Network Working Group Yakov Rekhter Internet Draft Juniper Networks Expiration Date: October 2004 Eric Rosen Network Working Group Cisco Systems Use of PE-PE GRE or IP in BGP/MPLS IP VPNs draft-ietf-l3vpn-gre-ip-2547-02.txt 1. 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. 2. Abstract This draft describes a variation of BGP/MPLS IP VPNs ([BGP-MPLS-VPN]) in which the outermost MPLS label of a VPN packet (the tunnel label) is replaced with either IP or a GRE encapsulation. This enables the VPN packets to be carried over non-MPLS networks. draft-ietf-l3vpn-gre-ip-2547-02.txt [Page 1] Internet Draft draft-ietf-l3vpn-gre-ip-2547-02.txt April 2004 3. 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]. 4. Summary for Sub-IP Area 4.1. Summary The base specification for BGP/MPLS IP VPNs ([BGP-MPLS-VPN]) specifies the procedures for providing a particular style of VPN, using MPLS label switched paths between Provider Edge (PE) routers. The base specification does not discuss other types of tunnels between PE routers. This draft extends the base specification by specifying the procedures for providing BGP/MPLS IP VPNs using GRE or IP tunnels (rather than MPLS LSPs) between PE routers. 4.2. Where does it fit in the Picture of the Sub-IP Work This work fits squarely in the PPVPN box. 4.3. Why is it Targeted at this WG The WG is chartered with considering the BGP/MPLS IP VPNs. This draft specifies procedures to allow that style of VPN to run on networks which do not implement MPLS in the core routers. Thus the draft allows the BGP/MPLS IP VPNs to meet additional requirements that are not met by the base specification. 4.4. Justification The WG should consider this document as it extends a style of VPN explicitly called out in the charter so that it becomes applicable to a wider range of IP-based backbone environments. draft-ietf-l3vpn-gre-ip-2547-02.txt [Page 2] Internet Draft draft-ietf-l3vpn-gre-ip-2547-02.txt April 2004 5. 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 obtains 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 that 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 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. 6. 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 an 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 router 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. draft-ietf-l3vpn-gre-ip-2547-02.txt [Page 3] Internet Draft draft-ietf-l3vpn-gre-ip-2547-02.txt April 2004 7. 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. 7.1. 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 MUST be acceptable. 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])). 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]). draft-ietf-l3vpn-gre-ip-2547-02.txt [Page 4] Internet Draft draft-ietf-l3vpn-gre-ip-2547-02.txt April 2004 7.2. 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. 8. 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) 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. draft-ietf-l3vpn-gre-ip-2547-02.txt [Page 5] Internet Draft draft-ietf-l3vpn-gre-ip-2547-02.txt April 2004 9. 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. 10. Acknowledgments Most of the text in this document is "borrowed" almost verbatim from draft-rosen-ppvpn-ipsec-2547-00.txt. 11. 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 12. Authors' Addresses Yakov Rekhter Juniper Networks E-mail: yakov@juniper.net Eric C. Rosen Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA, 01824 E-mail: erosen@cisco.com draft-ietf-l3vpn-gre-ip-2547-02.txt [Page 6]