Subject: [shim6] shim6 over 6to4

From: Iljitsch van Beijnum <[email-masked]>
Date: Mon, 1 Jun 2009 17:11:12 +0200

Erik and I had a short discussion in San Francisco on using shim6 with  
an IPv6 identifier and IPv4 locators. A good way to do this would be  
by running shim6 over 6to4, as the HBA protects the 6to4 addresses  
like normal and the 6to4 address maps directly to an IPv4 address.

I don't remember the details, but I came up with a rather convoluted  
way to do this and then when I started to write it down all of the  
complexity didn't seem necessary: simply run shim6 over 6to4. The main  
issue getting the packets with the right 6to4 addresses to the right  
routers with the right IPv4 addresses (assuming the host doesn't have  
two IPv4 addresses). Other than that, maybe some RFC 3484 preference  
magic could be useful.

Would it make sense to write down how this should work as an  
informational document?
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From: Brian E Carpenter <[email-masked]>
Date: Mon, 01 Jun 2009 16:46:47 +0100

On 2009-06-01 16:11, Iljitsch van Beijnum wrote:
> an IPv6 identifier and IPv4 locators. A good way to do this would be by
> running shim6 over 6to4, as the HBA protects the 6to4 addresses like
> normal and the 6to4 address maps directly to an IPv4 address.

Can you state the goal of this? It only makes sense if there are at least
two IPv4 addresses for the destination site, right? Is that a common enough
case to matter? Most IPv4 multihoming is pure PI, surely?

> 
> I don't remember the details, but I came up with a rather convoluted way
> to do this and then when I started to write it down all of the
> two IPv4 addresses). 

Do you mean the site egress 6to4 routers at the source? There shouldn't be any
issue for the site ingress at the far end. IPv4 routing will do that.

> Other than that, maybe some RFC 3484 preference
> magic could be useful.

What about mixed scenarios, where there's a pure IPv6 path and 6to4 path
to choose between?

> Would it make sense to write down how this should work as an

Maybe. But please clarify the goal first and maybe describe the scenario(s)
in more detail.

   Brian

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From: Brian E Carpenter <[email-masked]>
Date: Mon, 01 Jun 2009 16:46:47 +0100

Brian

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From: Iljitsch van Beijnum <[email-masked]>
Date: Mon, 1 Jun 2009 18:06:16 +0200

> case to matter? Most IPv4 multihoming is pure PI, surely?

Basically, any and all shim6 cases where there is no regular IPv6  
available.

In particular, the "basement multihoming" case would make sense here,  
where a user has two broadband connections that each provide an IPv4  
address and connectivity.

The interesting aspact of 6to4 is that it could be used by hosts that  
want multihoming, but not necessarily care about IPv6. If both sides  
do 6to4 the only penalty is some header overhead. But in the case  
where a host uses 6to4 and the other side native connectivity, there  
could be reduced performance.

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From: Geoff Huston <[email-masked]>
Date: Tue, 2 Jun 2009 06:41:02 +1000

On 02/06/2009, at 1:11 AM, Iljitsch van Beijnum wrote:

> Erik and I had a short discussion in San Francisco on using shim6  
> with an IPv6 identifier and IPv4 locators. A good way to do this  
> would be by running shim6 over 6to4, as the HBA protects the 6to4  
> addresses like normal and the 6to4 address maps directly to an IPv4  
> address.
>
> complexity didn't seem necessary: simply run shim6 over 6to4. The  
> main issue getting the packets with the right 6to4 addresses to the  
> right routers with the right IPv4 addresses (assuming the host  
> doesn't have two IPv4 addresses). Other than that, maybe some RFC  
> 3484 preference magic could be useful.
>

yes, that makes sense to me - tyhe write up may well resolve some of  
the questions I have in reading this brief description

  Geoff