EIGRP Bandwidth Configuration

Enhanced Interior Gateway Routing Protocol (EIGRP) is a Cisco proprietary classless routing protocol that uses a complex metric based on bandwidth and delay.

By default, EIGRP limits itself to bursting to half the link bandwidth.

This limit is configurable per interface using the ip bandwidth-percent command. The following example assumes EIGRP AS 7 and limits

EIGRP to one quarter of the link bandwidth:

Router(config)#int s0/0/0

Router(config-if)#ip bandwidth-percent eigrp 7 25

The real issue with WAN links is that the router assumes that each link has 1544 kbps bandwidth. If interface Serial0/0/0 is attached to a 128k fractional T1, EIGRP assumes it can burst to 768k and could overwhelm the line. This is rectified by correctly identifying link bandwidth.

Router (config)#int serial 0/0/0

Router (config-if)#bandwidth 128

The following shows a situation in which these techniques can be combined.

In this example, R1 has a 256 kbps connection to the Frame Relay network and two permanent virtual circuits (PVCs) with committed information rates (CIR) of 128 Kpbs and 64 Kbps. EIGRP divides the interface bandwidth evenly between the number of neighbors on that interface. What value should be used for the interface bandwidth in this case? The usual suggestion is to use the CIR, but the two PVCs have different CIRs. You could use the bandwidth-percent command to allow SNMP reporting of the true bandwidth value, while adjusting the interface burst rate to 25 percent, or 64 kbps.

R1(config)#int serial 0/0/0

R1 (config-if)#bandwidth 256

R1 (config-if)#ip bandwidth-percent eigrp 7 25

A better solution is to use sub-interfaces and identify bandwidth separately.

In the following example, s0/0/0.1 bursts to 64 k, and s0/0/0.2 bursts to 32 k, using EIGRP’s default value of half the bandwidth.

R1(config)#int serial 0/0/0.1

R1 (config-if)#bandwidth 128

!

R1(config)#int serial 0/0/0.2

R1 (config-if)#bandwidth 64

In cases where the hub interface bandwidth is oversubscribed, it may be necessary to set bandwidth for each sub-interface arbitrarily low, and then specify an EIGRP bandwidth percent value over 100 in order to allow EIGRP to use half the PVC bandwidth.