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InterVLAN Routing - Troubleshooting Tip

This is a pretty common mistake that comes up during hardware replacement efforts following a failure. The VLAN database must also be backed up to be able to fully restore the configuration of a failed device.

Another important point here, an SVI will not come up unless there is at least one port in the VLAN, with an active device connected to the port.

This section provides troubleshooting tips for common problems that you can encounter during the creation of VLANs on Catalyst switches that run Cisco IOS Software.

On switches that run Cisco IOS Software, you can use the switch itself for interVLAN routing, instead of an external router. When an SVI is created, it does not automatically create a VLAN in the Layer 2 database. In order for an SVI to come up, a VLAN must be created in VLAN database mode or (in later Cisco IOS Software releases) in global configuration mode. In order for the SVI to be fully active, which means that it is administratively up and line protocol is up, make sure to have at least one port as a member of that VLAN, with an active device connected to the port.

This same issue applies when you copy configurations from a different switch or restore configurations with VLANs that were created in VLAN database mode. You must also replace the VLAN database file (vlan.dat), or you must recreate the VLANs, as the procedure in the Create VLANs and Ports section of this document shows. If you copy the configuration from another switch, the VLAN database is not copied.

If the Layer 2 VLAN is not created on the switch, SVI interfaces show as UP/DOWN in the show ip interface brief command output when the configuration is applied to the switch. Ensure that all previous VLANs that were created in VLAN database mode or global configuration mode still exist after the configuration is copied to the switch.


Full text can be found here.

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