I recently switched to a Telfort FTTH subscription. This comes with a default modem/router (Experiabox V10) that is, to say the least, 'limited'. This subscription provides internet as well as IPTV.

So I want my FTTH to terminate in my Unifi USG. Without the IPTV this would be as simple as configuring the incoming WAN port on the USG with DHCP on VLAN 34:

telusg

and connecting the USG directly to the NT1.

But this wil break the IPTV functonality, which is coming in on VLAN 4. So between the NT1 and the USG I haved placed a switch with VLAN and IGMP snooping support. A Netgear GS105Ev2 to be exact.
I know that this also can be accomplished by using my Unifi switches, but I don't want the connection from my NT1 physically connected to my infrascture behind the USG.

Configuring the VLANs on the Netgear just sucks, the UI is HORRIBLE

I ended up with this configuration:

port01 = NT1
port02 = USG WAN
port03 = IPTV
port04 = IPTV

Make sure you are configuring the Advanced VLAN 802.1Q option:

safe1

And create the VLAN's with id 4 & 34.
Now link the VLAN 34 to port 01 and 02, both tagged:

Annotation-2019-05-01-105034

And VLAN 4 to port 01 tagged, and untagged to 03 and 04

Annotation-2019-05-01-105104

Now set the PVID of port 03 and 04 to VLAN 4 here:

Annotation-2019-05-01-105115

So you end up with this:

Annotation-2019-05-01-105043

And enable IGMP snooping for the IPTV vlan:

prosafe1

The USG WAN connection must stay the same, DHCP and VLAN 34. And everything will work. Or, atleast the basic IPTV functions.. the advanced features (netflix etc) won't work from the IPTV settop boxes with this config (BRIDGED vs ROUTED). This should be possible, but having three Chromecasts I don't care much about that.