v6 & DSL / Cable modems [was: Private use of non-RFC1918 IP space (IPv6-MW)] (IPv6-MW)

Scott Howard scott at doc.net.au
Thu Feb 5 01:35:21 UTC 2009

On Wed, Feb 4, 2009 at 4:16 PM, Patrick W. Gilmore <patrick at ianai.net>wrote:

> I guess I was thinking about v4 modems which do not get a subnet, just an
> IP address.  If we really are handing out a /64 to each DSL & Cable modem,
> then we may very well be recreating the same problem.

v4 just gets a single IP address, which is why we need NAT, and apparently
NAT is evil.

To some extent the /64 can be though of as "just an IP" from the ISP
perspective (in the same sense that an IPv4 IP is just a /32 "network"),
which has the ability for the CPE to then somehow split it out between
multiple hosts - probably using autoconfig (in the same way with IPv4 it's
"split up" by the port with NAT).

What happens when a customer wants to run multiple networks is something I
haven't seen answered yet - with NAT it's easy, but as I said, NAT is
apparently evil...

On Wed, Feb 4, 2009 at 5:20 PM, Matthew Moyle-Croft <mmc at internode.com.au>wrote:

> but my point was that people are starting to assume that v6 WILL mean
> static allocations for all customers.

By design IPv6 should mean _less_ static allocations than IPv4 - in the
event that a client disconnects/reconnects and gets a new /64 then their
network *should* automatically handle that fact, with all clients
automagically renumbering themselves to the new /64, updating DNS, etc.
Local communications won't be impacted as they should be using the
link-local address.

The bit that isn't clear at the moment is if (and how well) that will
actually work in practice.  And that brings us back to the good old catch-22
of ISPs not supporting IPv6 because consumer CPE doesn't support it, and CPE
not supporting it because ISP don't...


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