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Re: [moonv6] /120 prefix length at UNH

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From: Alain Durand (Alain.Durand@Sun.COM)
Date: 10/15/03


moonv6 post from Alain Durand <Alain.Durand@Sun.COM>

Bound, Jim wrote:

>With /120
>
>m = 8. n == variable depending on prefix format. this is aggregatable
>format. so the prefix stops at /64 and low order 64 is the EUI. meaning n
>MUST not be greater than 58. 58 + 8 == 64. So what I am saying is I beleive
>/120 or /96 does not step on the EUI but a /8 does step on the EU and does
>break 3315?
>

   | n bits | m bits | 128-n-m bits | 

   +------------------------+-----------+----------------------------+
   | global routing prefix  | subnet ID |       interface ID         |
   +------------------------+-----------+----------------------------+

I think you might have been loonking at the picture right to left instead of left to right! (just kidding)

With /120, you have: 

   |                        120 bits                    |    8 bits  |
   +------------------------+-----------+----------------------------+
   |       global routing prefix  + subnet ID           |interface ID|
   +------------------------+-----------+----------------------------+

Ok? So your Interface ID is effectively 8 bit long. This breaks 3315 as the global routing prefix is not starting with 000/3.

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