Set a specific reply address

Tom Schmitt TomSchmitt at
Thu May 3 12:31:20 UTC 2012

-------- Original-Nachricht --------
> Datum: Fri, 27 Apr 2012 14:06:58 +0100
> Von: Simon Hobson <dhcp1 at>
> An: Users of ISC DHCP <dhcp-users at>
> Betreff: Re: Set a specific reply address

> >I had (actually have) the same problem, tried both and they didn't help.
> >Like Glenn wrote, dhcpd then writes the wanted address in some 
> >fields of the DHCP paket, but the IP packet still uses the wrong 
> >source IP.
> Why is that a problem ? As long as it comes out of the right 
> interface, and has the right destination address, then it should 
> work. 

Sadly no. 
Normaly it does work, yes, but it became a problem when firewalls came into the game. They have only the service-IP for DHCP allowed and does not know anything about other interfaces on my DHCP-server. And there DHCP is failing if the packets are send with the wrong source IP in the IP-Header. :-(

Another example that came along was DHCP forwarding in a VPN-device, but this is a very specific problem.

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