IPv6 Addressing – Do You Choose to Practice?

Friday I posed an open-ended IPv6 addressing question. Today I'll start working towards the solution - but more importantly, I want to find out whether you personally, if you were preparing for the CCNA exam, would want to read/study IPv6 address (only), or whether you would also feel the need to practice IPv6 commands on gear/sim/Dynamips.

Before you answer, let me tell you an assumption I'd like to make when working through this: let's take Cisco's exam topics at face value. If you look at the CCNA and ICND2 exam topics, you'll see the following (quoting http://www.cisco.com/):

• Describe the technological requirements for running IPv6 in conjunction with IPv4 (including: protocols, dual stack, tunneling, etc).
• Describe IPv6 addresses

First, to review what I've said before about how to interpret Cisco's exam topics, look at the verb in both lines: "describe". Importantly, it doesn't say "configure", "verify", "troubleshoot", or "implement". Translated: a pure interpretation means that you should not expect to see IPv6 configuration or show commands on the CCNA exam.

Before I completely lose touch with reality, for the actual exam you have to truly temper what's listed in the exam topics by the fact that the exam topics are guidelines. The exams may (and sometimes do) cover more. But, for the sake of discussion herre, let's assume there's no IPv6-related commands covered on CCNA.

My next assumption: many of you that have read this far may not have the IPv6 addressing rules down. So, to help you answer last Friday's question, let me summarize the rules. That'll also help you answer the question "would I have bothered to do IPv6 from the CLI if I knew there was no coverage of IPv6 commands". Here's the short version:

IPv6 addresses are:

• 128 bits, written in hex, 4 digits at a time, separated by colons. (I call each set of 4 a "quartet").
• Addresses and prefixes can be abbreviated by omitting leading 0's in a quartet, abbreviating a quartet of 4 0's as a single 0, and by representing 1 set of multiple consecutive all-zero quartets as double colons (::).
• 2 sets of double colons are not allowed due to the ambiguity it creates.

The rules for defining the 2^nd half of EUI-64 formatted addresses using an interface's MAC address:

• TheEUI-64 keyword means that the interface's IPv6 address is formed with the configured 64 bit prefix plus a 64-bit EUI-64 formatted number
• To form the last 64 bits, start by splitting the MAC address in half (2 sets of 6 hex digits)
• FFFE is inserted into the middle of the MAC address
• The 7^th bit on the first byte (counting bits left-to-right, bits numbered 1 through 8), is set to binary 1 (if not already a 1).
• On Cisco router LAN interfaces, if configured to use a different MAC address (using the mac-address command), this process uses the configured MAC address
• Interfaces that don't have MAC addresses borrow a MAC from the lowest numbered LAN interface (eg, S0/0/0 borrows a MAC from Fa0/0 if the router has both a Fa0/0 and Fa0/1).
• I think this is trivia, but if the "borrowed-from" interface uses a locally configured MAC, the "borrowing" interface borrows the burned-in MAC address.

Frankly, that's a lot to digest in a short space, and it is certainly useful for study to read more detailed descriptions, with examples. But that's enough to at least answer the question about what the IPv6 addresses should be.

SPOLIER ALERT - you'll have to click next to see the next page where I'll list the partial answers to last Friday's IPv6 question, specifically the IPv6 addresses.

Finally, for today, I'd like to do a short survey. If you knew for sure that all IPv6 questions were conceptual, with no CLI commands, would you bother to do any hands-on practice or not? The hands-on practice can of course help you learn, but you could also read/study/do practice questions/etc to build your knowledge.

Let me know what you think. Thanks!

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