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An Introduction to EIGRP

About the Protocol

  • The algorithm used for this advanced Distance Vector protocol is the Diffusing Update Algorithm.
  • The metric is based upon Bandwidth and Delay values. Reliability and Load could also be used, but are not by default. The MTU is used as a tiebreaker and is not used in the metric formula.
  • For updates, EIGRP uses Update and Query packets that are sent to a multicast address. The Reliable Transfer Protocol used by EIGRP will start unicasting updates in the event that several multicast attempts are not acknowledged.
  • Split horizon and DUAL form the basis of loop prevention for EIGRP.
  • EIGRP is a classless routing protocol that is capable of Variable Length Subnet Masking.
  • Automatic summarization is on by default, but summarization and filtering can be accomplished anywhere inside the network. This is changed in 15.X IOS code where automatic summarization is disabled by default.

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