changing subnet mask

In the company I work, we have a problem, we have too less ip-adresses for all computers.
So what I want to do is changing the subnet mask so we get more ip-adresses (atm we have 255.255.255.128).
Me and my college are both new in the company we don't know very well how the network is installed, we cannot risk that the network goes down chancing it.

So my question is: if I change the 128 to 0 can that have any consequences?
Where do I have to look
We have the following operating systems running in our network: Unix, Windows NT Server, Windows 2000 Server, Windows 2003 Server, Windows NT 4.0 Workstation, Windows XP Workstation. :shock:
Yeah I know, I’m not happy with it either but i see it as a big challenge to change it.

I would really appreciate it if someone can tell me something about this.
Thank you for your time.

Your first key question is what IP address range you are using. If they are private addresses such as 192 or 172 or 10 then in principle you can do anything you want, as long as you make the necessary changes in all your systems. But if you have external addresses with a live connection to the internet then at a minimum you'll need to talk to your ISP

Your first key question is what IP address range you are using. If they are private addresses such as 199 or 172 or 10 then in principle you can do anything you want, as long as you make the necessary changes in all your systems. But if you have external addresses with a live connection to the internet then at a minimum you'll need to talk to your ISP

We are using a private addres.

Thank you very much for the fast reply

You need to think carefully about the changes then. It's not too bad if the network is straightforward but there are a few things you might have there that will need special thought. Things like internet access via NAT, routers, firewalls, remote access via VPN, if you have remote sites accessing your centre, if you have VLANs etc. If everything looks okay, then make a list of all your systems and devices so you can tick them off as the change is done.
You'll certainly need some downtime to do this. If you've got critical network components such as VLANs then sort these out first of all, as you won't get very far without the network. If you have DHCP, DNS or WINS servers I would do these next and then reboot them so that as you make the changes on other machines they can talk to these services and sort themselves out. Next on the list would be Active Directory or domain controllers, followed by member servers and then the user PCs.
Good luck!

you said your present subnet mask was 255.255.255.128 which in binary translates to :

11111111 . 11111111 . 11111111 . 10000000.
this means your company has employed a /25 IP subnet mask. it is very important to know which IP addresses are alloated to you. this is nearly everyone's question.
i also agree with bishop when he suggest to take into account all the other relevant information in deciding the next step. you should look into the as-built diagrams and informations related to your company's entire network setup. this will also shed some light on why your predecessors had used a /25 bit subnet mask and not something else. using a subnet mask with more bits would mean more network with less hosts, and using less than /25 would mean less networks with more hosts per network. its a very important decision you need to make before you go about changing subnet masks. decide whether you want to have more network options with a small amount of hosts per network, or a few network options which can accomodate large number of hosts.

i suggest that you make use of a proxy server so that you use private ip's then you can have all the ip u want