Vyatta Network OS Documentation

Learn how to install, configure and operate the Vyatta NOS, which helps drive our virtual networking & physical platforms portfolio.

Confederations

Confederations enable you to reduce the size and complexity of the iBGP mesh. In a BGP confederation, a single AS is divided into multiple internal sub-AS to help keep the number of iBGP peer connections manageable. Each sub-AS is assigned its own AS number; this is typically assigned from the private AS number space, which ranges from 64512 through 65534. Within a sub-AS, all the standard iBGP rules, including full-mesh peering, apply. The connections between confederation sub-AS use eBGP peering. One or more eBGP connections can be made between each sub-AS. The sub-AS are grouped as a confederation, which advertises as a single AS to external peers.

The following figure shows the large number of iBGP connections that must be configured in even a moderately sized AS. In this example, 14 routers are participating in iBGP.

Figure 1. iBGP full mesh

The following figure shows a BGP confederation that splits the single AS shown in the preceding figure into three sub-AS, which each use private AS numbers. Within each sub-AS, all of the iBGP peers are fully meshed. The sub-AS are connected to one another using an eBGP connection.

Figure 2. BGP confederation