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.The command is the router configuration command version 2.We will type this command on each router; since the command sequence is identical on all of the routers, only one is shown.Figure 7-35 shows the configuration of RIPv2 on Dallas.Dallas#configure terminalEnter configuration commands, one per line.End with CNTL/Z.Dallas(config)#router ripDallas(config-router)#version 2Dallas(config-router)#<Ctrl-Z>Dallas#<<<Figure 7-35 RIP Version 2 Configuration on Dallas>>>Typing the sequence of commands on each of our test routers converts them from running RIPv1 to RIPv2.Since we are configuring the RIP process, we must identify it with the router rip command (Line 3).The version 2 command (Line 4) tells IOS that it is to use version 2 on all of the interfaces that currently have RIP enabled unless we explicitly change the version on the interface itself.This command is added to the network commands that we entered when we configured RIPv1 in the preceding section.The RIP configuration on Dallas now looks like this:router ripversion 2network 172.16.0network 192.168.2.0The RIP configurations on FortWorth and Austin are similar, and the routing tables on the routers appear to be identical to the ones created with RIPv1 shown in Figure 7-32, Figure 7-33, and Figure 7-34.In Figure 7-34, we saw that Austin has a summary route to 172.16.0/16.This means that if Austin gets a packet destined for a subnet of the 172.16.0 network that does not really exist, such as 172.16.33.0, Austin will route it toward Dallas or FortWorth.This causes some minor overhead because the packet will cross the WAN just to be dropped at the other side.A side effect of this is the router that drops the packet will probably send an ICMP destination unreachable message back across the WAN to packet’s source thus causing more WAN overhead.Suppose that the WAN between Dallas and FortWorth were down.Figure 7-36 shows this occurrence.Since Dallas and FortWorth are both summarizing the 172.16.0 network to Austin, Austin will maintain the two equal-cost paths to the network, 172.16.0/16.When Austin receives a packet with a destination address that exists on the 172.16.10.0 subnet, such as 172.16.10.1, Austin cannot accurately tell which path is valid, and only one path will reach the address.The packet has a 50/50 chance of reaching its destination.<<<J119 – Figure 7-36 Broken Serial Link Between Dallas and FortWorth With Auto-Summarization>>>With RIPv2 we can turn off the auto-summarization feature that causes the summary route.We use the router configuration command no auto-summary to accomplish this.Figure 7-37 shows the disabling of auto-summarization on Dallas.lDallas#configure terminalEnter configuration commands, one per line.End with CNTL/Z.Dallas(config)#router ripDallas(config-router)#no auto-summaryDallas(config-router)#<Ctrl-Z>Dallas#<<<Figure 7-37 Disabling of RIPv2 Auto-Summarization on Dallas>>>All of the networks are now operational.After a few minutes, an examination of the IP routing tables on FortWorth and Austin reveals something interesting.Figure 7-38 shows the new IP routing table on FortWorth after RIPv2, and Figure 7-39 shows the new IP routing table on Austin.lFortWorth#show ip route[text omitted]172.16.0/16 is variably subnetted, 4 subnets, 2 masksC 172.16.20.0/24 is directly connected, Ethernet0R 172.16.10.0/24 [120/1] via 172.16.11.1, 00:00:17, Serial0C 172.16.11.0/24 is directly connected, Serial0R 172.16.0/16 [120/2] via 192.168.3.2, 00:00:23, Serial1R 192.168.1.0/24 [120/1] via 192.168.3.2, 00:00:23, Serial1R 192.168.2.0/24 [120/1] via 172.16.11.1, 00:00:17, Serial0[120/1] via 192.168.3.2, 00:00:23, Serial1C 192.168.3.0/24 is directly connected, Serial1FortWorth#<<<Figure 7-38 FortWorth IP Routing Table After Auto-Summarization Disabled on Dallas>>>lAustin#show ip route[text omitted]172.16.0/16 is variably subnetted, 4 subnets, 2 masksR 172.16.20.0/24 [120/2] via 192.168.2.1, 00:00:01, Serial1R 172.16.10.0/24 [120/1] via 192.168.2.1, 00:00:01, Serial1R 172.16 [ Pobierz caÅ‚ość w formacie PDF ]
