[ppml] IPv6 addressing plans
stephen at sprunk.org
Tue Sep 4 12:00:37 EDT 2007
Thus spake <michael.dillon at bt.com>
> Does anyone have any reasoning why a network spanning two or
> more of the RIR regions, should or should not get separate ISP
> allocations from each region?
> I'm not just interested in opinions, but also the reasoning behind
> them, especially any technical pros and cons.
> In addition, are there any characteristics that define a good IPv6
> addressing plan for a network operator?
> We've just received an IPv6 /22 from RIPE based solely on
> projections in our European network infrastructure. Fairly soon
> we will have to decide whether to internally assign chunks of that
> space to our North American network or to go to ARIN for a
> separate IPv6 allocation based on North American needs only.
It is generally assumed, if not stated explicitly in policy, that addresses
issued by an RIR are for use within that region only. If the use outside
the region is a negligible part of address use, nobody's going to complain,
but you shouldn't be assigning space _to customers_ in the US from a RIPE
block, and vice versa.
Also, if your network in the US is of non-negligible size, it's assumed that
the topology is going to be mostly independent and will be a separate AS
speaking BGP to your AS in Europe. In that case, your US network would be a
separate "organization", and would be no different in the RIRs' eyes than if
your networks were two independent companies. You probably have separate
legal entities in such a case anyways, though that's not technically
required for you to claim multi-organization status. Multiple organizations
should not "share" blocks between them, because that makes paperwork -- and
routing -- a mess.
Another thought is that using the same block in multiple regions would
defeat RIR-level aggregation; if RIPE-issued blocks are all exclusively used
in the RIPE region, smaller (i.e. non-global) players in other regions can
filter them from their routers and just point a static route for all of
RIPE's address space "that way", i.e. towards Europe. If, in contrast, you
use your RIPE block in the US, people can't do that and we're doomed to
every DFZ player having to carry redundant routes for other regions (or
implement difficult-to-maintain filter lists) just to handle the few
The main justification I see for using a block outside the region that
issued it is if your use in the other region is not sufficient to get a
block from the appropriate RIR. This might be the case for a European ISP
that buys a pipe to show up at a US IXP, or vice versa; addressing a couple
routers is not enough to get a block from the "correct" RIR, but it makes
sense to use addresses from the "wrong" RIR in such a case. Likewise, if an
end-user org has a PI assignment from a certain region, it makes sense that
all their sites worldwide would use addresses from that block _if they did
not have connectivity to the outside world except through the issuing
region_. For instance, if a office in Moscow has to go through HQ in the US
to reach the Internet (which is not unusual), they should be addressed from
that company's ARIN block; if they got a second connection in Europe, the
sites behind that connection should be renumbered to RIPE space.
Stephen Sprunk "God does not play dice." --Albert Einstein
CCIE #3723 "God is an inveterate gambler, and He throws the
K5SSS dice at every possible opportunity." --Stephen Hawking
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