IP Routing

EIGRP Metric

The EIGRP composite metric is computed exactly as the IGRP metric is and then multiplied by 256. Thus, the default expression for the EIGRP composite metric is:

Metric = [BandW +Delay]x 256

where BandW and Delay are computed exactly as for IGRP (see Section 3.2.2 in Chapter 3). In summary, BandW is computed by taking the smallest bandwidth (expressed in kbits/s) from all outgoing interfaces to the destination (including the destination) and dividing 10,000,000 by this number (the smallest bandwidth), and Delay is the sum of all the delay values to the destination network (expressed in tens of microseconds).

Further, note that the total delay (line 6), minimum bandwidth (line 6), reliability (line 7), minimum MTU (line 7), and load (line 8) for a path, which are used to compute the composite metric (line 5), are shown as output of the show ip route destination-network-number command:

   NewYork#sh ip route 172.16.50.0
   Routing entry for 172.16.50.0 255.255.255.0
     Known via "eigrp 10", distance 90, metric 2195456, type internal
     Redistributing via eigrp 10
     Last update from 172.16.250.2 on Serial0, 00:00:21 ago
     Routing Descriptor Blocks:
     * 172.16.50.0, from 172.16.250.2, 00:00:21 ago, via Serial0
5        Route metric is 2195456, traffic share count is 1
6        Total delay is 21000 microseconds, minimum bandwidth is 1544 Kbit 
7        Reliability 255/255, minimum MTU 1500 bytes
8        Loading 1/255, Hops 1

Converting route metrics between EIGRP and IGRP is very straightforward: EIGRP metrics are 256 times larger than IGRP metrics. This easy conversion becomes important when a network is running both IGRP and EIGRP, such as during a migration from IGRP to EIGRP.

Just like IGRP, EIGRP can be made to use load and reliability in its metric by modifying the parameters k1, k2, k3, k4, and k5 (see Section 3.2.2 in Chapter 3).

The constants k1, k2, k3, k4, and k5 can be modified with the following command:

metric weights tos k1 k2 k3 k4 k5

Warning

Cisco strongly recommends not modifying the k1, k2, k3, k4, and k5 values for EIGRP.