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Configuration Notes for the Implementation of EIGRP over Frame Relay and Low Speed Links
Document ID: 13672
Introduction Prerequisites Requirements Components Used Conventions Bandwidth Control Configuration Commands Configuration Problems Configuration Guidelines LAN Interfaces (Ethernet, Token Ring, FDDI) Point−to−Point Serial Interfaces (HDLC, PPP) NBMA Interfaces (Frame Relay, X.25, ATM)Pure Multipoint Configuration (No Subinterfaces) Pure Point−to−Point Configuration (Each VC on a Separate Subinterface) Hybrid Configuration (Point−to−Point and Multipoint Subinterfaces) Examples Oversubscribed Hub−and−Spoke Frame Relay Configuration (Subinterfaces) Full−mesh Frame Relay Configuration with Differing Access Line Speeds Related Information

Introduction
Enhanced Interior GatewayProtocol (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 existingconfigurations 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 entirenetwork is upgraded.

Prerequisites
Requirements
Readers of this document should have the basic understanding of: • EIGRP • Frame Relay

Components Used
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.

Conventions
For more information on document conventions, refer to Cisco Technical Tips Conventions.

Bandwidth Control
The enhanced implementation uses the configured interface bandwidth in order to determine how much EIGRP data to transmit in a givenamount 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 PVCcapacity 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.

Configuration Commands
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: • ipbandwidth−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 forpolicy reasons. The bandwidth−percent command can have values greater than 100 if the bandwidth is configured artificially low due to such policy reasons. For example, the following 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

This configuration allows IPX−EIGRP AS 210 to use 256Kbps (200%...