Allied Telesis AT-9448Ts/XP (Basic Layer 3) - Manual (Page 94)

Chapter 7: Troubleshooting
94
Twisted Pair Port Link LED is Off
When a twisted pair port on the switch is connected to a properly
operating end node, the Link LED for the port should be on. If a Link LED
is off, do the following:
Note
A 1000Base-T connection can take from five to ten seconds to
establish a link.
 Verify that the end node connected to the port is powered ON and is
operating properly.
 Check that the twisted pair cable is securely connected to the port on
the switch and to the port on the end node.
 Make sure that the twisted pair cable does not exceed 100m (328 ft).
 Verify that you are using the appropriate category of twisted pair cable.
For information, refer to Table 2 on page 20.
 Determine if a crossover cable is required. Since the twisted pair ports
feature auto MDI/MDI-X, you should be able to use a straight-through
cable regardless of the type of device you connect to a port. However,
if you disable Auto-Negotiation on a port and set a port’s speed and
duplex mode manually, the port defaults to MDI-X. Disabling Auto-
Negotiation may require manually configuring a port’s MDI/MDI-X
setting or using a crossover cable.
 Make sure that the operating parameters of the port on the switch are
compatible with the end node to which the port is connected. This may
require using the switch’s management software.
 In order for a switch port to successfully Auto-Negotiate its duplex
mode with an end node, the end node should also be using Auto-
Negotiation. Otherwise, a duplex mode mismatch can occur. A switch
port using Auto-Negotiation defaults to half-duplex if it detects that the
end node is not using Auto-Negotiation. This can result in a mismatch
if the end node is operating at a fixed duplex mode of full-duplex.
To avoid this problem, disable Auto-Negotiation on a switch port and
set the port’s speed and duplex mode manually if the end node has a
fixed duplex mode of full-duplex.
 The switch has a bad cable detection feature that enables it to
determine if a twisted pair cable has a electrical short that might cause
a network loop. If the switch detects a bad cable on a port, it does not
establish a link on that port. Try replacing the cable.