Help with DHCPv6 client-identifiers

sthaug at nethelp.no sthaug at nethelp.no
Sat Nov 19 13:43:15 UTC 2011


> > Then it is indeed fortunate that DHCPv6 doesn't do what you want.   Using
> > prefixes wider than /64 breaks IPv6.   That's why SLAAC doesn't do it.
> 
> RFC reference please. As far as I'm concerned, IPv6 supports prefix lengths
> right up to /128. Due to various protocol brokenness, it's difficult to
> configure hosts with longer prefixes than /64, but that is a different
> issue.

My guess: The language in RFC 4291 which says that interface identifiers
are 64 bits:

   For all unicast addresses, except those that start with the binary
   value 000, Interface IDs are required to be 64 bits long and to be
   constructed in Modified EUI-64 format.

> SLAAC assumes /64 maximum prefix length. That is a design decision
> within SLAAC. It's perfectly possible to use prefix lengths longer than
> /64 within IPv6. I know I can't do it with RA/SLAAC etc., which is why I
> was hoping to do it with DHCPv6, which is broken for quite separate reasons.

Agreed, prefix lengths longer than /64 work just fine. Any company that
tried to sell us equipment which only routed on the most significant 64
bits would be politely told where the exit was...

Steinar Haug, Nethelp consulting, sthaug at nethelp.no



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