EIGRP Practical Training in CCNA / CCNP

CCNA CCNP Practical Training in EIGRP

Objective

To evaluate the behavioral aspect of EIGRP peers by making them form neighbors, redistributing subnets and then by supplying duplicate router-id in the routers.

 Introduction/ Prerequisite

Enhanced Interior Gateway Protocol (EIGRP) is layer 3 protocol. It was initially CISCO proprietary, later it became a standard protocol. Its protocol number is 88. Its maximum hop count limit is 255 and its kept 100 by default. This is a very important topic of CCNA and CCNP which are very important networking training in current IT industry.

It is a classless routing protocol, supports VSLM and discontinuous networks by sending subnet mask information as part of a route advertisement. By default, summarization is enabled by default which can be removed by “no auto-summary command” in global configuration mode of “router EIGRP asn number” command
EIGRP is known to be an advance distance vector. It advertises routes and learns routes from the directly attached neighbors like a distance vector routing protocol (like RIP).It uses hello protocol to discover neighbors and forms neighbor relationships similar to a link-state routing protocol (like OSPF). Like link-state protocol, it only sent partial updates when a change occurs and not periodic updates. Hence it combines features of both distance vector and link state routing protocol hence it is called a hybrid protocol.

Configuration

Tasks

  • Create IP addresses on the routers as given in the configuration plus a loopback 2.2.2.2/24 on R1
  • Full reachability should be established by deploying EIGRP
  • Redistribute R1 subnet so that it can be seen as an external prefix in other router’s routing table
  • By default as there is no router-id configured on R1 and 2.2.2.2 being the loopback address on R1, router-id on R1 will be 2.2.2.2. Configure the same router-id as 2.2.2.2 on R3 and check routing changes.

Steps

  • On R1, Create a loopback 2.2.2.2.1/24, redistribute it in the EIGRP router command. Also, advertise interface IP address of 12 networks under router EIGRP command.

By configuring Loopback IP address 2.2.2.2/24, R1 takes it as router-id by default as can be seen below

  • For the rest of the routers( R2 and R3), advertise the networks in the router eigrp global mode. You will see the loopback of R1 being advertised as an external EIGRP prefix in the show IP routing table.

  • Apply the router-id as 2.2.2.2 (same of R1) manually on Router 3 using router-id command and check the same using show EIGRP 1 topology 1 command.

  • Due to the duplicate router-id of R1 and R3, we can see R1 external prefix not being advertised. Hence now R1 external prefix 2.2.2.2 is not advertised anymore.

Observation

If EIGRP sees duplicate router id’s then it will not install the external prefix in its routing table but duplicate router-id can still form neighbors. It will just install the internal prefixes. When the exact whole same configuration was done under “Router OSPF” global configuration, it was seen that with duplicate router-id neighbor-ship between peers were not even formed at all.

Verification Commands

“show ip eigrp 1 topology 1” to check router-id.

“do show ip eigrp neighbors” to see check neighbors

“do show ip route” to see routing table

“do show ip eigrp topology” to see topology table

Conclusion

EIGRP router-id can be same for forming neighborships unless external redistribute routes are injected. For OSPF router’s id cant be same for two routers as the router-id uniquely defines router to all other routers in the network.

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