Running out of private IP address

Hi everyone,

My company is gonna running out of all private IP. At this time, there are only 15 available in our DHCP server. Please give me some advise to prevent this problem before it really runns out of IP. Thank you.

 

I presume you are using an 192.168.0.0 address space. This is exactly why the 10.0.0.0 address space is so much better. It has thousands of addresses available rather than just 254.

OK, there are a couple of options. The simplest (without any more information from you) is to use a second subnet. This will work as long as your default gateway router knows about both subnets. The router will route traffic between the two subnets. Obviously there will be a little bit of latency as traffic passes over the router, but this shouldn't make a significant impact on the network performance.

To do this you will have to add a second IP address to the router's internal port. The address will need to be on the new subnet.

Personally, I'd use 10.0.0.0/255.255.0.0 as the new subnet and would then start migrating everything over to the new subnet. The two subnets can sit side by side, and therefore you can take your time migrating the devices over to the new subnet. When you finish migrating, you can let the old subnet drop.

You could also expand your current subnet by tweaking the subnet mask, but that may have an impact on other networks and things like VPNs. So we'd need more information about your network before going that way.

Personally, I'd take this opportunity to move to a subnet that would better suit the size of your network.

 

Hi eggieB,

Thanks for your advise. You said that need more information about our network, please let me some examples what kind of information do you need ? Thank you

 

What is the current address scheme of the network?

How many devices do you have?
Computers, printers, switches etc.


With a 192.168.x.x network you have 250+ usable addresses.
You could use a 255.255.254.0 subnet mask and open it up 10 fold if you wanted.

Until you explain more I have a feeling what your referring to is running out of DHCP addresses because of the DHCP scope.

 

And in order to change it to 192.168.1.x, you go to 192.168.1.1 (or whatever your router gateway is) and you should find where to go. All routers are different so I can't describe what to do next.

 

Today could be your lucky day, I just happened to have hit the same problem yesterday (1%) of addresses available. I came in early this morning and fixed my problem so hopefully I can help.

I am guessing you are using a Windows Server as your DHCP server, so here's what to do.

NOTE: This must be done when no one else is using the network (hence my 5am start time today).

Start by going in to services and stopping the DHCP server service.

Now go to %SystemRoot%\System32\ and make a copy of the folder called DHCP (this is where you DHCP database is stored).

For good measure make a backup of this key in your server's registry too: HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DHCPServer.

These will make it so you can restore if all goes pete tong.

Now restart your DHCP Server service as it needs to be running for you to change it.

Delete your existing scope and then create a new one, with a subnet mask of 255.255.254.0 and make the IP range something 10.0.10.1 - 10.0.11.250 (this is just an example of what ours is now).

Set all the DNS and Gateway settings.

Then anything on your network with a static IP, routers, switches, servers etc you need to manually change their subnet mask to 255.255.254.0

That should be about it then.

As I say I have just done this this morning, and people are just coming in to the office and the only problems I am seeing is with people who didn't switch their PC's off last night just needing to restart them so they get the new subnet.

Good Luck!

 

Wish I'd read this before responding to your posting in the server forum

Typo I think. The mask to use is 255.255.254.0

However, the key point is that you have to update the mask every where and not just for the DHCP scope.

As I said in the other post - why use a partial-octet subnet. Go the whole hog and use a mask of 255.255.0.0. Its much simpler.

 

Oooops yes indeed it was a typo thanks