[nycbug-talk] IPv6 and CIDR confusion

Isaac Levy ike at lesmuug.org
Fri Mar 23 18:23:40 EDT 2007

On Mar 23, 2007, at 6:01 PM, alex at pilosoft.com wrote:

> 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.

Gotig- learning something new every day.

>> 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.

Sure, but it doesn't seem to be the same...

> On Mar 23, 2007, at 5:00 PM, Jonathan Stewart wrote:
>> I was hoping to find something on wikipedia that would be a bit  
>> easier to work through for someone new to it but the RFC always  
>> works :)
>> http://tools.ietf.org/html/rfc2373

- so,

The IPv4 CIDR number comes from the number of 1's in the subnet mask  
when converted to binary, right?

So it seems the IPv6 notation is not the same thing at all- it's not  
the subnet mask, but the prefix length of the address.

That was confusing, now it's clear.

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

Alex- do you do the hexadecimal counting in your head dude?!?!?

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

- whaddya' mean?  That sounds interesting?


(p.s.: for a guy who seems so hellbent against IPv6, you sure know a  
lot of details...)

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