Confederations - Cisco CRS Configuration Manual
Ios xr virtual private network
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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
186
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
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