A free tool can be found at:
The website states:
ntop is a full featured tool, with hundreds of features, here is a summary of what ntop can do for you:
Display traffic statistics
Breakdown the network protocols running on your network
Store traffic statistics in RRDTool format for historical analysis and trending
Assist with identifying your users
Identify host operating systems without disturbing your network
Breakdown IP traffic by conversation
Breakdown IP traffic statistics by port
Breakdown IP traffic by subnet
Act as a NetFlow/sFlow probe and collector (as supported by Cisco, Juniper and Foundry devices
A commercial package with a lot of features can be found at Crannog.
It offers value for money (it did in my case).
Just look at the possibilities at:
and choose for NetflowTracker,
choose Network Overview,
make a selection in the Utilization graph,
in your selection click the right mouse and select All Traffic,
then select Address Reports
then select Addres Pairs.
A new graph is calculated.
In the buttonbar click on the icon left of the Notepad icon.
This reloads the page and resolves the IP addresses to domain names.
Just imagine this on your own network.