i am a student , i have three 2500 series router , serial connected r1 - r2 - r3 , and each router has three lan associated with each routers , i enabled both rip and igrp , then the routing table showed igrp router since the ad is low with rip , if i change the ad of igrp to 140 , then also igrp routes r shown , whats its cause , pls give me the exact command , thanks in advance