Configuring Flow Control On An Ethernet Interface - HP 5820X series Configuration Manual

To do...
2. Enter Ethernet interface view
3. Change the operating mode of
the Ethernet interface
After you change the operating mode of an Ethernet interface, all settings of the Ethernet interface are
restored to their defaults under the new operating mode.
The relationship between the PFC function and the generic flow control function is shown in

Configuring flow control on an Ethernet interface

Avoid packet drops on a link by enabling flow control at both ends of the link. The flow control function
enables the receiving end to require the sending end to suspend sending packets when congestion occurs.
The following flow control mechanisms are available:
Generic flow control, which controls transmission on a link for all packets as a whole. Both the HP
•
5800 and the HP 5820X switch series support this mechanism.
PFC, which controls transmission on a link based on 802.1p priority. Only the HP 5820X switche
•
series support this mechanism.
The subsequent sections describe the two mechanisms and how to configure them.
Configuring generic flow control on an Ethernet interface
An interface implements generic flow control by sending and receiving common pause frames. The
following generic flow control modes are available:
TxRx mode enables an interface to both send and receive common pause frames.
•
Rx mode enables an interface to receive but not send common pause frames.
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In Figure 1, when both Port A and Port B forward packets at 1000 Mbps, Port C is congested. To avoid
packet loss, enable flow control on Port A and Port B.
Figure 1 Flow control application scenario
Configure Port B to operate in TxRx mode, Port A in Rx mode:
When congestion occurs on Port C, Switch B buffers frames. When the amount of buffered frames
•
exceeds a certain value, Switch B sends a common pause frame out of Port B to ask Port A to
suspend sending packets. This pause frame also tells Port A for how long it is expected to pause.
Upon receiving the common pause frame from Port B, Port A suspends sending packets to Port B for
•
a period.
If congestion persists, Port B keeps sending common pause frames to Port A until the congestion
•
condition is removed.
To configure flow control on an interface:
Use the command...
interface interface-type interface-
number
port link-mode { bridge | route }
4
Remarks
—
Required.
By default, Ethernet interfaces
operate in bridge mode (as
Layer 2 Ethernet interfaces).
Table 2.