R. Bonica WorldCom Internet Draft Y. Rekhter Expiration Date: December 2002 Juniper Networks R. Raszuk E. Rosen D. Tappan Cisco Systems June 2002 CE-to-CE Authentication for Layer 3 VPNs draft-bonica-l3vpn-auth-03.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 authentication 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 representing a Virtual Private Network (VPN). Service providers assign customer interfaces to these VPN specific routing table instances. In doing so, the service provider assigns the customer interface to a VPN. The service provider assures VPN customers that all VPN traffic will remain within the VPN. Conversely, the service provider assures VPN customers that VPN interfaces will never receive datagrams originating outside of the VPN. In order to provide these assurances, the service provider must configure its PE routers correctly. If the service provider 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 authentication mechanism. VPN customers could use the CE-based authentication 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 magic cookie approach to VPN authentication. In order to support authentication, each VPN site sends the PE router that supports it a magic cookie. In many cases, the Customer Edge (CE) router originates the magic cookie. In configurations where the service provider manages the CE, the customer can designate another device contained by the VPN site as the magic cookie originator. Having received the magic cookie, the PE router sends an authentication request to a server that the customer controls. The query identifies the PE router, VPN, and interface. It also contains the magic cookie. If the authentication server explicitly rejects the authentication request, the PE router terminates the authentication process. Therefore, the PE router will neither accept traffic from the CE nor send traffic to the CE. If the authentication server explicitly accepts the authentication request, cannot be contacted or sends no response at all, the PE router joins the CE to the VPN. At this point, the PE will accept traffic from the CE and forward traffic to the CE. It will also accept routes from the CE and distribute them throughout the provider network. Having proceeded to this phase of the authentication process, the PE router distributes the magic cookie throughout the provider network. All PE's that support the VPN receive the magic cookie and relay it to each attached CE router that participates in the VPN. CE routers use the magic cookie to authenticate their VPN peers. If a CE receives a magic cookie that it cannot authenticate, it issues an alarm requesting operator intervention. The CE may also withdraw from the VPN, neither sending traffic to the VPN nor accepting traffic from the VPN until an operator clears the security condition. Note that the PE will not reveal any magic cookie information to the CE until it has received a magic cookie from the customer site that the CE supports. Note also that the authentication process does not rely upon the availability of an authentication server. In fact, authentication server deployment is optional. Some customers may choose not to deploy an authentication server and rely entirely upon authentication by CE routers. The magic cookie approach described by this document contains four components. These are 1) Customer-to-PE signaling, 2) PE-to- authentication server signaling, 3) PE-to-PE signaling and 4) PE-to- CE 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 service provider network. For example, assume that a service provider 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 service provider 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 service provider that an error has occurred and the service provider corrects the error. The service provider may or may not tell Customer A that his/her VPN has been breached. The CE-to-CE authentication mechanism, described herein, informs Customer A of the VPN breach. It provides immediate and automatic notification. Customers who seek to prevent accidental misconfiguration of the provider network should deploy the authentication server described above. Customers who merely require post-hoc notification of accidental misconfiguration need not deploy the authentication server. The CE-to-CE authentication mechanism does not protect VPN customers from intentional misbehavior on the service provider's part. The VPN customer must trust the service provider to implement this mechanism faithfully. 6. Customer-to-PE Signaling In order to support CE-based authentication, each VPN site must send one or more magic cookies to the PE router that supports it. In many cases, the CE will originate the magic cookie. In configurations where the service provider manages the CE, the customer may designate another device contained by the VPN site as the magic cookie originator. If the device that originates the magic cookie also maintains a BGP peering session with the PE, the originating device can piggyback magic cookie information on this BGP peering session. Section 8 of this document describes an extended BGP community attribute that supports this purpose. Section 10 of this document describes an ssh-service that also can be used to propagate magic cookies from CE to PE. This ssh-service can be used in any VPN configuration, including the configuration described above. 7. PE-to-Authentication Server Signaling Having received the magic cookie, the PE router sends an authentication request to a server that the customer controls. The authentication request identifies the PE router, VPN, and interface. It also contains the magic cookie. If the authentication server explicitly rejects the authentication request, the PE router terminates the authentication process. Therefore, the PE router will neither accept traffic from the CE nor send traffic to the CE. If the authentication server explicitly accepts the authentication request, cannot be contacted or sends no response at all, the PE router joins the CE to the VPN. At this point, the PE will accept traffic from the CE and forward traffic to the CE. It will also accept routes from the CE and distribute them throughout the provider network. Section 10 of this document describes an ssh-service that the PE can use to communicate with the authentication server. The authentication server can also use this ssh-service to send its response to the PE. 8. PE-to-PE Signaling In order to support CE-based authentication, the PE router must not activate routes to destinations that are contained by a directly connected VPN site until it has received a magic cookie from the VPN site. When the PE has received a magic cookie and attempted to contact the customer's authentication server, 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 magic cookie to each BGP update. To support this purpose, this document defines a new transitive extended community [EXTBGP] called CE-to-CE Authentication Token. This community uses the format of the Opaque extended community. The low-order octet of the Type field of the CE-to-CE Authentication Token is TBD (to be assigned by the IANA). The 6 octets of the Value field carries the magic cookie. It must contain an non-zero value. If the provider network does not use BGP to distribute VPN routes among PE routers, it can use the ssh-service described in Section 10 of this document to distributed magic cookies to remote PE routers. 9. PE-to-CE Signaling Previous sections of this document describe how the PE router acquires a magic cookie to be associated with each route that is active in its forwarding table. Section 6 describes how the PE acquires magic cookies from directly connected VPN sites. Section 8 describes how the PE acquires magic cookies from remote VPN sites. In order to support CE-based authentication, the PE router must relay these magic cookies to directly connected CE routers. If the PE and CE routers maintain a BGP peering session with one another, the PE can use this BGP peering session to send magic cookies to the CE. Section 8 of this document describes a BGP extended community attribute that supports this purpose. Section 10 of this document describes an ssh-service that also can be used to propagate magic cookies from PE to CE. This ssh-service can be used in any VPN configuration, including the configuration described above. The PE must relay every magic cookie that it has acquired regarding a VPN to each CE router that participates in the VPN. When the PE router receives a new magic cookie, it must relay it to the appropriate CE routers immediately. Furthermore, the PE router MUST not reveal any magic cookie information to CE routers that are contained by sites from which a magic cookie has not yet been received. 10. Cookie Propagation Using SSH VPN devices can use a new ssh-service over [SSH-TRAN] to announce or withdraw magic cookies. Specifically, the new ssh-service supports the following classes of cookie announcement and withdrawal: from CE to PE from PE to authentication server from PE to PE from PE to CE When the PE uses the new ssh-service to announce a magic cookie to the authentication server, the PE waits for the authentication device to accept or reject the magic cookie. The PE terminates the authentication process only if the authentication device explicitly rejects the cookie. When the SSH connection terminates, all magic cookies that were distributed through it are withdrawn implicitly. The following SSH message will support this service: byte ssh_cookie_exchange uint32 action uint64 cookie string vpn_identifier string interface_identifier string pe_identifier The following actions are defined: #define SSH_COOKIE_EXCHANGE_ANNOUNCE 1 #define SSH_COOKIE_EXCHANGE_WITHDRAW 2 #define SSH_COOKIE_EXCHANGE_ACCEPT 3 #define SSH_COOKIE_EXCHANGE_REJECT 4 The first 48 bits of the "cookie" field represent the magic cookie. The remaining 16 bits are set to zero. IANA will assign a number to the message described above [SSH-ARCH]. This number will be drawn from the range that is dedicated to client protocols (i.e., 128-191). If this ssh-service is being used to transfer magic cookies from PE to CE, and the PE maintains at least one VPN route with which no magic cookie is associated, the PE MUST announce a null magic cookie (i.e., value 0x000000000000). 11. Configurability Service providers can deploy the authentication mechanisms described above globally or on a per-VPN basis. In either case, a particular VPN site within the authentication domain may not be capable of announcing a magic cookie to the PE that supports it. In this case, the service provider can configure the PE router so that it will permit that particular CE router to join the authentication enabled VPN. The PE router will associate a null cookie (value 0x000000000000) with the VPN site that the CE supports. The PE route distribute this null cookie into the VPN as if it had been announced by the CE device. 12. Security Considerations If VPN customer receives a magic cookie that it cannot authenticate, the VPN customer should contact his/her service provider immediately. The VPN customer should also consider changing its magic cookie value, as the service provider may have revealed that value to an unauthorized party. If the VPN customer maintains backdoor interfaces outside of the VPN, the VPN customer MUST ensure that parties outside of the VPN cannot sends signaling traffic to PE-CE interfaces. 13. IANA Considerations IANA will assign a new extended BGP community sub-type, with the high-order octet of the Type field equal to 0x03. This BGP extended community type will represent the CE-to-CE Authentication Token. IANA will assign a number to the SSH message described in Section 10. This number will be drawn from the range that is dedicated to client protocols (i.e., 128-191). 14. Acknowledgements Thanks to Beth Alwin, Eduard Metz, Richard Morgan and Benson Schliesser for their comments on this draft. 15. 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 [SSH-ARCH], "SSH Protocol Architecture", Ylonen, T., Kivinen, T., Saarinen, M., Rinne, T., Lehtinen, S., November 19, 2001, draft- ietf-secsh-architecture-11.txt [SSH-TRANS], "SSH Transport Layer Protocol", Ylonen, T., Kivinen, T., Saarinen, M., Ri nne, T., Lehtinen, S., November 19, 2001, draft- ietf-secsh-transport-11.txt 16. 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 17. Full Copyright Statement Copyright (C) The Internet Society (2000). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. 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