In order to capture vlan traffic, you must include the parameter "vlan" in the expression or the capture command will not capture any data. If you specify a VLAN ID (e.g. "vlan 100") it will only capture traffic for that specific VLAN. If no VLAN ID (e.g. "vlan") is included in the expression, then the capture command will capture traffic across all VLANs.
|vlan 100 and port 80||Capture port 80 traffic on vlan 100|
|vlan and port 80||Capture port 80 traffic on all vlan's|