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Configuring Queuing and Flow Control
Configuring Flow Control
Link-Level Flow Control
IEEE 802.3x link-level flow control allows a congested receiver to communicate a transmitter at the other
end of the link to pause its data transmission for a short period of time. The link-level flow control feature
applies to all the traffic on the link.
The transmit and receive directions are separately configurable. By default, link-level flow control is disabled
for both directions.
On the Cisco Nexus device, Ethernet interfaces do not automatically detect the link-level flow control capability.
You must configure the capability explicitly on the Ethernet interfaces.
On each Ethernet interface, the switch can enable either priority flow control or link-level flow control (but
not both).
Configuring Priority Flow Control
By default, Ethernet interfaces negotiate PFC with the network adapter using the DCBX protocol. When PFC
is enabled, PFC is applied to traffic that matches the CoS value configured for the no-drop class.
You can override the negotiation result by forcing the interface to enable PFC.
Procedure
Step 1
Step 2
Step 3
Step 4
This example shows how to force-enable PFC on an interface:
switch# configure terminal
switch(config)# interface ethernet 1/2
switch(config-if)# priority-flow-control mode on
OL-26657-01
Command or Action
switch# configure terminal
switch(config)# interface type slot/port
switch(config-if)# priority-flow-control
mode {auto | on}
switch(config-if)# no
priority-flow-control mode on
Cisco Nexus 5000 NX-OS Quality of Service Configuration Guide, Release 5.1(3)N2(1)
Configuring Flow Control
Purpose
Enters global configuration mode.
Specifies the interface to be changed.
Sets PFC mode for the selected interface.
Specifies auto to negotiate PFC capability. This is
the default.
Specifies on to force-enable PFC.
(Optional)
Disables the PFC setting for the selected interface.
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