You can do this with a Proxy server. To monitor all http and https traffic, you'll have to block ports 80 and 443 from leaving your network, and configure the proxy server address on each and every machine on the network. If thats not possible, then you can transparently proxy. I.e. send all port 80 traffic to the ip and port of the proxy server. That won't work for https though as that canot be transparently proxied.