H3C Technologies H3C S7500E Series Switches - Manual (Page 30)

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Loopback detection on a given port is enabled only after the loopback-detection enable
command has been configured in both system view and the port view of the port.
Loopback detection on all ports will be disabled after you configure the undo loopback-detection
enable command in system view.
For loopback detection actions to take effect on a trunk or hybrid port, you need to configure the
loopback-detection control enable command in the port view of the port.
After you use the port link-type { access | hybrid | trunk } command to change the link type of
an interface, the loopback detection action configured on the interface with the
loopback-detection action command will be restored to the default. For details about the port
link-type command, see VLAN Configuration Commands in the Layer 2 - LAN Switching
Command Reference .
Configuring the MDI Mode for an Ethernet Port
The optical port of an SFP or XFP port does not support this function.
Two types of Ethernet cables can be used to connect Ethernet devices: crossover cable and
straight-through cable. To accommodate these two types of cables, an Ethernet port on the switch can
operate in one of the following three Medium Dependent Port (MDI) modes:
Across mode
Normal mode
Auto mode
An Ethernet port is composed of eight pins. By default, each pin has its particular role. For example,
pin 1 and pin 2 are used for transmitting signals; pin 3 and pin 6 are used for receiving signals. You can
change the pin roles through setting the MDI mode. For an Ethernet port in normal mode, the pin roles
are not changed. For an Ethernet port in across mode, pin 1 and pin 2 are used for receiving signals;
pin 3 and pin 6 are used for transmitting signals. To enable normal communication, you should connect
the local transmit pins to the remote receive pins. Therefore, you should configure the MDI mode
depending on the cable types.
Normally, the auto mode is recommended. The other two modes are useful only when the switch
cannot determine the cable type.
When straight-through cables are used, the local MDI mode must be different from the remote
MDI mode.
When crossover cables are used, the local MDI mode must be the same as the remote MDI mode,
or the MDI mode of at least one end must be set to auto.
Follow these steps to configure the MDI mode for an Ethernet port: