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: ronald.p.bonica@wcom.com
Yakov Rekhter
Juniper Networks, Inc.
1194 N. Mathilda Ave.
Sunnyvale, California 94089
Email: yakov@juniper.net
Eric C. Rosen
Cisco Systems, Inc.
250 Apollo Drive
Chelmsford, MA, 01824
Email: erosen@cisco.com
Robert Raszuk
Cisco Systems, Inc.
250 Apollo Drive
Chelmsford, MA, 01824
Email: raszuk@cisco.com
Dan Tappan
Cisco Systems, Inc.
250 Apollo Drive
Chelmsford, MA 01824
Email: tappan@cisco.com
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