Part 2: Configure and Verify EIGRP for IPv4

In this part of the lab, you will configure and verify EIGRP in the network. R1 and R3 will used Named EIGRP, while R2 will use Classic EIGRP. After you have established the network, you will examine the differences in how each version of EIGRP deals with metrics.

For the lab, you will use the Autonomous System number 27 on all routers.

Step 1: Configure Classic EIGRP for IPv4 on R2

a. Start the configuration of Classic EIGRP by issuing the router eigrp 27 command.

Open configuration window

b. Configure the EIGRP router ID using the eigrp router-id command. Use the number 2.2.2.2 for R2.

c. Identify the interfaces that should be speaking EIGRP and the networks that should be included in the EIGRP topology table. This is done with the network command. 

It is best to be as specific as possible when creating network statements, while balancing efficiency and the number of commands necessary. For our lab example, we will use network 10.0.0.0 255.255.224. to specify the interfaces. This covers less network space than 10.0.0.0/8, while including both interfaces with a single network command.

d. Verify the interfaces now involved in EIGRP with the show ip eigrp interfaces command.

Close configuration window

Step 2: Configure Named EIGRP for IPv4 on R1 and R3

a. Start the configuration of Named EIGRP by issuing the router eigrp [ name ] command. The name parameter can be a number, but the number does not identify an Autonomous System as it does with Classic EIGRP, it simply identifies the process. For our purposes, name the process BASIC-EIGRP-LAB.

Open configuration window

b. Enter into address-family configuration mode with the address-family ipv4 unicast autonomous-system 27 command.

c. Configure the EIGRP router ID using the eigrp router-id command. Use the number 1.1.1.1 for R1.

d. Identify the interfaces that should be speaking EIGRP and the networks that should be included in the EIGRP topology table. This is done with the network command. In this case, the configuration requires three network commands. An example for R1 follows:

Close configuration window

e. Repeat Steps 2a through 2d for R3 and D2. Use 3.3.3.3 for the router ID on R3, and 132.132.132.132 for the router ID on D2. Configure the appropriate network statements on both devices according to the Addressing Table.

Open configuration window

Close configuration window.

Open configuration window

Step 3: Verify EIGRP for IPv4

a. A few seconds after configuring the network statements, you should have seen syslog messages noting that EIGRP adjacencies have been formed.

*Feb 18 15:49:34.243: %DUAL-5-NBRCHANGE: EIGRP-IPv4 27: Neighbor 10.0.12.2 (GigabitEthernet0/0/0) is up: new adjacency

b. To verify that routing is working, ping from PC1 to interface Loopback 0 on R3 (192.168.3.1). The ping should be successful. You can also randomly ping other addresses in the topology.

c. On R1, examine the EIGRP entries in the IP routing table using the show ip route eigrp | begin Gateway command. As you can see, there is one path installed in the routing table for the network, and two paths for the 192.168.3.0/24 network. Take note of the metric values listed.

Open configuration window

d. Now examine the EIGRP topology table using the show ip eigrp topology all-links command. The all-links parameter instructs the router to display all available routes, including the ones that are not successors or feasible successors.

Remember that the topology table is EIGRP’s database of route information. EIGRP selects the best paths from this database, based on the DUAL algorithm, and offers them to the IP routing table. However, the IP routing table does not have to use those offered paths, because the router may have learned about the same network from a more reliable routing source, which would be a routing source with a lower administrative distance.

We will focus on the routes, highlighted in the above output, to 192.168.3.0/24 and 10.0.23.0/24. There are several things to notice:

• The entry for the 192.168.3.0/24.0 network shows two successors, while the entry for 10.0.23.0/24 shows only one successor. Both entries show two paths. The path with the lowest Feasible Distance (FD) is selected as the successor and is offered to the routing table. For 192.168.3.0/24, there are two paths with equal FD (2048000). Therefore, both are successors and both are offered to the routing table. In the case of 10.0.23.0/24, the FD is listed as 19660800. The path via 10.0.12.2 shows that number as the FD (first number in parentheses). The path via 172.16.1.2 shows an FD of 2621440, which is higher than the current feasible distance. So that path, although valid, is a higher cost path and is not offered to the routing table.
• The FD listed in the topology table does not match the metric listed in the routing table. For 192.168.3.0/24, the routing table shows the metric value 16000, while the topology table shows the FD as 2048000. This is due to the routing table having a limit of 4 bytes (32 bits) for metric information while EIGRP on R1 is using EIGRP wide metrics, which are 64 bits. Wide metrics are used by Named EIGRP by default. To work around the 32-bit metric size limitation in the routing table, EIGRP divides the wide-metric value by the EIGRP_RIB_SCALE value, which defaults to 128, as you will see next in the output for the show ip protocols command. The value 2048000 divided by 128 is 16000.

Note: A network with mixed EIGRP implementations (Named and Classic in the same routing domain), will have some loss of route clarity which could lead to sub-optimal path selection. The recommended implementation is to use Named EIGRP in all cases.

• There are no feasible successors listed in the topology table for 192.168.3.0/24 or 10.0.23.0/24. The feasibility condition requires that the reported distance (RD) to a destination network be less than the current feasible distance for a next-hop to be considered a feasible successor to the route. In the case of 10.0.23.0/24, the RD of the path via 172.16.1.2 is the second number listed: (2621440/1966080). Because the RD is equal to the current FD, this route is disqualified as a feasible successor. If the path via 172.16.1.2 were to be lost, R1 would have to send queries to find a new way to get to 10.0.23.0/24. Feasible successors only exist in the topology table. Only successors appear in the routing table.

e. To see the Routing Information Base (RIB) Scale and Metric Scale values, as well as other protocol information, issue the show ip protocols | section eigrp command.

f. To examine details about a particular path, issue the show ip eigrp topology [address] command.