IGP versus EGP

IGP versus EGP

6.3.4

This page will help students understand the differences between interior and exterior routing protocols.
Interior routing protocols are designed for use in a network that is controlled by a single organization. The design criteria for an interior routing protocol require it to find the best path through the network. In other words, the metric and how that metric is used is the most important element in an interior routing protocol.
An exterior routing protocol is designed for use between two different networks that are under the control of two different organizations. These are typically used between ISPs or between a company and an ISP. For example, a company would run BGP, an exterior routing protocol, between one of its routers and a router inside an ISP. IP exterior gateway protocols require the following three sets of information before routing can begin:

• A list of neighbor routers with which to exchange routing information
• A list of networks to advertise as directly reachable
• The autonomous system number of the local router

An exterior routing protocol must isolate autonomous systems. Remember, autonomous systems are managed by different administrations. Networks must have a protocol to communicate between these different systems.
Each AS must have a 16-bit identification number, which is assigned by ARIN or a provider, to use routing protocols such as IGRP and EIGRP.
The Interactive Media Activity will help students identify interior and exterior routing protocols.
This page concludes this lesson. The next page will summarize the main points from this module.

Routing protocols

Routing protocols

6.3.3

This page will give some examples of routing protocols and how they are used.
At the Internet layer of the TCP/IP suite of protocols, a router can use an IP routing protocol to accomplish routing through the implementation of a specific routing algorithm. Examples of IP routing protocols include the following:

• RIP - a distance vector interior routing protocol
• IGRP - the Cisco distance vector interior routing protocol
• OSPF - a link-state interior routing protocol
• EIGRP - the advanced Cisco distance vector interior routing protocol
• BGP - a distance vector exterior routing protocol

RIP was originally specified in RFC 1058. Its key characteristics include the following:

• It is a distance vector routing protocol.
• Hop count is used as the metric for path selection.
• If the hop count is greater than 15, the packet is discarded.
• Routing updates are broadcast every 30 seconds, by default.

IGRP is a proprietary protocol developed by Cisco. Some of the IGRP key design characteristics are as follows:

• It is a distance vector routing protocol.
• Bandwidth, load, delay and reliability are used to create a composite metric.
• Routing updates are broadcast every 90 seconds, by default.

OSPF is a nonproprietary link-state routing protocol.

• It is a link-state routing protocol.
• It is an open standard routing protocol described in RFC 2328.
• The SPF algorithm is used to calculate the lowest cost to a destination.
• Routing updates are flooded as topology changes occur.

EIGRP is a Cisco proprietary enhanced distance vector routing protocol. The key characteristics of EIGRP are as follows:

• It is an enhanced distance vector routing protocol.
• It uses unequal cost load balancing.
• It uses a combination of distance vector and link-state features.
• It uses Diffused Update Algorithm (DUAL) to calculate the shortest path.
• Routing updates are multicast using 224.0.0.10 triggered by topology changes.

Border Gateway Protocol (BGP) is an exterior routing protocol. The key characteristics of BGP are as follows:

• It is a distance vector exterior routing protocol.
• It is used between ISPs or ISPs and clients.
• It is used to route Internet traffic between autonomous systems.

The next page will discuss interior and exterior routing protocols.

Routing configuration

Routing configuration 

6.3.2 
This page will explain the steps that are used to configure a routing protocol.
To enable an IP routing protocol on a router, global and routing parameters need to be set. Global tasks include the selection of a routing protocol such as RIP, IGRP, EIGRP, or OSPF. The major task in the routing configuration mode is to indicate IP network numbers. Dynamic routing uses broadcasts and multicasts to communicate with other routers.
The router command starts a routing process.  
The network command enables the routing process to determine which interfaces send and receive routing updates.  
An example of a routing configuration is as follows:

GAD(config)#router rip

GAD(config-router)#network 172.16.0.0

For RIP and IGRP, the network numbers are based on the network class addresses, not subnet addresses or individual host addresses.
The Lab Activity will help students configure routers to start a routing process.
The next page will describe some routing protocols.