CCIE Enterprise Infrastructure · BGP

BGP — CCIE Enterprise Infrastructure

The complete BGP learning path for CCIE Enterprise Infrastructure: how sessions form, how prefixes are chosen and shaped, how the protocol scales with route reflection and confederations, and how it is designed, secured and repaired in production.

  • 24 complete lessons
  • 5 hr 20 min
  • Foundation

Confederations · Lesson 01 of 01

Splitting an AS with confederations

The other escape from the full mesh: break one AS into sub-AS's that run eBGP between them while looking like one AS to the outside.

  • 12 min lesson
  • 00:00 video
  • Foundation
Written lessonConfiguration

Written lesson

Sub-AS's under one identity

A confederation divides a single AS into smaller sub-AS's (member AS's), each an eBGP-like peering to the others but sharing one public AS number to the outside world. Inside, the sub-AS boundary gives you real AS_PATH loop prevention, so each sub-AS only needs a full mesh among its own members — much smaller. To the outside, the confederation AS-path segment is invisible: peers see only the confederation ID.

Configuration

Confederation identifiers

IOS / IOS XE
router bgp 65501
 bgp confederation identifier 65001
 bgp confederation peers 65502
 neighbor 10.1.0.2 remote-as 65502
 neighbor 10.0.0.9 remote-as 65501

Reflectors or confederations?

Both solve the full mesh. Route reflectors are simpler to add to an existing network and are far more common. Confederations partition the AS more cleanly and can help very large or merged networks, at the cost of more moving parts. Most enterprises choose reflectors.