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Supported Platforms
Related Documentation
- ACX, J, M, MX, QFX, SRX, T Series
- Understanding BGP
- Example: Configuring BGP Confederations
Understanding BGP Confederations
BGP confederations are another way to solve the scaling problems created by the BGP full mesh requirement. BGP confederations effectively break up a large autonomous system (AS) into subautonomous systems (sub-ASs). Each sub-AS must be uniquely identified within the confederation AS by a sub-AS number. Typically, sub-AS numbers are taken from the private AS numbers between 64,512 and 65,535.
Within a sub-AS, the same internal BGP (IBGP) full mesh requirement exists. Connections to other confederations are made with standard external BGP (EBGP), and peers outside the sub-AS are treated as external. To avoid routing loops, a sub-AS uses a confederation sequence, which operates like an AS path but uses only the privately assigned sub-AS numbers.
The confederation AS appears whole to other confederation ASs. The AS path received by other ASs shows only the globally assigned AS number. It does not include the confederation sequence or the privately assigned sub-AS numbers. The sub-AS numbers are removed when the route is advertised out of the confederation AS. Figure 1 shows an AS divided into four confederations.
Figure 1: BGP Confederations
Figure 1 shows AS 3 divided into four sub-ASs, 64517, 64550, 65300, and 65410, which are linked through EBGP sessions. Because the confederations are connected by EBGP, they do not need to be fully meshed. EBGP routes are readvertised to other sub-ASs.
Related Documentation
- ACX, J, M, MX, QFX, SRX, T Series
- Understanding BGP
- Example: Configuring BGP Confederations
Published: 2012-12-08
Download This Guide
Supported Platforms
Related Documentation
- ACX, J, M, MX, QFX, SRX, T Series
- Understanding BGP
- Example: Configuring BGP Confederations
