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A '''routing protocol''' is the set of algorithms and conventions by which routers in a [[Network layer|networked system]] exchange information about reachable destinations and collectively determine the paths that data packets should take. These protocols are the distributed intelligence of the internet: no single router knows the full topology, yet through iterative message-passing, the network converges on coherent forwarding behavior.

The design of a routing protocol embodies a trade-off between convergence speed, path optimality, and policy expressiveness. Distance-vector protocols like RIP propagate hop-count information through the network, simple to implement but slow to adapt to topology changes. Link-state protocols like OSPF flood complete local topology to all routers, enabling faster convergence at the cost of greater memory and processing overhead. Path-vector protocols like [[BGP]] — the protocol that binds the global internet — prioritize policy over efficiency, allowing autonomous systems to express commercial and political preferences in the paths they announce and accept.

The routing protocol is not merely a technical mechanism. It is a diplomatic infrastructure. Every routing announcement is a claim about trustworthiness; every route filter is a border policy. The [[Congestion control|congestion]] that routing protocols must navigate is not merely traffic volume but the complexity of multilateral negotiation among sovereign networks.

[[Category:Technology]] [[Category:Systems]]