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| 4.2 |  | Configuring Inter-VLAN Routing |
| 4.2.8 |  | Troubleshooting inter-VLAN routing |

The first step in troubleshooting Inter-VLAN routing is to ensure that routing is actually enabled using the show ip route command. If no entries are seen in the routing table then IP routing needs to be enabled with the command:

> Switch(config)#ip routing

Once routing has been verified ensure that the Layer 2 VLANs and the Layer 3 IP addressing are as intended using the show ip interfaces brief command. This command will also reveal whether routing is configured for an individual switch interface or an entire VLAN. If communications with a switch seems to be a problem, check that the IP address for the switch is in the appropriate VLAN and the gateway is set.

Assuming that the VLANs are appropriately addressed, it is useful to check that there are no Layer 2 problems by pinging within each VLAN and verifying that it is possible to reach the router interface with every VLAN.

If communications within the VLAN are correct but communications between the VLANs is not working then it would be wise to check Layer 3 configuration. Take particular care that the appropriate gateway is set on hosts and switch management interfaces.

Any remaining routing issues are likely to be the result of incorrectly configured routing protocols or the somewhat tricky native VLAN issue. In particular take care not to trunk a VLAN that is also the trunk’s native VLAN as the switch has no way of knowing whether to tag or not tag a frame. There are no specific debug or troubleshooting commands to identify problems with the native VLAN. Some Catalyst platforms will report an error when a port receives a tagged frame for VLAN that it was expecting to be untagged but not all models behave this way. The best strategy for dealing with native VLAN trunking problems is to maintain an awareness of the issue and to take care with the configuration.