Figure 3-4
Link types
DeviceB
DeviceC
PC3
VLAN3
VLAN3
PC4
PC1
VLAN2
VLAN2
PC2
3
2
3
2
2
3
Access link
Access link
Trunk link DeviceA
frames tagged with VLAN2
frames tagged with VLAN3
untagged frames in VLAN2
untagged frames in VLAN3
3
2
Trunk link
Access Link
Trunk Link
NOTE
l
A host does not need to know the VLAN to which it belongs. It sends only untagged frames.
l
After receiving an untagged frame from a host, a switching device determines the VLAN to which
the frame belongs. The determination is based on the configured VLAN assignment method such as
port information, and then the switching device processes the frame accordingly.
l
If the frame needs to be forwarded to another switching device, the frame must be transparently
transmitted along a trunk link. Frames transmitted along trunk links must carry VLAN tags to allow
other switching devices to properly forward the frame based on the VLAN information.
l
Before sending the frame to the destination host, the switching device connected to the destination
host removes the VLAN tag from the frame to ensure that the host receives an untagged frame.
Generally, only tagged frames are transmitted on trunk links; only untagged frames are transmitted on
access links. In this manner, switching devices on the network can properly process VLAN information
and hosts are not concerned about VLAN information.
Port Types
After the 802.1Q defines VLAN frames, some ports on the device can identify VLAN frames,
while others cannot. According to whether VLAN frames can be identified, ports can be
classified into four types:
l
Access port
Huawei AR530&AR550 Series Industrial Switch Routers
Configuration Guide - Ethernet Switching
3 VLAN Configuration
Issue 01 (2014-11-30)
Huawei Proprietary and Confidential
Copyright © Huawei Technologies Co., Ltd.
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