Troubleshooting LAN Switching Environments

The following sections cover the most common network issues in switched network environments:

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 TDR1 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.
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.

1TDR = Time Domain Reflectometer

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.
Subnet mask configuration error	Step 1 Check to see whether you can ping the switch from a device in the same subnet. Step 2 Check the subnet mask on the device from which you are pinging. Check the subnet mask on the LAN switch. Step 3 Determine whether the subnet mask on either device is incorrectly specified. If it is, reconfigure the switch or the device, as appropriate, with the correct subnet mask. Refer to the user guide for your LAN switch for information on how to check and configure the subnet mask on the switch. Refer to the vendor documentation for the other device for information on how to check and configure the subnet mask on that device.
No default gateway specified on switch or server	Step 1 Check whether there is a default gateway configured on the LAN switch. Check to make sure that all servers and other end systems on the LAN have a default gateway specification. Step 2 If any of these devices does not have a default gateway specified, configure a default gateway using the IP address of a router interface on the directly connected LAN. Refer to the user guide for your LAN switch for information on how to configure a default gateway on the switch. Refer to the vendor documentation for the other devices for information on how to configure a default gateway on those devices.
VLAN1 misconfiguration	Step 1 Make sure that all nodes that should communicate are attached to ports on the same VLAN. If ports are assigned to different VLANs, the attached devices cannot communicate. Step 2 If a port belongs to two or more VLANs, make sure that the VLANs are connected only by the overlapping port. If there are other connections, an unstable network topology can be created. Step 3 Eliminate any extraneous connections between the two VLANs.
Wrong port 25 connector option	If a switch port has two possible connectors, make sure that the physical connection matches the one configured in the Management Console.

1VLAN = virtual LAN

Possible Problem	Solution
Baud rate misconfigured	Step 1 Make sure that the LAN switch and the attached terminal or modem are configured to use the same baud rate and character format. The autobaud feature on most switches can match the baud rate for incoming calls, but the switch will not change from its configured rate when it is dialing out. Also, the autobaud feature will only match a rate lower than its configured rate. When it completes a call and disconnects, the switch returns to the last configured baud rate. Step 2 Test the connection using different baud rates. Refer to the user guide for your LAN switch for more information on how to attach a terminal or modem.
Incorrect cabling	A null-modem cable is needed when attaching a LAN switch directly to terminals or other stations. A straight-through cable is needed when attaching the switch to a modem. Figure 22-1 illustrates the pin connections to use when you connect the Catalyst 1600 to a terminal using a null-modem EIA/TIA-232 cable, or to a modem using a straight-through EIA/TIA-232 cable.

Possible Problem	Solution
Incorrect connector	Check to make sure that the Token Ring switch port is connected to the correct connector on the attached device. For detailed information on connector types, refer to the Catalyst 1600 Token Ring Switch User Guide.
Interface mode incorrect	Step 1 Make sure that the interface mode of the Token Ring switch port is appropriate for the attached device. The options are node mode and concentrator mode. Step 2 Check the port interface mode by reading the port LEDs or LCD panel. Step 3 You can change the port interface mode using the TrueView Catalyst 1600 Manager or by connecting a terminal to the serial interface and using the set port ifmode command. Command: set port ifmode port mode Description: Sets the port interface to node or concentrator mode. Parameters: port Port number mode Port interface (node or concentrator) For detailed information on interface modes, refer to the Catalyst 1600 Token Ring Switch User Guide.
Port ring speed incorrect	Step 1 Make sure the port ring speed is correct for the ring connected to the port. The options are 4 Mbps and 16 Mbps. Step 2 Check the ring speed by reading the port LEDs or LCD panel. Step 3 You can change the ring speed using the TrueView Catalyst 1600 Manager or by connecting a terminal to the serial interface and using the set port ifspeed command. Command: set port ifspeed port speed Description: Sets the ring speed for the port to 4 or 16 Mbps. Parameters: port Port number speed Ring speed (4 or 16) For more information on setting the port ring speed, refer to the Catalyst 1600 Token Ring Switch User Guide.

Possible Problem	Solution
Source routing not enabled	Step 1 Check whether source routing is enabled on the Catalyst 1600 and on the appropriate port. Check the status of source routing by reading the LCD panel. Step 2 You can enable source routing on the Catalyst 1600 and on each port using the TrueView Catalyst 1600 Manager or by connecting a terminal to the serial interface and using the enable port srb command. Command: enable port srb port Description: Enables the forwarding of source-routed frames by the port. Parameters: port Port number
Bridge number misconfigured	Step 1 Check whether the bridge number of the Catalyst 1600 is a hexa- decimal number in the range 0 through F and that there are no other devices with the same bridge number connecting the same rings. Check the bridge number by reading the LCD panel. Step 2 You can view the bridge number by using the TrueView Catalyst 1600 Manager or by connecting a terminal to the serial interface and using the show bridge characteristics command. Example: show bridge characteristics Bridge Name: switch B Bridge Number: 2 IP Address: 194.32.220.119 IP Subnet Mask: 255.255.255.0 Spanning Tree Root Priority: 40000
Ring number misconfigured	Step 1 Check the ring number of each Token Ring switch port and make sure each port has a different ring number. Check the ring number by reading the LCD panel. Step 2 If two Catalyst 1600 devices are connected by their Token Ring switch ports, make sure the ring number is identical for both Token Ring ports. Step 3 You can set the ring number using the TrueView Catalyst 1600 Manager, or by connecting a terminal to the serial interface and using the set port segment command. Command: set port segment port segment Description: Sets the ring number. Parameters: port Port number segment Ring number (001-FFF hexadecimal)

Possible Problem	Solution
VLAN misconfigured	Step 1 Make sure that VLANs are configured correctly and that each Catalyst 1600 has an up-to-date record of VLANs. To check the VLAN configuration, use the TrueView Catalyst 1600 Manager. Step 2 Before creating new VLANs, make sure you delete the existing VLANs that are causing problems with forwarding source-route broadcast frames. For detailed information on configuring VLANs, refer to the Catalyst 1600 Token Ring Switch User Guide.
Station type incorrect	Step 1 Check to make sure that the type of station connected to each Token Ring switch port is defined correctly. The options are Workstations and Anything. On Novell IPX and NetBIOS networks, the Catalyst 1600 uses the station type to block broadcast frames originating on workstation-only rings from being forwarded on other workstation-only rings. Step 2 To configure the station type for each Token Ring switch port, use the TrueView Catalyst 1600 Manager.

Possible Problem	Solution
Full- or half-duplex settings incorrect	Step 1 Check the switch port statistics. The following steps can be performed with the use of the Cisco TrueView Catalyst 1600 Manager application. The TrueView Catalyst 1600 Manager enables you to Find the status of a port Set the ring speed of a Token Ring port Select the port interface mode to be node or concentrator Select the port type to be classic or full duplex Assign a locally administered address to a Token Ring port or reset the hard-wired address Configure source routing and spanning-tree parameters for a Token Ring port View source-routing counters for a Token Ring port Set the type of station that is connected to the Token Ring port, to enable the Catalyst 1600 to block IPX and NetBIOS all-routes broadcast and single-route broadcast frames originating on workstation-only rings and destined for other workstation-only rings Step 2 If there are FCS1 and alignment errors on the port, check whether the port is configured for full duplex. Step 3 If the port is full duplex, check whether the other device is a repeater or half-duplex device. If it is half duplex, configure the switch port for half duplex. Step 4 If there are late collisions, check whether the port is configured for half duplex. Step 5 If the port is half duplex, check whether the other device is full duplex. If it is, configure the switch port for full duplex.
Cabling distance exceeded	Step 1 Check the switch port statistics. If you see excessive FCS, late-collision, or alignment errors, the maximum cabling distance might be exceeded. Step 2 Check the cable distance using a cable tester or TDR2. Verify that the VLAN segment lengths attached to the switch meet Ethernet/IEEE 802.3 specifications. Step 3 If the distance is out of specification, reduce the length of the cable run.
Bad adapter in attached device	Check the switch port statistics. If excessive errors are found, run the adapter card diagnostic utility to determine the problem. Refer to the user guide for your LAN switch for more information. The following example of the show port counters command displays the type of information that can be collected for each port on the switch: show port counters 2 Bytes Transmitted: 19,339,380 Bytes Received: 455,390 Non-broadcast Frames Transmitted: 1,029 Non-broadcast Frames Received: 2,747 All Routes Explorer Frames Received: 0 All Routes Explorer Frames Transmitted: 4,289 Spanning Tree Explorer Frames Received: 259 Spanning Tree Explorer Frames Transmitted:28,065 Receiving Segment Mismatch Discards: 0 Duplicate Segment Mismatch Discards: 0 ARE Hop Count Exceeded Discards: 0

1FCS = frame check sequence 2TDR = Time Domain Reflectometer