VLAN on Switch - what functions serves the Bridge

RouterOS Beginner Basics
1

Hi,

I own a CRS112-8P-4S-IN and configured my VLANs directly on the switch like the WIKI states.

My question is: what function does the bridge (still) serve then?

  • Do the ports of a VLAN on the switch also need to be bridged together?
  • Do I need to enable VLAN filtering on the bridge also?
  • Where would I place a VLAN interface? On the bridge?

Best regards!

2

Yes. A bridge has two personalities - an ethernet switch and interface to the CPU. By default ethernet ports connected to the CPU through a switch chip use port based VLANs to segregate the traffic - this is not visible in Winbox / CLI. Placing ethernet ports into a bridge changes the switch chip configuration so the ports are connected together, then 802.1Q VLANs configuration can be made in under /interface ethernet switch


  • Do I need to enable VLAN filtering on the bridge also?

On CRS1xx/2xx and RouterBoards enabling bridge VLAN filtering disabled hardware switching. Typically you either use a VLAN-aware bridge which utilises CPU resources, or a non-VLAN-aware bridge with hardware switching & VLAN filtering.


  • Where would I place a VLAN interface? On the bridge?

Yes, it provides the interface between the VLAN and CPU. If you are switching many VLANs you would typically only have a single VLAN to the CPU for management access.

3

Thanks for your help, much appreciated!