Answers

Figure 1: Three Router Topology

The IPv6 Configuration that Existed at the Beginning of the Lab

Examples 1, 2, and 3 show the additional IPv6 configuration that existed in the configuration at the beginning of this lab.

interface GigabitEthernet0/1
 ipv6 address 2122::1/64
 no shutdown

Example 1: R1 Config

interface GigabitEthernet0/1
 ipv6 address 2223::/64 eui-64
 no shutdown
!
interface GigabitEthernet0/2
 ipv6 address 2122::/64 eui-64
 no shutdown

Example 2: R2 Config

interface GigabitEthernet0/1
 ipv6 address 3000::/64 eui-64
 no shutdown
!
interface GigabitEthernet0/2
 ipv6 address 2223::2/64
 no shutdown

Example 3: R3 Config

This lab takes a much different approach than the other Config Lab posts. How did you do?

To begin, open another window to the lab post, just so you can see the show ipv6 interface command output more easily. Pick any example command, and you will notice:

1. On the 2^nd line, a Link Local address (begins with FE80)
2. A few lines below, a heading “Global Unicast Addresses”
3. On the next line, one global unicast address

Now look hard at the last four quartets of each interface’s global unicast address versus the link local address. For each interface, those values are the same. When the router is configured with a global unicast address, it creates a matching link local address, copying the second half (last four quartets) from the global unicast address.

Next, scan Examples 1 through 5 in the lab post for the lines that list the global unicast addresses. Some list a notation of “EUI-64”, and some do not. Then compare that output to the topology figure. It just so happens that the initial configuration for this lab has some ipv6 address commands that use the eui-64 keyword, and some do not. (As a reminder, this keyword tells the router to derive the second half of the IPv6 address, rather than it being configured in the ipv6 address command.)

So, some conclusions you can reach from this analysis are:

• Each interface listed in the lab’s Examples 1 through 5 have an ipv6 address command that configures an address.
• These interfaces configure a prefix, along with the eui-64 parameter:
  • R2 G0/1
  • R2 G0/2
  • R3 G0/1
• These interfaces configure the entire address, and do not include an eui-64 parameter:
  • R1 G0/1
  • R3 G0/2

Frankly, the above analysis is enough to know what was configured. The rest of the analysis explains the rest of the output, and also explains how you can know that OSPF has not yet been enabled.

Each router interface in the lab lists several supported multicast addresses. An interface needs either the ipv6 address command configured or an ipv6 enable command configured to enable IPv6 on the interface. Once enabled, the interface supports the following multicast IPv6 addresses, which happen to be listed on every interface in the lab:

• FF02::1 – All nodes
• FF02::2 – All routers

Next, each interface lists either one or two solicited node multicast addresses. These addresses begin with:

• FF02::1:FF

The solicited node multicast address then ends with the same 6 hex digits as any unicast address on the interface (including link local addresses).

Note that IOS enables the FF02::1, FF02::2, and the appropriate solicited node multicast addresses automatically, without extra configuration, so there is no matching configuration to predict.

Finally, the lab stated that the intent was to use OSPFv3. However, OSPFv3 uses the following multicast addresses, which would be enabled on any interface on which OSPFv3 had been enabled:

• FF02::5 – All OSPF routers
• FF02::6 – All OSPF DRs and BDRs

Because these two multicast addresses are not listed on any of the interfaces shown in the lab, you can predict that OSPFv3 had not yet been configured.

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. When configuring, add just one IPv6 interface subcommand and then issue a show ipv6 interface command and look for the notes about unicast and multicast addresses.
2. Continue to configure one interface at a time, and then repeat the show ipv6 interface command, until you get a sense for which configuration commands cause the various unicast and multicast addresses to appear in the show command output.