Network Monitoring bridge... possible? how?

[zeegy]

I appreciate that there a lot of awesome tools out there such ClearOS, Untangle and the like.

Most of these devices are used to provide all one solutions or to act as a gateway similar.
What I would like is a some software that I can place as a server, solely for analysis of data that passes through essentially a bridge and reports how much bandwidth is in use, broken down by IP or similar to help me diagnose what is using up my bandwidth that comes in, or back from the gateway
Ideally, I do not want this server to manage DHCP, DNS or NAT – It is simply sat in between the gateway and the lan and monitors traffic coming in and out.

Anyone know of any tools that can do this? I have enclosed a diagram to help you understand what I am trying to do.
Or, am I looking at it the wrong way? I need to keep the existing router, so using untangle as my gateway and using my modem/router in modem only mode is not an option.

 

[zeegy]

Could you give a bit of background to why replacing the router isn't an option?

Sure, the router is also a load balancer. I know that some tools like untangle support WAN balancing too but the company want to keep with a hardware solution.

Additional latency will be minimal, but the new infrastructure will be a lot, lot better than what they have had before. it will still seem quicker to them.

I agree, there is the risk of failure, which is why i like this idea more than replacing the router... if the server fails, disconnect the two leads from the server, get a coupler and join the network together without this in the middle