EIGRP offers the following radical improvements over RIP and IGRP:
Fast convergence -- convergence is almost instantaneous when a feasible successor is available.
Variable Length Subnet Masks are supported -- subnet mask information is exchanged in EIGRP updates. This allows for efficient use of the address space, as well as support for discontiguous networks.
Route summarization at arbitrary bit boundaries, reducing routing-table size.
No regular routing updates -- network bandwidth and router CPU resources are not tied up in periodic routing updates, leading to improved network manageability.
Ease of configuration -- EIGRP can be configured with almost the same ease as IGRP. However, troubleshooting DUAL can be difficult.
These EIGRP benefits come at the price of higher memory requirements (in addition to the routing table, EIGRP requires memory for the topology table and the neighbor table). DUAL is complex and can be very CPU-intensive, especially during periods of network instability when CPU resources are already scarce. Also, don’t forget that the EIGRP is a Cisco proprietary protocol.
EIGRP is in use today in several mid-sized networks.
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