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Newly migrated 2008 R2 DHCP Server not assigning addresses to other networks

So I did a 2003 to 2008 R2 migration of our DHCP this weekend. Today it seems as though anyone not in the same network as our DHCP server is NOT getting an address - they pull an IPIPA address instead.

Setup:
DHCP is in 10.1.1.x network
Clients in 10.1.x.x networks don't pull address

My migration path that I followed was very straight-forward. Basically a backup of existing and imported in to 2008. No IPs on the servers have been changed so my DHCP now resides at a different address than it did before the migration as I still have shares on that old 2003 box that I have yet to move. (I know some instructions recommend you add the old IP as a secondary address on the new server)

I have verified that the new scopes are all active. The old DHCP server has been de-authorized and the DHCP service on that box has been DISABLED.

Any thoughts? The majority of my currently leased addresses are due to expire in about 8 hours.
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Commented:
Silly question,

Did you authorized the new server, and started the service?

Author

Commented:
Yup, well at least it says "unauthorize" now anyway if you right click on the server and "deactivate" if you click on one of the other scopes.

Like I said though - seems to be fine for those machines in the 10.1.1.x scope - just issues with 10.1.x.x scopes that its a problem.

Bit of an update as well - I can add that a PC in the 10.1.70.x scope that was left on over the weekend during my upgrade appears to not have any issue - so looks like it renewed its IP and carried on its merry way. Maybe it was only machines in "other" scopes that weren't on the network that aren't pulling. I'll try and get more info on that.

Author

Commented:
So just to add a bit more - seems like anyone who had a machine on when their lease expired is not having an issue. The two laptop users who are having issues brought their machines home with them and now cannot pull an address.

As a test I put our training room on 10.1.20.x VLAN and restarted two of the machines - they both do NOT pull an address.
Commented:
You could start a wireshark on your DHCP server, and sniff for DHCP messages (DHCPDISCOVER, DHCPOFFER etc.) to get a clearer picture of what's going on when the clients are requesting adresses.

Author

Commented:
Good idea - ok so set that up and created a filter for DHCP v4 (the only one I'm running in my network btw) and I do see lots of DHCP Inform and ACK traffic - I do not see anything coming from any other scopes.

I set one of my training room PCs with a static addy in the 10.1.20.x scope and it connected fine and all worked well. Changed it back to DHCP and it just gives me an error saying that it cannot contact the DHCP server.

Something else I should note - I am using a ip-helper address of the OLD DHCP server for my VLANs - I'm suspecting thats where my problem is. Going to try changing that to the new DHCP server and see what happens.
So just to put this issue to bed - it was the ip-helper address on the vlans - they were all pointing to my old DHCP server which has been decomissioned. Once I added the new DHCP server helper address it started handing out addresses right away.

Thanks for your help slakic - setting up the Wireshark helped me realize that no traffic at all was getting to the DHCP server which led me to revisit my switch config.

Author

Commented:
Issue ended up being ip-helper address on the switch which was the root-cause - Slakic's suggestion to use Wireshark led me to question the config on the vlans.