Twisted Pair Port Link LED is Off

AT-9400 Series Gigabit Ethernet Switches Installation Guide

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:

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 9 on page 50.

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.

Note

A 1000Base-T connection can take from five to ten seconds to establish a link.

If a switch port is using Auto-Negotiation, the default setting, to set its speed and duplex mode settings, the end node connected to the port should also be using Auto-Negotiation to prevent a duplex mode mismatch. This can occur because a switch port that is using Auto- Negotiation will default to the half-duplex mode if it detects that the end node is not using Auto-Negotiation. If the end node is operating at a fixed duplex mode of full-duplex, the result will be a mismatch of settings on the two devices, with the switch port using half-duplex and the end node using full-duplex.

To avoid this problem, you should 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.