Troubleshooting IP Routing Protocols (CCIE Professional Development Series)

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EIGRP and IGRP are similar in some ways, but they differ in other ways. EIGRP and IGRP use the same equation to calculate metrics to the destination network. EIGRP and IGRP also use the same technique in doing unequal -cost load balancing. However, EIGRP keeps a topol-ogy table of the network and uses the DUAL algorithm to select a loop-free path . EIGRP uses the notions of successor and feasible successor and the query process to achieve fast convergence. EIGRP also carries the subnet mask information when sending out routing update. This enables EIGRP to support discontiguous networks and VLSM, which makes EIGRP a scalable routing protocol capable of fitting today's network requirements. Table 6-1 shows the summary comparison between IGRP versus EIGRP.

Table 6-1. Comparison Table of IGRP Versus EIGRP

IGRP EIGRP

Metric calculated as follows :

Metric calculated as follows:

IGRP Metric x 256

Does not support VLSM and discontiguous networks Supports VLSM and discontiguous networks
Does not keep neighbor relationships Keeps neighbor relationships in a neighbor table
Is vulnerable to routing loops Keeps a topology table of the network and uses the DUAL algorithm to select a loop-free path
Has slow convergence time Has fast convergence time because of feasible successor and query process
Does not retransmit lost IGRP update packets Has a reliable transport mechanism to retransmit lost EIGRP packets
Does not support manual summarization and classless route aggregation Supports manual summarization and classless route aggregation
Does not understand 0.0.0.0/0 as default route Understands 0.0.0.0/0 as default route
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