Versatile Routing and Services with BGP: Understanding and Implementing BGP in SR-OS

Chapter 1

Getting Started

Although this book does not discuss the operation of BGP as a path-vector protocol, it's worth a quick recap on how a BGP speaker processes and stores routes in the Routing Information Bases (RIBs). The RIB within a BGP speaker is made up of three distinct parts: the Adj-RIB-In, the Loc-RIB, and the Adj-RIB-Out. The Adj-RIB-In stores routing information learned from inbound UPDATE messages advertised by peers to the local router. The routes in the Adj-RIB-In represent routes that are available to the path decision process. The Loc-RIB contains routing information the local router selected after applying policy to the routing information contained in the Adj-RIB-In. These are the routes that will be used by the local router. The Adj-RIB-Out stores information the local router selected for advertisement to its peers. This information is carried in UPDATE messages sourced by this router when advertising to peers. In summary, the Adj-RIB-In contains unprocessed routing information advertised by peers to the local router, the Loc-RIB contains the routes that have been selected by the local BGP speaker's best-path decision process, and the Adj-RIB-Out contains the routes for advertisement to peers in UPDATE messages. I'll use this terminology throughout the book, and may interchangeably use Adj-RIB-In or simply RIB-In, and Adj-RIB-Out or simply RIB-Out.

Enabling BGP in its most basic form is a very simple exercise. All you need is an IP interface toward a BGP ...