Subject: (ngtrans) 6to4

From: Richard Draves <[email-masked]>
Date: Mon, 15 Feb 1999 15:29:32 -0800

The more I think about the 6to4 proposal, the more I like it. When I first
saw the idea last fall, I thought "why not just use a tunnel to join the
6bone". So I want to explain why I'm enthusiastic about it now.

Configured tunnels a la the 6bone have two major problems, as I see it.
First, the 6bone can be difficult to join. You have to find someone already
on the 6bone willing to create a tunnel so you can join. Second, service is
lousy. There are multiple dimensions to lousy - seems like half the time the
routing is screwed up, and when it is working the latencies and packet loss
rates are worse than talking to the same sites via v4. I'll speculate that
the 6bone is generally more broken than the v4 internet because it's used
less and so gets less attention and priority, and the performance is worse
because the configured tunnels do not match well to the underlying v4
topology so packets end up traversing more physical links.

The "tunnel broker" idea solves the first problem, making it easy for anyone
to join. I was very pleased to hear Alain & Marc present their work at the
interim meeting. However, although it solves the first problem it might make
the second problem worse - there's even less reason to believe the
configured tunnel topology will make sense vis a vis the v4 topology.

I think 6to4 is great because it can replace the 6bone and let isolated v6
sites communicate over the v4 internet efficiently. Packets are tunneled
directly to the v6 destination site, so they are routed efficiently
according to the v4 topology. The v6 routing infrastructure is not affected.

From the point of view of aggregatable addressing, the v4 internet becomes a
v6 provider, and as usual a site gets address space from its provider. So an
isolated v6 site gets global addresses from the v4 internet's prefix (the
6to4 prefix). When an isolated v6 site gets a native v6 ISP, then it
renumbers the same as usual when adding or switching to a new ISP.

I plan to implement 6to4 soon (certainly in time for our next MSR IPv6
release) and it would be great to have an officially assigned 6to4 prefix.
How long will this take?

It would also be great to have connectivity between the 6bone and 6to4
sites. I think this is easily possible - we just need one or more well-known
gateway routers with both 6to4 and 6bone addresses. Isolated 6to4 sites can
be configured with routes for 3ffe::/16 to the gateways. Inside the 6bone,
we need to propogate a route for the 6to4 prefix, so 6bone sites can send
packets to 6to4 addresses. I'm afraid I don't know much about BGP - I hope
this isn't hard to do?

One issue with 6to4 that occurs to me - it doesn't provide for multicast
connectivity between isolated v6 sites.

An outline of one solution to this problem: How about hashing global-scope
v6 multicast addresses to a set of global-scope v4 multicast addresses? Then
v6 multicast traffic is tunneled over the corresponding v4 multicast
address. The gateway for a site joins and leaves v4 multicast groups,
depending on which v6 multicast groups its routing protocols are telling it
are of interest to its site. The downside of course is that because of
collisions in the hash, this means some multicast traffic will get carried
to sites that don't actually want it.

Rich

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From: Brian E Carpenter <[email-masked]>
Date: Wed, 17 Feb 1999 07:21:17 +0000

Rich,

We firmly intend to get an improved 6to4 draft out by the cutoff date.
version -00 is somewhat broken. But thanks for yr enthusiasm.

As for the prefix, if there is WG support I will ask the WG
chairs to ask IANA for this. It could take a while of course.

   Brian

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From: Jim Bound <[email-masked]>
Date: Wed, 17 Feb 1999 11:27:56 -0500

Brian,

I am with Rich on this one. 6to4 is a winner IMO.  You have my support
for this work.  

/jim

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From: Randy Bush <[email-masked]>
Date: Wed, 17 Feb 1999 08:47:40 -0800 (PST)

> I am with Rich on this one. 6to4 is a winner IMO.  You have my support

Jim,

Along with the rah rah, you might give some real technical resoponse to
Alain Durand's comments.

randy

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From: Randy Bush <[email-masked]>
Date: Wed, 17 Feb 1999 09:22:25 -0800 (PST)

> ...

<grrrr> apologies for public on a private message.  this list has reply-to:
set.  <grrrrr>

randy

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From: Francis Dupont <[email-masked]>
Date: Wed, 17 Feb 1999 20:09:08 +0100

In your previous mail you wrote:

   Second, (6bone) service is lousy.
   There are multiple dimensions to lousy - seems like half the time the
   routing is screwed up, and when it is working the latencies and packet loss
   rates are worse than talking to the same sites via v4. I'll speculate that
   the 6bone is generally more broken than the v4 internet because it's used
   less and so gets less attention and priority, and the performance is worse
   because the configured tunnels do not match well to the underlying v4
   topology so packets end up traversing more physical links.
   
=> I think the solution is not to jump into a new version of automatic
tunnels but it is to switch from the 6bone to a *real* thing !
The 6ren is a good way to get that because usually RENs have
plenty of bandwidth, know how to setup pre-production stuff and
have no immediate profitability concern... Of course 6ren will be
mainly based on native infrastructure (no hack like tunnels).

I agree with Alain, the issue is the strategy (from the core or
from the edges). I strongly prefer `from the core' because it gives
a better service, I think you prefer `from the edges' because you are
at Microsoft (PC software) not at Cisco (routers) (:-)...
(of course both will occur)

In fact the problem with 6to4 is it can add another step:

automatic tunnels -> configured tunnels -> 6to4 -> native IPv6
                                        ^^^^^^^

Automatic tunnels were great, we need them at the beginning
(I still have a log of a telnet session to ::204.123.39.2
with the date "Thu Mar 30 10:41:42 1995") but today they
are no more great... I am afraid 6to4 will become the same!

=> I think the only way to get a decent multicast service is to have
a native one. I dislike tunnels and DVMRP!

Thanks

[email-masked]

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From: Brian E Carpenter <[email-masked]>
Date: Thu, 18 Feb 1999 13:56:54 +0000

Francis,

6to4 is a way to hop over ISPs who will not run native IPv6.
Obviously, if we could convince all ISPs to run native IPv6,
6to4 would never be needed. But I want to face reality.

   Brian