subnet prefix length > 64 breaks IPv6?

Chuck Anderson cra at WPI.EDU
Wed Dec 28 01:05:34 UTC 2011

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

More information about the NANOG mailing list