To determine the best route (successor) and the backup route (feasible successor) to a
destination, EIGRP uses the following two parameters:
?– Advertised distance: The EIGRP metric for an EIGRP neighbor to reach a particular
network
?– Feasible distance: The advertised distance for a particular network learned from an EIGRP
neighbor plus the EIGRP metric to reach that neighbor
A router compares all feasible distances to reach a speci?¬?c network and then selects the lowest
feasible distance and places it in the routing table. The feasible distance for the chosen route
becomes the EIGRP routing metric to reach that network in the routing table.
The EIGRP topology database contains all the routes that are known to each EIGRP neighbor.
Routers A and B send their routing tables to Router C, whose table is displayed in Figure 5-2. Both
Routers A and B have pathways to network 10.1.1.0/24, as well as to other networks that are not
shown.
Figure 5-2 Router C EIGRP Tables
Router C has two entries to reach 10.1.1.0/24 in its topology table. The EIGRP metric for Router
C to reach both Routers A and B is 1000. Add this cost (1000) to the respective advertised distance
IP EIGRP Neighbor Table
Next-Hop Router Interface
Router A
Router B
Ethernet 0
Ethernet 1
IP EIGRP Topology Table
Network
Feasible Distance
(EIGRP Metric)
EIGRP
Neighbor
Advertised
Distance
10.
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