Foundation Summary

The "Foundation Summary" section of each chapter lists the most important facts from the chapter. Although this section does not list every fact from the chapter that will be on your exam, a well-prepared candidate should, at a minimum, know all the details in each "Foundation Summary" before going to take the exam.

The main concepts of EIGRP are as follows :

  • DUAL

  • Loop-free networks

  • Incremental updates

  • Multicast addressing for updates

  • Advanced distance vector protocol

  • Loop-free routing tables

  • Support for different topologies

  • Rapid convergence

  • Reduced bandwidth use

  • Protocol independence at Layer 3

  • Compatibility with IGRP

  • Easy configuration

  • Use of a composite metric

  • Unequal-cost load balancing

Cisco identifies four main components of EIGRP:

  • Protocol-dependent modules

  • RTP

  • Neighbor discovery and recovery

  • DUAL

Table 13-5 summarizes the EIGRP packet types sent between neighbors.

Table 13-5. Summary of Packet Types

Packet Type









To find and maintain neighbors for the neighbor table. The packet has a 0 in the Acknowledgment field.





A Hello packet with no data. It has a positive number in the Acknowledgment field.


Unicast and multicast

(Reply to a single router is unicast, but a change in topology table is multicast.)



Route information sent to affected routers.





A part of DUAL. Queries are sent out when a route in the topology table goes down and there is no FS.

Figure 13-7 shows the actions taken when a router receives a query from another router asking for an alternative route to a destination. Note that if the queried router has no route to offer, it is still obliged to respond to the querying router.

Figure 13-7. EIGRPMaintaining the Topology Table, Router D


Figure 13-8 illustrates the logic flow in a router that realizes a link has been lost, which may occur because a directly connected interface has lost a carrier signal or because the router has received an update or query.

Figure 13-8. EIGRPMaintaining the Topology Table, Choosing a Feasible Successor


CCNP BSCI Exam Certification Guide
CCNP BSCI Exam Certification Guide (CCNP Self-Study, 642-801) (3rd Edition)
ISBN: 1587200856
EAN: 2147483647
Year: 2002
Pages: 194
Authors: Clare Gough © 2008-2017.
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