Confederations - Cisco NCS 540 Series Configuration Manual
L3vpn; for ios xr release 6.3.x
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Also See for NCS 540 Series:
- Hardware installation manual (60 pages) ,
- Command reference manual (84 pages) ,
- Configuration manual (19 pages)
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MPLS L3VPN Overview
Confederations
A confederation is multiple subautonomous systems grouped together. A confederation reduces the total
number of peer devices in an autonomous system. A confederation divides an autonomous system into
subautonomous systems and assigns a confederation identifier to the autonomous systems. A VPN can span
service providers running in separate autonomous systems or multiple subautonomous systems that form a
confederation.
In a confederation, each subautonomous system is fully meshed with other subautonomous systems. The
subautonomous systems communicate using an IGP, such as Open Shortest Path First (OSPF) or Intermediate
System-to-Intermediate System (IS-IS). Each subautonomous system also has an eBGP connection to the
other subautonomous systems. The confederation eBGP (CEBGP) border edge routers forward next-hop-self
addresses between the specified subautonomous systems. The next-hop-self address forces the BGP to use a
specified address as the next hop rather than letting the protocol choose the next hop.
You can configure a confederation with separate subautonomous systems two ways:
• Configure a router to forward next-hop-self addresses between only the CEBGP border edge routers
• Configure a router to forward next-hop-self addresses between the CEBGP border edge routers (both
Note
eBGP Connection Between Two Subautonomous Systems in a Confederation figure illustrates how two
autonomous systems exchange routes and forward packets. Subautonomous systems in a confederation use
a similar method of exchanging routes and forwarding packets.
The figure below illustrates a typical MPLS VPN confederation configuration. In this configuration:
• The two CEBGP border edge routers exchange VPN-IPv4 addresses with labels between the two
• The distributing router changes the next-hop addresses and labels and uses a next-hop-self address.
• IGP-1 and IGP-2 know the addresses of CEBGP-1 and CEBGP-2.
(both directions). The subautonomous systems (iBGP peers) at the subautonomous system border do not
forward the next-hop-self address. Each subautonomous system runs as a single IGP domain. However,
the CEBGP border edge router addresses are known in the IGP domains.
directions) and within the iBGP peers at the subautonomous system border. Each subautonomous system
runs as a single IGP domain but also forwards next-hop-self addresses between the PE routers in the
domain. The CEBGP border edge router addresses are known in the IGP domains.
autonomous systems.
L3VPN Configuration Guide for Cisco NCS 540 Series Routers, IOS XR Release 6.3.x
Confederations
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