EIGRP-Enhanced Interior Gateway Routing Protocol

What is EIGRP

Enhanced Interior Gateway Routing Protocol
Hybrid or Advanced distance vector protocol
Cisco Proprietary protocol.
It’s metric is based Bandwidth, Delay, Load. Reliability and MTU, which are normally referred as K-Values.
Among these K- values, we only use Bandwidth and delay which are enabled by default.
So, we can simply say it as Metric is based on Bandwidth and Delay only.
EIGRP supports only MD5 Authentication
EIGRP can do Equal and Unequal Load-Balancing.
Metric = bandwidth (slowest link) + delay (sum of delays)
AD Value:

EIGRP TABLES:

EIGRP form neighbors by sending hello packets.
Once Hello packed are matched at both routers, they form neighbor-ship and the information will be stored in EIGRP Neighbor Table
Routes from the Neighbor table is sent to the Topology Table.
Routes from Topology Table are filtered and moved to the Routing Table.

Advertise Distance and Feasible Distance:

Consider the above Example:

There are Two main terms : Advertised distance and Feasible distance.

Next two important terms are Successor and Feasible Successor.

Successor : Best Route from the Successor is copied to the Routing table.
Feasible Successor : The Backup of the Successor is said to be Feasible Successor.

But there is a criteria to be satisfied in a network to have Feasible Successor.

Feasible distance of the Successor > Advertise distance of the Feasible Successor

If you look at a above table, you can see the Router-2 as Successor with the Feasible distance of 25.
Then what about a Feasible successor, you can see that the feasible successor is Router-3, and not Router-1.
The reason behind this is that the Successor is Router-2 which has a Feasible distance of 25 and the Feasible Successor should have a Advertise distance to be less than the Feasible distance of the Successor.

EIGRP Commands

Router-1#show ip eigrp neighbors

It provides neighbor IP Address, Local Interface to which the Neighbor is connected and uptime.

Router-1#show ip eigrp topology

It provides all the available path to reach the destination through EIGRP
Feasible distance , Advertise distance and Local Interface information also provided.

Router-1#show ip route eigrp

It provides the best route to reach the destination
The information provided are AD value, Network segment, next-hop, local interface connected to next-hop.

Unequal Load Balancing

Unequal Load Balancing can be done only in EIGRP.
It can be done using Variance command.
Variance command acts like a Multiplier.
By using this command, we can accomplish, two routes in this the routing table. For a same destination with different

That's it about EIGRP

PGR Spot