I'm hopeful this is an easy one for someone. I'm struggling to understand why egress packets are being VLAN tagged in a particular circumstance.
I have an old-model 260GS running SwOS 1.17. I have a computer attached to an access port, and then a (incorrectly configured IMO) trunk port heading off elsewhere. Please see the screenshots  showing the config of the ports in question.
I've mirrored egress from the trunk port, and can see in Wireshark that packets from the computer have VLAN tag of 2. Why is this the case? The trunk port is not set to add the tag if missing, and from the docs  my understanding was that the default VLAN ID for the port will not actually modify the packet unless there's an egress rule to do this? The computer on the access port is sending untagged packets.
If somebody could explain why/where the packets are being tagged that would be greatly appreciated. Thanks in advance.
Switch will treat both untagged and "Default VLAN ID" tagged ingress packets as they are tagged with this VLAN ID. VLAN tag itself will be added only if there is VLAN Header = add if missing specified on egress port