DHCP Subnet mask problem

[wizzer]

Hi I'm running Windows NT server 4 and it's set up to use the 10.x.x.x range of IP addresses, in the DHCP manager the range is set from 10.0.0.1 to 10.0.0.255 and the subnet mask is set to 255.255.255.0 however i'm sure that the subnet mask should be 255.0.0.0 for this range of addresses (Some of my older equipment wont accept this subnet mask with one of these IP addreses). I can't change the subnet mask that is set though. Do I have to delete the scope thats there at the moment and re-create it? What effect will doing this have on the computers which currently lease addresess from the server?

Thanks for any help!

James.

 

[ShackDaddy]

I'm surprised that you are having trouble using a 24-bit mask with this address range. As long as you are only working with a single switching/hub subnet and aren't using any statics outside the 10.0.0.x range, DHCP shouldn't cause you any problems. In any case, if you delete the scope and recreate it, you should be safe as long as you don't add any new clients to the network until all the current clients have had a chance to renew their existing addresses. Basically, a client will try to renew its current IP address on the server, and if the address is available in the scope, it will be automatically be assigned to it.

ShackDaddy

 

[OzDog]

I am a little perplexed.

What are the older devices you are talking about? Are they PCs or just devices with network ports?? How old?

The thing about TCP/IP is that you can technically use any number of bits (between 1 and 30) for the mask. That means anything from 128.0.0.0 to 255.255.255.252 should be valid. This is called variable length subnetting and is part of the TCP/IP standard. All your devices should let you specify this, or accept it from DHCP.

I don't know your situation, but if you are running a small network, have you considered using the Class C private range (192.168.16.x)? This uses a default mask of 255.255.255.0, and maybe the devices will accept that.

With a little more info, I may be able to help more...

Cheers,
Sam

 

[wizzer]

My older devices are Zeta Smartservers ( a kind of ISDN router), if I set the ip of the device at, say 10.0.0.30, if i put in the subnet mask as 255.255.255.0 and try to save it - it just tells me that the subnet mask is invalid. When I put it in as 255.0.0.0 it accepts this. All these devices used to be on a class C range but we have moved premises and have to conform to the network which is in place there using the 10.x.x.x range. The problem is that some of the devices on the NT network using the 255.255.255.0 subnet mask are having problems communicating with the Smartserver devices.

Thanks for all the help so far! I'm going to try altering the the DHCP scope to use the 255.0.0.0 subnet mask tonight and see how I get on.

 

[seanos]

The only reason using a class C range wouldnt work is if there are more than 253 devices on your network.
Is this the case??

 

[wizzer]

I've re-configured my DHCP scope to have to have the subnet mask 255.0.0.0 with no problems.

It's not fixed the main problem which does seem to be realted to the old Smartserver routers and we have now decided to take these out of use so I don't need to do anything about it!

Thanks for all the advice.