31 Days Before Your CCNA Exam

220 31 Days Before Your CCNA ExamFigure 13-4Calculating the EIGRP Default MetricDefault metric = [K1*bandwidth + K3*delay] * 256Because both K1 and K3 equal 1, the formula simplifies to: bandwidth + delaybandwidth = speed of slowest link in route to the destinationdelay = sum of delays of each link in route to the destinationSlowest bandwidth:(10,000,000/bandwidth kbps) * 256Plus the sum of the delays: + (sum of delay/10) * 256= EIGRP metricR2#show ip routeD 192.168.1.0/24 [90/3014400] via 192.168.10.10, 00:02:14, Serial0/0/1Because the bandwidth might default to a value that does not reflect the actual value, you can usethe interface command bandwidth to modify the bandwidth metric:Router(config-if)#bandwidth kilobitsIn the topology shown in Figure 13-3, notice that the link between R1 and R2 has a bandwidth of64 kbps, and the link between R2 and R3 has a bandwidth of 1024 kbps. Example 13-11 shows theconfigurations used on all three routers to modify the bandwidth.Example 13-11 Modifying the BandwidthR1(config)#interface serial 0/0/0R1(config-if)#bandwidth 64R2(config)#interface serial 0/0/0R2(config-if)#bandwidth 64R2(config-if)#interface serial 0/0/1R2(config-if)#bandwidth 1024R3(config)#interface serial 0/0/1R3(config-if)#bandwidth 1024Modifying Hello Intervals and Hold TimesHello intervals and hold times are configurable on a per-interface basis and do not have to matchwith other EIGRP routers to establish adjacencies. The syntax for the command to modify thehello interval is as follows:Router(config-if)#ip hello-interval eigrp as-number secondsIf you change the hello interval, make sure that you also change the hold time to a value equal toor greater than the hello interval. Otherwise, neighbor adjacency will go down after the hold timeexpires and before the next hello interval. The command to configure a different hold time is asfollows:Router(config-if)#ip hold-time eigrp as-number seconds