Network Working Group Yakov Rekhter Internet Draft Juniper Networks Expiration Date: October 2003 Eric Rosen Network Working Group Cisco Systems Use of PE-PE GRE or IP in RFC2547 VPNs draft-ietf-l3vpn-gre-ip-2547-00.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 RFC2547 [RFC2547] in which the outermost MPLS label of a VPN packet is replaced with either IP or a GRE encapsulation. This enables the VPN packets to be carried over non-MPLS networks. draft-ietf-ppvpn-gre-ip-2547-03.txt [Page 1] Internet Draft draft-ietf-ppvpn-gre-ip-2547-03.txt April 2003 3. Summary for Sub-IP Area 3.1. Summary The base specification for RFC2547 VPNs, i.e., draft-rosen- rfc2547bis-03.txt, 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 the RFC2547 style of VPN using GRE or IP tunnels (rather than MPLS LSPs) between PE routers. 3.2. Where does it fit in the Picture of the Sub-IP Work This work fits squarely in the PPVPN box. 3.3. Why is it Targeted at this WG The WG is chartered with considering the RFC2547 style of VPN. This draft specifies procedures to allow that style of VPN to run on networks which do not implement MPLS in the core switches, and/or in environments in which increased security is needed. Thus the draft allows the RFC2547 style of VPN to meet additional requirements that are not met by the base specification. 3.4. 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-ppvpn-gre-ip-2547-03.txt [Page 2] Internet Draft draft-ietf-ppvpn-gre-ip-2547-03.txt April 2003 4. Introduction In "conventional" RFC2547 VPNs, when a PE router receives a packet from a CE router, it looks up the packet's destination IP address in a VRF. As a result of this lookup, it obtains an MPLS label stack, a data link header, 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 on the MPLS label stack is always a label which will not be seen until the packet reaches its point of egress from the network. This label represents a particular route within the packet's VPN. The purpose of the upper labels is to cause the packet to be delivered to the router which understands the bottom label. What we discuss here are procedures creating an MPLS packet which carries ONLY the bottom label, and then using either GRE or IP encapsulation to carry that MPLS packet across the network. That is, the upper labels are replaced with an IP header, and in the case of GRE encapsulation a GRE header as well. 5. Motivations "Conventional" RFC2547 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 RFC2547 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 RFC2547 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 upper labels to be replaced with either IP or (IP + GRE) header. This encapsulating header would encapsulate an MPLS packet containing only a bottom label. The encapsulation header would have the address of the egress PE in its destination IP address field, and this would cause the packet to be delivered to the egress PE. In this procedure, the ingress and egress PEs themselves must support MPLS, but that is not an issue, as those routers must necessarily have RFC2547 VPN support, whereas the transit routers arguably should be able to be "vanilla" routers with no special MPLS or VPN support. draft-ietf-ppvpn-gre-ip-2547-03.txt [Page 3] Internet Draft draft-ietf-ppvpn-gre-ip-2547-03.txt April 2003 6. Specification In short, the technical approach specified here is: 1. Continue to use MPLS to identify a VPN-IP route, by continuing to add an MPLS label stack to the VPN packets. However, the label stack will carry only one label, the current "bottom label." 2. An MPLS-in-GRE [mpls-over-gre], or MPLS-in-IP [mpls-over-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. 6.1. MPLS-in-IP/MPLS-in-GRE Encapsulation by Ingress PE When a PE receives a packet from a CE, it looks up the packet's IP destination address in the VRF corresponding to that CE. This enables it to find a VPN-IP route. The VPN-IP route will have an associated MPLS 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 itself. The IP destination address field of the encapsulation header will contain the value of the associated BGP Next Hop attribute; this will be an IP address of the egress PE. (This description is not meant to specify an implementation strategy; any implementation procedure which produces the same result is acceptable.) 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 are NOT IGP- visible links, and routing adjacencies are not 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. draft-ietf-ppvpn-gre-ip-2547-03.txt [Page 4] Internet Draft draft-ietf-ppvpn-gre-ip-2547-03.txt April 2003 6.2. 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. 7. Implications on packet spoofing 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 VPNs against spoofed packets. 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). 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 the their use at all border routers can affect the performance seen by all traffic entering the SP's network. 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. 8. Security Considerations Some of the security issues are discussed in the section "Implications on packet spoofing". The rest of security issues will be discussed at a later time. draft-ietf-ppvpn-gre-ip-2547-03.txt [Page 5] Internet Draft draft-ietf-ppvpn-gre-ip-2547-03.txt April 2003 9. Acknowledgments Most of the text in this document is "borrowed" almost verbatim from draft-rosen-ppvpn-ipsec-2547-00.txt. 10. References [RFC2547bis] BGP/MPLS VPNs, Rosen et. al., draft-rosen-rfc2547bis- 03.txt, 2/01. [mpls-over-ip] "MPLS Label Stack Encapsulation in IP", Doolan, P., Katsube, Y., Malis, A., Wilder, R., Worster, T. draft-worster-mpls- in-ip-03.txt [mpls-over-gre] "MPLS Label Stack Encapsulation in GRE", Rekhter, Y., Tappan, D., Rosen, E., draft-rekhter-mpls-over-gre-01.txt 11. 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-ppvpn-gre-ip-2547-03.txt [Page 6]