Interior vs. Exterior Routing Protocols

Routing is the process of moving data from one network to another. Routing is unnecessary unless you have multiple networks on different address ranges (different combinations of IP addresses and masks, for example). If you don't, you need to look at bridging or switching. You don't need to run a routing protocol unless you have multiple networks served by more than one router (and even then, manual static routes are easier for small networks). Once you get beyond three routers, it's time to start thinking about dynamic routing protocols. If you are connecting your networks to the Internet, you will also need to think about running more than one kind of routing protocol.

INTERIOR GATEWAY PROTOCOLS

Interior Gateway Protocols (IGPs) handle routing within an Autonomous System. In plain English, IGP's figure out how to get from place to place between the routers you own. These protocols keep track of how to get from one destination to the other inside a network or set of networks that you administrate (all of the networks you manage combined are usually just one Autonomous System). IGP's are how you get all the networks communicating with each other. Think of Interior

IGP's fall into two categories:

  Distance Vector Protocols
     Routing Information Protocol (RIP)
     Interior Gateway Routing Protocol (IGRP)

  Link State Protocols
     Open Shortest Path First (OSPF)
     Intermediate System to Intermediate System (IS-IS)
 

EXTERIOR GATEWAY PROTOCOLS

To get from place to place outside your network(s), i.e. on the Internet, you must use an Exterior Gateway Protocol. Exterior Gateway Protocols handle routing outside an Autonomous System and get you from your network, through your Internet provider's network and onto any other network. BGP is used by companies with more than one Internet provider

Examples of an EGP:
    Border Gateway Protocol (BGP)
    Exterior Gateway Protocol (Replaced by BGP)