Practical BGP

BGP Confederations

As discussed in Chapter 3, another option to consider when scaling an iBGP core is splitting a single network into smaller routing domains and then gluing them back together as a BGP confederation. Simply put, a confederation is a set of autonomous systems that appear as single autonomous to those outside the confederation. Figure 4.15 illustrates a confederation.

• Router A peers with B using eBGP; from router A's perspective, B is in AS 65500, which is defined as the confederation ID.

• Router B peers with C using iBGP within the sub-AS 65200.

• Router C peers with D using eBGP (or what's often referred to as eiBGP); from router C's perspective, D is in AS 65300 (which again is a sub-AS of 65500).

• Router D peers with E using eBGP, ...