Subject: Re: DHCPv6 support for /127s, for ISP subscriber PPP/PPPoE p2p links (Re: router vs. host discussion in 6man today for the /127 draft)

From: Lorenzo Colitti <[email-masked]>
Date: Fri, 2 Apr 2010 17:25:53 -0700

On Tue, Mar 30, 2010 at 5:03 AM, Mark Smith <
[email-masked]> wrote:

> I'm happy with using /64s for PPPoE links. However, if the /127 draft is
> accepted, then I'd want to be able to take advantage of them on
> PPP/PPPoE sessions - if there is an approved mechanism available to
> save address space I may as well use it.
>

Why would you do this as opposed to, say, unnumbered addresses?

The draft only specifies /127 for inter-router links. What if there's a host
on the other side? And what if whatever is on the other side of the link
wants to pass on IPv6 connectivity the connectivity to other hosts in its
network? Please don't say that it needs to do NAT66.

---

From: Mark Smith <[email-masked]>
Date: Sat, 3 Apr 2010 16:10:23 +1030

Hi Lorenzo,

On Fri, 2 Apr 2010 17:25:53 -0700

> Why would you do this as opposed to, say, unnumbered addresses?

From my IPv4 experience with unnumbered P2P links, I'd much rather have
a distinct address on each end of a link, although I've since learned
that the benefits that I value rely on the device following the strong
host model.

> on the other side?

When you're thinking about PPPoE/PPP scenarios, the most common one is
inter-router. If a end-host is running PPPoE/PPP then I think it is a
reasonable assumption that it'll handle any /127 point-to-point methods
correctly.

> And what if whatever is on the other side of the link
> network?
> Please don't say that it needs to do NAT66.

I certainly wouldn't recommend any form of NAT. I'm all for giving
customers lots of subnets in addition to the subnet on the link between
them and the SP. That does presume that the customer's device is a
router and is able to request prefixes for its downstream interfaces via
DHCPv6 PD.

I can see that if the /127s are accepted, and you choose not to use
them when you can, people are going to accuse you of "wasting" address
space, and it'd be hard to convince them otherwise even if you use the
simplicity/it's only waste when you get nothing for it argument (that
isn't working very well on this list and others either it seems). So I'm
identifying a scenario where I think they could be commonly used and
would tend to provide a more useful benefit, in comparison to the much
small number of infrastructure P2P links in networks. Right now though,
one of the drawbacks the /127 proposal is that there is an underlying
assumption of static configuration at both ends of the link, which
makes it impractical for the scenario I've described.

Regards,
Mark.