A router is used to bridge network domains.  A device on a network will use the destination IP, its own IP, and the subnet mask to determine if the destination is on the same network segment or not.  If the destination is on the same segment, the packet is sent to the destination, otherwise it is sent to the best matching router or default gateway.

Consequently, all devices on your 172.16.x.x/16 network will consider themselves on the same segment and won't go through the routers.

Off hand it sounds like what you need is a switch with ACL (access control list) functionality.  Your router's switch portion may have this capability (you will need to investigate).  This would allow you to create a set of ports that is only accessible via a subset of the range.  In other words, it is still one network segment (not subnetted), but traffic will only flow from one switch bank to the other if it is coming from approved side of the fence.


 

Thanks for the reply, networking really isn't my strong point!!

If the Staff and Training network were on a different class of network would that cause problems e.g.

Staff: 172.16.0.1
Training: 192.168.0.1

How would I get the staff network to talk to the Training network?

Cheers

I think this approach would work.  Both of these ranges are private so as long as there is no defined routing path, attempts to access an off limits domain would go nowhere.

In order to get the staff side to be able to access the training side, I think you would need a router with two interfaces for the staff.  One interface (say eth0) would connect to the 192.168.0.x network and the other (eth1) would go to your default (internet) connection like it does now.  You would then tell the staff's router that traffic for the 192.168.0.x range routes via eth0 and make eth1 the default gateway.  

This could even be achieved with a PC being used as a router instead of a dedicated device.  There may be some other, i.e. better, ways to do this too but this isn't my strong point either.  For example, a good router may have multiple ports on it and you can specify some of them being on one range and some on another, I am really not sure what the state of the hardware is today.