Network switch collisions and fragments

Try statically assigning both the switchport and the master's ethernet port to a specific speed/duplex setting (10 Half, 100 Full, etc - I believe the setting command in the master is 'set ethernet mode'). I think there are threads around here somewhere documenting peoples experiences and what has worked best for them in the past. I know in times past (specifically with older linksys gear) that I had best luck with 10 Half. Lately, though, it seems things have gotten better and it hasn't been much of an issue for me. You may try upgrading to the latest firmware just in case they've made some improvements also. That said, sometimes experimentation is the key to success on this one. Also, it is possible that you have an inferior network cable contributing to the problem.
Also, the web pages on the master have a tendency to be on the slow side, particularly on NI-x000 masters with duet firmware (I think that's accurate, I haven't paid much attention lately though I believe things have gotten a bit better on the web server speeds.)

I would change network cable first. Usually it is the cause of such problem.