Subject: RE: presentation notes

From: Richard Draves <[email-masked]>
Date: Mon, 15 Nov 1999 15:28:18 -0800

> My concern is about phasing out the transition mechanisms
> .
> Going from 6to4 to native IPv6 seems to me much easier
> than going from IPv4 compatible to native IPv6.
> The reason being that, when a site use the 6to4 mechanism,
> everything within the site is already native. Meaning IPv6
> site infrastructure, routers, ...
> With IPv4 compatible, communication is directly from
> a dual stack host to another dual stack host, no IPv6 infrastructure
> whatsoever is used.
> 
> Given that, if a site use IPv4 compatible and 6to4 at the same time
> it will be much easier when it will move to native IPv6 if already
> the communication were using 6to4 than IPv4 compatible addresses.
> 
> For this reason, I think we should differentiate 6to4 and 
> IPv4 compatible
> and give priority to 6to4.

In practice, I would expect 6to4 will mostly be used to give addresses to
nodes that do not have v4 connectivity. That's the big win of 6to4. So the
vast majority of nodes with 6to4 addresses will not have v4-compatible
addresses. So this will be moot.

6to4 gateways might be assigned both v4-compatible and 6to4 addresses, but
it will be equally efficient to reach them using either address. So for
them, no need to make a distinction.

Can you flesh out a transition scenario where giving a preference to 6to4
addresses over v4-compatible addresses will help the transition?

> In the same line, having "default" somewhere in the middle may
> have some strange impact if people start using by mistake
> not yet defined addresses (outside of 2000::/3)

So are you suggesting giving a middle preference to 2000::/3 and last place
to ::/0? I don't like biasing against new address formats like that, it
might inhibit innovation.

Thanks,
Rich
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From: Alain Durand <[email-masked]>
Date: Tue, 16 Nov 1999 12:16:51 +0100

>addresses. So this will be moot.

I disagree there. My view of 6to4 is to give a global prefix to a site
that can not have v6 service at the same time as v4 service from its ISP.
This, regardless to the fact that you have or not enough IPv4 addresses
on your hosts. Actually some hosts may have IPv4 addresses, some not.

>addresses over v4-compatible addresses will help the transition?

Let's take the example of a site where you introduce IPv6 gradually
using 6to4 and IPv4 compatible techniques.
The servers that will need to be accessed both from the v6 world
and the v4 world are assigned a 6to4 IPv6 address, an IPv4 address
(global or private), and an IPv4 compatible address.

Within the same site, some subnets are v6 aware, meaning that
there is an IPv6 router advertising 6to4 prefixes and some others are
not, meaning that no IPv6 prefix is advertised.
On those nets, IPv6 dual stack hosts may use IPv4 compatible addresses
to connect to the servers.

When those subnets become IPv6 aware, i.e. an IPv6 router is installed,
all the sudden the dual stack hosts get a 6to4 IPv6 address on top of the
IPv4 compatible one. Network admin might espect those hosts to use
the address derived from this 6to4 prefix and not the IPv4 compatible address.

In that case, the transition will be easier if 6to4 addresses were giving
a better priority over v4 compatible.

         - Alain.