Re: [dhcwg] Re: DHCP behind NAT

Bernard Dugas <bernard.dugas@is-production.com> Sat, 01 September 2001 12:07 UTC

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Date: Sat, 01 Sep 2001 13:57:07 +0200
From: Bernard Dugas <bernard.dugas@is-production.com>
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To: Ted Lemon <mellon@nominum.com>
Cc: dhcwg@ietf.org
Subject: Re: [dhcwg] Re: DHCP behind NAT
References: <200108311654.f7VGslj00311@grosse.bisbee.fugue.com>
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Hello,

Ted Lemon a écrit :
> I agree with you, by the way, that your proposed way of doing this is
> better than the way that RFC2131 does it.   The problem is not that
> you're wrong, but that you're too late - this behavior was
> canonicalized in RFC951, and that's the last time it was possible to
> fix this the way you propose.   :'}

It's the 1st time that somebody tells me I've been born too late,
normally this is the opposite ;-)

Note that answering the ip source address is exactly the same that
answering the giaddr in a normal routed network, as the relay is the ip
source. So the proposed patch is not changing any behaviour in a normal
routed network, it's just changing behaviour in NAT context.

> I would recommend that you investigate the
> subnet selection option.   Send the address to which you want the
> reply sent in giaddr, and use the subnet-selection-option to store the
> address you would otherwise have stored in giaddr.

So I have to tell that to Cisco, so they change the way their NAT handle
DHCP relayed packet : only their NAT knows what is the right address to
answer to.

> There's no way to make your proposed change RFC2131 at this late date.
> Too many devices have been deployed that follow the current protocol
> specification. 

So ISC DHCPD will be the only available with a patch for NAT context,
and I will be the only ISP with a NAT service for its customers ;-)

More seriously, what is the point of a Request For Comment if valid
comments can't be  included ? Actually, I had no time to learn the
normal process of IETF, so I may have missed some points in the process.
I should spend some time on that.

Did you see the patch at :
http://www.is-pronet.com/download/dhcp-3.0rc11_NAT_patch.tar.gz

By the way, the ip source address is now in the lease struct, but not
the udp source port : a complete patch should certainly add it.

Thanks a lot for your answer, and for your work with this powerful ISC
DHCP server.
-- 

 __________ Bernard DUGAS ________________________________________
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