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Chapter 6
Troubleshooting TCP/IP Connectivity
To aid in the calculation of the best route and load sharing, EIGRP utilizes
several databases of information. These databases are as follows:
The route database, where the best routes are stored
The topology database, where all route information resides
A neighbor table that is used to house information concerning other
EIGRP neighbors
Each of these databases exists for IP-EIGRP, IPX-EIGRP, and AT-EIGRP
or AppleTalk-EIGRP. Therefore, it is possible for EIGRP to have nine active
databases when all three protocols are configured on the router.
Neighbor Formation
The manner in which EIGRP establishes and maintains neighbor relation-
ships is derived through its link-state properties. EIGRP uses the Hello pro-
tocol (similar to OSPF) to establish and maintain peering relationships with
directly connected routers. Hello packets are sent between EIGRP routers to
determine the state of the connection between them. Once the neighbor rela-
tion is established via the Hello protocol, the routers can exchange route
information.
Incremental routing
updates
Advertises only changes, instead of the entire
route table.
Classless routing
Supports subnet and VLSM information.
Configurable metrics
Allows metric information to be set through con-
figuration commands.
Equal-cost load
balancing
Allows traffic to be sent equally across multiple
connections.
T A B L E 6 . 7
EIGRP Features (continued)
Feature
Description
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