Routing Protocols
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Topic:Computer_networks:Routing Protocols
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[edit] Introduction
Routing Protocols are used to dynamically propagate network routes to other routers on the network. This saves administrative work as each route required by a network does not have to be manually configured on every router in the network.
Routing protocols are defined in three broad classes Distance Vector, Link State, and Hybrid. Distance Vector devices calculate the route by how far away (in hops) the destination is, while Link State protocols can use many other values such as bandwidth, latency, reliability and load. Hybrids, as the name implies, use a mixture of Distance Vector and Link State methods.
[edit] Routing Protocols
[edit] Distance Vector
Distance Vector routing protocols broadcast their entire routing table to other routers on the network at specified intervals.
- RIP
The Routing Information Protocol (RIP) is a routing protocol that was designed for small networks. It can handle a maxiumum of 16 hops and is a classful routing protocol meaning that it does not support Variable Length Subnet Masks (VLSM) and does not support authentication.
- RIPv2
The Routing Information Protocol version 2 (RIPv2) makes improvements to the original RIP protocol by adding classless routing (CIDR)and authentication to its list of features, however the 16 hop count limitation still remains to allow for backwards compatability.
- IGRP
The Interior Gateway Routing Protocol (IGRP) is a routing protocol developed by Cisco Systems to make up for shortcomings of RIP version 1. Instead of the 16 hop count limit imposed by RIP, IGRP supports up to 255 hops.
[edit] Link State
Link State routing protocols gather information about the state and what other devices are connected to it's links, this information is then flooded through the network, to each router in an Autonomous System. Routers then use this topology information to build it's routing table. Each device then sends periodic messages, "hellos" to each other, to ensure the topology matches their records. If the device detects a change (e.g. A link going down), this change is propagated to all devices, who then recalculate their routing tables, accounting for the changes.
When all devices have identical topology records, and have recalculated their routing tables, the network is said to have converged.
[edit] Hybrid
- EIGRP
The Enhanced Interior Gateway Routing Protocol (EIGRP) is a routing protocol developed by Cisco Systems to expand upon IGRP. It utilizes the Diffusing Update Algorithm (DUAL) to determine the best possible loop-free path through a routed network. EIGRP maintains routing data in three tables known as the Neighbor Table, Topology Table, and Routing Table.
- IS-IS
- OSPF
[edit] Gateway Protocols
- IS-IS
- BGP
