to recover the MPLS packet, for MPLS switching purposes. It is to be noted that if a) A MPLS packet is received by an egress PE, with no IPsec encapsulation and b) An IPsec encapsulation was expected by the egress PE for that MPLS packet, it should be discarded. How this is achieved depends on the implementation. 4. Security Considerations Security issues are discussed in section 1. 5. Acknowledgments Lot of the text in this document is written using [MPLS-IP-GRE, 2547IPsec] We would like to thank the authors of these documents. Thanks to Yakov Rekhter and Kireeti Kompella for the discussions that led to this draft. Thanks also to Nischal Sheth for his comments. 6. References [MPLS-IP-GRE] "Encapsulating MPLS in IP or GRE", T. Worster, Rekhter Y., Work in Progress, Rosen E., draft-ietf-mpls-in-ip-or-gre-01.txt [2547GRE] "Use of PE-PE GRE or IP in RFC2547 VPNs", Yakov Rekhter, Eric Rosen, Work in Progress, draft-ietf-l3vpn-gre-ip-2547-00.txt [2547IPsec] "Use of PE-PE IPsec in RFC2547 VPNs", Rosen E., De Clercq J., Pridaens O., T'Joens Y., Sargor C., Work in Progress, draft-ietf-l3vpn-ipsec-2547-03.txt draft-raggarwa-mpls-ipsec-00.txt [Page 5] Internet Draft draft-raggarwa-mpls-ipsec-00.txt January 2004 [IP-SEC-ARCH] "Security Architecture for the Internet Protocol". S.Kent, K. Seo, Work in Progress, draft-ietf-ipsec-rfc2401bis-01.txt [ESP] "IP Encapsulating Security Payload (ESP)", S. Kent, Work in Progress, draft-ietf-ipsec-esp-v3-06.txt [AH] "IP Authentication Header", S. Kent, Work in Progress, draft-ietf-ipsec-rfc2402bis-05.txt [IKE] Harkins, D., Carrel, D., "The Internet Key Exchange", RFC 2409, November 1998. Author Information Rahul Aggarwal Juniper Networks 1194 North Mathilda Ave. Sunnyvale, CA 94089 Email: rahul@juniper.net Christian Jacquenet France Telecom 3, avenue Francois Chateau CS 36901 35069 Rennes Cedex France Phone: +33 2 99 87 63 31 Email: christian.jacquenet@francetelecom.com Jeremy De Clercq Alcatel Fr. Wellesplein 1, 2018 Antwerpen, Belgium. Email: Jeremy.De_Clercq@alcatel.be IPR Notice 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. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. 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