8
Loopback testing includes the following types:
•
Internal loopback testing
—Tests the device where the Ethernet interface resides. The
Ethernet interface sends outgoing packets back to the local device. If the device fails to receive
the packets, the device fails.
•
External loopback testing
—Tests the inter-device link. The Ethernet interface sends incoming
packets back to the remote device. If the remote device fails to receive the packets, the
inter-device link fails.
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
, and
shutdown
commands are not available during a loopback test.
•
A loopback test cannot be performed on an interface configured with the
port up-mode
command.
•
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 enable loopback testing 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.
Enable loopback testing.
loopback
{
external
|
internal
}
By default, no loopback test is
performed.
Configuring generic flow control on an Ethernet interface
To avoid dropping packets 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. Generic flow control includes the
following types:
•
TxRx-mode
generic
flow
control
—Enabled by using the
flow-control
command. 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 its peer, it suspends sending packets
to its peer.
•
Rx-mode generic flow control
—Enabled by using the
flow-control receive enable
command. With Rx-mode generic flow control enabled, an interface can receive flow control
frames, but it cannot send flow control frames:
{
When congestion occurs, the interface cannot send flow control frames to its peer.
{
When the interface receives a flow control frame from its peer, it suspends sending packets
to its 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.
This feature is mutually exclusive with PFC.