Yannie wrote

The difference between the General port and Trunk port is when forwarding frames, General port decides to forward the frames with or without tag according to the egress rule, while Trunk port forwards the frames with tags.

This notation of TRUNK and GENERAL ports was once introduced by Cisco to control the egress behavior of frames being internally forwarded to (arriving on) a trunk port.

During forwarding operations all frames always have a tag. I give you an example: Assume an untagged frame enters the switch on port 1 and gets tagged with VLAN ID 100 due to the port's PVID=100. The frame is being forwarded as a tagged frame internally and arrives on port 8 which is member of several VLANs including VLAN 100 and also has a PVID of 100.

Question now is: how should the switch handle this frame on egress on port 8?
The ancient solution to answer this question was the introduction of two trunk types: TRUNK and GENERAL.

• With a TRUNK port, the tag 100 got removed on egress on port 8 since the port's PVID is 100.
• With a GENERAL port, the tag 100 was left intact on egress on port 8 even due its PVID is 100.

Thus, for a TRUNK port its Port VLAN defined by the Port VLAN ID (PVID) determined whether to remove a tag on egress (not on forwarding operations as some FAQs suggest).

However, this can be much better controlled by marking the port as tagged or untagged member of this VLAN 100.

Nowadays, TP-Link switches always use trunk ports which behave like former GENERAL ports used in TP-Link firmwares two generations back. The old switches are EoL meanwhile. The GENERAL / TRUNK port types have been removed many years ago in 2nd generation firmwares already, it has not been changed in the 3rd generation firmwares (the latest generation with the brand-new web UI).

Don't let you confuse, there are no GENERAL ports anymore, albeit you still find this ancient port type in the CLI commands. It will force admins who were used to this old notation to use (former) GENERAL ports for trunks.

But those ports are trunk ports as per definition (trunk = port which is member of two or more VLANs). Whether tags are removed from a trunk port on egress is decided by the tagged/untagged attribute. Note that this attribute is related to both directions, ingress and egress.

The consequence of this change is that you now can create asymmetric VLANs where a port can be an untagged member of two or more VLANs and tags can be removed from frames in both VLANs on egress. This was not possible with so-called TRUNK ports in older firmwares.