[147920] in North American Network Operators' Group
Re: subnet prefix length > 64 breaks IPv6?
daemon@ATHENA.MIT.EDU (Chuck Anderson)
Tue Dec 27 20:06:38 2011
Date: Tue, 27 Dec 2011 20:05:34 -0500
From: Chuck Anderson <cra@WPI.EDU>
To: nanog@nanog.org
Mail-Followup-To: nanog@nanog.org
In-Reply-To: <CAPLq3UOF0WzrYe0ak94u=Hgd9rM-Wo=_OygMHDwroKt7Q5zGfA@mail.gmail.com>
Errors-To: nanog-bounces+nanog.discuss=bloom-picayune.mit.edu@nanog.org
On Wed, Dec 28, 2011 at 04:58:19AM +0530, Glen Kent wrote:
> It seems ISIS and OSPFv3 use the link local next-hop in their route
> advertisements.
>
> We discussed that SLAAC doesnt work with prefixes > 64 on the ethernet
> medium (which i believe is quite, if not most, prevalent). If thats
> the case then how are operators who assign netmasks > 64 use ISIS and
> OSPF, since these protocols will use the link local address?
>
> I had assumed that nodes derive their link local address from the
> Route Advertisements. They derive their least significant 64 bytes
> from their MACs and the most significant 64 from the prefix announced
> in the RAs.
Each prefix on an interface can have a different prefix length.
Link-locals always have a prefix length of 64, even if a global
address assigned to the same interface has a different length. Also,
the link-local address is derived locally without any information from
RAs.
