Understanding Trunk, Hybrid, Access Ports and VLAN Tagging (Tag/Untag, PVID) on Huawei Switches

The article explains the relationships among Trunk, Hybrid, and Access ports and the VLAN tagging concepts of Tag, Untag, and PVID, focusing on Huawei switch implementations.

Definitions :

1. Trunk port : can carry packets of multiple VLANs simultaneously, typically used for links between switches.

2. Hybrid port : also carries multiple VLANs and can be used for switch‑to‑switch links or switch‑to‑server connections.

3. Access port : belongs to a single VLAN and is usually used to connect end devices such as computers.

4. Tag and Untag : a tag is the VLAN identifier attached to a packet; an untagged packet carries no VLAN ID.

5. PVID (Port VLAN ID): the VLAN ID assigned to an untagged port. When an untagged packet enters the switch, the switch adds the PVID as a tag; if the packet already carries a tag, the switch generally does not add another tag.

Port Tag and Untag Behavior :

If a port is configured as untagged, all packets forwarded out of that port are sent without a VLAN tag; incoming tagged packets lose their tag when passing through the untagged port. Conversely, a tagged (tagged) port adds a VLAN tag to any untagged packet that enters it, using the ingress port’s PVID as the VLAN ID.

Encapsulation Types :

• ISL : Cisco‑specific trunking where all packets are tagged.

• 802.1Q : Designed for compatibility with devices that do not support VLANs; it allows one VLAN to be untagged while the others are tagged.

Configuration Example (Huawei) :

[Switch-Ethernet0/1]int e0/1

[Switch-Ethernet0/1]port link-type hybrid

[Switch-Ethernet0/1]port hybrid pvid vlan 10

[Switch-Ethernet0/1]port hybrid vlan 10 20 untagged

[Switch-Ethernet0/2]int e0/2

[Switch-Ethernet0/2]port link-type hybrid

[Switch-Ethernet0/2]port hybrid pvid vlan 20

[Switch-Ethernet0/2]port hybrid vlan 10 20 untagged

With this configuration, PCs connected to e0/1 and e0/2 can communicate, but the traffic traverses different VLANs in each direction.

Traffic Flow Example :

When PC1 sends data, the packet is tagged with VLAN 10 (the PVID of e0/1) and entered into the switch. Because e0/2 allows VLAN 10, the switch forwards the packet to e0/2; since VLAN 10 is configured as untagged on e0/2, the switch strips the tag before delivering it to PC2, so the PC1→PC2 path uses VLAN 10.

Conversely, PC2’s reply is tagged with VLAN 20 (the PVID of e0/2). The switch forwards it to e0/1, where VLAN 20 is untagged, so the tag is removed before reaching PC1, making the PC2→PC1 path use VLAN 20.