（
2
）
TRUNK:
The TRUNK port can be added in multiple VLANs, and the egress rule of the port
is TAG. The TRUNK port is generally used to connect the cascaded network devices for it
can receive and forward the packets of multiple VLANs. When the packets are forwarded
by the TRUNK port, its VLAN tag will not be changed.
（
3
）
GENERAL:
The GENERAL port can be added in multiple VLANs and set various egress
rules according to the different VLANs. The default egress rule is UNTAG. The PVID can
be set as the VID number of any VLAN the port belongs to.
¾
PVID
PVID (Port Vlan ID) is the default VID of the port. When the switch receives an un-VLAN-tagged
packet, it will add a VLAN tag to the packet according to the PVID of its received port and forward
the packets.
When creating VLANs, the PVID of each port, indicating the default VLAN to which the port
belongs, is an important parameter with the following two purposes:
（
1
）
When the switch receives an un-VLAN-tagged packet, it will add a VLAN tag to the packet
according to the PVID of its received port
（
2
）
PVID determines the default broadcast domain of the port, i.e. when the port receives UL
packets or broadcast packets, the port will broadcast the packets in its default VLAN.
Different packets, tagged or untagged, will be processed in different ways, after being received by
ports of different link types, which is illustrated in the following table.
Receiving Packets
Port Type
Untagged Packets
Tagged Packets
Forwarding Packets
Access
If the VID of packet is
the same as the PVID
of the port, the packet
will be received.
If the VID of packet is
not the same as the
PVID of the port, the
packet will be dropped.
The packet will be
forwarded after removing its
VLAN tag.
Trunk
The packet will be
forwarded with its current
VLAN tag.
General
When untagged
packets are
received, the port
will add the default
VLAN tag, i.e. the
PVID of the ingress
port, to the packets.
If the VID of packet is
allowed by the port, the
packet will be received.
If the VID of packet is
forbidden by the port,
the packet will be
dropped.
If the egress rule of port is
TAG, the packet will be
forwarded with its current
VLAN tag.
If the egress rule of port is
UNTAG, the packet will be
forwarded after removing its
VLAN tag.
Table 6-1 Relationship between Port Types and VLAN Packets Processing
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