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Re: subnet prefix length > 64 breaks IPv6?
From: Chuck Anderson <cra () WPI EDU>
Date: Tue, 27 Dec 2011 20:05:34 -0500

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

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

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