Configuring Generic Flow Control On An Ethernet Interface - HP FlexFabric 12900 Series Configuration Manual

Step
3. Perform a loopback test.

Configuring generic flow control on an Ethernet interface

IMPORTANT:
Enabling or disabling flow control on an interface might shut down and then bring up the interface. Make
preparations before enabling or disabling this feature.
To avoid packet drops on a link, you can enable generic flow control at both ends of the link. When
traffic congestion occurs at the receiving end, the receiving end sends a flow control (Pause) frame to ask
the sending end to suspend sending packets.
With TxRx mode generic flow control enabled, an interface can both send and receive flow control
•
frames. When congestion occurs, the interface sends a flow control frame to its peer. When the
interface receives a flow control frame from the peer, it suspends sending packets.
With Rx flow mode generic control enabled, an interface can receive flow control frames, but it
•
cannot send flow control frames. When the interface receives a flow control frame from its peer, it
suspends sending packets to the peer. When congestion occurs, the interface cannot send flow
control frames to the peer.
As shown in
be congested. To avoid packet loss, enable flow control on Port A and Port B.
Figure 1 Flow control on ports
When TxRx mode generic flow control is enabled on Port B and Rx mode generic flow control is enabled
on Port A:
When Port C is congested, Switch B buffers the packet. When the buffered packets reach a specific
•
size, Switch B learns that the traffic forwarded from Port B to Port C is too heavy and exceeds the
forwarding capability of Port C. In this case, Port B with TxRx mode generic flow control enabled
sends generic pause frames to Port A and tells Port A to suspend sending packets.
• When Port A receives the generic pause frames, Port A suspends sending packets to Port B for a
certain period, which is carried in the generic pause frames. Port B sends generic pause frames to
Port A until congestion is removed.
To handle unidirectional traffic congestion on a link, configure the flow-control receive enable command
at one end and the flow-control command at the other end. To enable both ends of a link to handle traffic
congestion, configure the flow-control command at both ends.
To enable generic flow control on an Ethernet interface:
Step
1. Enter system view.
Figure 1, when both Port A and Port B forward packets at the rate of 1000 Mbps, Port C will
Command
system-view
Command
loopback { external | internal }
7
Remarks
By default, no loopback test is
performed.
Remarks
N/A