EIGRP Verification Commands & Troubleshooting

EIGRP Verification Commands & Troubleshooting

This article describe how to verify the implementation of EIGRP for IPv4 in a small routed network and you will learn EIGRP Verification Commands & Troubleshooting. If you want to learn how to configure EIGRP on Cisco Router you can visit here.

show ip eigrp neighbors

Before EIGRP can send or receive updates, routers must establish adjacencies with their neighbors, and do so by exchanging EIGRP hello packets.Use the show ip eigrp neighbors command to view the neighbors table and verify that EIGRP has established an adjacency with its neighbors. For each router, you should be able to see the IPv4 address of the adjacent router and the interface that router uses to reach that neighboring EIGRP. With this topology, each router has two neighbors included in the neighbors table.

The result of the show ip eigrp neighbors command includes the following:

• Column H : lists the neighbors in the order in which they were discovered.
• Address : IPv4 address of the neighbor.
• Interface : the local interface on which this greeting packet was received.
• Hold : the current wait time. When a greeting packet is received, this value is reset to the maximum timeout for that interface and then a countdown to zero is performed. If it reaches zero, the neighbor is considered inactive.
• Uptime : the amount of time since this neighbor was added to the neighbors table.
• SRTT and RTO (average round trip time and retransmission timeout): used by RTP to manage reliable EIGRP packets.
• Q Cnt (tail count): must always be zero. If it is more than zero, there are EIGRP packets waiting to be sent.
• Seq Num (sequence number): used to track update, query and response packets.

The show ip eigrp neighbors command is very useful for checking and solving EIGRP problems.

SHOW IP PROTOCOLS COMMAND

The show ip protocols command shows the parameters and other information about the current status of any active IPv4 routing protocol process configured on the router.
The show ip protocols command shows different types of results specific to each routing protocol.

The result in Image indicates several EIGRP parameters, including the following:

1. EIGRP is an active dynamic routing protocol on R1, configured with autonomous system number 1.
2. The EIGRP router ID of R1 is 1.1.1.1.
3. The administrative distances of EIGRP on R1 are internal AD of 90 and external AD of 170 (default values).
4. By default, EIGRP does not automatically summarize networks. Subnets are included in routing updates.
5. The adjacencies of EIGRP neighbors that R1 has with other routers used to receive EIGRP routing updates.

Note : Prior to IOS 15, automatic EIGRP summarization was enabled by default.

The information in the Routing Information Sources field can help identify a router suspected of delivering defective routing information. The Routing Information Sources field lists all the EIGRP routing sources that Cisco IOS software uses to build its IPv4 routing table. For each origin, observe the following:

• IPv4 address
• Administrative distance
• Time when the last update of this origin was received

ADMINISTRATIVE DISTANCE

As shown in the figure, EIGRP has a default AD of 90 for internal routes and 170 for routes imported from an external source, such as default routes. Compared to other IGPs, EIGRP is preferred by Cisco IOS, because it has the lowest administrative distance. EIGRP has a third AD value of 5, for summary routes.

ANALYSIS OF THE IPV4 ROUTING TABLE

Another way to verify that EIGRP and other router functions are configured correctly is to examine the IPv4 routing tables with the show ip route command .
As with any dynamic routing protocol, the network administrator must verify the information in the routing table to ensure that it is completed as expected, based on the settings entered.
For this reason, it is important to have a good level of knowledge of the routing protocol configuration commands , as well as the routing protocol operations and the processes used by said protocol to arm the IP routing table.
The state of automatic summarization can make a difference in the information shown in the IPv4 routing table. If an earlier version of IOS is used, automatic summarization can be disabled using the no auto-summary command of the router configuration mode:
Router (config-router) # no auto-summary
The following figure shows the topology of R1, R2 and R3.

IPV4 ROUTING TABLE ANALYSIS EXAMPLE

In Image, the IPv4 routing table is examined by the show ip route command . EIGRP routes are indicated in the routing table with a D.
The letter "D" represents EIGRP because the protocol is based on the DUAL algorithm.

The show ip route command shows the complete routing table, including dynamically discovered remote networks, directly connected routes and static routes. For this reason, it is usually the first command used to verify convergence .
Note that on R1 routes to three remote IPv4 networks were installed in your IPv4 routing table:

• 172.16.2.0/24, received from router R2 on the Serial interface0 / 0/0
• 192.168.1.0/24, received from router R2 on the Serial interface 0/0/1
• 192.168.10.8/30, received from R2 on the Serial0 / 0/0 interface and from R3 on the Serial0 / 0/1 interface

The R1 has two routes to the 192.168.10.8/30 network, because its cost or metric to reach that network is the same when using both routers. These are known as " routes of the same cost ." R1 uses both routes to reach this network, what is known as “ load balancing ”.

In Image, the routing table of R2 is shown. Note that similar results are shown, including a route of the same cost for the 192.168.10.4/30 network.

In Image, the R3 routing table is shown. Remote networks are discovered through EIGRP, including a route of the same cost for the 172.16.3.0/30 network.