EIGRP

EIGRP Summary

The characteristics of EIGRP follow:

 Hybrid routing protocol (distance vector that has link-state protocol characteristics).

 Use DUAL, first proposed by E. W. Dijkstra and C. S. Scholten, to perform distributed shortest-path routing while maintaining freedom from loops at every instant. Although many researchers have contributed to the development of DUAL, the most prominent work is that of J. J. Garcia-Luna-Aceves.

 Cisco Proprietary created in 1994.

 First released in IOS 9.21

 Uses IP protocol 88.

 Makes Automatic summarization on network Class boundary.

 Classless protocol (supports VLSM).

 Have the power to shut the Auto-summarization And make a configured manual Summarization.

 Default composite metric of bandwidth and delay.

 You can factor load, MTU and reliability into the metric.

 Eigrp metric is the same as IGRP*256, It uses the smallest B.W,Reliablity,Load & MTU with the Comulative delay upon the path…..The MTU doesn’t actually used in the Metric calculations, 
        But is included in the EIGRP Routing updates.

 Sends route updates to multicast address 224.0.0.10, and nei. Reply’s back with   Unicast Address.  

 Sends non-periodic, partial, and bounded updates.

 Send Hello packets every 5 sec. and Hold down timer is 15 sec. 

 For Low speed Hello is every 60 sec. with hold down time 180 sec. 

 By default, EIGRP uses no more than 50 percent of the bandwidth of a link.

 Support for authentication via MD5 Only.

 Uses DUAL for loop prevention, and generating Succ./Fesible Succ.

 Maximum paths for Load-balancing are 6  & default is 4 , maximum are 16 in IOS 12.3(2)T and later IOS releases

 By default, Equal-Metric load balancing. If Unequal-Metric load sharing is used the router will load share inversely proportional to the metrics of the paths.  

 Administrative distance is 90 for EIGRP internal routes, 170 for EIGRP external routes, and 5 for EIGRP summary routes.

 Potential routing protocol for the core of a network; used in large networks.

 For neighbor relation to be established, both routers must send and receive Hello or Ack packets from each other, they must have the same AS #, and the same Metric K values.

 Eigrp doesn’t restrict that neighbors must have the same Hello & dead interval timers, Unlike OSPF.

 Has a Maximum hop count of 255, the default is 100 in the last IOS releases.      



           The composite metric for each EIGRP route is calculated as

EIGRP metric = IGRP metric  * 256 
    IGRP  metric = [k1*BWIGRP(min) + (k2* BWIGRP(min))/(256-LOAD) + k3*DLYIGRP(sum)]
                              x [k5/(RELIABILITY + k4)]

If k5 is set to zero, the [k5/(RELIABILITY+k4)] term is not used.

Given the default values for k1 through k5, the composite metric calculation used by EIGRP reduces to the default metric:

IGRP metric = BWIGRP(min) + DLYIGRP(sum)
BWIGRP(min) = 107/BW(min)
DLYIGRP(sum) = DLY(sum) /10