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Restrictions and guidelines
• After you enable this feature on an Ethernet interface, the interface does not forward data
traffic.
• You cannot perform a loopback test on the following Ethernet interfaces:
{ Ethernet interfaces manually brought down (displayed as in ADM or Administratively
DOWN state).
{ Ethernet interfaces configured with the port up-mode command.
• The
speed, duplex, and shutdown commands cannot be configured on an Ethernet
interface in a loopback test.
• After you enable this feature on an Ethernet interface, the Ethernet interface switches to full
duplex mode. After you disable this feature, the Ethernet interface restores to its duplex setting.
Procedure
1. Enter system view.
system-view
2. Enter Ethernet interface view.
interface interface-type interface-number
3. Enable loopback testing.
loopback{ external | internal }
Forcibly bringing up a fiber port
About forcibly bringing up a fiber port
As shown in Figure 2, a fiber port uses separate fibers for transmitting and receiving packets. The
physical state of the fiber port is up only when both transmit and receive fibers are physically
connected. If one of the fibers is disconnected, the fiber port does not work.
To enable a fiber port to forward traffic over a single link, you can use the
port up-mode command.
This command forcibly brings up a fiber port, even when no fiber links or transceiver modules are
present for the fiber port. When one fiber link is present and up, the fiber port can forward packets
over the link unidirectionally.
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