31 Days Before Your CCNA Exam

196 31 Days Before Your CCNA ExamExample 14-7traceroute from PC1 to PC3 Fails at R3C:\>tracert 192.168.2.10Tracing route to 192.168.2.10 over a maximum of 30 hops:1 92 ms 74 ms 75 ms 172.16.3.12 114 ms 110 ms 126 ms 172.16.2.23 * * * Request timed out.4 ^CC:\>From the output, you can see that R2 (172.16.2.2) responded to PC1. R2 then routes the next traceto R3. We know this because R2 has a default route pointing to R3. However, when the tracearrives at R3, it does not have a route back to PC1, so it drops the packet. R3 needs a route back tothe 172.16.3.0/24 network.Before configuring three separate static routes for each of the 172.16.0.0 networks, notice that thethree routes can be summarized into one route. We reviewed summary routes on Day 21, so wewill not detail the process here. Example 14-8 shows the three routes in binary with the bits incommon highlighted.Example 14-8Summary Route Calculation for R310101100.00010000.00000001.0000000010101100.00010000.00000010.0000000010101100.00010000.00000011.00000000Therefore, the summary route would be 172.16.0.0/22. Although not part of the current addressingscheme, this summary static route would also include the route 172.16.0.0/24.You can now configure R3 with one static route:R3(config)#ip route 172.16.0.0 255.255.252.0 serial 0/0/1Now PC1 can successfully trace a route to PC3 as shown in Example 14-9.Example 14-9traceroute from PC1 to PC3 SucceedsC:\>tracert 192.168.2.10Tracing route to 192.168.2.10 over a maximum of 30 hops:1 70 ms 82 ms 78 ms 172.16.3.12 99 ms 103 ms 87 ms 172.16.2.23 156 ms 161 ms 151 ms 192.168.1.14 246 ms 242 ms 242 ms 192.168.2.10Trace complete.C:\>