Ping End Device; Spanning Tree Loops; Switch Performance; Autonegotiation And Network Interface Cards - Cisco IE 4010 Hardware Installation Manual

Troubleshooting
Diagnosing Problems

Ping End Device

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.

Spanning Tree Loops

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 the neighbor, but the
traffic from the neighbor is not received by the switch. A broken cable, other cabling problems, or a port issue can 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.

Switch Performance

Speed, Duplex, and Autonegotiation
Port statistics that show a large number of alignment errors, frame check sequence (FCS), or late-collisions errors, might
mean a speed or duplex mismatch.
A common issue 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.

Autonegotiation and Network Interface Cards

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 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 the NIC. You can resolve this by upgrading the NIC
driver to the latest version.

Cabling Distance

If the port statistics show excessive FCS, late-collision, or alignment errors, verify that the cable distance from the switch
to the connected device meets the recommended guidelines. See the Cable and Connectors, page
47
53.