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DHCP Migration 2008 to 2012R2

Posted on 2014-01-15
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Last Modified: 2014-01-16
Dear Experts,

Im in the process of migrating, DHCP from 2008 to 2012R2.
I create all the scope detail, reservations...

At first the scope overlaps with the 2008 scope, 172.16.2.1 - 200
I stop the 2008 DHCP service, perform an IP release/renew on a test machine and nothing.
Checking the event logs shows

The IP address lease 172.16.2.1 for the Network Card with network address xxxxxxxxx has been denied by the DHCP server xxxxxxxx (The DHCP Server sent a DHCPNACK message).

I have since deleted the Scope totally and placed it on a differnet range. 172.16.4.1 - 172.16.4.200

Now I just get a timeout that the DHCP server can not be contacted. The 2012 r2 server is authorised but im not sure why it wont give out addresses.
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Question by:Rio_10
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6 Comments
 

Author Comment

by:Rio_10
ID: 39782046
I did some more testing and it appears to be an issue with the subnet on the scope.

its doesnt seem to work with a 255.255.252.0 subnet but does with a 255.255.0.0
the DHCP server is on 172.16.10.201 with 255.255.252.0 so the scope was set with 172.16.2.1 -200 with 255.255.252.0. This should work but the clients do not get an IP, any reason why
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LVL 43

Expert Comment

by:Steve Knight
ID: 39784086
Is this all one subnet, or multiple VLAN's

Does the server's own IP address range agree with the range being given out by the DHCP server including the subnet mask?

Might be worth getting wireshark or network monitor to see what is coming through

BTW I haven't tried into a 2012 server yet but you can normally dump the DHCP settings, amend as needed and re-import if you aren't aware using:

netsh dhcp server \\dhcpserverip scope 172.16.0.0 dump > dhcp.txt

then can edit the dhcp.txt file as needed, delete the scope manually and re-import with:

netsh exec dhcp.txt

Might be worth checking what IP address is showing as bound to the DHCP server, double check it is authorised, look in NETSTAT -AN that dhcp port is listning etc.

Steve
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LVL 51

Accepted Solution

by:
Netman66 earned 1000 total points
ID: 39784372
Based on the server's IP and mask, the network range is 172.16.8.1-172.16.11.255.

You can't give out 172.16.2.0 network addresses as it's not on the same network.

Adjust the scope to be in the network range above and it should work.
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LVL 43

Assisted Solution

by:Steve Knight
Steve Knight earned 1000 total points
ID: 39787245
Netman66, Had misread the subnet mask earlier, though wouldn't the original request and offer work, though the dhcp client would then not be able to communicate with the DHCP server to complete the transaction.

If he wants those addresses 255.255.240.0 is smallest logical, /20 at a quick look though why you would want a flat network of that size without VLAN's seems unusual.

Would seem more logical to split off into smaller more manageable chunks and issue DHCP for different scopes within that?

Steve
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LVL 51

Expert Comment

by:Netman66
ID: 39787278
@Steve

You can make it work, but you would need to mask the server so it's on all local networks (thus why it worked when giving out /16 addy) and create scopes for each vlan.  The server will assign an address based on the incoming subnet.

You also need to ensure that inter-vlan routing is working or at least between the server vlan and all the others for this to work.

So, that being said, change the subnet mask on your dhcp server to 255.255.0.0 to cover all class B addresses - or figure out what mask will allow your server to live in each local subnet.
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Author Closing Comment

by:Rio_10
ID: 39787789
Thanks guys, the subnet was incorrect. I created 255.255.240.0 and all is ok
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