Q:

How do you get 2 local networks to talk to each other?

So I have a bunch of switches which connect up some PCs on a data network and IP Phones and other devices on a telephone network
Devices on the data network are configured both statically and via DHCP to use to following range:
Network: 192.168.50.0 / 24
Gateway: 192.168.50.254 (Cisco ADSL router - provides access to the internet)
The IP Phones are all configured statically to use the following range:
Network: 192.168.51.0 / 24
Gateway: None
Now if you are on the data network, and you want to connect to a device on the telephone network, you have to change you have IP from 50.x network to the 51.x network.
What I'd like to know is how do you achieve communication without needing to change IPs? All the data for both networks runs through the same switches. The switches are currently sitting on the 50.x network.
I presume we would need a router, or some sort of routing device or rule? This seems overkill though because all the devices are connected to the same switches, and are in the same broadcast domain.

A:

I'm an amateur when it comes to networking, but I think you can do this by setting a proper netmask to cover a wide range of IPs. Perhaps 255.255.254.0 to your main router between the two networks?
It's similar to "192.168.50.0/23". You can use a subnet mask calculator (on Linux you have gip program) or one online such as:
http://www.aboutmyip.com/AboutMyXApp/SubnetCalculator.jsp?ipAddress=192.168.50.0&cidr=23
Address:    192.168.50.0    11000000.10101000.00110010.00000000
Netmask:    255.255.254.0   11111111.11111111.11111110.00000000
Wildcard:   0.0.1.255   00000000.00000000.00000001.11111111
Network Address:    192.168.50.0 / 23   11000000.10101000.00110010.00000000
Broadcast Address:  192.168.51.255  11000000.10101000.00110011.11111111
First host: 192.168.50.1    11000000.10101000.00110010.00000001
Last host:  192.168.51.254  11000000.10101000.00110011.11111110
Total host count:   510 

