Network Working Group Yakov Rekhter Internet Draft Juniper Networks Expiration Date: April 2005 Eric Rosen Network Working Group Cisco Systems Use of PE-PE GRE or IP in BGP/MPLS IP Virtual Private Networks draft-ietf-l3vpn-gre-ip-2547-03.txt Status of this Memo This document is an Internet-Draft and is subject to all provisions of section 3 of RFC 3667. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she become aware will be disclosed, in accordance with RFC 3668. 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 March 2, 2005. Copyright Notice Copyright (C) The Internet Society (2004). draft-ietf-l3vpn-gre-ip-2547-03.txt [Page 1] Internet Draft draft-ietf-l3vpn-gre-ip-2547-03.txt October 2004 1. Abstract This draft describes a variation of BGP/MPLS IP Virtual Private Networks (VPNs) in which the outermost MPLS label of a VPN packet (the tunnel label) is replaced with either IP or a Generic Routing Encapsulation (GRE). This enables the VPN packets to be carried over non-MPLS networks. 2. Specification of Requirements 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 [RFC2119]. 3. Introduction In "conventional" BGP/MPLS IP VPNs ([BGP-MPLS-VPN]), when an ingress PE router receives a packet from a CE router, it looks up the packet's destination IP address, or in the case of Carriers' Carriers the packet's top MPLS label in a VRF (the VRF is chosen based on the packet's ingress attachment circuit ([BGP-MPLS-VPN])). As a result of this lookup, the (ingress) PE router determines an MPLS label stack, a data link header, and an output interface. The label stack is prepended to the packet, the data link header is prepended to that, and the resulting frame is queued for the output interface. The bottom label in the MPLS label stack prepended to the packet is called the VPN route label ([BGP-MPLS-VPN]). The VPN route label will not be seen until the packet reaches the egress PE router. This label controls forwarding of the packet by the egress PE router. The upper label in the MPLS label stack is called the tunnel label ([BGP-MPLS- VPN]). The purpose of the tunnel label is to cause the packet to be delivered to the egress PE router which understands the VPN route label. What we discuss here are procedures for creating an MPLS packet which carries the VPN route label, but does not carry the tunnel label, and then using either GRE or IP encapsulation to carry that MPLS packet across the network. That is, the tunnel label is replaced with an IP header, and in the case of GRE encapsulation a GRE header as well. draft-ietf-l3vpn-gre-ip-2547-03.txt [Page 2] Internet Draft draft-ietf-l3vpn-gre-ip-2547-03.txt October 2004 4. Motivations "Conventional" BGP/MPLS IP VPNs require that there be an MPLS Label Switched Path (LSP) between a packet's ingress PE router and its egress PE router. This means that a BGP/MPLS IP VPN cannot be implemented if there is a part of the path between the ingress and egress PE routers which does not support MPLS. In order to enable BGP/MPLS IP VPNs to be deployed even when there are non-MPLS routers along the path between the ingress and egress PE routers, it is desirable to have an alternative which allows the tunnel label to be replaced with either IP or (IP + GRE) header. The encapsulation header would have the address of the egress PE router in its destination IP address field, and this would cause the packet to be delivered to the egress PE router. In this procedure, the ingress and egress PE routers themselves MUST support MPLS, but that is not an issue, as those routers MUST necessarily have BGP/MPLS IP VPN support, whereas the transit routers arguably should be able to be "vanilla" routers with no special MPLS or VPN support. 5. Specification In short, the technical approach specified here is: 1. Continue to use MPLS to identify a VPN route, by continuing to add an MPLS label stack to the VPN packets. Between the ingress and the egress PE router the top label of the label stack will contain that label (the top label will be the VPN route label). 2. An MPLS-in-GRE or MPLS-in-IP [MPLS-GRE-IP] encapsulation will be used to turn the above MPLS packet back into an IP packet. This in effect creates a GRE or an IP tunnel between the ingress PE router and the egress PE router. The net effect is that an MPLS packet gets sent through a GRE or an IP tunnel. 5.1. MPLS-in-IP/MPLS-in-GRE Encapsulation by Ingress PE The following description is not meant to specify an implementation strategy; any implementation procedure which produces the same result is acceptable. When an (ingress) PE router receives a packet from a CE router, it draft-ietf-l3vpn-gre-ip-2547-03.txt [Page 3] Internet Draft draft-ietf-l3vpn-gre-ip-2547-03.txt October 2004 looks up the packet's destination IP address, or in the case of Carriers' Carriers the packet's top MPLS label in a VRF (the VRF is chosen based on the packet's ingress attachment circuit ([BGP-MPLS- VPN])). This enables the (ingress) PE router to find a VPN-IP route. The VPN-IP route will have an associated VPN route label and an associated BGP Next Hop. The label is pushed on the packet. Then an IP (or IP+GRE) encapsulation header is prepended to the packet, creating an MPLS-in-IP (or MPLS-in-GRE) encapsulated packet. The IP source address field of the encapsulation header will be an address of the ingress PE router itself. The IP destination address field of the encapsulation header will contain the value of the associated BGP Next Hop; this will be an IP address of the egress PE router. The effect is to dynamically create an IP (or GRE) tunnel between the ingress and egress PE routers. No apriori configuration of the remote tunnel endpoints is needed. Note that these tunnels SHOULD NOT be IGP-visible links, and routing adjacencies SHOULD NOT be supported across these tunnel. Note also that the set of remote tunnel endpoints is not known in advance, but is learned dynamically via the BGP distribution of VPN-IP routes ([BGP-MPLS-VPN]). The IP address of the remote tunnel endpoints is carried in the Network Address of the Next Hop field of the MP_REACH_NLRI BGP attribute ([RFC2858]). 5.2. MPLS-in-IP/MPLS-in-GRE Decapsulation by Egress PE We assume that every egress PE is also an ingress PE, and hence has the ability to decapsulate MPLS-in-IP (or MPLS-in-GRE) packets. After decapsulation, the packets SHOULD be delivered to the routing function for ordinary MPLS switching. 6. Implications on packet spoofing It should be noted that if the tunnel MPLS labels are replaced with an unsecured IP encapsulation, like GRE or IP, it becomes more difficult to protect the VPNs against spoofed packets. This is because a Service Provider (SP) can protect against spoofed MPLS packets by the simple expedient of not accepting MPLS packets from outside its own 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). In contrast to protection against spoofed MPLS packets, protection against spoofed IP packets requires having all the boundary routers of the SP to perform filtering; either (a) filtering out packets from "outside" of the SP which are addressed to PE routers, or (b) draft-ietf-l3vpn-gre-ip-2547-03.txt [Page 4] Internet Draft draft-ietf-l3vpn-gre-ip-2547-03.txt October 2004 filtering out packets from "outside" of the SP which have source addresses that belong "inside" and, in addition, filtering on each PE all packets which have source addresses that belong "outside" of the SP. The maintenance of these filter lists can be management- intensive, and, depending on the implementation, their use at all boundary routers may affect the performance seen by all traffic entering the SP's network. However, such filters may be required for reasons other than protection against spoofing of VPN packets, in which case the additional maintenance overhead of these filters to protect (among other things) against spoofing of VPN packets may be of no practical significance. Note that allocating IP addresses used for GRE or IP tunnels out of a single (or a small number of) IP block could simplify maintenance of the filters. The filtering described in the previous paragraph works only within a single SP network. It is not clear whether (and how) this filtering could be extended to support multiple SP networks. That makes the scheme described in this document fairly problematic in the multi- provider environment. 7. Security Considerations Security considerations in [MPLS-GRE-IP] apply here as well. Additional security issues are discussed in the section "Implications on packet spoofing" above. 8. IANA Considerations No actions for IANA required. draft-ietf-l3vpn-gre-ip-2547-03.txt [Page 5] Internet Draft draft-ietf-l3vpn-gre-ip-2547-03.txt October 2004 9. Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights 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; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr at ietf.org. 10. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM 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. draft-ietf-l3vpn-gre-ip-2547-03.txt [Page 6] Internet Draft draft-ietf-l3vpn-gre-ip-2547-03.txt October 2004 11. Copyright Statement Copyright (C) The Internet Society (2004). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 12. Acknowledgment Most of the text in this document is "borrowed" almost verbatim from draft-rosen-ppvpn-ipsec-2547-00.txt. Funding for the RFC Editor function is currently provided by the Internet Society. 13. Normative References [BGP-MPLS-VPN] "BGP/MPLS IP VPNs", Rosen E., Rekhter, Y., draft-ietf- l3vpn-rfc2547bis-01.txt [MPLS-GRE-IP] "Encapsulating MPLS in IP or Generic Routing Encapsulation (GRE)", Rekhter, Y., Rosen, E., draft-ietf-mpls-in-ip- or-gre-06.txt [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2858] "Multiprotocol Extensions for BGP-4", Rekhter, Y., Chandra, R., Katz, D., RFC2858, June 2000 14. Authors' Addresses Yakov Rekhter Juniper Networks E-mail: yakov@juniper.net Eric C. Rosen Cisco Systems, Inc. E-mail: erosen@cisco.com draft-ietf-l3vpn-gre-ip-2547-03.txt [Page 7]