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AT-9108, AT-8518, AT-8525, and AT-8550 User's Guide
Port
No link light on 10/100 Base port:
Configuration
If patching from a hub or switch to another hub or switch, ensure
that you are using a CAT5 cross-over cable. This is a CAT5 cable that
has pins 1&2 on one end connected to pins 3&6 on the other end.
Excessive RX CRC errors:
When a device that has auto-negotiation disabled is connected to a
Gigabit switch that has auto-negotiation enabled, the switch links at
the correct speed, but in half duplex mode. The switch 10/100
physical interface is uses a method called parallel detection to bring
up the link. Because the other network device does not participating
in auto-negotiation (and does not advertise its capabilities), parallel
detection on the switch is only able to sense 10Mbps versus
100Mbps speed, and not the duplex mode. Therefore, the switch
establishes the link in half duplex mode using the correct speed.
The only way to establish a full duplex link is to either force it at both
sides, or run auto-negotiation on both sides (using full duplex as an
advertised capability, which is the default setting on the switch).
Caution
A mismatch of duplex mode between the switch and the network
device will cause poor network performance. Viewing using the
show
command on the switch may display a constant increment
port rx
of CRC errors. This is characteristic of a duplex mismatch between
devices. This is NOT a problem with the switch.
Always verify that the switch and the network device match in
configuration for speed and duplex.
No link light on Gigabit fiber port:
Check to ensure that the transmit fiber goes to the receive fiber side
of the other device, and vice-versa. All gigabit fiber cables are of the
cross-over type.
The switch has auto-negotiation set to on by default for gigabit
ports. These ports need to be set to auto off (using the command
) if you are connecting it to
config port <port #> auto off
devices that do not support auto-negotiation.
Ensure that you are using multi-mode fiber (MMF) when using a
1000Base-SX GBIC, and single mode fiber (SMF) when using a
1000Base-LX GBIC. 1000Base-SX does not work with SMF.
1000Base-LX works with MMF, but requires the use of a mode
conditioning patchcord (MCP).
B-5
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