Subject: RE: WGLC ent-analysis-03: DSTM

From: "Christian Huitema" <[email-masked]>
Date: Mon, 22 Aug 2005 11:37:21 -0700

>    While DHCPv4 may or may not require minor tweaks (e.g., relating to
>    link-layer adaptation),
> 
> => using DHCPv4 over a tunnel is *not* a minor tweak.

Let see. Assume that you have a native IPv6 "site", over which you can
reliably send multicast packets. Assume that we have defined IPv6
multicast addresses that reach all the nodes within that scope. Then,
you can pretty much port DHCP and ARP over that scope, using the node's
IPv6 address instead of the Ethernet address. You obtain a basic "IPv4
over IPv6" solution. It is hard to be simpler than that.

Obviously, there are a few tricky issues. We need a payload type for
IPv4 (done) and another for ARP (not done). We need a way to properly
delineate the scope of the IPv6 "site", probably using an IPv6 prefix
that shall be configured on every node. We need to get the multicast
addresses registered, and probably registered in a way that attaches
them to the selected IPv6 prefix.

The design becomes a little bit harder if we cannot use multicast,
either because it is not reliable or because it creates too much
overhead. But there are solutions -- certainly simpler than doing IPv4
over ATM.

-- Christian Huitema

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From: Pekka Savola <[email-masked]>
Date: Tue, 23 Aug 2005 13:47:12 +0300 (EEST)

I've changed the subject line, as a placeholder for future 
discussions..

>> => using DHCPv4 over a tunnel is *not* a minor tweak.
[...]
> overhead. But there are solutions -- certainly simpler than doing IPv4

Well, we could have the same assumptions as DHCPv6 -- either 
multicast, or relays (certainly not just multicast).

But can't we just make the assumptions:
  1) the tunnel is point-to-point, so neither side performs ARP (so we 
may not need to define ARP), just throws the packets over.

  2) DHCPv4 server must reside at the tunnel end-point.

Isn't it then pretty much irrelevant which L2 addresses are used by 
the client (in the payload) as long as they're a good identifier in 
the DHCP server's database?

Note that I don't see modifications to DHCPv4 client or server 
software as a problem (but hopefully the changes should be minimized), 
because those sites wanting to deploy v6 dominant networks require 
lots of software updates in any case.

Maybe this discussion should go over at DHC WG, though.

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings

---

From: Stig Venaas <[email-masked]>
Date: Tue, 30 Aug 2005 11:42:55 +0200

> over IPv6" solution. It is hard to be simpler than that.

Sounds quite a bit like 6over4 (:

Stig