client refuses to accept offer

Simon Hobson dhcp1 at
Thu May 13 17:55:13 UTC 2010

anctop wrote:

>  > I notice that your router is not in the same subnet as the client.
>>  That is probably a misconfiguration.  The router should probably be
>> or similar.  Maybe this is why your clients are rejecting
>>  the offers.
>The router setting does look unusual, but this is what the local net.
>admin has told me for configuring static IP addresses.

It's wrong. The router needs to be in the same subnet as the client - 
otherwise the client doesn't know how to reach it. It is possible to 
setup static routes, but that precludes using DHCP !

>  > I'm confused ! You say there is no traffic to/from the DHCP server,
>>  but then say it's from to
>>  The initial DHCP-Discover will be from as the client doesn't
>>  have an IP address at this time. It's always to (the
>>  broadcast address) as it doesn't know the address if the server.
>>  The server will respond to the broadcast address as well.
>By "no traffic to/from the DHCP server", I mean none of the wireshark
>DHCP entries has the address of my server as source or destination.

I get it now. As I explained, there's a lot of broadcast traffic 
since the client and server need to communicate when the client 
doesn't have an IP address.

>I think Randall C Grimshaw may have told the most likely cause.
>>  Sounds like the network is suppressing your DHCP, possibly using Cisco
>>  DHCP-snooping or similar. This would not be surprising in an 
>>enterprise environment
>>  where DHCP can be very disruptive. Its use should always be 
>>coordinated through
>>  your central administration.
>I'll try to justify it.

A simple test for that is to use your own cheap switch between server 
and client - so the traffic doesn't go through the main switches. In 
fact, for testing, I'd generally advise that you start off on an 
isolated network so that your can't kill the company network if you 
get it wrong. We had out internal network taken down twice a few 
months ago when people got new Windows mobiles and starting playing 
with the features. One of the features was the mobile data -> 
wireless LAN gateway, and the mobile automatically connected to the 
internal wireless, on the same address as the real gateway :-/

Simon Hobson

Visit for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

More information about the dhcp-users mailing list