ISP customer assignments

Adam Armstrong lists at
Tue Oct 13 23:11:06 UTC 2009

eric clark wrote:
> So far, I have only dabbled with IPv6, but my reading of the RFCs is that
> VLSM for lengths beyond /64 is not required. Subsequently, to use anything
> longer is an enormous gamble in an enterprise environment. I envision
> upgrading code one day and finding that your /127 isn't supported any more
> and they forgot to mention it. I'll stick to /64, though it does seem a
> horrible waste of space.
> Someone else might have read the RFC differently though.
I'm sure there's an RFC somewhere talking about Classful addressing 
pre-CIDR. Perhaps we should stop using CIDR in IPv4. It might stop 
working one day. ;)

Operational reality helps to refine RFCs. Many people are already using 
longer prefixes for infrastructure and other purposes, so it's unlikely 
to go away. The only real issue is that some old hardware may not 
support prefixes longer than /64 in hardware and so may drop to software 

I don't know of any examples of this though.


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