We are in the process of implementing a security appliance internal to our network. We have keymarked several servers whose traffic the device will listen to passively. In order to properly size the appliance, our vendor has asked for bandwidth numbers. All of these servers are located on a single switch (a 48-port 10/100/1000 Catalyst 3560). Overall switch utilization is pretty low. I've seen overall switch utilization, but how would I find out bandwidth on a switch port?
"show controllers utilization" will give you bandwidth utilization for each port and for the switch fabric itself . Easiest way to look at all ports , one of my favorite commands . This is only valid on fixed config switches like the 3560 , 3750, 2950,2960 etc... wish they would put this in all their switches.
if you have telnet access to the switch
show interface g0/x
there are load parameters expressed as x/255
with 255/255 means full used
1/255 means empty
there is one for input and one for output
You can also check the byte counters for input and output packets and doing the command evey hour you can build a baseline.
the handy tool for this kind of data are tools like MRTG that uses SNMP queries to build traffic graphs that can be showed in a web page
this can be useful not only for providing this answer
Hope to help