Configuring The Mdi Mode For An Ethernet Port - 3Com S7906E Configuration Manual

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 a device 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 device
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:
To do...
Enter system view
Enter Ethernet port view
Configure the MDI mode for the
Ethernet port
Use the command...
system-view
interface interface-type
interface-number
mdi { across | auto | normal }
1-11
Remarks
—
—
Optional
Defaults to auto. That is, the
Ethernet port determines the
physical pin roles (transmit or
receive) through negotiation.