EIGRP (ENHANCED INTERIOR GATEWAY ROUTING PROTOCOL)

1.   Advanced distance vector routing protocol.

2.   Interior gateway protocol.

3.   Uses DUAL (Diffusing Update Algorithm) algorithm. It ensures loop free network.

4.   Supports only MD5 authentication.

5.   Administrative distance:

·     Summary route = 5

·     Internal route = 90

·     External route = 170

6.   Metric: uses composite metrics

·     Bandwidth = 1(default)

·     Load = 0

·     Delay = 1(default)

·     Reliability = 0

·     MTU = 0(never takes part in metric calculation)

7.   Only protocol to support backup path.

8.   Uses concept of Autonomous System number. (0-65535)

9.   Default hop count 100. Max supported hop count 255.

10.                Maximum paths supported for load balancing 32, default 4.

11.                 Route from one AS can’t cross its boundary.

12.                 EIGRP IP protocol number is 88.

13.                 EIGRP works at network layer of OSI model.

14.                 Classless routing protocol.

15.                 Performs unequal cost load balancing.

16.                 EIGRP is a routing loop free protocol.

17.                  In DVRP, router only passes best path information to neighboring router.

18.                 EIGRP Timers:

·     Hello timer: 5 secs.

·     Hold timer: 15secs.

·     Active timer: 180secs

19.                 EIGRP Packets:

·     Hello packet: In every 5 secs. Discover the neighbor, form neighbor ship and as a keep alive check. Also called as unreliable hello packets because no ack being sent by receiver.

·     Update packet: send triggered/incremental update at 224.0.0.10 (multicast).

·     Acknowledgement packet: It is basically an EIGRP hello packet containing no data. For every successful delivery, there will be an ack sent through RTP (Reliable Transport Protocol). Maximum retransmission of update packet will be only for 16 times. Always sent to a unicast address.

·     Query Request packet: When best path goes down, query request will be send to neighbor router to search for backup/alternate path.

·     Query reply packet: For every query request, there will be a query reply packet. There will be ack for every successful query request packet. Within 180secs, query reply must be sent. But after 90 secs, a reminder is sent to neighbor router reminding about status of query request packet.

20.                 If an EIGRP router is actively searching for alternate path, then it is said to be in active state. And, if it gets stuck in this state, then it is known as Stuck in Active (SIA) state. In this case, neighbor ship will be refreshed.

21.                 If everything is ok i.e. router is not searching for any backup path, then it is said to be in passive state.

22.                 Reliable Transport Protocol is responsible for sending acknowledgement in EIGRP.

23.                 EIGRP Tables:

·     Neighbor Table: contains neighbor information and directly connected networks.

·     Topology table: contains best and backup path information.

·     Routing table: contains only best path information.

24.                 Neighbor ship conditions:

·     Network must match.

·     Authentication must match.

·     AS number must match.

·     K-value must match.

·     If you have manually defined static neighbor at one end, then it must be defined at both ends.

25.                 EIGRP Router ID: Unique identification of EIGRP router in a network. There are multiple ways to define router id.

·     Manually configure (most effective)

·     Highest loopback IP (2^nd most effective )

·     Highest IP on any physical interface (3^rd )

26.                EIGRP Modes:

·     Named mode- new method.

·     Classic mode-old method.

v Configuration commands

·     To  enable EIGRP on a router for a network:

Router(config)#router eigrp AS no

Router(config-router)#network a.b.c.d subnet mask/wildcard bits

·     To check routing table:

Router#show ip route

·     To check topology  table:

Router#show ip eigrp topology

·     To check neighbor  table:

Router#show ip eigrp neighbors

·     To clear eigrp neighbor ship:

Router#clear ip eigrp neighbors

·     To debug eigrp packets:

Router#debug eigrp packets

·     To check current running protocol on router:

Router#show ip protocols

·     To check in detail information of a route in topology table:

Route#show ip eigrp topology 1.0.0.0/8

·     To check in detail information of a route in routing table:

Route#show ip route 1.0.0.0/8

·     To change administrative distance:

Router(config)#router eigrp AS no

Router(config-router)#distance eigrp (internal routes) (external routes)

·     To change router-id of an eigrp router:

Router(config)#router eigrp AS no

Router(config-router)#eigrp router-id 100.0.0.1

·     To change maximum-paths for load balancing:

Router(config)#router eigrp AS no

Router(config-router)#maximum-paths 32

·     To change metric values:

Router(config)#router eigrp AS no

Router(config-router)#metric weights 0 (K1) (K2) (K3) (K4) (K5)

·     To change maximum hop count:

Router(config)#router eigrp AS no

Router(config-router)#metric maximum-hops 255

·      To statically define a neighbor:

Router(config)#router eigrp AS no

Router(config-router)#neighbor 12.0.0.1 fastEthernet 0/0

·     To make an interface as passive:

Router(config)#router eigrp AS no

Router(config-router)#passive-interface  fastEthernet 0/0

·     To make backup path as best path for load balancing:

Router(config)#router eigrp AS no

Router(config-router)#variance (multiplier)

·     To change eigrp timers:

Router(config)#interface fastEthernet 0/0

Router(config-if)#ip hello-interval eigrp AS no (value)

Router(config-if)#ip hold-time eigrp AS no (value)

·     To populate default route information to all routers:

Router(config)#router eigrp AS no

Router(config-router)#redistribute static