Internal BGP as PE-CE Protocol

1
Internal BGP as PE-CE Protocol

• Pedro Marques roque_at_juniper.net
• Robert Raszuk rraszuk_at_cisco.com
• Dan Tappan tappan_at_cisco.com
• Luca Martini luca_at_level3.net

2
Problem
AS 10458
AS 65001
AS 65001
Provider
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

3
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.

4
Rent-a-core
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.

5
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.

6
IGP interaction

• Shouldnt 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.

7
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 apply external rules
external advertise as-is existing rules
peer
origin
8
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.

9
Thank You

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