EIGRP is an enhanced hybrid routing protocol that is used to dynamically route traffic in large, complex networks. It uses a composite metric based on bandwidth, delay, reliability and load to calculate the best route and store them in the topology and routing tables. The Diffusion Update Algorithm is used for fast convergence by storing feasible successors as backup routes to quickly respond when the primary route fails.

1. EIGRP
ENHANCED INTERIOR GATWAY PROTOCOL
1

2. OBJECTIVES:
 Describe the background and history of Enhanced Interior
Gateway Routing Protocol (EIGRP).
 Define EIGRP Terminology.
 explain control packets in EIGRP
 Calculate the composite metric used by EIGRP.
 Describe the concepts and operation of DUAL.
2

3. EIGRP
 It is an enhancement of IGRP.
 Hybrid routing protocol (distance vector + link-state)
 Developed in 1985 to overcome RIPv1’s limited hop count.
 Was an cisco proprietary routing protocol till 2013, now open standard.
 Classless protocol.
 Symbol in routing table is ‘D’.
 Administrative distance = 90.
 Fast convergence : use DUAL.
 METRIC is determined by (B.W, delay, load, and reliability).
 Max hop count = 224.
 Support multiple network layer protocol ( IP, IPX, AppleTalk).
 Uses multicast address 224.0.0.10
3

4. EIGRP TERMINOLOGY
 Neighbor table:-
table contain all neighbors.
 Topology table:-
table contain all routes to all networks.
 Routing table:-
table contain the best route to all networks.
 Successor:-
best route.
 Feasible successor:-
backup for best route.
4

5. control packets in EIGRP
 Hello packet:–
used to discover & form adjacencies with neighbors, UDP, Multicast.
 Query packet:-
ask neighbors about routing information, TCP, Unicast/ Multicast.
 Update packet:-
send routing update, TCP, Unicast/ Multicast.
 Reply packet:-
respond to the query packet, TCP, Unicast.
 Acknowledgment packet:-
used to acknowledge receipt of update, query & reply packets , UDP,
Unicast.
5

6. METRIC
 Composite metric
 metric = [ K1 * bandwidth + (K2 * bandwidth)/256 - load) + K3 * delay] * [
K5/(reliability + K4)]
 It don’t consider single criteria to calculate the metric but uses numbers
of criteria which includes bandwidth, load, delay, reliability, and maximum
transfer unit (MTU).
 K value for B.W and delay by default equal to 1, and other values of k is
zero.
 metric = [ K1 * bandwidth + K3 * delay]
6

7. DIFFUSION UPDATE ALGORITHM(DUAL)
 This algorithm stores neighbor’s routing information in a local
topology table.
 If a primary route in the routing table fails, Dual can take a backup
path from the topology table and place it in the routing table.
 If no backup route is found in the topology table, it will generate a
query packet sent to the neighbor.
7