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Re: Verizon DSL moving to CGN
From: Tore Anderson <tore () fud no>
Date: Sun, 07 Apr 2013 10:15:10 +0200

* Mikael Abrahamsson

My point is that people seem to scoff at CGN. There is nothing stopping
anyone putting in CGN for IPv4 (that has to be done to handle IPv4
address exhaustion), then giving dual stack for end users can be done at
any time.

Face it, we're running out of IPv4 addresses. For basic Internet
subscriptions the IPv4 connectivity is going to be behind CGN. IPv6 is a
completely different problem that has little bearing on CGN or not for
IPv4. DS-Lite is also CGN, it just happens to be done over IPv6 access.
MAP is also CGN.

I'm ok with people complaining about lack of IPv6 deployment, but I
don't understand people complaining about CGN. What's the alternative?

Technically I agree with all of the above. However, going for the NAT444
flavour of CGN might well delay or lower the perceived importance of
IPv6 deployment within an ISP. The immediate problem is IPv4 service
continuity, and if that is to be accomplished without IPv6 being part of
it, it's easy to postpone doing anything about IPv6.

I went to an interesting presentation from Kabel Deutschland last month,
who have deployed DS-Lite to their residential subscribers. One of the
messages was that once the decision was made to implement DS-Lite to
deal with IPv4 exhaustion, there was no problem getting the necessary
support to deploy IPv6 - it was no longer a separate and
non-revenue-generating problem, but an essential building block needed
for their IPv4 service continuity. (MAP and 464XLAT would yield the same
effect, of course.)

To answer your earlier question - yes, I'd very much prefer to have
DS-Lite over NAT444, because only the former will ensure that I get
native IPv6 once my native IPv4 gets taken away. With NAT444, I'm no
closer to having IPv6 than I was before NAT444.

That said, there are of course some things that may make anything except
NAT444 undeployable. Verizon might have old DSLAMs that cannot deal with
IPv6, or customer-controlled/owned (layer-3) HGWs. If so, their hands
are tied.

Tore Anderson

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