Cisco Systems WSC2960S24TSSRF User Manual

Ping from the directly connected switch first, and then work your way back port by port, interface by 
interface, trunk by trunk, until you find the source of the connectivity issue. Make sure that each switch 
can identify the end device MAC address in its Content-Addressable Memory (CAM) table.

STP loops can cause serious performance issues that look like port or interface problems.

A unidirectional link can cause loops. It occurs when the traffic sent by the switch is received by its 
neighbor, but the traffic from the neighbor is not received by the switch. A broken fiber-optic cable, other 
cabling problems, or a port issue could cause this one-way communication.

You can enable UniDirectional Link Detection (UDLD) on the switch to help identify unidirectional link 
problems. For information about enabling UDLD on the switch, see the “Understanding UDLD” section 
in the switch software configuration guide on Cisco.com.

If the port statistics show a large amount of alignment errors, frame check sequence (FCS), or 
late-collisions errors, this might mean a speed or duplex mismatch.

A common issue with speed and duplex occurs when duplex and speed settings are mismatched between 
two switches, between a switch and a router, or between the switch and a workstation or server. 
Mismatches can happen when manually setting the speed and duplex or from autonegotiation issues 
between the two devices.

To maximize switch performance and to ensure a link, follow one of these guidelines when changing the 
duplex or the speed settings.

Let both ports autonegotiate both speed and duplex. 

Manually set the speed and duplex parameters for the interfaces on both ends of the connection.

If a remote device does not autonegotiate, use the same duplex settings on the two ports. The speed 
parameter adjusts itself even if the connected port does not autonegotiate.

Problems sometimes occur between the switch and third-party network interface cards (NICs). By 
default, the switch ports and interfaces autonegotiate. Laptops or other devices are commonly set to 
autonegotiate, yet sometimes autonegotiation issues occur.

To troubleshoot autonegotiation problems, try manually setting both sides of the connection. If this does 
not solve the problem, there could be a problem with the firmware or software on your NIC. You can 
resolve this by upgrading the NIC driver to the latest version.