Computer Networking Routing Protocols: RIP, OSPF, EIGRP, BGP & AD

RIP (Routing Information Protocol)

Distance-vector routing protocol; uses hop count as its metric (max 15 hops, 16 is unreachable); updates every 30 seconds.

OSPF (Open Shortest Path First)

Link-state routing protocol; uses cost (bandwidth) as its metric; uses Dijkstra's algorithm; scalable using hierarchical Areas (Area 0 = Backbone).

EIGRP (Enhanced Interior Gateway Routing Protocol)

Advanced distance-vector (hybrid) routing protocol; Cisco proprietary (now open); uses composite metric (Bandwidth and Delay).

BGP (Border Gateway Protocol)

Path-vector exterior gateway protocol (EGP); routes traffic between different Autonomous Systems (AS) across the global Internet.

IS-IS (Intermediate System to Intermediate System)

Link-state interior gateway protocol (IGP); operates at Layer 2; similar to OSPF but frequently used in large service provider networks.

Distance-Vector Routing Protocols

Routing protocols that send their entire routing table to directly connected neighbors at fixed periodic intervals (e.g., RIP).

Link-State Routing Protocols

Routing protocols where routers flood link status throughout the area, construct a full map (topology) of the network, and calculate the shortest path (e.g., OSPF, IS-IS).

Exterior Gateway Protocol (EGP)

A category of routing protocols used to exchange routing information between different Autonomous Systems (e.g., BGP).

Interior Gateway Protocol (IGP)

A category of routing protocols used to exchange routing information within a single Autonomous System / administrative domain (e.g., OSPF, EIGRP, RIP).

Administrative Distance (AD)

A metric used by routers to select the best path when there are two or more different routes to the same destination from different routing protocols (Lower AD = More Trusted).