EIGRP, or Enhanced Interior Gateway Routing Protocol, is a Cisco proprietary routing protocol designed for use within an autonomous system (AS) in an IP network. It is an advanced and efficient routing protocol that combines the benefits of distance vector and link-state routing protocols. EIGRP provides features such as rapid convergence, scalability, and support for multiple network protocols.
Several commands can be used on a Cisco router to enable you to troubleshoot and verify EIGRP configuration. Listed below are some of the IOS commands and we use the topology below as an example:
Show IP route: displays the entire routine table
Show ip route eigrp: shows only eigrp entries in the routing table
Show ip eigrp neighbors: show all EIGRP neighbors
Show ip eigrp topology: show entries in the EIGRP table
Debug eigrp packet: show hello packets sent/received between adjacent routers
Debug ip eigrp notification: shows eigrp changes and updates as they occur on your network.
Below is the display of the show ip route command on the Cisco router:
HQ#show ip route
10.0.0.0/30 is subnetted, 3 subnets
C 10.10.1.0 is directly connected, Serial0/0/1
C 10.10.10.0 is directly connected, Serial0/0/0
D 10.20.20.0 [90/2681856] via 10.10.10.2, 00:31:47, Serial0/0/0
[90/2681856] via 10.10.1.2, 00:28:25, Serial0/0/1
172.17.0.0/24 is subnetted, 1 subnets
D 172.17.1.0 [90/2172416] via 10.10.10.2, 00:26:51, Serial0/0/0
C 192.168.10.0/24 is directly connected, FastEthernet0/0
D 192.168.20.0/24 [90/2172416] via 10.10.1.2, 00:26:44, Serial0/0/1
C 200.165.199.0/24 is directly connected, Loopback0
HQ#
The display above shows all the routes there is in the routing table. The Cs are directly connected. The Ds (DUAL) are the EIGRP routes and the default distance is 90, which represents internal EIGRP routes.
Show ip eigrp neighbours command:
HQ#show ip eigrp neighbors
IP-EIGRP neighbors for process 1
H Address Interface Hold Uptime SRTT RTO Q Seq
(sec) (ms) Cnt Num
0 10.10.10.2 Se0/0/0 12 00:39:13 40 1000 0 14
1 10.10.1.2 Se0/0/1 10 00:35:48 40 1000 0 14
HQ#
The above display of the show ip eigrp neighbors command.
- The H field shows the order in which a neighbor is discovered.
- ii. The hold time is how long the local router (this router) has to wait for a hello packet to arrive from a neighbor.
iii. The uptime shows how long adjacency with neighbors has been established
- The SRTT field is the smooth round-trip timer. This means the time it takes for this router to link with a neighbor and back. It normally has a value that is used to determine how long a waiting time is after a multicast reply from a neighbor. If The router does not receive a reply in time, it will result in using a unicast to complete the communication.
- The RTO(Retransmission Time Out) field is the amount of time EIGRP waits before retransmitting a packet.
- The Qvalue field shows the number of messages in the queue. Take note that large values mean problems.
vii. The Seq field indicates the sequence number of the last update from a neighbour. This in a way is used to maintain synchronization and to avoid duplicate messages.
The Show IP eigrp Topology:
HQ#show ip eigrp topology
IP-EIGRP Topology Table for AS 1
Codes: P – Passive, A – Active, U – Update, Q – Query, R – Reply,
r – Reply status
P 10.10.10.0/30, 1 successors, FD is 2169856
via Connected, Serial0/0/0
P 10.20.20.0/30, 2 successors, FD is 2681856
via 10.10.10.2 (2681856/2169856), Serial0/0/0
via 10.10.1.2 (2681856/2169856), Serial0/0/1
P 10.10.1.0/30, 1 successors, FD is 2169856
via Connected, Serial0/0/1
P 192.168.10.0/24, 1 successors, FD is 28160
via Connected, FastEthernet0/0
P 172.17.1.0/24, 1 successors, FD is 2172416
via 10.10.10.2 (2172416/28160), Serial0/0/0
P 192.168.20.0/24, 1 successors, FD is 2172416
via 10.10.1.2 (2172416/28160), Serial0/0/1
P 200.165.199.0/24, 1 successors, FD is 128256
via Connected, Loopback0
HQ#
On the display above, each route is preceded by a P, which indicates that the route is in a passive state which is a good thing.
If a route is preceded by A (active state), that shows that the router has lost connection to the route or network. Looking carefully, you will find two numbers in parentheses, the first is the feasible distance (FD), and the second is the advertised distance of a remote network
The FD (Feasible Distance) indicates feasible distances to each remote network plus the next hop router in which a packet takes to its destination.
The successor indicates only one successor to a remote network In some cases, there are feasible successor or backup routes to a network which will be displayed on a large network with multiple routes configured, like that on the 10.20.20.0 network above.
Both routes can be found in the topology table, but only those with the lowest metrics will be copied and placed into the routing table.
