By default EIGRP limits itself to using no more than 50% of the interface bandwidth. Although, this is not very significance on high speeds like on Ethernet, it becomes critical on low speed links, especially on Nonbroadcast Multiaccess Address (NBMA) networks like Frame Relay.
If the interface bandwidth configuration cannot be changed because of routing policy considerations, or for any other reason, the bandwidth-percent command should be used to control the EIGRP bandwidth. On low-speed interfaces, raising the available bandwidth for EIGRP above the default of 50 percent is advisable in order to improve convergence.
For example, this configuration allows IP-EIGRP AS 100 to use 40Kbps (70% of 56Kbps) on Serial 0:
interface Serial 0
ip bandwidth-percent eigrp 100 70