I was planning on writing this great breakthrough piece on IPv6 subnet sizes, like how many /48s are in a /32 or how many /56s are in a /24, etc… But then I stumbled across a great PDF from ARIN and realized that all the work was already done. So I ended up not posting anything.

The ARIN Doc

I continue to get questions on this topic though, and the ARIN doc is actually a tad hard to find unless you already know exactly where to look for it, so I changed my mind and decided to just post up their chart here. It goes from /0 to /128 and compares classful, IPv4 and IPv6 subnets with the number of addresses in each prefix size for each address type listed. Then, on the last page, it also includes a list of IPv6 prefix lengths (subnet masks) and details the number of /48, /56 and /64 subnets within each one. All in all a great reference sheet to have handy when laying out IPv6 subnet plans. Take a look:

You can also find more great info from ARIN here. Enjoy!

Published On: January 26th, 2011 / Categories: IPv6 / Tags: , , , , , /


  1. Naveen K Lakshman 1 February 2011 at 10:46 - Reply

    Hi Chris,

    Great work keep it up. howz IPv6 Migrations inside Juniper Internal Networks.

  2. […] how many networks will be needed to support the next 5 years of growth. One nibble up from /64 is /60, which gives you a maximum of 16 /64s. If you need more than that, jump to the next nibble; a /56, which gives you up to 256 /64 networks […]

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