DHCP Migration 1

[SLMHC]

The OS partition (win2k) on my old DHCP server was getting close to full, so I used this MS article,

http://support.microsoft.com/kb/325473,

to migrate to a new Win2k3 server. The migration worked as I was able to import my old settings into the new server, and authorized the server. I then uninstalled the DHCP services from the old server(i think this is where I went wrong).

I came in this morning to a number of PCs not getting IPs. I tried to /release /renew to no avail. Now a number of my subnets cannot update their IPs. As the clients IP lease time runs out I get new calls about no network connection. As a temp solution I have set these clients manually.

Is there any way to force an update on the client?

-Dave

 

[GlenJohnson]

Make sure the problem machines have there cache cleared. Run ipconfig /all on a problem machine, and compare that to one on a good machine. What's the os of the client side? Good luck.

Glen A. Johnson
Johnson Computer Consulting

 

[SLMHC]

Both Win2k SP4 & XP SP2 are having issues. It seems to be more a subnet issue than a client type issue. 10.1.1.x subnet had a short lease time and over the weekend all seemed to have updated to the new DHCP server. 10.1-9.1.x had longer lease times (6-8 days).

Would restarting the DHCP on the old server and not enabling them help?


-Dave

 

[FaiTHLeSS]

Was there a UDP/IP helper setup on one of your core switche(s) that pointed to the IP of the DHCP server? If so you will need to change this to point to the IP of the new server.

The helper allows clients on different subnets to locate DHCP servers on other subnets from which they are on.

 

[SLMHC]

I checked the config and didnt see anything so I next checked the tech support info and found:

ip helper-address 10.1.1.1

This is a Cisco 2610 w/ only a CLI available to me. Any know the command to check if this is a DHCP helper-address?

-Dave

 

[SLMHC]

faithless, thanks for the direction pointer...i had a sneaking suspicion that I had to look to the router...i just didn't know what to look for.

I found out how to change the help-address here:

http://www.thespeedtest.com/?p=56

and saving the running config here:

http://www.joshgentry.com/cisco/cisco.htm#sect3.4

-Dave

 

[SLMHC]

After another day the helper addresses are not working. This is truly puzzling.

Any other ideas?

-Dave

 

[FaiTHLeSS]

Possible to give the new DHCP server the same IP as the old DHCP server?

Are there any firewalls between the subnets to that could be blocking requests going the the DHCP.

 

[SLMHC]

Old DHCP is still PDC emulator, so i don't think so.

no firewalls inside the network.

-Dave

 

[IRudebwoy]

Put a network analyzer on the server to see what is really going on. While capturing packets on the server renew the lease on a problem client.

If you see DHCPREQUEST's with the MAC address of the client you're almost there. The proper sequence for a working client is REQUEST (to server) -> REPLY (to client) -> ACK(nowledge to server the IP assignment). Before the server replies to the client, and assigns its IP address, it pings the address to verify it's available. If your server can't reach the subnet the request came from it cannot assign the address. If your server can reach the subnet it's almost certain a configuration issue.

If you don't see the requests they are being held up somewhere or misdirected, double check your layer 3 devices (switches and routers) for the UDP helper mentioned by FaiTHLeSS earlier.

Happy hunting!

 

[IRudebwoy]

BTW, wireshark is a free analyzer that can decode many protocol types.

 

[SLMHC]

Is there something I can filter by?

-Dave

 

[SLMHC]

Ive been watching the logs for a while and the only DHCP info I see is the ports on my router.

DHCP Discover - Transaction ID....

I did a renew on the local subnet and saw the following:
DHCP Discover
DHCP Offer
DHCP Request
DHCP ACK

it then goes on to register with DNS...

I do not see this for remote subnets.


-Dave

 

[IRudebwoy]

If you can't see activity from the clients on the problem subnets that means your client's discover packet is not making it to the server. Check for UDP helpers and dhcp-relay settings on your switches and routers that server the problem areas.

How are you connected to you remote subnets? Are they over a WAN link?

 

[SLMHC]

I rechecked the UDP helpers on my router, they are present. none of my other switches have them. i checked the clients after lunch any they now have IPs given out by the new DHCP server. I didn't really do anything, just let some time pass.

-Dave