R. Bonica WorldCom Internet Draft Y. Rekhter Expiration Date: August 2003 Juniper Networks R. Raszuk E. Rosen D. Tappan Cisco Systems February 2003 CE-to-CE Member Verification for Layer 3 VPNs draft-ietf-l3vpn-auth-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 [RFC-2026]. 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 document describes a CE-based verification mechanism that PPVPN customers can use to detect security breaches caused by misconfiguration of the provider network. 3. Overview Provider Provisioned Virtual Private Networks (PPVPN) support routing privacy among customer interfaces. In order to support routing privacy, Provider Edge (PE) routers maintain multiple forwarding table instances, with each forwarding table instance containing routes for one or more Virtual Private Networks (VPN). Service providers (SP) assign customer interfaces to these VPN specific routing table instances. In doing so, the SP assigns the customer interface to a VPN. The SP assures VPN customers that all VPN traffic will remain within the VPN. Conversely, the SP assures VPN customers that VPN interfaces will never receive datagrams originating outside of the VPN. In order to provide these assurances, the SP must configure its PE routers correctly. If the SP assigns a customer interface to the wrong forwarding table instance, or commits some other configuration error, unauthorized parties might join a VPN, while legitimate VPN members are unaware of the security breach. Therefore, some VPN customers may require a CE-based verification mechanism. VPN customers could use the CE-based verification mechanism to protect themselves against security breaches caused by misconfiguration of the provider network. This document describes such a mechanism. Specifically, this document describes a token-based approach to VPN membership verification. In order to support verification, each VPN site sends the PE router that supports it a token. In many cases, the Customer Edge (CE) router originates the token. In configurations where the SP manages the CE, the customer can designate another device contained by the VPN site as the token originator. Having received a token, the PE joins the VPN site to the VPN. The PE accepts and activates routes to the VPN site and distributes those routes throughout the provider network. The PE router also distributes the token throughout the provider network. All PE's that support the VPN receive the token and relay it to each directly connected customer device that participates in the VPN. Customer devices use the token to verify VPN membership. If a customer device receives a token that it does not recognize, it issues an alarm requesting operator intervention. The customer device may also withdraw from the VPN, neither sending traffic to the VPN nor accepting traffic from it until an operator clears the security condition. Note that the PE will not reveal any tokens to a customer device until it has received a token from the site that the customer device supports. The token-based approach described by this document contains three components. These are: Customer-to-PE signaling PE-to-PE signaling PE-to-Customer signaling This document dedicates a section to each component. 4. 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]. 5. Motivation Currently, PPVPN customers cannot detect security breaches that are caused by accidental misconfiguration of the SP network. For example, assume that an SP maintains two VPN's. The first VPN supports Customer A while the second VPN supports Customer B. Assume also that Customer B requests an new VPN service connection. The SP processes Customer B's request, but accidentally configures Customer B's new connection into Customer A's VPN. Typically, Customer B is first to detect the problem. Customer B tells the SP that an error has occurred and the SP corrects the error. The SP may or may not tell Customer A that his/her VPN has been breached. The CE-to-CE verification mechanism, described herein, informs both customers of the VPN breach. It provides immediate and automatic notification. It does not prevent the breach or the misconfiguration that caused it. The CE-to-CE verification mechanism does not protect VPN customers from intentional misbehavior on the SP's part. The VPN customer must trust the SP to implement this mechanism faithfully. 6. Customer-to-PE Signaling In order to support CE-based verification, each VPN site must send one or more tokens to the PE router that supports it. In many cases, the CE will originate the token. In configurations where the SP manages the CE, the customer may designate another device contained by the VPN site as the token originator. If the device that originates the token also maintains a BGP peering session with the PE, the originating device can piggyback token information on this BGP peering session. Section 7 of this document describes an extended BGP community attribute that supports this purpose. Section 9 of this document describes a new UDP-based protocol that also can be used to propagate tokens from customer equipment to PE. This protocol can be used in any VPN configuration, including the configuration described above. 7. PE-to-PE Signaling In order to support CE-based verification, the PE router must not activate routes to destinations that are contained by a directly connected VPN site until it has received a token from the VPN site. When the PE has received a token, it will activate those routes and advertise them to its iBGP peers. (That is, the PE will advertise those routes to remote PE routers that support the VPN.) If the provider network uses BGP to distribute VPN routes among PE routers, it appends the token to each BGP update. To support this purpose, this document defines a new transitive extended community [EXTBGP] called CE-to-CE Verification Token. This community uses the format of the Opaque extended community. The high-order octet of the Type field of the CE-to-CE Authentication Token is 0x03. The low-order octet of the Type field is 0x02. The 6 octets of the Value field carries the token itself. If the provider network does not use BGP to distribute VPN routes among PE routers, it can use the UDP-based protocol described in Section 9 of this document to distribute tokens to remote PE routers. 8. PE-to-Customer Signaling Previous sections of this document describe how the PE router acquires a token to be associated with each route that is active in its forwarding table. Section 6 describes how the PE acquires tokens from directly connected VPN sites. Section 7 describes how the PE acquires tokens from other PE routers. In order to support CE-based verification, the PE router must relay these tokens to directly connected customer devices. The customer device can be a CE router or a directly connected host. If the PE and customer device maintain a BGP peering session with one another, the PE can use this BGP peering session to send tokens to the CE. Section 7 of this document describes a BGP extended community attribute that supports this purpose. Section 9 of this document describes a new UDP-based protocol that also can be used to propagate tokens from PE to customer device. This protocol can be used in any VPN configuration, including the configuration described above. The PE must relay every token that it has acquired regarding a VPN to each directly connected customer device that participates in the VPN. When the PE router receives a new token, it must relay it to the appropriate customer devices immediately. Furthermore, the PE router MUST not reveal any tokens to customer devices that are contained by sites from which a token has not yet been received. 9. VPN Token Propagtion Protocol The VPN Token Propagtion Protocol is used to distribute tokens. Figure 1 depicts the format of all messages. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version | AuType | Token (Octets 1 - 2) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Token (Octets 3-6) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Authentication | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Authentication | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1 The Version field is equal to 1. The Token field contains the verification token. The AuType field indicates how this message should be authenticated. It may contain the following values: No Authentication 0 Simple Password 1 Message Digest-5 2 The Authentication field contains 64 bits of authentication data used to authenticate the message. The AuType field specifies how these 64 bits are to be used. The VPN Token Propagtion Protocol establishes soft state between PE and customer device. Announcements expire automatically upon expiration of a configurable timer. Therefore announcements must be repeated periodically. By default, announcements expire in 5 minutes, and should be refreshed every minute. The VPN Token Propagation Protocol obtains transport services from UDP. All VPN Token Propagation Protocol messages are directed to UDP port 3694. 10. Configurability SPs can deploy the verification mechanisms described above globally or on a per-VPN basis. In either case, a particular VPN site within the verification domain may not be capable of announcing a token to the PE that supports it. In this case, the SP can configure the PE router so that it will permit that particular VPN site to join the VPN. The PE router will associate a null token (i.e., 0x000000000000) with the VPN site. The PE router will distribute this null token into the VPN as if it had been announced by the VPN site. Although the null token may be useful during migration periods, customer should avoid its long term use. 11. Security Considerations If VPN customer receives a token that it does not recognize, the VPN customer should contact his/her SP immediately. The VPN customer should also consider changing its token value, as the SP may have revealed that value to an unauthorized party. 12. IANA Considerations IANA will assign a new extended BGP community sub-type, with the high-order octet of the Type field equal to 0x03 and low-order octet equal to 0x02. This BGP extended community type will represent the CE-to-CE Authentication Token. IANA will has assigned UDP port number 3694 to the VPN Token Propagation Protocol, described in Section 9. 13. Acknowledgements Thanks to Beth Alwin, Eduard Metz, Richard Morgan, Benson Schliesser and Paul Hoffman for their comments on this draft. 14. Normative References [RFC-1771], Rekhter, Y., Li, T., "A Border Gateway Protocol (BGP- 4)", RFC 1771, March 1995. [RFC-2026], Bradner, S., "Internet Standards Process Revision 3", RFC 2026, Harvard University, October 1996. [RFC-2119], Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, Harvard University, March 1997 [EXTBGP], "BGP Extended Communities Attribute", Ramachandra, S., Tappan, D., Rekhter, Y., June 2001, draft-ietf-idr-bgp-ext- communities-02.txt 15. Author's Addresses Ronald P. Bonica WorldCom 22001 Loudoun County Pkwy Ashburn, Virginia, 20147 Phone: 703 886 1681 Email: email@example.com Yakov Rekhter Juniper Networks, Inc. 1194 N. Mathilda Ave. Sunnyvale, California 94089 Email: firstname.lastname@example.org Eric C. Rosen Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA, 01824 Email: email@example.com Robert Raszuk Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA, 01824 Email: firstname.lastname@example.org Dan Tappan Cisco Systems, Inc. 250 Apollo Drive Chelmsford, MA 01824 Email: email@example.com 16. Full Copyright Statement Copyright (C) The Internet Society (2003). All Rights Reserved. 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