4000 Router Series Interface Configuration Guide

Performing an internal loopback test on an Ethernet interface

If an Ethernet interface does not work correctly, you can perform an internal loopback test on it to test all

on-chip functions related to the interface. An Ethernet interface in a loopback test does not forward data

traffic.

Configuration restrictions and guidelines

• On an administratively shut down interface (displayed as in ADM or Administratively DOWN state),

you cannot perform an internal 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 an internal loopback

test.

loopback internal

By default, no internal loopback

test is performed.

Configuring generic flow control on an Ethernet interface

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. When the sending end receives a flow control frame from

the receiving end, the sending end suspends sending packets.

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

2. Enter Ethernet interface

view.

interface interface-type

interface-number

N/A

3. Enable generic flow control.

flow-control

By default, generic flow control is

disabled on an Ethernet interface.