Enhanced Interior Gateway Protocol (EIGRP) was significantly enhanced in Cisco IOS® Software releases 10.3(11), 11.0(8), 11.1(3) and later. The implementation was changed to have more control over the amount of bandwidth utilized by EIGRP and improve the performance on low-speed networks (including Frame Relay) and in configurations with many neighbors.
For the most part, the changes are transparent. Most existing configurations should continue to operate as before. However, in order to take advantage of the improvements for low speed links and Frame Relay networks, it is important to properly configure the bandwidth on each interface on which EIGRP is running.
Although the enhanced implementation will interoperate with the earlier version, the full benefits of the enhancements may not be realized until the entire network is upgraded.
Readers of this document should have the basic understanding of:
- Frame Relay
This document is not restricted to specific software and hardware versions.
The information presented in this document was created from devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If you are working in a live network, ensure that you understand the potential impact of any command before using it.
For more information on document conventions, refer to Cisco Technical Tips Conventions.
The enhanced implementation uses the configured interface bandwidth in order to determine how much EIGRP data to transmit in a given amount of time. By default, EIGRP will limit itself to using no more than 50% of the interface bandwidth. The primary benefit of controlling EIGRP’s bandwidth usage is to avoid losing EIGRP packets, which could occur when EIGRP generates data faster than the interface line can absorb it. This is of particular benefit on Frame Relay networks, where the access interface bandwidth and the PVC capacity may be very different. A secondary benefit is to allow the network administrator to ensure that some bandwidth remains for passing user data, even when EIGRP is very busy.
The amount of bandwidth is controlled by two interface subcommands:
- router-number percent
- bandwidth nnn
and one of the following for IP, AppleTalk, and IPX EIGRP, respectively:
- ip bandwidth-percent eigrp as-number percent
- appletalk eigrp-bandwidth-percent as-number percent
- ipx bandwidth-percent eigrp as-number percent
The bandwidth-percent command 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 due to such policy reasons.Read more…