Using /126 for IPv6 router links

Christopher Morrow morrowc.lists at
Wed Jan 27 05:11:41 UTC 2010

On Tue, Jan 26, 2010 at 11:53 PM, Mark Smith
<nanog at> wrote:

> The general intent of the /48 allocation is that it is large enough for
> nearly everybody, with nearly everybody including all but the largest

'nearly everybody with a single site' sure. I know of more than a few
VPN deployments (enterprises with remote offices) that have +1k remote
sites. For these you're quickly talking about:
1) get PA (maybe, maybe not a good plan, see renumbering headaches)
2) get a large number of /48's (assume median size is 2048 - 1 /36)

I know of one vpn deployment with +12k sites: a /34

I agree that a large majority of 'end sites' (enterprises) will be
services with a single /48 from PA space, unless they want to
multihome, or have more than 1 site and want some convenience.

> of organisations. IOW, it's meant to be "nearly one-size-fits-all", to
> try to ensure almost everybody gets as much address space as they'll
> ever need at the time of their first request. An addressing plan for
> anything less than the largest organsation that doesn't fit within
> a /48 or will exceed it fairly rapidly is probably too inefficent.
> ps. Remember that I'm one of the ones advocating using /64s everywhere,
> so what ever you do, don't use "ruthlessly efficient" to describe my
> position - use that for the /126 or /127 crowd ;-)

I'd note I'm not a 'ruthless efficiency' guy either, just 'how ops is
done today' and 'there be dragons, be aware what you step into'. I
think, and I'll start a fresh copy of this thread to articulate it,
there have been 4-5 different issue conflated in this discussion,
which is making things complicated.


> Regards,
> Mark.

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