This document provides tips for troubleshooting basic problems with your Catalyst 6000 family switch, Catalyst 5000 family switch, Catalyst 4000 family switch, Catalyst 2926G series switch, Catalyst 2926 series switch, Catalyst 2948G switch, or Catalyst 2980G switch.
For complete information on installing and configuring your switch, refer to the hardware and software documentation for your switch model.
| Problem
| Possible Solutions
|
|---|
1
| Cannot connect to a switch through the console port
| - Make sure you are using the correct type of cable (refer to the hardware documentation for your switch supervisor engine).
- Make sure the terminal configuration matches the switch console port configuration---default console port settings are 9600 baud, 8 data bits, no parity, 1 stop bit (2 stop bits if the supervisor engine is from the Catalyst 6000 family).
- Make sure the cable pinouts are correct for your supervisor engine (refer to the hardware documentation for your switch supervisor engine).
|
2
| Cannot communicate with another device:
- Cannot Telnet to the switch
- Cannot communicate with a local or remote host
| - Make sure the LINK LED for the port is green.
- Check the cabling:
- Host-to-switch 10BaseT connections and router-to-switch 10BaseT or 100BaseTX connections typically are made using a straight-through cable.
- Switch-to-switch 10BaseT or 100BaseTX connections typically are made using a rollover cable.
- For SC- or ST-type fiber connections, make sure transmit (Tx) on one end of the link connects to receive (Rx) on the other end of the link.
- Make sure the interface you are connecting to (sc0 or me1) is configured UP (use the show interface command to check).
- Make sure the IP address, subnet mask, and VLAN membership of the switch interface (sc0 or me1) is correct (use the show interface command).
- To prevent conflicts, make sure the me1 and sc0 interfaces are configured with IP addresses and subnet masks in different subnets (use the show interface command to check), or disable one of the interfaces using the set interface {sc0 | me1} disable command.
- Make sure the host configuration (IP address, subnet mask, default gateway, speed, and duplex setting) is correct.
- If you cannot connect to the switch through the me1 interface, make sure the connected device is configured for half-duplex 10-Mbps operation.
- If the host is in the same subnet as the switch interface, make sure the switch interface and the switch port to which the host is connected are assigned to the same VLAN (use the show interface and show port commands to check).
- If the host is in a different subnet, make sure the default gateway (default route) on the switch is configured with the address of a router in the same subnet as the switch interface (use the show ip route command).
- Check the status of the port connection---should be "connected" (use the show port command).
- Check the spanning-tree state on the port (use the show spantree mod_num/port_num command)---if the port is in listening or learning mode, wait until the port is in forwarding mode and try to connect to the host again.
- Make sure the speed and duplex settings on the host and the appropriate switch ports are correct (use the show port command).
- If the connected device is an end station:
- Enable spanning-tree PortFast on the port (use the set spantree portfast enable command)---PortFast places the port in forwarding mode immediately, bypassing listening and learning modes (do not use this feature for connections to non-end station devices).
- Disable trunking on the port (use the set trunk mod_num/port_num off command).
- Disable channeling on the port (use the set port channel port_list off command)---you must specify a valid port range with this command---you cannot specify a single port.
- Make sure the switch is learning the MAC address of the host (use the show cam dynamic command).
- If possible, try connecting to another port.
|
3
| Cannot autonegotiate the port speed/duplex
| - Make sure autonegotiation is configured on both ends of the link (use the show port command)---you cannot configure settings manually on one end of the link and configure the other end of the link for autonegotiation.
- If autonegotiation fails when you connect a client NIC to the switch, check the NIC and drivers to make sure that autonegotiation is supported.
- If autonegotiation is supported and properly configured but you still cannot connect, turn off autonegotiation and set the speed and duplex manually (use the set port speed and set port duplex commands).
|
4
| Cannot establish a connection across a trunk link
| - Make sure the trunking mode configured on both ends of the link is valid---the trunking mode should be on or desirable on one end and on, desirable, or auto on the other end (use the show trunk command).
- Make sure the trunk encapsulation type configured on both ends of the link is valid (use the show trunk command).
- Make sure the port is trunking and that the allowed VLAN list allows the desired VLAN range to pass through (use the show trunk command).
- On IEEE 802.1Q trunks, make sure the native VLAN is the same on both ends of the trunk (use the show trunk command).
If you still cannot establish a connection, see the solutions for Problem 2. If the trunk connection is to a router, see the solutions for Problem 5.
|
5
| Cannot establish a trunk link between a switch and a router
| - Make sure the port is connected and is not receiving any physical-layer (alignment and FCS) errors (use the show port command on the switch).
- Make sure the duplex and speed are set properly between the switch and the router (use the show port command on the switch; use the show interface command on the router).
- Make sure you configure the physical router interface with one subinterface for each VLAN for which you want to route traffic (use the show interface command).
- Make sure that each subinterface on the router has the proper encapsulation type, VLAN number, IP address, and subnet mask configured (use the show interface command).
- Make sure the router is running a release of Cisco IOS software that supports trunking (use the show version command).
|
6
| Need to add or remove VLANs from the allowed VLAN list for a trunk
| - Remove one or more VLANs from the allowed VLAN list on a trunk port (use the clear trunk mod_num/port_num vlans command)---you cannot remove VLAN 1 from the allowed VLAN list.
- Add one or more VLANs to the allowed VLAN list on a trunk port (use the set trunk mod_num/port_num vlans command).
|
7
| Unable to load-balance VLANs between parallel trunks connecting switches (all VLAN traffic traverses one trunk)
| - Make sure the portvlanpri value for a given VLAN is lower on the trunk that you want to be in forwarding mode for that VLAN and higher on the trunk that you want in blocking mode for that VLAN (use the show spantree mod_num/port_num command to check the portvlanpri value).
- Make sure that the portvlanpri values for a given VLAN are identical on both ends of each trunk link.
- Check which VLANs are in forwarding mode and which are in blocking mode on the trunk (use the show spantree mod_num/port_num command).
- Check the MAC address of the root bridge for each VLAN (use the show spantree vlan_num command). The MAC address of the root bridge should be different for each VLAN.
- Return the ports to their default configuration (use the clear spantree portvlanpri command).
|
8
| VTP is not updating the configuration on other switches when the VLAN configuration changes
| - Make sure the switches are connected through trunk links---VTP updates are exchanged only over trunk links (use the show trunk command).
- Make sure the VTP domain name is the same on the appropriate switches---VTP updates are only exchanged between switches in the same VTP domain (use the show vtp domain command).
- Check if the switch is in VTP transparent mode---only switches in VTP server or VTP client mode update their VLAN configuration based on VTP updates from other switches (use the show vtp domain command).
- If you are using VTP passwords, you must configure the same password on all switches in the VTP domain. To clear an existing VTP password, use the set vtp passwd 0 command.
|
9
| Cannot form an EtherChannel port bundle
| - Make sure all the ports in the bundle belong to the same VLAN or are all trunk ports (use the same trunk mode, encapsulation, and allowed VLAN list on all ports). Use the show port or show trunk command to check the port configuration.
- Make sure all ports in the bundle have the same speed and duplex settings (use the show port command).
- Make sure the port configuration is the same on both ends of the link.
- Only ports in desirable and auto mode will negotiate a channel (either desirable-auto or desirable-desirable). Ports in on mode will only form a functional channel with other ports in on mode (they will not negotiate a channel with ports in desirable or auto mode).
|
10
| Cannot see Cisco Discovery Protocol (CDP) neighbors
| - Make sure CDP is enabled on the appropriate ports (use the show cdp port command).
- Make sure CDP is supported and enabled on the connected device.
|
