[nycbug-talk] IPv6 and CIDR confusion

alex at pilosoft.com alex at pilosoft.com
Fri Mar 23 18:01:57 EDT 2007

On Fri, 23 Mar 2007, Isaac Levy wrote:

> Hi All,
> When searching for info about IPv6 netblocks, I found: "IPv6 uses a
> CIDR-style architecture for address allocation"
> -but it's not actually CIDR?
It is classless.

> Does anyone know where to find out about the breakdown of netblocks?
> (e.g. what is a /64 for IPv6?  What is the equivalent of an IPv4 Class
> C, (/24 with 254 usable addresses?))
There's no such thing as classes. Duh.

/64 for ipv6 is still the same, SLASH SIXTY FOUR.

To have 254 usable IP addresses, you can have a /120.

Now, the interesting thing is, most v6 capable routers only will route on 
the top 64 bits of the prefix.


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