Relay agents, NAT, and offers to giaddr

David W. Hankins David_Hankins at
Fri Sep 15 22:02:15 UTC 2006

On Fri, Sep 15, 2006 at 02:10:36PM -0700, Alan DeKok wrote:
>    Maybe I'm crazy, but my tests with ISC & a hacked-up test client 
> indicate that so long as giaddr is set, that's where the reply goes. 
> I've successfully had it renew leases for IP address X that were unicast 
> from IP Y (i.e. giaddr).

The only exception is for DHCPACKs in response to DHCPINFORMs.

Such packets are explicitly required by RFC to be delivered to 'ciaddr'
regardless of any other input (even and especially if giaddr is set).

Suffice to say we do not even do this, due to the...imaginative ways
that client systems (notoriously MS 'dot net' devices and Macromedia
Shockwave/Flash widgets) have interpreted that same document.

ISC Training!  October 16-20, 2006, in the San Francisco Bay Area,
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David W. Hankins	"If you don't do it right the first time,
Software Engineer		you'll just have to do it again."
Internet Systems Consortium, Inc.	-- Jack T. Hankins

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