4
Loopback tests include the following types:
•
Internal loopback test
—Tests all on-chip functions related to the Ethernet interface.
•
External
loopback
test
—Tests the hardware of the Ethernet interface. To perform an external
loopback test on the Ethernet interface, connect a loopback plug to the Ethernet interface. The
switch sends test packets out of the interface, which are expected to loop over the plug and
back to the interface. If the interface fails to receive any test packets, the hardware of the
interface is faulty.
Configuration restrictions and guidelines
•
On an administratively shut down Ethernet interface (displayed as in
ADM
or
Administratively
DOWN
state), you cannot perform an internal or external loopback test.
•
The
speed
,
duplex
,
mdix-mode
, and
shutdown
commands are not available during a
loopback test.
•
During a loopback test, the Ethernet interface operates in full duplex mode. When a loopback
test is complete, the port returns to its duplex setting.
Configuration procedure
To perform a loopback test on an Ethernet interface:
Step Command
Remarks
1.
Enter system view.
system-view
N/A
2.
Enter Ethernet interface
view.
interface
interface-type
interface-number
N/A
3.
Perform a loopback test.
loopback
{
external
|
internal
}
By default, no loopback test is
performed.
Configuring generic flow control on an Ethernet interface
CAUTION:
Configuring generic flow control on an Ethernet interface will cause link-up and link-down events
before the interface finally stays up.
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.
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 Command
Remarks
1.
Enter system view.
system-view
N/A
