IPv6 Address Formatting

So, I’ve come to the in depth IPv6 studies for my CCNP – I figure I’d take some notes on my blog to help others out who take this path.

I know, I should’ve gotten gotten some exposure to this on my CCNA studies, and I did, but not enough to totally absorb it.

OK, Take a deep breath. I know some people, including myself, were a little intimidated by this – but it CAN be done!

So, let get started :

With IPv6, the standard IPv4 32-bit addressing scheme goes out the window. Now a 128-bit addressing scheme is adopted.

IPv4 provided a total of 4,294,967,296 addresses. Ready for this one? IPv6 now provides this many addresses :

340,282,366,920,938,463,463,374,607,431,768,211,456  –  340 Undecillion addresses.

I’ve read somewhere that this is actually enough addresses to give every atom on the earth’s surface an address, and then 100 Earth’s there-after. You can check me on that, but I am writing this from memory. Seems like we will NEVER run out eh? Well, this brings up one of my favorite XKCD comics – http://xkcd.com/865/

To prevent confusion and over/under/random-use and to help with the public allocations, the RFC states that we will leave 85% of the IPv6 spectrum unused until the standard is revised. When that will be? I don’t think anyone knows, but there was a time when we though IPv4 would provide enough addresses for everything….

As you can see, this would become a bit less than ideal to try and manage. That being said, the powers at be decided to divide the addresses into 8 groups of 4 hexadecimal characters each. The IP address in v6 land no longer consists of 4 octects of 8 bits. Now it consists of 8 groups of 16 bits per character and since it is hexadecimal the bits can be set to values ranging from 0 through F – and if you do the math, this comes out to be 2^128’s combinations of characters. Which adds up to that crazy number listed above.

An example being :

2001:0050:0000:0000:0000:0AB4:1E2B:98AA  –  A far cry from, I would say.

Again, to make this all a bit more comprehensive and manageable, the powers at be allowed us some lee-way on how we can write and handle the addresses. You are able to drop the groups of consecutive zero’s. But, here’s the kicker, this can only be done ONCE per address.

If we were to apply this to the address listed above, it would become :


Now, still a bit unrly to have to try and type into a cmd prompt to ping something, so there is another rule we can apply. We are allowed to drop leading zeros within the address. Again, if we were to apply this to the address above, it would become :


This brings it down to something, though not exactly EASY to remember or type – but a hell of a lot more manageable than the first number we started with.

That sums up the formatting of the addresses, and is a very high level overview – but I just wanted to point out the 2 rules that can be applied to “short-handing” the address to make it a little less stressful on your brain. As I know I needed.

As always, thoughts and insights are greatly appreciated.

Until next time.


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