BGP and OSPF for Engineers

Static routes work when a network is small and paths rarely change. They become difficult to maintain when routers have redundant links, offices connect and disconnect, providers advertise thousands of prefixes, or a failed path needs an automatic replacement.

Routing protocols distribute reachability information and update routing tables as topology or policy changes. They do not forward application packets themselves. Their job is to give the forwarding plane a usable set of prefixes and next hops.

OSPF and BGP solve different parts of that problem. Open Shortest Path First, or OSPF, builds a topology view and computes paths inside an administrative network. Border Gateway Protocol, or BGP, exchanges prefix reachability and policy information between autonomous systems and across large internal networks.

Understanding the boundary between them is more useful than treating them as competing protocols.