Answers

Figure 1: Simple Hub and Spoke Topology

ipv6 route 2000::/64 3000::2
ipv6 route 2001::/64 3001::2
ipv6 route 2002::/64 3002::2

Example 1: Core Config

ipv6 route 3001::/64 3000::1
ipv6 route 2001::/64 3000::1
ipv6 route 3002::/64 3000::1
ipv6 route 2002::/64 3000::1

Example 2: Branch1 Config

ipv6 route 3000::/64 3001::1
ipv6 route 2000::/64 3001::1
ipv6 route 3002::/64 3001::1
ipv6 route 2002::/64 3001::1

Example 3: Branch2 Config

ipv6 route 3000::/64 3002::1
ipv6 route 2000::/64 3002::1
ipv6 route 3001::/64 3002::1
ipv6 route 2001::/64 3002::1

Example 4: Branch3 Config

Commentary

When configuring static routes, it is important to ensure that you have all of the correct IPv6 subnet information, just a little difference in subnet mask can make a big difference in routing behavior.

For this lab you were tasked with configuring static routes to all remote subnets on all routers. The figure shows six different subnets. The Core router connects to three subnets, so it will need three static routes. Each branch router connects to two subnets, so each branch router will need static routes for four different subnets.

For Core, the three remote LAN subnets are 2000::/64,2001::/64 and 2002::/64. Just to help us get our bearings, Table 1 lists the three destination subnets, with router Core’s outgoing interface and next-hop global unicast address:

Table 1: Data to Use in Router Core’s Static IPv6 Routes

The configuration, shown in Example 1, repeats the ipv6 route command three times. Each time it lists the destination subnet per the first column of the table, and the next hop address per the last column. For example, the complete command to configure one static route would be ipv6 route 2000::/64 3000::2.

For Branch1, before thinking about the configuration command, think about the topology in the figure. Branch1 has two connected subnets. Then, to send packets to the other four subnets, router Branch1 will always send the packets out its G0/1 interface to the Core router next. As a result, and as seen in Example 2, all four of Branch1’s routes list 3000::1 as the next hop address. The four commands each list a different destination subnet: 3001::/64, 2001::/64, 3002::/64 and 2002::/64.

Branch2 uses the same basic logic as router Branch1. Branch2 has two connected subnets, four remote subnets, and all four static routes for the remote subnets points to router Core next. In Branch2’s case, the next-hop address of the Core router is 3001::1. As seen in Example 3, the four ipv6 route commands list 3001::1 as the next-hop address, with subnets 3000::/64, 2000::/64, 3002::/64 and 2002::/64 in the four different commands.

As you probably guess by now, Branch3 uses the same basic logic as routers Branch1 and Branch2. Branch3 has two connected subnets, four remote subnets, and all four static routes for the remote subnets points to router Core next. In Branch3’s case, the next-hop address of the Core router is 3002::1. As seen in Example 4, the four ipv6 route commands list 3002::1 as the next-hop address, with subnets 3000::/64, 2000::/64, 3001::/64 and 2001::/64.

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. 

1. Connect to the command line of each of the PCs and attempt to ping the other PCs. If each of the static routes was configured correctly everyone should have connectivity to each other.
2. Also try the tracert or traceroute6 command on each PC, referencing another PC’s address, to see the various next-hop IPv6 addresses.