Trying to get a local network talk via a VPNto another internal network is not something I want to try and do again in a hurry. However – once I had my local machine at home chatting nicely with our hosted production server network I realised that something came to my attention that hasn’t for years – since I was doing GCSE computing actually.
There are actually 3 internal network ranges available for any type of network that is used at home or for business.
We are talking about a Local Area Network (not the Internet here), these ranges were reserved for the express purpose of being reused all over the world for internal and private networks. This is because there are only a finite number of IP addresses and waaaaay to many computers to be able to apply one IP to a machine.
Most routers, modems and switches that you can buy retail come pre configured to use either the 192.168.0.0 or 10.0.0.0 IP range. There is however a third private range available 172.16.0.0. These are all defined by RFC1918. I can ony assume the third gets forgotten about because its a damn sight harder to remember that the other two.
| Class | From | To | CIDR Mask | Decimal Mask |
|---|---|---|---|---|
| Class “A” or 24 Bit | 10.0.0.0 | 10.255.255.255 | /8 | 255.0.0.0 |
| Class “B” or 20 Bit | 172.16.0.0 | 172.31.255.255 | /12 or /16 | 255.240.0.0 or 255.255.0.0 |
| Class “C” or 16 Bit | 192.168.0.0 | 192.168.255.255 | /16 or /24 | 255.255.0.0 or 255.255.255.0 |
The reason this came up was that the server network and my machines network were on the same subnet. My machine believed therefore that all machines in the 192.168.0.0 range were not on the other side of my router via the VPN. So by changing my subnet to another of the IP ranges solved the problem. At this point I thank Rackspace for their great customer support.
