EIGRP Terminology

EIGRP has a number of terms that must be understood by a candidate for the CCIE Security written exam. Table 2-10 defines some of the common terminology used in EIGRP.

Table 2-10 EIGRP Terms




A router in the same autonomous system (AS) running EIGRP.

Neighbor table

EIGRP maintains a table with all adjacent routers. To view the EIGRP neighbors, use the IOS command show ip eigrp neighbors.

Topology table

EIGRP maintains a topology table for all remote destinations discovered by neighboring routers. To view the topology table, the IOS command is show ip eigrp topology.


A packet used to monitor and maintain EIGRP neighbor relationships; they are multicast.


A query packet that is sent to neighboring routers when a network path is lost; can be multicast or unicast.


A reply packet to a query packet; they are unicast.


Acknowledgment of an update packet, typically a hello packet with no data; they are unicast.


How long a router waits for a hello packet before tearing down a neighbor adjacency.

Smooth Route Trip Time (SRTT)

Time taken to send a packet reliably to an acknowledgment. SRTT is the average delta between the time a packet is sent and the arrival of the neighbor's acknowledgment.

Retransmission Timeout (RTO)

RTO is the time a router waits for the arrival of the neighbor's acknowledgment.

Feasible distance

Lowest metric to remote network.

Feasibility condition (FC)

A condition under which the sum of a neighbor's cost to a destination and the cost to this neighbor is less than current successor's cost.

Feasible successor

A neighboring router with a lower AD.


A neighboring router that meets the feasibility condition.

Stuck in Active (SIA)

An EIGRP router waiting for all acknowledgments from neighboring routers for all the queries sent.


When a router is querying neighboring routers about a network path.


Normal route operation to a remote destination.

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