Caveats regarding QoS and the Catalyst 6500 switch include the following:
Etherchannel? Etherchannel ports require identical QoS configurations on the individual ports.
IGMP snooping? QoS does not support IGMP traffic, if IGMP snooping is enabled on the switch.
MSFC? Any traffic sourced from MSFC to the egress port has a CoS value of 0.
Flexwan? Traffic incoming from a Flexwan module has its CoS value always set to 0.