[Dnsmasq-discuss] Cannot assign IPv6 address for /96 subnet

[Dan Williams]

On Tue, 2013-02-19 at 21:06 +0000, Simon Kelley wrote:
> So, I did some testing. I configured an server interface with 
> prefix-length 96, and configured dnsmasq with a dhcp-range and 96 prefix.
> 
> Using dhclient, I got a lease successfully.
> 
> The only problem is that dhclient configured the client's interface with 
> prefix-length 64.
> 
> I moment's thought shows that this is expected: there is nowhere in the 
> DHCPv6 messages for the prefix-length information to be passed to the 
> client. There _is_ a prefix-length field in router-advertisements. but 
> AFAIK, there's no way for the DHCPv6 client to use that information.
> 
> Of course if you're using RA for address-allocation, using SLAAC, the 
> prefix length has to be 64 anyway.

We had this discussion for NM a long time back.  dhclient hardcodes the
prefix to /64 because there's no agreement in the standards on prefixes,
and last I knew, DHCPv6 didn't even have a prefix/netmask option.  It
turns out that's kinda pointless anyway, so we ignore that /64 from
dhclient and hardcode it to /128 or something like that.

But the point is, until standards get changed and dhclient updates to
use them, you're stuck wtih a /64 or whatever you choose to override
that as.

Dan