Routing Protocols allow routers to dynamically advertise and learn routes, determine which routes are available and which are the most efficient routes to a destination. Routing protocols provide the layer 3 network state update and populate routing tables on the layer 3 switch/router. However, some popular layer three protocols, such as Internet Protocol (IP), Novell Internetwork Packet eXchange (IPX), and AppleTalk are called routed protocols, which transport data across the network.

There are two types of routing protocols: Distance Vector Routing and Link State Routing. Basically, Distance Vector protocols determine best path on how far the destination is, while LinkState protocols are capable of using more sophisticated methods taking into consideration link variables, such as bandwidth, delay, reliability and load.

Distance Vector protocols judge best path on how far it is. Distance can be hops or a combination of metrics calculated to represent a distance value. The IP Distance Vector routing protocols still in use today are: Routing Information Protocol (RIP v1 and v2) and Interior Gateway Routing Protocol (IGRP €“ developed by Cisco).

A Link-state routing is a concept used in routing of packet-switched networks in computer communications. Link-state routing works by having the routers tell every router on the network about its closest neighbors. The entire routing table is not distributed from any router, only the part of the table containing its neighbors.

Some of the link-state routing protocols are the OSPF, IS-IS and EIGRP. Novell's NLSP (NetWare Link State Protocol) is also a link-state routing protocol, which only supports IPX. This type of routing protocol requires each router to maintain at least a partial map of the network. When a network link changes state (up to down, or vice versa), a notification, called a link state advertisement (LSA) is flooded throughout the network. All the routers note the change, and re-compute their routes accordingly.

Distance-vector routing protocols are simple and efficient in small networks, and require little, if any management. However, they do not scale well, and have poor convergence properties, which has led to the development of more complex but more scalable link-state routing protocols for use in large networks.

LinkState Routing protocols provide greater flexibility and sophistication than the Distance Vector routing protocols. They reduce overall broadcast traffic and make better decisions about routing by taking characteristics such as bandwidth, delay, reliability, and load into consideration, instead of basing their decisions solely on distance or hop count.

Protocol Structure

Routing Protocols

Related Terms: OSPF, IS-IS, EIGRP, NLSP, Distance Vector Routing Protocol, LinkState Routing, NHRP, RIP, RSVP, VRRP, EGP, IGRP, NARP