Static Routing and Distance Vector Routing Protocols - CCIE Routing and Switching Exam Certification Guide - page 347

The composite metric is calculated with the following formula:

EIGRP metric = {k1 × BW + [(k2 × BW)/(256 - load)] + k3 × delay} × {k5/(reliability + k4)}

In this formula, BW is the lowest interface bandwidth in the path, and delay is the sum of all
outbound interface delays in the path. Reliability and load are measured dynamically by the
router. A 100 percent reliability is expressed as 255/255. Load is expressed as a fraction of 255.
An interface with no load is represented as 1/255.

Bandwidth is inverse minimum bandwidth (in kbps) of the path in bits per second, which is
scaled by a factor of 256 10 7 . ×

10 7 )/BW min.
Delay is the sum of the outgoing interface delays (in microseconds) to the destination. A delay
of all 1s (that is, a delay of hexadecimal FFFFFFFF) indicates that the network is unreachable.

The formula for bandwidth is as follows: (256 ×

The formula for delay is as follows: [sum of delays] × 256.

Reliability is specified as a fraction of 255. That is, 255/255 is 100 percent reliability or a
perfectly stable link. A value of 229/255 represents 90 percent reliability.

Load is specified as a fraction of 255. A load of 255/255 indicates a completely saturated link.
A load of 127/255 represents a 50 percent saturated link.

By default, k1=k3=1 and k2=k4=k5=0. The default composite metric for EIGRP, adjusted for
scaling factors, is as follows:

{ [10 7 /BW min ] + [sum_of_delays] }
BW min is in kbps and the sum of delays are in 10s of microseconds. The bandwidth and delay
for an Ethernet interface are 10 Mbps and 1ms, respectively.

EIGRP metric = 256 ×

The calculated EIGRP BW metric is as follows:

10 7 /BW = 256 10 7 /10,000 256 × ×

= 256 10000

= 256000

×

The calculated EIGRP delay metric is as follows:

256 × sum of delay = 256 × 1ms

= 256 10 microseconds

= 25600 (in tens of microseconds)

× 100 ×