DTAG VLAN7 tagging one modem or router?

DTAG requires VLAN7 tagging. The modem vmg1312-b30a supports it in bridge mode.
OpenWrt supports it like

config switch_vlan
        option device 'switch0'
        option vlan '7'
        option ports '1t 6t'

What is the preferred way to seven tag the ethernet frames?
Is it just a matter of choice - a preferred flavour - or is there any advantage of doing it on the router or on the modem?
Doing it on the modem lets me bake the images with one custom setting less, which is currently a tiny advantage.

currently i do it on the wrt because it looks cleaner to me if the pppoe-frame is "final" when it leaves my setup and the modem does not have to mess with it.

i dont have to swconfig since my wan-port does not go via the switch...

afaik iptv uses a second vlan, so that would be another reason to do it on openwrt.

but i am also interested in other reasonings :slight_smile:

So I ended up doing it on both :wink: This is because I use an additional VLAN to access the BT homehun5a that serves as my "bridged" modem. In that case two VLAN are conceptionally simpler on the LAN side of the modem and to avoid any vlan trunking issues, the modem's wan does the "real" vlan7 tag the ISP sees :wink:

Doing it on both, would mean that the router adds it and the modem does "overwrite" it?


I mean, it would not be added twice, right.
In the meanwhile I have tried to figure out how the performance might be influenced in case of the modem takes the frames and adds the Header / Tag.
But I have no clue.

Yes, the BTHH5A has a switch on the LAN side (connected via eth1 to the CPU but I am not sure) and a dedicated xdsl-modem for (my) WAN (ptm0) side, I bridge ptm0.7 and eth1.7 and get single tagged frames on the wan, just as dtag expects it.
As indicated I do this so I can reach the modems luci interface vie VLAN2 and get a hold on the dsl stats and counters...