IPv6 Addressing on Routers: Cert Guide PT Labs for ICND1 Chapter 30

IPv6 addresses can be long and confusing when you first learn about them. Configuring the addresses, seeing devices abbreviate them, interpreting those abbreviations, and thinking through addresses in devices that use EUI-64 rules can really help solidify your understanding of IPv6 addressing rules. This latest post details where to find the Packet Tracer files for the examples from my ICND1 100-105 book for Chapter 30, which works through several IPv6 address configuration details.

A Quick Note about the New CCNA

For those of you reading this post between when it was posted in August 2019, and the date Cisco released their newest CCNA exam (200-301) in February 2020, just a few notes.

• • This post is about the examples in a chapter of the books about the CCNA R&S and CCENT exams that Cisco offered from 2016 through early 2020.
  • I plan to update this post (and similar posts in the series) for the chapters in the new books for the CCNA 200-301 exam.
  • In the mean time, there’s plenty of time to get your CCNA R&S certification before February 2020 – so dig in!
  • You can preorder the CCNA 200-301 Official Cert Guide, Volume 1 from Cisco Press or from Amazon. The links to order Volume 2 should be active soon.

Advice before You Begin

The big idea is pretty simple: Repeat the Examples in the Official Cert Guide as part of your lab practice for CCNA.

To get your head around what kind of content is here in the blog for these labs, read both of these posts or at least the second post:

• Intro to the Cert Guide PT Labs
• Details of how to use Cert Guide PT Labs

After reading those posts, you have the context, so onward to the details!

What’s in This Post

Intro to the Book Chapter: A brief description of the topics in that chapter of the book.

Chapter Examples and .PKT File Reference: A section that lists the examples in the chapter, the .pkt files supplied, and reminders/notes about cases in which we don’t supply all three files for any one example.

Tips and Exceptions: When we build the files, we come across items that we think might confuse you when trying the examples with PT. We write those notes in this section!

Intro to the Book Chapter

If you are reading the book and make it to this chapter, you will have already learned how IPv6 addresses work. At this point, you just need to assign each router interface an IPv6 address. The examples in the chapter work through doing just that, with you supplying the full 128-bit address, assigning the first half and using EUI-64 to build the rest, or through some other dynamic mechanism. Additionally, this chapter uses examples to look at link-local addresses and a few of the common IPv6 multicast addresses that routers enable by default when a router interface is enabled for IPv6 routing.

Chapter Examples and .PKT File Reference

Download this ZIP file to get all the .pkt files for this chapter: 

This table tells you what files to expect in the ZIP, and which examples happen to use interface IDs that can be exactly replicated in PT:

Reminders: Purpose of Each Type of .PKT File

Topology File: The file contains all devices and cables in the associated figure along with any implied extra devices. The purpose: you never had to add a device or cable. It also contains a few configuration commands that do not affect the example, but help you navigate, for instance, it sets hostnames, passwords (always “cisco”), and interface descriptions.

Initial Config: The file contains everything in the Topology file, plus all configuration listed or implied by the words and figures leading up to the example. That is, it attempts to match the state of the network just before the first line of the example.

Ending Config: The file adds the configuration listed in the example to the Initial Config file – nothing more, nothing less.

Table Lists “None” or Other Strange Terms?

Some examples have all three types of PKT files, however, some Examples have no PT files, and some have a mix of fewer than three files. Here’s a reminder of why. You can check this earlier post for more background if you care to know more.

Initial Config as “None”: If the table says “yes” for the Topology and Ending config, but not the Initial config, then the Topology file has all configuration needed at the beginning of the example.

Ending Config as “None”: The Ending config will be shown as “None” when the example as printed in the book does not have any configuration commands.

All Three Files as “None”:  We do not supply .pkt files for that example.

Use x-y:  Use Example x-y’s ending config file because the example continues earlier example x-y.

Tips and Exceptions

This section lists our comments about using PT to do the examples. When we built the files, when we saw any behavior that we thought might make it more difficult to perform the example, we noted that fact so we could list it here, in case it might help you with the examples.

Issue 1: EUI-64 Logic is Incorrect in Packet Tracer

PT does not do the EUI-64 bit flip correctly compared to real gear. Specifically:

Real gear flips the 7th bit of the interface ID part of the address when building that value. That is, if the bit is a 0, it becomes a 1, or if it begins as a 1, it flips to a 0. PT sets that bit’s value to be a 1, regardless of its initial value.

For instance, if the hex value being converted begins with hex 02:

• Hex: 02
• Binary: 00000010
• The correct flip of 7th bit: 00000000
• The correct new hex value: 00
• PT choice to set the 7th bit to 1: 00000010 (unchanged)
• PT (incorrect) hex value: 02

So, while you can do the examples in this chapter, note that some of the examples in the book will not match the output in PT because of this issue.

Issue 2: Packet Tracer does not use Configured MAC Addresses Correctly

Before understanding the issue, it helps to recall a few facts about how routers work with MAC addresses.

First, when creating examples in the book (or any learning exercise) that uses EUI-64, I often use the mac-address value interface subcommand. This command overrides the universal MAC address of the interface so that the device uses the configured MAC address instead.

Second, when real router serial interfaces need to build an IPv6 address using EUI-64 rules, they have an issue to overcome: they need a MAC address, but serial interfaces do not inherently have MAC addresses. In such cases, they use the MAC address of an interface that has a MAC address, specifically the interface with the lowest internal number for an interface, which is typically the lowest numbered Ethernet interface for the interface numbers we see in configuration mode.

The issue with PT comes in the combination of the first two ideas. If the configuration uses the mac-address command to set the first LAN interface’s MAC address, real gear behaves differently than PT. The difference comes in how a serial interface grabs a MAC address to use:

• Real: Serial interfaces use the configured MAC address per the mac-address interface subcommand.
• PT: Serial interfaces use the universal MAC address ignoring the configured MAC address per the mac-address command.

As a result, we cannot control the resulting IPv6 addresses calculated with EUI-64 on serial interfaces in PT.

Example 30-5

This example uses the EUI-64 process, and as a result of the two differences between PT and real gear, you cannot force PT to match the same EUI-64 based IPv6 addresses as shown in the examples in the book. However, rather than just not supporting the example, we offer a different variation.

The PT files for this example have a default MAC address is 0000.9702.6c01 on the lowest numbered LAN interface. EUI-64 will use this MAC address to generate the IPv6 address of 2001:DB8:1111:1:201:97ff:fe02:6c01, which is different than the address shown in the example in the book, but still useful for learning.

Example 30-7

The PT output cannot match the book because PT does not behave like real gear with EUI-64 calculations as noted earlier. In this case, the PT files for this example have a default MAC address is 0000.9702.6c01 (same value as the earlier examples) on the lowest numbered LAN interface. PT will list these addresses:

• 2001:DB8:1111:1:201:97ff:fe02:6c01
• FE80::201:97ff:fe02:6c01

Example 30-8

This example focuses on the IPv6 multicast addresses listed in the output of the example. Note that PT lists these correct multicast addresses that match the output in the book:

• FF02::1
• FF02::2
• FF02::A

Additionally, it should list one multicast address that does not match the book’s output, but that multicast address is based on a unicast address, and as noted in this post, PT will use different unicast addresses when using EUI-64. In this case, PT will list multicast address FF02::1:FF02:6C01, which is the solicited-node multicast address based on the unicast IPv6 address used by PT.

Example 30-9

PT does not support the specific command in this example in the book: show ipv6 interface brief g0/0. However, both of these commands are supported in PT and list output that includes the information in the book example about interface G0/0:

• show ipv6 interfaces brief
• show ipv6 interface g0/0