DHCP scope issue

[wfr33man1]

Asking this out to the general Cisco community:

I have a DHCP superscope setup on a Win2K3 server which is in the 209.180.X.X range. I moved it to a new DHCP server which is in the 192.168.X.X range. None of my clients could obtain an IP address. I changed the ip helper-address to the 192.168.X.X server and still no one was able to obtain an IP address. I cut back to the original configuration and all is well.

Anyone have any ideas as to why the move didn't work? I was first thinking that it had something to do with the 209.180.X.X addresses and the 192.168.X.X, but after going over varying scenarios I'm stumped.

[Richard Burts]

Some additional detail about what you did and the results from it would help. What I think I understand is that you created a new scope(s) on a different server without changing the helper address and it did not work (no big surprise there). You changed the helper address to point to the new server and it did not work (that may be an interesting question). Then you went back to the original configuration  and it worked (no big surprise there).

When you configured the scopes in the 192.168 range did you change the IP address of the layer 3 interface for the clients is located? If you did not change the IP address then that is why the new scope did not work. If you did change the IP address then we need more detail about what you did to be able to determine the cause of this issue.

HTH

Rick

[wfr33man1]

Rick, thanks for answering my post. Here's some clarity on the issue:

I moved DHCP scope 209.180.X.X from the server 209.180.X.X to a new server 192.168.X.X. I changed the ip helper address from 209.180.X.X to 192.168.X.X (new server IP).

None of the clients could obtain DHCP addresses.

I believe this is due to the IP on the VLAN 209.180.X.X is secondary and not primary for the interface.

the interface config is as follows:

interface vlan X

ip address 205.143.X.X/24

ip address 209.180.X.X/24 secondary

ip helper-address 209.180.X.X

The DHCP offer will only come from the 205.143.X.X as it's the primary address on the interface. I think I'm right, but would like to know for sure.

Thanks,

Will

[Richard Burts]

Will

Thanks for the additional information which is quite helpful. Yes you are correct that configuring a secondary address complicates things when you are using DHCP and is the cause of your issue. See this link for a potential solution which can use DHCP pool for the secondary address, but to be used only as overflow if the primary pool is exhausted.

https://supportforums.cisco.com/discussion/11421896/secondary-ip-address-and-dhcp

HTH

Rick

[paul driver]

Hello

"I believe this is due to the IP on the VLAN 209.180.X.X is secondary and not primary for the interface."

Using secondary addressing on the L3 interface and then applying an dhcp scope to the secondary can cause an issue-

There is a feature called ip dhcp smart-relay which accommodates secondary addressing for dhcp, It works when dhcp offers from the primary dhcp scope fails ( primary scope maxed out or is unavailable)

try to add this to your L3 interface-

Also as this is a windows dhcp server, are you using Active directory and if so are they authorized and activated and  reachable within the network?

res

Paul

[wfr33man1]

The problem was with the primary interface IP address being different from the DHCP scope. I had to enable the ip dhcp-smart-relay command globally and things now work just fine.

The Secondary IP address is where I was trying to get the DHCP to answer from and it wouldn't without enabling this command.