My Experiences on learning Routing Protocols

EIGRP Routing

The Precursor - IGRP

The Interior Gateway Routing Protocol was developed by Cisco in 1980s as a competitor to RIP (Routing Information Protocol ) .

The Interior Gateway Routing Protocol has the following features :

1) It is a Distance Vector Routing Protocol , in fact it was one of the world's first distance vector routing protocol.

2) It is Broadcast based.

3) It was developed as a competitor to RIP.

4) Utilizes link Bandwidth and Delay as Routing protocol metrics with Load and Reliability  as optional metrics for the routing protocol . (15 hops is no longer the limit)

5) It has 90 second updates .

6) It has load balancing over unequal cost paths.

IGRP metrics calculation to determine the cost of each link is done by the following formula

where K1 =1 , K2 = 0 , K3 = 1 , K4=K5=0

The default metric for IGRP is Bandwidth and Delay 

Bandwidth used for the calculation is the lowest bandwidth of the link along the path 

Delay is the sum of all the delays of the link along the paths

When you observe the values of K2, K4 and K5 , all of them show a value of 0 by default  , therefore only Bandwidth and Delay as taken as default metrics.

If we want to take in Load and Reliability as factors we need to set the values of K2, K4 and K5 to something other than 0

Problems common to RIP and IGRP 

1) Does not support VLSM and discontigious networks

2) Periodic full routing updates 

EIGRP Introduction

EIGRP Advantages:

1) Advanced Distance Vector protocol .

2) 100% Loop Free.

3) Faster Convergence .

4) Less Network Constraints than OSPF

5) Incremental Updates

6) Supports VLSM and discontigious networks

7) Classless Routing 

8)Compatible with existing IGRP

9)Uses multicast instead of broadcast for routing updates (RIP and IGRP use broadcast)

10) Utilizes link bandwidth and delay 

EIGRP Metric = IGRP Metric x 256

11) Unequal cost paths load balancing

12) More flexible than OSPF.

EIGRP Packet Types

1) Hello Packet - Establish neighbour relationship . This contains the basic K values, hold timers, Autonomous system numbers etc , basically all the values required for establishing neighbour relation

2) Update packet - Send routing updates in case of routing changes .

3) Query packet  When EIGRP looses a route , EIGRP has the capability to find out another route by querying its neighbors . This is done via query packet.

4) Reply  packet - Response to a query packet 

5) Acknowledgement packet - Acknowledgement of a reliable packet (Protocol number 88)

[Note - EIGRP does not use TCP or UDP to send out Acknowledgement packets ,  it  makes use of its own protocol as defined by protocol number 88]