Network Working Group K. Ishiguro
Internet Draft IP Infusion Inc.
Expiration Date: September 2003 V. Hallivuori
Tellabs Oy
March 2003
Use of Multiple Instance of OSPF
for the PE/CE protocol in BGP/MPLS VPNs
draft-ishiguro-ppvpn-pe-ce-ospf-02.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
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Abstract
This document describes a simple way to use OSPF for Provider Edge
(PE) router and Customer Edge (CE) router communication in BGP/MPLS
VPNs [RFC2547BIS]. [VPN-BGP-OSPF] proposes a complicated way to
achieve VPN route propagation as Type-3 LSAs. This document
describes the use of multiple instances of OSPF in conjunction with
standard BGP/OSPF route redistribution mechanisms to maintain
reachability information throughout VPNs. With this mechanism, VPN
routes are propagated as Type-5 LSAs.
1. Conventions used in this document
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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 [ii].
2. Overview
[RFC2547BIS] is widely used to provide VPN services to customers. In
[RFC2547BIS] architecture, a Customer Edge (CE) router can
communicate with a Provider Edge (PE) router using any routing
protocol. Use of OSPF for PE and CE communication is a little bit
complicated due to the nature of OSPF protocol. OSPF has several
types of routing information in the protocol. OSPF Link State
Advertisements (LSAs) are categorized into different types.
[RFC2547BIS] uses BGP for PE to PE communication. So when OSPF
routes are exported and exchanged using BGP, some of OSPF information
may be dropped.
[VPN-BGP-OSPF] provides a way to propagate customer OSPF routes as
type 3 LSAs (intra-area routes) to other CE routers. To achieve this
propagation, an additional mechanism is proposed for both OSPF and
BGP. These mechanisms are only needed when customers want to
propagate OSPF routes as type 3 LSAs to other CE routers. However,
when customers do not require this propagation, the overall mechanism
can be simplified.
This document proposes a light-weight method of using OSPF for the PE
and CE protocol. In this mechanism, customer routes are exchanged as
AS-External information in OSPF.
The benefit of this mechanism:
- Neither protocol changes nor additional features are required in
OSPF and BGP.
- Any OSPF area configuration can be used between PE and CE
communication.
- BGP does not carry any additional information over provider
backbone.
- Same mechanism can be used by other IGPs such as IS-IS.
The drawback of this mechanism:
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- Configuration where two VPN sites are connected by two links:
a VPN link and direct (backdoor) link. Each site is in a
different OSPF area and there is an OSPF adjascency over the
backdoor link.
In this case, backdoor link routes will be the primary routes.
This is because intra-area routes are preferred over AS
external routes. If one wants the primary route to be the
route via the VPN link, [VPN-BGP-OSPF] is needed.
- OSPF routes are exchanged as AS-External information. So the
routes may be overlapped with real AS-External information
This mechanism does not provide any OSPF LSAs transparency among cus-
tomer VPN sites. Because of the mechanism, VPN network reachability
information can be exchanged with minimum effort .
3. Requirements
A PE router MUST have the capability of running multiple instances of
OSPF, where each OSPF instance can be associated with a particular
VRF.
Each OSPF instance MAY be bound to a specific VRF (1:1). Other for-
mation such as a single OSPF to multiple VRFs (1:n) or multiple OSPF
to the same VRF (n:1) is left for futher study.
A PE router MUST have the capability to redistribute OSPF and BGP
routes to/from a particular VRF. Import/export to/from particular
VRFs to BGP is governed via Route Targets.
There is no special requirement for CE router.
4. OSPF/VRF/BGP Redistribute Procedure
PE router and CE router communicate by leveraging OSPF to exchange
reachability information. Any OSPF area configuration can be used
between PE and CE. Each VPN domain's OSPF route is distinguished by
OSPF multiple instance.
Each OSPF instance is bound to a specific VRF, so that OSPF routes
are installed into the proper VRF. The OSPF routes in VRF are
exported to BGP governed via Route Targets configuration.
A PE router exchanges VPN reachability information using
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[RFC2547BIS]. Other PE routers have the reachability information in
VRF. A PE router redistributes the routes from VRF to OSPF as Type-5
LSA originated from redistributed route.
Example Setup:
- OSPF instance 100 is bound to VRF foo.
- OSPF instance 200 is bound to VRF bar.
- Each OSPF instance's route is installed into each VRF.
- OSPF to BGP redistribute is done via VRF so that OSPF routes
are imported to BGP with Route Targets configuration.
- PE sends a BGP update to another PE router.
- Another PE router installs the routes to particular VRF by Route
Targets configuration.
- BGP to OSPF redistribute is done via VRF. OSPF has AS-External
LSA of remote site network.
5. Security Considerations
Security issues are not discussed in this memo.
6. Acknowledgements
Thanks to Robert May and Eric Rosen for their comments.
7. Reference
[RFC2547BIS] Rosen, E., et. al., "BGP/MPLS VPNs",
<draft-ietf-ppvpn-rfc2547bis-03.txt>, October 2002.
[VPN-BGP-OSPF] Rosen, E. et al., "OSPF as the PE/CE Protocol in
BGP/MPLS VPNs,"
<draft-rosen-vpns-ospf-bgp-mpls-06.txt>,
February 2003.
8. Author's Address
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Kunihiro Ishiguro
IP Infusion Inc.
111 W. St. John Street, Suite 910
San Jose CA 95113
e-mail: kunihiro@ipinfusion.com
Ville Hallivuori
Tellabs Oy
Sinimaentie 6
FIN-02630 Espoo, Finland
e-mail: ville.hallivuori@tellabs.com
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