how does ip accounting works in MSFC? I am trying to capture what are the traffic going in and out of a busy interface vlan using the said command, but it seems like no packet were captured?
IP accounting should have little effect on a MSFC. Most traffic on a catalyst switch is routed using the supervisor's hardware, namely the Policy Feature Card.
If you want to know how much traffic is being routed through a vlan and what type of traffic it is, use Netflow Data Export.