Reply to remote unicast DHCP requests

Glenn Satchell glenn.satchell at
Tue May 3 15:39:35 UTC 2011

On 05/04/11 01:23, Paúl Ortiz Imedio wrote:
> Simon Hobson wrote:
>  >In that case, your setup is operating correctly - it is your
>  >expectations that are wrong !
>  >You could have saved a lot of effort by asking earlier, and
>  >mentioning the authoritative/DHCPNAK element to the story.
>  >If setting the server as authoritative results in it DHCPNAKing
>  >the request, then the requested address is not valid according
>  >to the DHCP server setup. Setting the server to
>  >non-authoritative results in it simply ignoring the invalid
>  >request - by design.
>  >So you need to determine why the server believes the requested
>  >address to be invalid.
> I know that is what I need to solve, but I cannot guess what is
> wrong because my scenario is quite simple:
> CLIENT - net1 - RELAY - net2 - SERVER
> The server configuration only defines the remote subnet (net1).
> It has no subnets defined for DHCP at local interfaces (net2).
> I looked for an explanation at the code and then I found what I
> reported in my first post: the request is being discarded
> because the server receives the packet through a local
> interface (connected to net2) with no shared network associated.
> The content of the DHCPREQUEST is:
> - ciaddr = IP of the valid lease
> - yiaddr = siaddr = giaddr = 0
> - client HW address
> - options: 53 and 55
So do you have a definition for net2 in dhcpd.conf?

There needs to be a minimal definition, even if there are no clients on 
that subnet. Something like:

subnet a.b.c.0 netmask { }

(with whatever the appropriate subnet and netmask is.)

That should all be fine. The dhcp server is always going to receive 
requests via the local network interface.

I think you are confused by the shared network bit in the source code. 
That's probably checking for an additional ip range that could be valid 
in the local subnet.

Are there other clients on net1 that do work? Or do all clients fail to 
renew? Can you ping the client from the dhcp server? Is the default 
router set properly on the client via the initial dhcp request? Is there 
a firewall in there anywhere, either between the subnets or on the 
device in question?


More information about the dhcp-users mailing list