Routing TCP[s]IP (Vol. 11998)

The difficulty with the internetwork of Figure 11.37, when running classful routing protocols on RTB, is that network 172.16.0.0 is variably subnetted. The solution is to use a 28-bit mask on RTB's E1 interface while RTC still uses a 27-bit mask for the same subnet. This solution works because 172.16.1.96 remains distinct in the internetwork of Figure 11.37, whether it is subnetted with a 27-bit mask or a 28-bit mask.

RTB's configuration is:

interfaceEthernet0 ipaddress172.16.1.146255.255.255.240 ! interfaceEthernet1 ipaddress172.16.1.98255.255.255.240 ! routerrip redistributeigrp1metric1 passive-interfaceEthernet0 network172.16.0.0 ! routerigrp1 redistributeripmetric10000100025511500 passive-interfaceEthernet1 network172.16.0.0

This configuration changes RTB's E1 mask back to a 27-bit mask. However, RIP does not advertise subnet 172.16.1.144/28. To remedy this problem, a static route is entered to that subnet but with a 27-bit mask. Because the mask references RTB's E0 interface, it is redistributed into RIP automatically.

interfaceEthernet0 ipaddress172.16.1.146255.255.255.240 ! interfaceEthernet1 ipaddress172.16.1.98255.255.255.224 ! routerospf1 redistributeripmetric50subnets network172.16.1.00.0.0.255area0 ! routerrip redistributeospf1metric2 passive-interfaceEthernet0 network172.16.0.0 ! ipclassless iproute172.16.1.128255.255.255.224Ethernet0

RTB's configuration is:

interfaceEthernet0 ipaddress172.16.1.146255.255.255.240 ipsummary-addresseigrp1172.16.2.0255.255.255.0 ! interfaceEthernet1 ipaddress172.16.1.98255.255.255.224 ! routereigrp1 redistributeisislevel-2metric10000100025511500 passive-interfaceEthernet1 network172.16.0.0 ! routerisis net00.0000.1234.abc1.00 summary-address172.16.1.128255.255.255.128 redistributeeigrp1metric20metric-typeexternallevel-2