In order to prevent Enhanced Interior Gateway Routing Protocol (EIGRP) updates from overwhelming the interface, Cisco IOS Software provides control over how much bandwidth it can consume on the physical interface.
By default, EIGRP limits itself to using no more than 50 percent of the interface bandwidth.
Although, this is not very significant on high speeds like Ethernet, it becomes critical on low speed links, especially on Nonbroadcast Multiaccess Address (NBMA) networks like Frame Relay.
The access interface bandwidth and the Permanent Virtual Connection (PVC) capacity may be very different.
A secondary benefit is that it allows the network administrator to ensure that some bandwidth remains for passing user data, even when EIGRP is very busy.
You must consider the three important rules while configuring the EIGRP bandwidth percentage on the NBMA interfaces.
If these rules are not followed, EIGRP or the data packets can be lost.
These are the critcal rules:
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The traffic that EIGRP is allowed to send on a single Virtual Circuit (VC) cannot exceed the capacity of that VC. |
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The total EIGRP traffic for all virtual circuits cannot exceed the access line speed of the interface. |
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The bandwidth allowed for EIGRP on each Virtual Circuit must be the same in each direction. |
Issue the bandwidth-percent
command.This tells EIGRP what percentage of the configured bandwidth it may use.
The default is 50 percent.
Since the bandwidth command is also used to set the routing protocol metric, it may be set to a particular value to influence route selection for policy reasons.
The bandwidth-percent command can have values greater than 100 if the bandwidth is configured artificially low for policy reasons.
For example, this configuration allows IP-EIGRP AS 109 to use 42Kbps (75% of 56Kbps) on Serial 0:
| interface Serial 0 bandwidth 56 ip bandwidth-percent eigrp 109 75 |
For more information and examples of how to configure EIGRP bandwidth percentage over NBMA networks like Frame Relay you may wish to refer to:
Cisco NBMA Interfaces (Frame Relay, X.25, ATM)
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