Routing protocols are protocols with which routers communicate with each other. They are used to optimize path selection for switching messages across multiple networks. Optimal path selection can be cost or bandwidth optimized, it can take into account link utilization, number of hops, transmission speed or real-time behavior.
Routing protocols can work with statically predetermined routes or use dynamic routing. Dynamic route assignment is performed during network operation and takes into account network extensions, load changes and congestion.
InIP networks, data packets are delivered on the basis of IP addresses. The routing protocols used for this purpose can use routing tables and establish links to the destination addresses. If the routes are fixed, we are talking about static routing; if the routes are compiled by the routing protocols, we are talking about dynamic routing. Routing protocols differ in the routing algorithms used, metrics used, exchange mechanisms, convergence, and administrative overhead. They can be divided into Interior Routing Protocols( IRP) and Exterior Routing Protocols( ERP).
The first group includes routing protocols with distance vector algorithms such as the Gateway to Gateway Protocol( GGP), Routing Information Protocol( RIP), Interior Gateway Routing Protocol( IGRP), and Enhanced Interior Gateway Routing Protocol( EIGRP), with link-state algorithms work the Intermediate System to Intermediate System Protocol( IS-IS) and Open Shortest Path First( OSPF). Among the Exterior Routing Protocols (ERP), there are also those that work with preferences and policies such as the Exterior Gateway Protocol( EGP). Others, such as the Border Gateway Protocol( BGP), which uses the Path Vector method, and still others, such as the Interdomain Routing Protocol( IDRP), which works with link-state algorithms.
In other wide- area networks, mobile networks, and local area networks, routing is determined by other algorithms and metrics, such as the suppression of redundant structures with the spanning tree protocol or source routing.