Configuring Loopback Detection For An Ethernet Port - 3Com 4210 9-Port Configuration Manual

If you specify a source aggregation group ID, the system will use the port with the smallest port
number in the aggregation group as the source.
If you specify a destination aggregation group ID, the configuration of the source port will be copied
to all ports in the aggregation group and all ports in the group will have the same configuration as
that of the source port.

Configuring Loopback Detection for an Ethernet Port

Loopback detection is used to monitor if a port of a switch is looped back.
After you enable loopback detection on Ethernet ports, the switch can monitor if an external loopback
occurs on them. If there is a loopback port found, the switch will deal with the loopback port according to
your configuration.
1) If a loop is found on an access port, the system will set the port to the block state (ports in this state
cannot forward data packets), send log and trap messages to the terminal, and remove the
corresponding MAC forwarding entry.
If you have additionally enabled the loopback port auto-shutdown function on the port, the system
will shut down the port, and send log and trap messages to the terminal. After the loop is removed,
you need to use the undo shutdown command to bring up the port.
If you have not enabled the loopback port auto-shutdown function on the port, the port will
automatically resume the normal forwarding state after the loop is removed.
2) If a loop is found on a trunk or hybrid port, the system sends log and trap messages to the terminal.
If you have additionally enabled the loopback port control function or the loopback port
auto-shutdown function, the system will deal with the port accordingly:
If the loopback port control function is enabled on the port, the system will set the port to the block
state (ports in this state cannot forward data packets), send log and trap messages to the terminal,
and remove the corresponding MAC forwarding entry. After the loop is removed, the port will
automatically resume the normal forwarding state.
If the loopback port auto-shutdown function is enabled on the port, the system will shut down the
port and send log and trap messages to the terminal. After the loop is removed, you need to use the
undo shutdown command to bring up the port.
You cannot enable both the loopback port control function and the loopback port auto-shutdown
function on a port. If you do so, the function configured later will take effect.
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