Symptom: When installing new services on the network such as wireless or VoIP, VLANs are typically used to isolate this traffic from other users. This requires each switch port supporting these services to be configured for the proper VLAN. If this is not done properly, the service may not work. The IP Phone may not register with the call manager, the PC connected to the phone may not be able to connect to key servers, or the wireless users may not get proper addressing for the wireless environment.

Cause: The switches responsible for connecting these services have not been properly configured. Perhaps it was not communicated within the organization to reconfigure certain ports to support new services.
Resolution: Test the port to verify which VLANs are supported. If possible, use a VLAN Tag to generate VLAN specific traffic to check which VLANs are configured on the port. Check the IP address provided by the DHCP server to determine which VLAN is being provided to the port if it is untagged. Alternatively, check the switch configuration to validate the VLAN configuration.