Internal BGP as PE-CE Protocol

Pedro Marques roque@juniper.netRobert Raszuk rraszuk@cisco.com

Dan Tappan tappan@cisco.comLuca Martini luca@level3.net

Problem

When BGP is used as PE-CE protocol, it uses External BGP rules: as-path perpending, etc.

Accept looped routes in CE-1 Rewrite customer AS# with provider AS#

CE-1 PE-1 PE-2 CE-2

ProviderProvider

AS 10458AS 10458 AS 65001AS 65001AS 65001AS 65001

Route AdvertisementRoute Advertisement

as-path 65001as-path 65001

as-path 10548 65001as-path 10548 65001

Continued

When CE connections are not isolated islands and exchange BGP routes with any other party, it just gets messier.

Customer island peers with the service provider (for Internet service, for instance).

Customer islands exchange routes with outside world: Provider AS# appears in the path.

Never ending requests for as-path rewrite hacks.

Rent-a-core

Traditional network design: Core distributes routing information to sites.

Reflectors participate in top level iBGP mesh. Pop/Site routers receive routing information

from their respective RRs. IGP may be stub area if there are no backdoor

links. These are often managed independently.

CE-1 RR-1 RR-2 CE-2

CoreCore

Proposed model

PE routers are route reflectors to each CE site location.

Customer network attributes are pushed into an “attribute stack” at ingress.

This deals with interference on local-preference, communities, MEDs, etc.

At egress “attribute stack” is poped. cluster is perpended when advertising to CE side.

cluster-list performs loop avoidance.

IGP interaction

Shouldn’t require a single IGP between distinct sites.

Even if an IGP is running between all sites it may not be able to compare inter-site metrics (Provider assigned) and intra-site.

Perform implicit “next-hop self” on the PE/RR when advertising to CE. when advertising to other PEs.

PE/RR makes decisions by taking inter-cluster metrics always higher than intra-cluster.

Deployment

Mix and match of eBGP and iBGP in the same VPN. Proposed attribute (ATTR_SET) consists of

customer AS# plus attributes in original path. This allows a PE to know what to advertise to

a given CE.

iBGP eBGP

internal if same as# use internal rules

pop and applyexternal rules

external advertise as-is existing rules

peerpeeroriginorigin

Summary

Using iBGP between PE and CE requires a few extra considerations: non-interference of customer attributes in

provider network. IGP/next-hop dependencies. apply external rules when crossing as

boundaries. iBGP interaction can provide

transparency to customer network. as-path manipulation hacks only get you

so far.

Thank You

For more details see:draft-marques-ppvpn-ibgp-00.txt