Port Configuration

No link light on 10/100 Base port:

If patching from a switch to another switch, ensure that you are using a category 5 (CAT5) crossover cable. This is a CAT5 cable that has pins 1 and 2 on one end connected to pins 3 and 6 on the other end.

Excessive RX CRC errors:

When a device that has autonegotiation disabled is connected to an Extreme Networks switch with autonegotiation enabled, the Extreme Networks switch links at the correct speed, but in half-duplex mode. The Extreme Networks switch 10/100 physical interface uses a method called parallel detection to bring up the link. Because the other network device is not participating in autonegotiation (and does not advertise its capabilities), parallel detection on the Extreme Networks switch is able only to sense 10 Mbps versus 100 Mbps 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 either to force it at both sides, or run autonegotiation on both sides (using full-duplex as an advertised capability, which is the default setting on the Extreme Networks switch).


A mismatch of duplex mode between the Extreme switch and another network device causes poor network performance. Viewing statistics using the show ports rxerrors command on the Extreme Networks switch may display a constant increment of CRC errors. This is characteristic of a duplex mismatch between devices. This is NOT a problem with the Extreme Networks switch.

Always verify that the Extreme Networks switch and the network device match in configuration for speed and duplex.

No link light on Gigabit fiber port:

Check that:
  • The transmit fiber goes to the receive fiber side of the other device and vice-versa. All Gigabit fiber cables are of the crossover type.

  • The Gigabit ports are set to Auto Off (using the command configure ports port_list {medium [copper | fiber]} auto off speed speed duplex [half | full]) if you are connecting the Extreme Networks switch to devices that do not support autonegotiation.

    By default, the Extreme Networks switch has autonegotiation set to On for Gigabit ports and set to Off for 10 Gigabit ports.

  • You are using multimode fiber (MMF) when using a 1000BASE-SX small form-factor pluggable (SFP), and single-mode fiber (SMF) when using a 1000BASE-LX SFP. 1000BASE-SX technology does not work with SMF. The 1000BASE-LX technology works with MMF but requires the use of a mode conditioning patchcord (MCP).