Configuring VLANs 579When a port is in General mode, all VLAN features are configurable. Wheningress filtering is on, the frame is dropped if the port is not a member of theVLAN identified by the VLAN ID in the tag. If ingress filtering is off, alltagged frames are forwarded. The port decides whether to forward or drop theframe when the port receives the frame.VLAN TaggingPowerConnect M6220, M6348, M8024, and M8024-k switches support IEEE802.1Q tagging. Ethernet frames on a tagged VLAN have a 4-byte VLAN tagin the header. VLAN tagging is required when a VLAN spans multipleswitches, which is why trunk ports transmit and receive only tagged frames.Tagging may be required when a single port supports multiple devices that aremembers of different VLANs. For example, a single port might be connectedto an IP phone, a PC, and a printer (the PC and printer are connected viaports on the IP phone). IP phones are typically configured to use a taggedVLAN for voice traffic, while the PC and printers typically use the untaggedVLAN.When a port is added to a VLAN as an untagged member, untagged packetsentering the switch are tagged with the PVID (also called thenative VLAN)of the port. If the port is added to a VLAN as an untagged member, the portdoes not add a tag to a packet in that VLAN when it exits the port.Table 21-2. Switchport Mode BehaviorMode VLAN Membership FramesAcceptedFrames Sent IngressFilteringAccess One VLAN Untagged Untagged Always OnTrunk All VLANs that existin the systemTagged Tagged Always OnGeneral As many as desired Tagged orUntaggedTagged orUntaggedOn or OffNOTE: A stack of switches behaves as a single switch, so VLAN tagging is notrequired for packets traversing different stack members.
