Bridged modem through vlan trunk is that doable ? (problem with vlan, wrt1900ac)


I'm trying to setup what I think is a simple architecture but I'm hitting some walls with the vlan setup.
So, first, what I'm trying to achieve is this:
I've a cable modem that I've to put in bridge mode, this is in a isolated room of my house, with some other peripherals next to it. (ROOM A)
pretty far away, I've to put my wrt1900ac, with a big bunch of other computers and peripheral. (ROOM B)
There is a single cable going through ROOM A and B (and no easy way to have another one)

What I'm trying is this:

Room A:
modem -> managed switch -> untagged vlan (i.e 20)
peripherals -> managed switch -> untagged vlan (1)
managed switch -> 1 port tagged 20 and 1 -> ROOM B

Room B:
wrt1900ac -> a port (Wan ? Lan ?) Tagged 20 and 1
all other ports untagged 1 (for not managed switches and all other computers)

I managed to setup the switch (I think)

My problem is, in luci, when trying to setup something like this (or any variation without the wan in the switch and moving the trunk on one of the lan port), I'm not able anymore to communicate with router (even with wifi, that I did not even touched), and the configuration rolls back (thanks)

I know that if this works (at the vlan level, at least), I'll have to do something about he firewall zones (assign wan zone to the vlan20), but, one problem after the other :slight_smile:

So I've two questions:

  • Is that the (best) way to achieve what I want (without having to buy other hardware or destroy walls) ?
  • What am I doing wrong with my unlucky attempts ?

Thanks a lot !

My guess is the following:
By activating VLAN filtering, you switch br-lan from untagged to br-lan.1. But unless you configure br-lan.1 in the interface section before "saving & applying" the new VLAN set-up in the device section, you loose br-lan when your change to the device section is commited, LuCI detects that and gets you out of that mess by reverting your change.

So here is how it might work:

  1. navigate to the Network menu
  2. select the Interfaces tab
  3. click the edit button for the LAN interface (which should say br-lan in the small print)
  4. under Device enter custom br-lan.1 & click save
  5. this brings you back to the interfaces tab, where you click the greenish save button BUT NOT the blue "Save & Apply" button yet.
  6. instead switch to the Devices tab and click the blue Configure... button for br-lan
  7. go the Bridge VLAN Filtering and make your desired changes (making sure that all the untagged stuff sits on VLAN ID1)
  8. click save there
  9. which drops you back to the Devices tab
  10. finally click "Save & Apply"

This should get you are working set-up...

Hi @moeller0,

Thanks to your great (and dumb-proof) explanations, I was able to set it up. I took me a long time because, I don't know why, I had to setup vlan based on mac in the switch.
So, now, my conf looks like this:

wan and lan4 can be used the same way, I made both of them working to make some experimentation because of the lack of performance.

What I mean with that is that now, I am "only" able to sustain 250Mbits where I should have 400Mbits (and maybe soon more)

I see the sirq going up to 50% while doing speedtest (in download, upload is limited to 20Mbits, and I can get it without a problem (sirq: 30%).

Is there anything I can do to get back the usual speed or it can not work this way ?

PS: I put the wan in the bridge because it was the only device I was able to use (the bridge). Trying to create the vlan devices on the wan, and the attributing the wan.10 as wan interface resulted into Unknown error (DEVICE_CLAIM_FAILED) (and I really don't have a clue if that could improve the speed)

Any better setup idea someone has to share ?

  • Your description would lead one to believe that the setup is stepping out to the CPU, rather than staying in the switch fabric.
  • Although your numbers would be below where it should matter, the switch to DSA currently only supports one CPU-port. If you are building an image, you could see if the relevant bits of PR4036 to get multi-port buy you any extra throughput. It appears to be working fine on wrtpac targets.