EIGRP Notes

Hybrid Routing Protocol as it contains most characteristics of a distance vector protocol as well as some characteristics of a link state protocol.

EIGRP offers many advantages over other routing protocols, including the following:

  • Supports VLSM— EIGRP is a classless routing protocol and carries the subnet mask of the route in its update.
  • Rapid convergence— By using the concept of feasible successors, defined by DUAL, EIGRP is capable of preselecting the next best path to a destination. This allows for very fast convergence upon a link failure.
  • Low CPU utilization— Under normal operation, only hellos and partial updates are sent across a link. Routing updates are not flooded and are processed only periodically.
  • Incremental updates— EIGRP does not send a full routing update; it sends only information about the changed route.
  • Scalable— Through the use of VLSM and a complex composite metric, EIGRP networks can be vast in size.
  • Easy configuration— EIGRP supports hierarchical network design, but it does not require the strict configuration guidelines, such as the ones needed for OSPF.
  • Automatic route summarisation— EIGRP will perform automatic summarisation on major bit boundaries.
  • MD5 route authentication— As of Cisco IOS Software Release 11.3, EIGRP can be configured to perform MD5 password authentication on route updates.
It uses IP protocol 88.
  • Chooses route primary on bandwidth and delay although other factors can be added to the equation such as load, reliability and MTU.

Whenever you are influencing routing decisions in IGRP or EIGRP, use the metric of delay over bandwidth. Changing bandwidth can affect other routing protocols, such as OSPF. Changing delay affects only IGRP and EIGRP.

Please note that most of the information on this page has been copied from: http://www.informit.com/library/content.aspx?b=CCIE_Practical_Studies_I&seqNum=116