A recent quote I provided for a paper by industry veteran Tim O'Neil published on lovemytool.com, reminded me that sometimes the hardest problems can figured out with the simplest tools. Take a recent experience I had resolving a performance issue with a particular server in a server farm. It’s somewhat ironic that I actually solved the problem by inserting a hub as an analyzer tap (SPAN was not an option in this particular situation) in an otherwise 100 Mbps full duplex connection.
The server did about 4 Mbps per second connected directly to a switch port and nearly 80 Mbps when we inserted the hub. The problem was recognized immediately - an auto negotiate mismatch between the switch and server and we didn’t even need to look at the packets.
It's also a good idea to keep a constant check on switch port collision and CRC statistics via your SNMP monitoring tool. High values are one such indication of a duplex mismatch. Yes, even today, we still see such problems from time to time. Mike Pennacchi over at Protocol Specialists LLC, keeps reminding me of such.
BTW, real hubs are hard to find these days. Everything has gone to a "switch on on chip" and that's what you find inside today's purported hubs. My recommendation is to grab a few pocket-sized hubs for your team before it's too late. The NetGear Dual-Speed (DS) 10/100 Mbps hub models, are my favorite and you can still find some on eBay.