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Hi,
I need some advice and BIG help with my archer c3200

Here's the situation:

I got my archer c3200 last week, V1 US, firmware 16-07-04
my connection is 15mbps DOWN/ 1mbps UP

I set up two 5G connections and my LAN for the desktop, what happens is that when I'm playing on Steam (CSGO), my ping is about 30ms regular, but when my girlfriend is in the other room watching netflix in the TV, my ping increases big time, around 400ms, and it's definitely impossible to play. I tried to read and read here to find solutions but nothing suits me exactly as I need and I'm a bit noob on this things. PLEASE ADVICE ME!

I'm trying to give 100% priority to the desktop so when She's watching netflix in the other room, it doesn't affect my ping while playing. Is this possible?
I also don't have the QOS option or some gaming feature to boost me.

correct me if I'm wrong.
I did this:

I set up my ports for steam like it says in the website. https://support.steampowered.com/kb_article.php?ref=8571-GLVN-8711




and then I tried to give priority to the LAN connection, following the steps I found here, but I got this error message.









what can I do? I'm clueless, and also I remember that with my OLD router, I used to play normal, and when she was in the other room with the TV my ping didn't increase THAT much, It was about 150ms............

PLEASE HELP ME!