DHCP problem

Darren Dunham ddunham at taos.com
Tue Sep 14 19:04:30 CEST 2004


> > Hi all,
> > I have some problem checking dhcp service on 4 windows dhcp servers
> > from a Linux Machine. The string error is 
> > 
> > (command: ./check_dhcp -s 10.10.10.10) DHCP problem: Received 3
> > DHCPOFFER(s), 0 of 1 requested servers responded, max lease time = 0
> > sec.  
> > 
> > I think it's due to a firewall or netowrk configuration but i don't
> > know what port needs to be opened in the firewall..... 
> > 
> 
> AFAIK, DHCP is a broadcast protocol and as such the DHCP server must be
> on the same LAN segment, with no firewall in between, to be able to see
> DHCP offers.

That's not quite correct.  DHCP's ancestor BootP was specifically
written to overcome some of the network limitations of using RARP as an
IP request protocol.

While the client will often broadcast the packet, it's pretty easy to
configure a router or relay-agent to pick up the packet and forward it
to a DHCP server on another segment for the response. 

Also, the error message states that the client recieved a DHCPOFFER.
It's the later phase of DHCPREQUEST that is failing.  I don't think that
would happen if there were a pure firewall/reachability issue here.

UDP ports 67 and 68 are used for BootP/DHCP communication.

-- 
Darren Dunham                                           ddunham at taos.com
Senior Technical Consultant         TAOS            http://www.taos.com/
Got some Dr Pepper?                           San Francisco, CA bay area
         < This line left intentionally blank to confuse you. >


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