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 From:  "Jewell, Michael" <mjewell at law dot umaryland dot edu>
 To:  'Ulrik Lunddahl' <ul at proconsult dot dk>, "m0n0wall at lists dot m0n0 dot ch" <m0n0wall at lists dot m0n0 dot ch>
 Subject:  RE: DHCP Relay and DHCP server at the same time.
 Date:  Wed, 1 Feb 2012 10:13:24 -0500
If you can't get Relay/Server working together, an alternative option is to create a second scope on
Windows Server and set up relay on the Opt2 Interface. This will let you define a small block of
available addresses and leave the rest of the subnet open for static assignment.

I do the same thing on my printers subnet,  all printers are static assigned but when I install a
new printer it gets an address from the pool of 10 IPs, then I change it after I have verified it
has connectivity.  On HP printers it has a side effect of pre-populating the Static fields for you
with all the right info and you just have to change the last octet of the address.


-----Original Message-----
From: Ulrik Lunddahl [mailto:ul at proconsult dot dk] 
Sent: Wednesday, February 01, 2012 4:40 AM
To: m0n0wall at lists dot m0n0 dot ch
Subject: [m0n0wall] DHCP Relay and DHCP server at the same time.

Hi Everyone!

Today i had the joy of not knowing what was going on my network...:)

My setup is with 4 physical interfaces, WAN (static), LAN (Servers), OPT1 (Client PCs), OPT2 (IT

I have a Windows DHCP server on the LAN subnet, and is using DHCP Relay on the OPT1 interface to
Relay DHCP request to the DHCP server, this has been working for quite some time, no problems at

Yesterday I enabled the DHCP server on the OPT2 interface, most equipment is switches, UPS'es and
Remote Management Cards for server, so thay have static IP addresses, but when I bring my notebook
or install new equipment I would be nice to have a DHCP service on this subnet/VLAN, so I enabled

It was not working, as in, I did not get an IP address on my notebook as expected, so I wrote it on
the tofix list and went home.

This morning clients on the OPT1 interface complained about lost network connectivity due to missing
DHCP service, the DHCP server was fine, so I went on an disabled the DHCP server on the OPT2
interface, and immediately the DHCP Relay was working again, and the problem was solved.

Is it possible that the DHCP Relay and the DHCP Server is not working at the same time, of course it
cannot be active on the same subnet, but should it not function on different subnets ?

The OPT2 interface is new, it used to be on a separate m0n0wall installation, but a few days ago I
consolidated my firewalls.

Can anyone give me a hint to where to pinpoint the error ?

Med venlig hilsen, Best regards
Ulrik Lunddahl

Sales Manager - Salgschef
PROconsult Data A/S - Rugårdsvej 15 - 5000  Odense C
Tel: +45 63113333 - Tel dir: +45 63113341 - Mobil: +45 26363341 - Fax: +45 63113344
E-mail: ul at proconsult dot dk<mailto:ul at proconsult dot dk> - Web site: