Internet DRAFT - draft-ietf-ppvpn-l3vpn-auth
draft-ietf-ppvpn-l3vpn-auth
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-ppvpn-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-
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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
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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: 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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