20
5.2.3 Port-based VLAN
The messages of the switch include tag and untag messages.
Figure 4-4 Tag position
Untag is the general Ethernet message. The network adapter of the general PC can recognize the
message to communicate.
The VLAN tag head refers to the 4bytes VLAN information after the source MAC address and the
destination address. In the above figure, the blue pane is the VLAN tag head. Generally, the network
adapter of the general PC cannot recognize this kind of message. Therefore, the Switch needs to use
VLAN tag head to distinguish different VLANs, and different VLANs cannot communicate with each
other. Sometimes, you do not need to communicate among between different VLANs. Therefore,
different port types enable different VLANs to communicate.
Port Types
The port types include Access, Trunk and Hybrid.
●
Access: The port belongs to one VLAN, and is used to connect to the computer port.
●
Trunk: The port allows multiple VLANs to pass, to receive and send messages of multiple VLANs,
and is used to connect between the switches.
●
Hybrid: The port allows multiple VLANs to pass, to receive and send messages of multiple VLANs,
and is used to connect between the switches, and connect the user's computer.
When processing the data, the Hybrid port and the Trunk port are the same. The only difference is
when they are sending data, the Hybrid port allows sending messages of multiple VLANs without a
tag, while the Trunk port only allows sending the default VLAN messages without a tag.
Table 4-3 Linkage type and frame processing methods for default VLAN
Port
Type
For messages without
Tag
For messages with Tag
For message to be sent
Access
Receive the message and
put the Tag of the default
VLAN.
●
When VLAN ID is the
same as the default
VLAN ID, receive the
message.
●
When the VLAN ID is
different from the
default VLAN ID,
discard the message.
Discard Tag and send
out the message.
