System information

Troubleshooting LAN Switching Environments
Book Title
22-452
LAN Switching: No Connectivity to LAN or WAN
Symptom: A LAN switch cannot connect to devices on another LAN or across a WAN. Attempts
to ping the switch from remote devices or to ping from the switch to remote devices fail.
Table 22-2 outlines the problems that might cause this symptom and describes solutions to those
problems.
Table 22-2 LAN Switching: No Connectivity to LAN or WAN
Possible
Problem Solution
Incorrect or
faulty cabling
Step 1 Check whether the Connected LED on the LAN switch port is on.
Step 2 If the LED is not on, check to make sure you are using the correct cable and that it is
properly and securely attached. For example, make sure that you are not using a rolled
cable where a straight-through cable is required, or vice versa.
Step 3 Make sure the cable is correctly wired. Refer to the user guide for your LAN switch for
information on cable pinouts.
Step 4 Use a TDR
1
or other cable-checking device to verify that the cable has no opens, shorts,
or other problems.
Step 5 Swap the cable with another of the same kind to see whether the cable is bad. If
connections are now possible, the cable is faulty.
Step 6 Replace or fix the faulty cable as necessary.
1 TDR = Time Domain Reflectometer
Power supply
problem
Step 1 Check the Power LED. If it is not on, make sure the LAN switch is plugged in and is
powered on.
Step 2 Check for a blown fuse. If the fuse is blown, refer to the user guide for your LAN switch
for information on replacing the fuse.
Hardware
problem
Step 1 Check whether the Connected LED on the port is on.
Step 2 If the LED is not on and the cabling is intact, there might be a bad switch port or other
hardware problem.
Step 3 Check whether the Module Enabled LED is on for FDDI and Fast Ethernet modules.
Step 4 If the LED is not on, remove and reseat the module.
Step 5 Check the switch hardware and replace any faulty components.
Possible
Problem Solution
IP address
misconfigured or
not specified
Step 1 Check whether there is an IP address configured on the LAN switch. Check to make
sure there is an IP address on the device from which you are pinging the switch.
Step 2 If the IP address is misconfigured or is not specified on either device, change or add
the IP address as appropriate.
Refer to the user guide for your LAN switch for information on how to check and configure the
IP address on the switch. Refer to the vendor documen- tation for the other device for
information on how to check and configure the IP address on that device.