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

Mark Andrews Mark_Andrews at isc.org
Thu Feb 5 01:51:10 UTC 2009

In message <f1dedf9c0902041735x4a9cb6f9nc5b5bbf1201a240e at mail.gmail.com>, Scott
 Howard writes:
> 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).

	You hand out multiple /64's.  As many as the client requests
	up to a /56 or /48 depending apon which break point you

	The address space is assigned to ISP's on the presumption
	that you will be handing out the equivalent of /56's or /48's
	worth of address space to each customer.
> 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>wro
> te:
> > 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...
>   Scott.
Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org

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