Clients getting wrong IP info from DHCP server

[pac0124]

We have our DHCP server setup to issue IP, Gate etc.. to all of our win 9x/2K/XP workstations using the following IP 192.168.1.50 ->> 100. About 2 years ago we connected another LAN with it's own server, DHCP etc to connect and get access to our AS/400 through a switch. This was to allow 3 PC's with a Dual Boot OS with a second NIC card with Static IP's (192.168.1.30 ->> 32) get access. Their LAN IP use is 125.x.x.x sub 255.255.255.0. We never had a problem until about 2 weeks ago we started to get user's workstations with their IP. Not all workstations are getting their IP info just a few.

It was thought that because the 2 DHCP servers had separate network ID's that the clients from either side would not pickup any IP's from each others DHCP server. My first thought was someone on the other side created an authorized scope with our network ID that created a rogue DHCP server. But it is being debated.

Can someone maybe clearup any misconceptions we apparently are having?

Thanks

 

[ricpinto]

Can you give a crude illustration how's the 2 network was setup. Include the routers, switches, servers,as400, w/s, etc. and also the ranges of each dchp servers. This way it's easier to exchange ideas.

 

[pac0124]

Sorry for being short on information, I was running out of time. (LAN 1) - 6 Windows 2K servers. The DC has DNS, DHCP, Exchange 5.5 and print server. 1 Backup server, 1 web server, 1 file server and the rest have specific applications installed. We only have 1 AS/400.

We have about 75 workstations on this network. About 30 are win 98 serveral are XP Pro, the rest are W2K pro.

The DHCP scope is has IP allocation from 192.168.1.50 to 150, subnet mask 255.255.255.0, router 192.168.1.10, DNS settings are set to the DC DNS server which also fowards to the ISP DNS IP.

1 PIX firewall for the DSL connection.

All the switches in the LAN are HP ProCurve Switches.

(LAN 2) - This information is going to be difficult, the new IT admin refuses to tell us the scope and or let anyone look at the settings on the DHCP server. With the previous admin, he would have told us what we needed and helped us out to figure out what happened. This much I can tell you. 3 PC's with Windows 2000 Pro have 2 NIC cards installed. To access our AS/400 the 3 PC's previously was running win 98 se, and they reboot the PC to win 98. These PC's have a static IP configuration for our network. These PC's are connected to there switch in a closet somewhere in the building. At the main closet in the data center, a cat 5 cable runs through to an uplink port on our Procurve. I don't remember their exact IP at the moment but this is what I remember, 125.125.x.x. They have about 15 servers that are windows 2000.

Hope this helps

 

[ricpinto]

Ok it doesn't help either because LAN2 is not transparent.

Question:

Is the 2 network is separated by a router (just to make sure)?
------------

Basically router don't broadcast as a default so DHCP don't cross to other LAN as well. They activate DHCP relay agent (IP helper for Cisco) to extend the range of DHCP accross diff subnet. Now did you already disable broadcast and DHCP relay agent on your router?

 

[pac0124]

Ok, No router between the 2 lans, a straight connection. Looks like the problem is not filtering the broadcast for the DHCP server, correct? Any recommandations as to type of router I would need? make model if possible.

Thanks

 

[ricpinto]

Anyway what you want is to isolate the broadcast and DHCP servers then you can use any new router box (linksys, netgear, smc etc etc, they are cheap nowadays. If you have the budget then go for Cisco). But remember to check the settings, make sure DHCP relay agent is not supported or turned off.

 

[bcastner]

http://support.microsoft.com/?kbid=303351