4. Manageability

4.1 Capabilities announcement

The addition of many new features to the BGP protocol raises the question of how to manage backward compatibility when introducing new functions.

In BGP, there is no version management of the features supported by a router, where a version N + 1 would integrate all the features of version N. This means that a BGP router can implement a very recent feature, without necessarily implementing other older features. A router wishing to establish a BGP session must therefore discover the list of functions supported by its neighbor, so as to use only those functions supported by both routers.

From the outset, the RFC 4271 defining BGP addressed the issue of introducing new features and managing compatibility. To...