Answers

Figure 1: Four Switches with Trunks

Example 5: R1 Config

Example 6: R2 Config

Example 7: R3 Config

Example 8: R4 Config

Commentary

When configuring static routes, it is important to ensure that you have all of the correct IP subnet information because even a small difference in a subnet mask can make a big difference in routing behavior.

For this lab, you were tasked with configuring static routes between the routers so that each of their LANs would be able to route packets to each other. Because there are four different routes in this topology, this means that there will be three remote LAN subnets that need to have routes configured per router.

For R1, the three remote LAN subnets are: 192.168.100.64/26, 192.168.100.128/26, and 192.168.100.192/26. The first route would be for R2’s LAN, the common subnet between the routers uses the 172.16.100.0/24 network. R2’s IP address on this shared LAN is 172.16.100.2, making this address the next-hop address in the static route. The complete command to configure this static route would be ip route 192.168.100.64 255.255.255.192 172.16.100.2.

R1’s second static route, for the subnet off R3’s G0/2 interface, would use R3’s IP address on this shared LAN of 172.16.100.3. The complete command to configure this static route would be ip route 192.168.100.128 255.255.255.192 172.16.100.3.

R1’s third and final route would be for the subnet off R4’s G0/2 interface, with R4’s IP address on the central LAN of 172.16.100.4 as the next-hop. The complete command to configure this static route would be ip route 192.168.100.192 255.255.255.192 172.16.100.4.

R2 likewise has three static routes, one each for the three remote LAN subnets: 192.168.100.0/26, 192.168.100.128/26 and 192.168.100.192/26. Note that of the three commands in Example 6, one references R1’s address as next hop, one references R3’s address as next-hop, and one references R4’s address as next-hop. Take the time to look at the subnet ID and mask in each command, compared to the figure; you should see correlation, with R1 as next-hop for the route to the subnet off R1’s G0/2 interface, and so on.

Similarly, R3 has three static routes, referencing R1, R2, and R4 as next-hop routers for three different remote subnets. R4 also has three static routes, with R1, R2, and R3 as the next-hop routers.

Known Issues in this Lab

This section of each Config Lab Answers post hopes to help with those issues by listing any known issues with Packet Tracer related to this lab. In this case, the issues are:

Why Would Cisco Packet Tracer Have Issues?

(Note: The below text is the same in every Config Lab.)

Cisco Packet Tracer (CPT) simulates Cisco routers and switches. However, CPT does not run the same software that runs in real Cisco routers and switches. Instead, developers wrote CPT to predict the output a real router or switch would display given the same topology and configuration – but without performing all the same tasks, an actual device has to do. On a positive note, CPT requires far less CPU and RAM than a lab full of devices so that you can run CPT on your computer as an app. In addition, simulators like CPT help you learn about the Cisco router/switch user interface – the Command Line Interface (CLI) – without having to own real devices.

CPT can have issues compared to real devices because CPT does not run the same software as Cisco devices. CPT does not support all commands or parameters of a command. CPT may supply output from a command that differs in some ways from what an actual device would give. Those differences can be a problem for anyone learning networking technology because you may not have experience with that technology on real gear – so you may not notice the differences. So this section lists differences and issues that we have seen when using CPT to do this lab.

Beyond comparing your answers to this lab’s Answers post, you can test in Cisco Packet Tracer (CPT) or Cisco Modeling Labs (CML). In fact, you can and should explore the lab once configured. For this lab, once you have completed the configuration, try these verification steps. 

Answer on Paper, or Maybe Test in Lab

Next, write your answer on paper. Or if you have some real gear or other tools, configure the lab using them.

If you do implement the entire network in a lab, you can test the solution by going to each PC and pinging the other three. All the pings should work. Additionally, you could use an extended ping command to ping from each router’s G0/2 interface to each other router’s G0/2 interface IP address. For instance, from R1, the command ping 192.168.100.193 source 192.168.100.1 would test the forward route to R4’s G0/2 subnet, and the reverse route back to R1’s G0/2 subnet.