What is EIGRP Neighbor and Topology Table?

Enhanced Interior Gateway Routing Protocol (EIGRP) is a networking protocol used by computer networks for configuration, making routing decisions, and automating them. EIGRP is a Cisco proprietary protocol that is, it is accessible on Cisco routers. Later on, its functionality was changed to an open standard and was available under RFC 7868. It is used on routers for sharing routes with other routers inside the same AS.

EIGRP Neighbor table:

It preserves the state information about other neighbors that are present within the same AS, and also the information about the stored neighbor can be seen by typing the command “show ip eigrp neighbors”.

RB#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H   Address             Interface        Hold Uptime     SRTT    RTO    Q    Seq
                                           (sec)         (ms)          Cnt   Num
0   192.157.11.3         Fa0/0           11 01:16:07      18     201    0     26

1. Handle (H): It tells about the arrangement in which the neighbor proximity was formed. The value of the first router will be 0, the value of the second router will be 1, the value of the third router will be 1, and so on.
2. Address: It is the neighbors IP address.
3. Interface: It is the connected neighbor’s interface.
4. Hold time (sec): It is the neighbor hold-down timer per EIGRP that is it holds a neighbor if it does not receive a hello and when it expires, the neighbor contiguity is dropped. The hold time is 15 seconds by default.
5. Uptime: Uptime tells for how long the neighbor has been up.
6. Smooth round-trip time (SRTT): It tells about the time taken in milliseconds to send and receive an acknowledgment packet back when an EIGRP packet is sent to the neighbor.
7. Retransmission timeout (RTO): It tells about the time taken in milliseconds that EIGRP will wait for the acknowledgment before it resends a packet from its retransmission queue to the neighbor.
8. Q count (Q Cnt): It is the total number of packets (Query, Update or Reply) waiting in the queue for transmission. It should ideally be 0, otherwise, it indicates that there might be some congestion in the network.
9. Sequence number (Seq Num): It shows the seq number of the previously received packet (update, query, or reply) from the EIGRP neighbor.

Topology Table:

This table stores a lot of information such as the routes learned and received by the EIGRP neighbors. The topology table information can be seen by using the “show ip eigrp topology” command. Protocol-dependent modules are in charge of sending the information in the topology table.

RB#show ip eigrp topology
IP-EIGRP Topology Table for AS(1)/ID(1.3.1.2)

Codes: P - Passive, A - Active, U - Update, Q - Query, R - Reply,
       r - reply Status, s - sia Status

P 1.3.1.0/24, 1 successors, FD is 119463
       via Connected, Loopback0
P 1.3.2.0/24, 1 successors, FD is 163270
       via 192.157.11.3 (163270/119463), FastEthernet0/0
P 192.157.11.0/24, 1 successors, FD is 29273
       via Connected, FastEthernet0/0

1. Passive (P): It means that the router is not actively looking for the routes.
2. Active (A): It means that there is some instability in the network.
3. Feasible Distance (FD): It means Metric to a destination.
4. 163270/119463: The first part is the feasible distance and the second part is the advertised distance.
5. Feasible Distance: It is the total distance from the destination
6. Advertised Distance: It is the total distance from neighbor to destination.