Internal BGP as PE-CE
Protocol
Pedro Marques roque@juniper.net
Robert Raszuk rraszuk@cisco.com
Dan Tappan tappan@cisco.com
Luca Martini luca@level3.net
Problem
AS 65001
AS 65001
AS 10458
Provider
CE-1
PE-1
PE-2
CE-2
Route Advertisement
as-path 65001
as-path 10548 65001
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#

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
Core
CE-1
RR-1
RR-2
CE-2
Traditional network design:
 Core distributes routing information to sites.



Pop/Site routers receive routing information
from their respective RRs.


Reflectors participate in top level iBGP mesh.
IGP may be stub area if there are no backdoor links.
These are often managed independently.
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 localpreference, 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.

origin
peer
iBGP
eBGP
internal
if same as# use pop and apply
internal rules
external rules
external
advertise as-is
existing rules
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