When link pause (flow control) is not enabled on back-to-back Nexus 5000 switch links, packets are dropped while sending traffic on a no-drop class.
If the peer Nexus 5000 switch supports PFC TLV with DCBX, then configuring flowcontrol send on and flowcontrol receive on will not enable the link pause. You have to disable the PFC TLV sent by DCBX on that interface.
Use one of the following commands to verify:
•Use the show interface ethx/y flowcontrol command and check to see if the operating state is off.
•Use the show interface ethx/y priority-flow-control command and check to see if the operating state is on.
Configure the following commands under interface ethx/y to enable link pause instead of PFC on back- to-back switch links.
•no priority-flow-control mode on
•flowcontrol receive on
•flowcontrol send on