Preamble
As far as I can tell OpenWrt uses ip link add link $netdev name $1 type vlan id $vid to create
/devices/virtual/net/ethX.VID
with 802.1Q VLAN Support being the driver for that virtual interface
[1] stipulates such as
802.1q tagged virtual LAN interface
On such interface:
- ethX.VID being slaved off the master/parent device ethX
- ingress 802.1Q-encapsulated frames on ethX with a VID are being untagged, then re-presented to the network stack as untagged ingress frames on ethX.VID
- egress frames on ethX.VID are being 802.1Q tagged with associated VID, then passed to ethX for transmission
Questions
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what happens with untagged ingress frames on ethX? (expect dropping)
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what happens with 802.1Q tagged but none-associated VID ingress frames on ethX? (expect dropping)
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if as expected those frames are being dropped than how come ethX.VID on the WAN port works when the ingress frames however are untagged?
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With [2] stipulating:
When you bridge non-VLAN and VLAN interfaces together, the system takes care about adding VLAN ID when sending packet from non-VLAN to VLAN interface, and it automatically removes the VLAN ID when sending packet from VLAN interface to non-VLAN one.
[a] which part of the system is the caretaker since it would not appear to be a common functionality for a Linux bridge device, or is it?
[b] what happens in this context when bridging a driver-level VLAN with a DSA interface?
[1] https://www.linux.org/docs/man8/ip-link.html
[2] https://openwrt.org/docs/guide-user/network/vlan/switch_configuration