IT Certification

What’s a EIGRP? It’s an important CCNA LAB. If you want to pass the CCNA certification, you must understand it.

Let’s look back the EIGRP knowledge:

* EIGRP is the Enhanced Interior Gateway Routing Protocol.
    * EIGRP is a Cisco proprietary routing protocol based on their original Interior Gateway Routing Protocol. EIGRP can only be used on networks where all routers are Cisco routers.
    * The administrative distance for EIGRP is 90 and 170 for internal and external EIGRP, respectively.

What features does EIGRP offer?

    * Automatic redistribution of routes between IGRP and EIGRP.
    * Ability to turn off and on EIGRP and IGRP on individual interfaces of the router.
    * Fast network convergence thanks to EIGRP’s DUAL algorithm (convergence is when all routers know about all the networks that every other router is offering).
    * Incremental Updates that save network bandwidth and speed convergence.
    * Reduced router CPU load, as compared to IGRP.
    * EIGRP uses neighbor discovery to find and keep track of neighboring routers. Neighbor discovery uses multicast IP and is not tied to whether or not the the IP network is properly configured.
    * EIGRP prevents routing loops on the network
    * Supports variable length subnet masks (VLSM)
    * Automatic Route Summarization

Now let us correct a EIGRP question:

Access to the router CLI can be gained by clicking on the appropriate host. All passwords on all routers are cisco.

IP addresses are listed in the chart below.

Answer and explanation:
We should check the configuration of the new added router first because it does not function properly while others work well. From the command line interface of R3 router, enter the show running-config command

From the output above, we know that this router was wrongly configured with an autonomous number (AS) of 22. When the AS numbers among routers are mismatched, no adjacency is formed.
(You should check the AS numbers on other routers for sure)

To solve this problem, we simply re-configure router R3 with the following commands:

R3>enable (you have to enter cisco as its password here)
R3#configure terminal
R3(config)#no router eigrp 22
R3(config)#router eigrp 212
R3(config-router)#network 192.168.60.0
R3(config-router)#network 192.168.77.0
R3(config-router)#no auto-summary
R3(config-router)#end
R3#copy running-config startup-config

Check R1 router with the show running-config command:

Notice that it is missing a definition to the network R3. Therefore we have to add it so that it can recognize R3 router

R1>enable (you have to enter cisco as its password here)
R1#configure terminal
R1(config)#router eigrp 212
R1(config-router)#network 192.168.77.0
R1(config-router)#end
R1#copy running-config startup-config

Now the whole network will work well. You should check again with ping command from router R3 to other routers!