CCDE In-Depth by Orhan Ergun

Author:Orhan Ergun [Ergun, Orhan]
Language: eng
Format: azw3
Publisher: ROSA_PENN
Published: 2016-10-27T16:00:00+00:00

BGP Add-Path

With shadow RR or shadow sessions, there are secondary IBGP sessions between RR and PEs. But the same behavior can be achieved with BGP Add-Path without an extra IBGP session between Route Reflector and the Route reflector clients.

BGP Add-path uses path-identifier to distinguish the different next hops over one IBGP session.

In BGP, if multiple paths are sent over the same BGP session, the last one is kept since it is seen as the latest update. When using VPN route reflectors, you can use multiple route reflectors for different prefixes if scalability is a concern. Based on route targets, we can use route reflector Group-1 to serve odd route target values and route reflector Group-2 to serve even route target values.

In this solution, PEs send all the RT values to both route reflector groups. They receive and process all the prefixes, but based on odd/even ownership they filter out the unwanted ones. However, processing the prefixes which will be filtered anyway is not efficient.

Instead, route target constraints should be deployed so route reflectors can signal to the PE devices that are route reflector clients their desired route target values.

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