You can use Enhanced IGRP to integrate several existing networks that are using different routing protocols.
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Enhanced IGRP supports three network level routing protocols:

• IPX RIP
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• AppleTalk RTMP
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• IP RIP
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Each of these has protocol-specific, value-added functionality.
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Routers running IPX Novell Enhanced IGRP

• support incremental
  Service Advertisement
  Protocol (SAP) updates
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• remove the RIP limitation
  of 15 hop counts
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• provide optimal path use
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For more information on this see the CBT Systems course £RImplementing IPX Enhanced IGRP for Cisco Routers£r.
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Routers running AppleTalk Enhanced IGRP

• support partial, bounded
  routing updates
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• provide load sharing
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• provide optimal path use
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For more information on this see the CBT Systems course £RImplementing Routing for AppleTalk on Cisco routers£r.
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The IP implementation of Enhanced IGRP supports variable length subnet masks (VLSMs) to allow network administrators to more efficiently allocate IP addresses.
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This implementation can redistribute routes learned by OSPF, IP RIP, IS-IS, EGP, or BGP.
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For example, two routers could use Enhanced IGRP to convert and exchange IP RIP routing information.
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A router may be sending updates for Enhanced IGRP for IP, Enhanced IGRP for IPX and Enhanced IGRP for AppleTalk.
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This would appear to be demanding on bandwidth.
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However, Enhanced IGRP saves on WAN link bandwidth by sending routing updates only when routing information changes.
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The updates sent contain information only about the link that has changed.
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In addition, the updates that are sent are bounded, meaning that they go only to affected routers.
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Since Enhanced IGRP routers exchange information from their own routing tables, WAN link bandwidth is not consumed with routing updates from non-adjacent routers.
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Unlike routing protocols that use a single metric such as a hop count, Enhanced IGRP uses a composite set of metrics to determine the best path to a destination.
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Enhanced IGRP can determine that a single 19.2 kbps hop between networks is significantly slower than a 3-hop path through multiple T1 links.
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Enhanced IGRP routers use a metric structure similar to that used by IGRP routers.
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As a result, Enhanced IGRP routers and IGRP routers can easily exchange routing information.
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When you are integrating Enhanced IGRP into existing networks you should plan a phased implementation.
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In a large network you cannot change the configuration of all routers simultaneously.
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To achieve minimal disruption you should begin by adding Enhanced IGRP to the routers at the periphery of the network.
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Since peripheral routers generally talk to each other through the core, you cannot change the routing protocol in the core if the peripheral routers are not configured for the new protocols.
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When the peripheral routers are configured for Enhanced IGRP, you can then concentrate on changing the core.
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If your network contains only one autonomous system (AS), route redistribution between the routers is automatic.
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During migration from IGRP to Enhanced IGRP you configure the routers within the same AS with both IGRP and Enhanced IGRP.
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The routers then have both an IGRP and an Enhanced IGRP process active, sharing the same AS number.
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Once Enhanced IGRP has acquired all of the routing information in the IGRP tables, you can terminate the IGRP process.
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If there are two ASs, the AS boundary router will run separate routing processes with different AS numbers.
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In this case, the network administrator must configure redistribution manually.
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Once the boundary routers are configured for Enhanced IGRP, you can then integrate Enhanced IGRP into the core network.
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Your company wants you to implement Enhanced IGRP on your network.
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To do this you must

• enable IP Enhanced IGRP at
  each router
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• define the directly connected
  networks with which each
  router interfaces
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In order to configure the routers you must be in Privileged mode.
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You enter Configuration mode by typing £Rconfig£r at the prompt and pressing £UReturn£u to configure from terminal.
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Starting with the SanFran router you enter the command £Rrouter eigrp 109£r.
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The number 109 is the number of the AS to which this router belongs.
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This enables Enhanced IGRP routing on the SanFran router.
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Next you must define the networks with which the SanFran router interfaces.
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You enter the command £Rnetwork 172.16.0.0£r.
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172.16.0.0 is the number of the network which will be advertised by the SanFran router.
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The SanFran router is now configured for Enhanced IGRP.
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You exit configuration mode by pressing £UCtrl+Z£u.
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You can save the configuration in NVRAM by entering £Rcopy runn start£r.
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Next, you configure the London router.
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You log on remotely to the London router using Telnet by entering £Rtelnet london£r and then entering the London router's logon password, £Rcbtcbt£r.
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As before you need to be in Privileged mode on the London router before you can configure it.
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You enter Privileged mode by typing £Renable£r at London's command prompt and entering its password, £Rcisco£r.
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Then you enter Configuration mode by typing £Rconfig£r and pressing £UReturn£u to configure from terminal.
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You enable Enhanced IGRP routing on the London router by entering £Rrouter eigrp 109£r.
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You define the networks with which the London router interfaces by entering £Rnetwork 172.16.0.0£r.
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The London router is now configured for Enhanced IGRP routing.
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You exit the Configuration mode by pressing £UCtrl+Z£u.
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You save the configuration in NVRAM by entering £Rcopy runn start£r.
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You then log out of the London router and exit back to the SanFran router by typing £Rexit£r.
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The Dublin and Sydney routers are configured in the same way.
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Assume that you are in the process of configuring your company's internetwork.
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You are configuring it to run Enhanced IGRP.
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You have already configured the SanFran and London routers.
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You log on to the Dublin router by entering £Rdublin£r at the prompt.
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You can also do this by entering £Rtelnet dublin£r or £Rtelnet 172.16.66.2£r or £Rtelnet 172.16.67.2£r.
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You then enter the password, in this case £Rcbtcbt£r.
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You enter Privileged mode by typing £Renable£r and entering the password £Rcisco£r.
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You enter Configuration mode by typing £Rconfig£r and pressing £UReturn£u to configure from terminal.
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You enter £Rrouter eigrp 109£r to enable Enhanced IGRP routing on the router.
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Next you need to define the networks with which the Dublin router interfaces.
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You enter £Rnetwork 172.16.0.0£r to define the networks with which the Dublin router interfaces.
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You press £UCtrl+Z£u to exit Configuration mode.
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You then save the configuration in NVRAM using the command £Rcopy runn start£r.
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And you log out of the Dublin router and exit back to the SanFran router by typing £Rexit£r.
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You next log into the Sydney router by entering £Rtelnet 172.16.65.1£r at the SanFran Privileged mode prompt.
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You enter the password, £Rcbtcbt£r.
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You must be in Privileged mode on the Sydney router, so you enter £Renable£r and the password £Rcisco£r.
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Then you enter Configuration mode by typing £Rconfig£r.
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You enable Enhanced IGRP routing on the Sydney router by entering £Rrouter eigrp 109£r.
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You then define the networks with which the Sydney router interfaces.
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These are defined by entering £Rnetwork 172.16.0.0£r.
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And you exit configuration mode by pressing £UCtrl+Z£u.
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You save the configuration to NVRAM by entering the command £Rcopy runn start£r.
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You then log out of the Sydney router and exit back to the SanFran router by typing £Rexit£r.
