Foundation Summary

The "Foundation Summary" is a collection of quick reference information that provides a convenient review of many key concepts in this chapter. For those of you who already feel comfortable with the topics in this chapter, this summary will help you recall a few details. For those of you who just read this chapter, this review should help solidify some key facts. For any of you doing your final preparations before the exam, these tables and figures will be a convenient way to review the day before the exam.

Table 7-9 summarizes the EIGRP packet types sent between neighbors.

Table 7-9 Summary of Packet Types

Packet Type



Unreliable Purpose



X 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.

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


Route information sent to affected routers.




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

NOTE Any packet sent as a reliable multicast will be sent as a unicast if the neighbor does not acknowledge the packet. The packet will be retransmitted up to 16 times. This will speed up convergence and is an attempt to prevent the route being SIA. For this reason, some documentation will state that queries and hellos are sent both multicast and unicast. Because unicasts in this situation are used as a backup in case of failure, the answer in the exam would be multicast.

Table 7-10 summarizes the commands covered in this chapter.

Table 7-10 Summary of Commands

Table 7-10 summarizes the commands covered in this chapter.

Table 7-10 Summary of Commands



router eigrp autonomous

Starts the EIGRP processes on the router with the specified

system number

autonomous system number.

network network number

Shows the networks to be advertised.

no auto-summary

Given a hierarchical addressing design, disables the

automatic summarization to the Internet NIC network


ip summary address eigrp autonomous

Enables you to manually summarize the networks,

system number address mask

having disabled automatic summarization.

bandwidth speed of line

Is issued at the interface level and is a logical construct to

manually determine the real bandwidth. This command is

used mainly on serial lines. Bandwidth will influence some

routing decisions and dial-on-demand implementations.

ip bandwidth-percent eigrp

Enables you to change the bandwidth percentage. EIGRP

autonomous-system-number [percent]

by default will only take up to 50 percent of bandwidth.

variance multiplier number

Allows unequal paths to load-balance. Paths included in the

equation will send a proportional amount of traffic across

the unequal links.

ipx router eigrp autonomous

Configures EIGRP for IPX.

system number

ipx sap-incremental eigrp

States to EIGRP that incremental updates should be used.

autonomous system number

By default, the process will send periodic updates out LAN

interfaces and incremental updates through WAN interfaces.

If an FDDI ring were used as a backbone, it would be

advantageous to use incremental updates if all the devices

on the ring were Cisco systems.

show ip eigrp neighbors

Displays information drawn from the neighbor table.

show ip eigrp topology

Displays information drawn from the topology table.

show ip eigrp traffic

Shows the EIGRP traffic passing through the router.

Was this article helpful?

0 0

Post a comment