DHCP Gives out wrong Subnet Mask

[cisscott]

Windows 2K Adv Server

I have set up a test network at home, with a Windows 2K Adv Server, and 3 clients, all running XP Pro. Everything is working perfectly, except that the clients are getting the wrong subnet mask from DHCP. The subnet is 10.0.0.x. I have the subnet mask set to 255.255.255.0 in TCP/IP properties. However, in the DHCP Mgmt Console, the Server Scope Properties has the mask as 255.0.0.0 .. The box is greyed out and I do not have the option to change it. I have tried various setting with the Mask Discovery in DHCP. I have checked my router to be sure it isnt issuing DHCP, and originally it was, but I disabled it and rebooted everything and am stil unable to get DHCP to issue 255.255.255.0. Any hints ? Thanks !!

 

[cisscott]

Further Clarification... "ipconfig /all" on the server says it is operating in the 255.255.255.0 mask. I cannot find anywhere on the system where the dhcp snap-in could be pulling that other mask from. I have 4 ip addresses configured on the same NIC (for IIS websites) but they are all set up as 255.255.255.0 as well, and confirmed in ipconfig.

 

[JockFrog]

Hi Cisscott,

10.0.0.0 is a Class A private network /8 255.0.0.0 by default your DHCP server will suggest the mask should be but you can change it
10.10.0.0 is Class B technically /16 255.255.0.0
10.10.120.0 is Class C /24 255.255.255.0 technically

If the DHCP server options are greyed there must be something defined elsewhere. Have you did a ipconfig/ release
ipconfig/ renew? to get the new address + mask

 

[cisscott]

Thanks for the reply. Actually I figured it out. It was one of those "couldn't see the forest for the trees" deals. I just deleted the scope and recreated it, and changed the mask, instead of accepting the default.