Confederations - Cisco CRS Configuration Manual

Confederations

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
Cisco IOS XR Virtual Private Network Configuration Guide for the Cisco CRS Router, Release 6.1.x
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The following figure illustrates the exchange of VPN route and label information between autonomous
systems.
Figure 33: Exchanging Routes and Labels in an MPLS VPN Inter-AS with ASBRs
(both directions). The subautonomous systems (iBGP peers) at the subautonomous system border do
Implementing MPLS Layer 3 VPNs