PLANET GSW-4804SF - Manual (Page 60)

User’s Manual of GSW-4804SF
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802.1Q VLAN Configuration
There are up to 256 configurable VLAN groups. By default when 802.1Q is enabled, all ports on the switch belong to default
VLAN (VID 1). The default VLAN cannot be deleted.
Understand nomenclature of the Switch
Tagging and Untagging
Every port on an 802.1Q compliant switch can be configured as tagging or untagging.
。 Tagging: Ports with tagging enabled will put the VID number, priority and other VLAN information into the header of
all packets that flow into those ports. If a packet has previously been tagged, the port will not alter the
packet, thus keeping the VLAN information intact. The VLAN information in the tag can then be used by
other 802.1Q compliant devices on the network to make packet-forwarding decisions.
。 Untagging: Ports with untagging enabled will strip the 802.1Q tag from all packets that flow into those ports. If the
packet doesn't have an 802.1Q VLAN tag, the port will not alter the packet. Thus, all packets received
by and forwarded by an untagging port will have no 802.1Q VLAN information. (Remember that the
PVID is only used internally within the Switch). Untagging is used to send packets from an
802.1Q-compliant network device to a non-compliant network device.
Frame Income
Frame Leave
Income Frame is tagged Income Frame is untagged
Leave port is tagged Frame remains tagged Tag is inserted
Leave port is untagged Tag is removed Frame remain untagged
Here pay attention to the explainion of “Access”,”Always Untag” and “Trunk”.
。 Access: Ports will strip the 802.1Q tag from all packets that out of those ports. If the packet doesn’t have an 802.1Q
VLAN tag, the port will not alter the packet. Thus, all packets received by and forwarded by an untagging port will
have no 802.1Q VLAN information. Untagging is used to send packets from an 802.1Q-compliant network device to
a non-compliant network device.
Ports with “Access” mode belong to a single untagged VLAN.
。 Trunk: Ports with tagging enabled will put the VID number, priority and other VLAN information into the header of all
packets that out of those ports. If a packet has previously been tagged, the port will not alter the packet, thus
keeping the VLAN information intact. The VLAN information in the tag can then be used by other 802.1Q
compliant devices on the network to make packet forwarding decisions.
。 Always Untag: The port belongs to VLANs, and each VLAN is user-defined as tagged or untagged (full 802.1Q
mode). Ports will strip the 802.1Q tag from all packets that out of those ports.