I have BT's fibre optic broadband and am supposed to get a max speed of 75mbps. If I use the router which is supplied by the provider I get roughly this. However if I connect my firewall (Netgear UTM5) directly to the modem I get a max speed of approx 53mbps. If I connect the modem to the provider supplied router and then the provider router to mine everything works fine. I checked to make sure the connection is running at full duplex and also have tried 2 different modems made by 2 different manufacturers but still no change.
I am also seeing the same behaviour on another of my networks which has the same modem and a Netgear UTM9S
What could be causing this strange behaviour?
Any help is greatly appreciated