DHCP serving has stopped working

Something happened in our server room over the weekend that had me in the office late Saturday night replacing two switches.
After powering down both racks, I have an issue where none of the computers that use DHCP are getting the settings required for our network.
If they are set to static, everything works fine.  So I think the issue is with the DHCP server.

We have a Juniper Netscreen NS-50 hardware firewall/router that does the DHCP serving.
It is supposed to hand out an address in the range, it's private IP as the gateway and a Windows Server box's IP for the primary DNS.

I can see that DHCP is still enabled in the NS50, so either it's not working properly or it's clashing with something else on our network...

How can I fault find this in order to get it working again?
Reece DoddsAsked:
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Reece DoddsConnect With a Mentor Author Commented:
The issue has been resolved.
It was a setting in the new D-Link switch's web interface under the "DHCP Server Screening"...
I had to enable the port our firewall is connected to as "Trusted" and then add it's IP address as a "Trusted DHCP Server".  Once I applied those changes, everything started working.

@ radhakrishnan2007 - I said that the Juniper firewall IS our DHCP server... the 2003 box only does DNS and AD.  The Firewall router is much much more advanced that the type of router you're thinking of.   Our wireless routers are all set to AP mode, so I knew they weren't the problem.
Sanga CollinsConnect With a Mentor Systems AdminCommented:
If you look at the logs on the NS50 do you see any error about another DHCP server on the network? The other issue you can check for is misconfigured DHCP range or lease times. I sometimes see issues with netscreen where lease times are very long so after major network shakeup, IPs are not realeased back to the pool so computers can use them.
Radhakrishnan RSenior Technical LeadCommented:

It happeneded due to DHCP conflicts, you need to disable the DHCP on the firewall then the actual server DHCP will start offering leased IP's from itself.

I had faced the same issue some time back. I was enabling DHCP on the wireless router and the server stopped serving dhcp addressed. As soon as i stopped the DHCP on the router, it started working again.

Hope this helps.
Reece DoddsAuthor Commented:
Self resolved.
Looking at the Junipers logs did help a little as I could see that it was trying to assign IP's but failing.  Then I looked at the switch's logs and discovered that DHCP Server Screening setting under the "Security" section of the switch.  Thanks though
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