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When will a packet be tagged/untagged with a VLAN tag in these cases:

  • On a Cisco switch
  • On a 8021q subinterface in Linux (for example, eth0.10)
  • On VMWare ESXi (with VLAN ID in VMNetwork setting)

And what is the VLAN broadcast behavior on a linux bridge?

Consider this model: I have a Linux machine with interface eth0 (physically) connected to an access port on VLAN 10 on a Cisco switch. On the Linux machine I configured interface eth0.10 to connect to Linux bridge br0 with a VLAN 10 IP address. So when a machine on VLAN 10 sends a packet to that Linux machine, how the packet will go and will it reach others machines connected to br0?

  • As @MFT points out, ethernet frames (not packets, which know nothing about VLANs) are not tagged on an access port, Unfortunately, your host, server, and VM configurations are off-topic here. You could try to ask about those on Server Fault for a business network, or on Super User for a personal network. – Ron Maupin Nov 25 '16 at 17:02
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Since the frames will originate from the switchport of the cisco switch and it is set to access, it will never be tagged. Summary of the flow below.

Machine on VLAN 10 (untagged) -> cisco ingress port (untagged) -> cisco egress port (untagged) -> Linux machine eth0 (untagged)

eth0.10 will never see any packets as there are no tags in place. Since you bridged eth0.10 to br0, br0 will not see packets as well. You will see packets on br0 if eth0 was bridged directly to br0.

  • So in which case a tag is removed from a frame? – Qtag Nov 26 '16 at 14:36
  • On the Cisco switch side set the port to trunk mode and allow VLAN 10. At that point eth0.10 will see frames that will, in turn, show up in br0. For any new VLAN's you'll need to set up eth0.x and a new bridge. FWIW good practice is to set the bridge number to be significant - so eth0.10 connects to br10 and in the future eth0.50 would go to br50. – rnxrx Nov 28 '16 at 3:58

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