Provider Provisioned VPN WG Hamid Ould-Brahim
Internet Draft Bryan Gleeson
draft-ouldbrahim-bgpvpn-auto-01.txt Peter Ashwood-Smith
Expiration Date: September 2001 Nortel Networks
Eric C. Rosen
Cisco Systems
Yakov Rekhter
Juniper Networks
Luyuan Fang
AT&T
Jeremy De Clercq
Alcatel
March 2001
Using BGP as an Auto-Discovery
Mechanism for Network-based VPNs
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [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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Internet-Drafts are draft documents valid for a maximum of six
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
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The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
In any Network-Based VPN (NBVPN) scheme, the Provider Edge (PE)
routers attached to a common VPN must exchange certain information
as a prerequisite to establish VPN-specific connectivity. In
[RFC2547-bis], VPN-specific routes are exchanged, along with the
information needed to enable a PE to determine which routes belong
to which VPNs. In [VPN-VR], VR addresses must be exchanged, along
with the information needed to enable the PEs to determine which VRs
are in the same VPN ("membership"), and which of those VRs are to
have VPN connectivity ("topology"). Once the VRs are reachable
through the tunnels, routes ("reachability") are then exchanged by
running existing routing protocol per VPN basis. The purpose of this
draft is to define a common BGP based auto-discovery mechanism used
for both the virtual router [VPN-VR] and [RFC2547-bis]
architectures. Each scheme uses the mechanism to automatically
discover the information needed by that particular scheme.
Interworking scenarios between [RFC2547-bis] and the virtual router
models are also discussed.
1. Introduction
In any Network-Based VPN (NBVPN) scheme, the Provider Edge (PE)
routers attached to a common VPN must exchange certain information
as a prerequisite to establish VPN-specific connectivity. In
[RFC2547-bis], VPN-specific routes are exchanged, along with the
information needed to enable a PE to determine which routes belong
to which VPNs. In [VPN-VR], virtual router (VR) addresses must be
exchanged, along with the information needed to enable the PEs to
determine which VRs are in the same VPN ("membership"), and which of
those VRs are to have VPN connectivity ("topology"). Once the VRs
are reachable through the tunnels, routes ("reachability") are then
exchanged by running existing routing protocols per VPN basis.
The purpose of this draft is to define a common BGP based auto-
discovery mechanism used for both the virtual router [VPN-VR] and
[RFC2547-bis] architectures. Each scheme uses the mechanism to
automatically discover the information needed by that particular
scheme. The BGP multiprotocol extension attributes are used to carry
either the virtual router or the RFC2547 auto-discovery information.
Interworking scenarios between [RFC2547-bis] and the virtual router
models are also discussed.
2. Network Based VPNs Reference Model
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Both the virtual router and [RFC2547-bis] architectures are using a
network reference model as illustrated in figure 1.
PE PE
+--------------+ +--------------+
+--------+ | +----------+ | | +----------+ | +--------+
| VPN-A | | | VPN-A | | | | VPN-A | | | VPN-A |
| Sites |--| |Database /| | BGP route | | Database/| |-| sites |
+--------+ | |Processing| |<----------->| |Processing| | +--------+
| +----------+ | Distribution| +----------+ |
| | | |
+--------+ | +----------+ | | +----------+ | +--------+
| VPN-B | | | VPN-B | | -------- | | VPN-B | | | VPN-B |
| Sites |--| |Database /| |-(Backbones)-| | Database/| |-| sites |
+--------+ | |Processing| | -------- | |Processing| | +--------+
| +----------+ | | +----------+ |
| | | |
+--------+ | +----------+ | | +----------+ | +--------+
| VPN-C | | | VPN-C | | | | VPN-C | | | VPN-C |
| Sites |--| |Database /| | | | Database/| |-| sites |
+--------+ | |Processing| | | |Processing| | +--------+
| +----------+ | | +----------+ |
+--------------+ +--------------+
Figure 1: Network based VPN Reference Model
It is assumed that the PE routers can use BGP to distribute
information to each other. This may be via direct IBGP peering, via
direct EBGP peering, via multihop BGP peering, through
intermediaries such as Route Reflectors, through a chain of
intermediate BGP connections, etc. It is assumed also that the PE
knows what architecture it is supporting (either the virtual router,
or [RFC2547-bis] architectures, or both).
3. Carrying VPN information in BGP Multi-Protocol Extension Attributes
The BGP-4 multiprotocol extensions are used to carry various
information about VPNs for both architectures. This is done as
follows. The NLRI is a VPN-IP address or a labeled VPN-IP address.
VPN-specific information associated with the NLRI is encoded either
as attributes of the NLRI, or as part of the NLRI itself, or both.
The address prefix in the NLRI field is ALWAYS within the VPN
address space, and therefore MUST be unique within the VPN. The
address specified in the BGP next hop attribute, on the other hand,
is in the service provider addressing space.
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In the case of the virtual router, the NLRI address prefix is an
address of one of the virtual routers configured on the PE. Thus
this mechanism allows the virtual routers to discover each other, to
set up adjacencies and tunnels to each other, etc. In the case of
[RFC2547-bis], the NLRI prefix represents a route to an arbitrary
system or set of systems within the VPN.
4. Interpretation of VPN Information in the [RFC2547-bis] model
The [RFC2547-bis] model interprets the NLRI reachability
information. The BGP attributes (in particular, the Route Target
Extended Community) are used by the PE routers to assign the routes
to particular VPN database/processing contexts, and hence implicitly
determine the topology. The BGP Next Hop attribute specifies the
remote end point of the tunnel to be used when sending packets whose
destination addresses match the corresponding NLRI. For details, see
[RFC2547-bis].
5. Interpretation of VPN Information in the [VPN-VR] model
5.1 Membership Discovery
The VPN-ID format as defined in [RFC-2685] is used to identify a
VPN. All virtual routers that are members of a specific VPN share
the same VPN-ID. A VPN-ID is carried in the NLRI in order to
associate a particular VR address to the VPN.
5.1.1 Encoding of the VPN-ID in the NLRI
For the virtual router model, the VPN-ID is carried within the route
distinguisher (RD) field. In order to hold the 7-bytes VPN-ID, the
first byte of RD type field is used to indicate the existence of the
VPN-ID format. A value of 0x80 in the first byte of RD's type field
indicates that the RD field is carrying the VPN-ID format. In this
case, the type field range 0x8000-0x80ff will be reserved for the
virtual router case.
5.1.2 VPN-ID Extended Community
A new extended community is used to carry the VPN-ID. The first byte
of the VPN-ID extended community will be used to indicate the
presence of the VPN-ID format. A value of 0x20 indicates that the
remaining 7 bytes following the first byte of the type field holds a
VPN-ID value. In this case an extended community with type field in
the range of 0x2000-0x20ff will be used exclusively for the virtual
router case. The BGP UPDATE message will carry information for a
single VPN (when used with a VPN-ID extended community). The use of
VPN-ID extended community allows a PE to perform route filtering per
VPN basis.
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5.2 VPN Topology Information
A new extended community is used to indicate different VPN topology
values. A type 0x0020 represents the VPN topology field. The first
two bytes (of the remaining 6 bytes) are reserved. The actual
topology values are carried within the remaining four bytes. The
following topology values are defined:
Value Topology Type
1 "Hub"
2 "Spoke"
3 "Mesh"
Arbitrary values can also be used to allow specific topologies to be
constructed. VPN connectivity between two VRs within the same VPN is
achieved if and only if at least one of them is a hub (the other is
a hub or a spoke), or if both VRs are part of a full mesh VPN
topology.
5.3 Tunnel Discovery
Network-based VPNs must be implemented through some form of
tunneling mechanism, where the packet formats and/or the addressing
used within the VPN can be unrelated to that used to route the
tunneled packets across the backbone. There are numerous tunneling
mechanisms that can be used by a network based VPN (e.g., IP/IP
[RFC-2003], GRE tunnels [RFC-1701], IPSec [RFC-2401], and MPLS
tunnels [MPLS-ARCH]). Each of these tunnels allows for opaque
transport of frames as packet payload across the backbone, with
forwarding disjoint from the address fields of the encapsulated
packets. A provider edge router may terminate multiple type of
tunnels and forward packets between these tunnels and other network
interfaces in different ways.
BGP can be used to carry tunnel endpoint addresses between edge
routers. Depending on the type of tunneling mechanism used on a PE,
tunnel endpoint addresses can be used to establish either IPSec, IP
in IP, or GRE tunnels.
The BGP next hop will carry the service provider tunnel endpoint
address. As an example, if IPSec is used as tunneling mechanism, the
IPSec tunnel remote address will be discovered through BGP, and the
actual tunnel establishment is achieved through IPSec signaling
protocol.
When MPLS tunneling is used, a label carried in the NLRI will
indicate which VR can be reached through the address carried in the
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NLRI. A single service provider tunnel endpoint address can be used
to reach multiple VRs (therefore multiple VPNs).
6. Virtual Router and [RFC2547-bis] Interworking Scenarios
Two interwoking scenarios are considered when the network is using
both virtual routers and [RFC2547-bis]. The first scenario is a CE-
PE relationship between a PE (implementing [RFC2547-bis]), and a VR
appearing as a CE to the PE. The connection between the VR, and the
PE can be either direct connectivity, or through a tunnel (e.g.,
IPSec).
The second scenario is when a PE is implementing both architectures.
In this particular case, a single BGP session configured on the
service provider network can be used to advertise either [RFC2547-
bis] VPN information or the virtual router related VPN information.
From the VR and the [RFC2547-bis] point of view there is complete
separation from data path and addressing schemes. However the PE's
interfaces are shared between both architectures.
A PE implementing only [RFC2547-bis] will not import routes from a
BGP UPDATE message containing the VPN-ID extended community. On the
other hand, a PE implementing the virtual router architecture will
not import routes from a BGP UPDATE message containing the route
target extended community attribute.
The granularity at which the information is either [RFC2547-bis]
related or VR-related is per BGP UPDATE message. Different SAFI
numbers are used to indicate that the message carried in BGP
multiprotocol extension attributes is to be handled by the VR or
[RFC2547-bis] architectures. SAFI number of 128 is used for [RFC2547-
bis] related format. A value of 129 for the SAFI number is for the
virtual router (where the NLRI are carrying a labeled prefixes), and
a SAFI value of 140 is for non labeled addresses.
7. Use of BGP Capability Advertisement
A BGP speaker that uses VPN information as described in this
document with multiprotocol extensions should use the Capability
Advertisement procedures to determine whether the speaker could use
Multiprotocol Extensions with a particular peer. The Capability Code
field is set to 1 (which indicates Multiprotocol Extensions
capabilities).
8. Security Considerations
This draft does not introduce any new security considerations to
either [VPN-VR] or [RFC2547-bis].
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9. References
[BGP-COMM] Ramachandra, Tappan, "BGP Extended Communities
Attribute", February 2000, work in progress
[BGP-MP] Bates, Chandra, Katz, and Rekhter, "Multiprotocol
Extensions for BGP4", February 1998, RFC 2283
[BGP-MPLS] Rekhter Y, Rosen E., "Carrying Label Information in
BGP4", January 2000, work in progress
[MPLS-ARCH] Rosen, Viswanathan, and Callon, "Multiprotocol Label
Switching Architecture", August 1999, work in progress
[MPLS-ENCAPS] Rosen, Rekhter, Tappan, Farinacci, Fedorkow, Li, and
Conta, "MPLS Label Stack Encoding", October 1999,work in progress
[RFC-1701] Hanks, S., Li, T., Farinacci, D. and P. Traina, "Generic
Routing Encapsulation (GRE)", RFC 1701, October 1994.
[RFC-2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
October 1996.
[RFC-2026] Bradner, S., "The Internet Standards Process -- Revision
3", RFC2026, October 1996.
[RFC-2401] Kent S., Atkinson R., "Security Architecture for the
Internet Protocol", RFC2401, November 1998.
[RFC-2685] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC2547-bis] Rosen E., et al, "BGP/MPLS VPNs", work in progress.
[RFC-2685] Fox B., et al, "Virtual Private Networks Identifier", RFC
2685, September 1999.
[VPN-VR] Ould-Brahim H., et al., "Network based IP VPN Architecture
using Virtual Routers", work in progress.
[VPN-BGP] Ould-Brahim H., et al., "BGP/VPN: VPN Information
Discovery for Network-based VPNs", work in progress.
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10. Acknowledgments
to be supplied.
11. Author's Addresses
Hamid Ould-Brahim
Nortel Networks
P O Box 3511 Station C
Ottawa, ON K1Y 4H7, Canada
Email: hbrahim@nortelnetworks.com
Phone: +1 613 765 3418
Bryan Gleeson
Nortel Networks
2305 Mission College Blvd
Santa Clara CA 95054
Phone: +1 (505) 565 2625
Email: bgleeson@shastanets.com
Peter Ashwood-Smith
Nortel Networks
P.O. Box 3511 Station C,
Ottawa, ON K1Y 4H7, Canada
Phone: +1 613 763 4534
Email: petera@nortelnetworks.com
Eric C. Rosen
Cisco Systems, Inc.
250 Apollo drive
Chelmsford, MA, 01824
E-mail: erosen@cisco.com
Yakov Rekhter
Juniper Networks
1194 N. Mathilda Avenue
Sunnyvale, CA 94089
Email: yakov@juniper.net
Luyuan Fang
AT&T
200 Laurel Avenue
Middletown, NJ 07748
Email: Luyuanfang@att.com
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Phone: +1 (732) 420 1920
Jeremy De Clercq
Alcatel
Francis Wellesplein 1
B-2018 Antwerpen, Belgium
Phone: +32 3 240 47 52
Email: jeremy.de_clercq@alcatel.be
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Ould-Brahim, et al. March 2001 [Page 10]