Subject: Re: dhcpd(8) _cannot_ be completely disabled on an interface
To: Andrew Brown , Dennis Ferguson <>
From: John Nemeth <>
List: tech-net
Date: 01/09/2002 18:52:40
On May 30, 10:56am, Andrew Brown wrote:
} >The way sending the response back is usually accomplished is to manually
} >add an ARP entry for the host at its new address, if the incoming interface
} >was an ethernet, or to configure the arrival interface's destination
} >with the new address if the incoming interface was point-to-point.  Then
} >you can send the response back addressed to the host's new address on
} >a regular UDP socket.  In fact just broadcasting the response back will
} >work as well, too, the client is required to verify that the response is
} >to its own request from the contents of the dhcp packet in any case.
} and...if the address isn't on the local network, then adding an arp
} entry will fail, no?  i ought still to be able to answer such a dhcp

     Why would it?  It just wouldn't do you a lot of good.  UNIX
doesn't prevent you from doing dumb things since that would also
prevent you from doing clever things (in this case, think Mobile IP).

} request, no?  i'm stuck on seeing the possibility of a discrepancy

     Yes.  You need to send the answer to the DHCP relay agent that
forwarded the request to you.

} between the link layer address that the packet comes from and the link
} layer address as embedded in the dhcp packet itself...kinda like the

     This would be case if a packet was relayed.  The DHCP server would
see the "link layer add that the packet comes from" as being the MAC
address of the relay agent.

}-- End of excerpt from Andrew Brown