How does my network choose a server?

[Mike404xx]

I’m uneducated so bare with me.
I’m wondering how my network chooses which servers to use when connecting to any sort of online website or video game.
If I plug my modem directly into the pc, I notice that it consistently connects to different servers than it would if I have a router wired in as well.
With the router connected it consistently connects to servers that have a higher ping, whether it’s just a speed test or gaming.
Also it doesn’t connect to random servers it consistently connects to the same ones depending on how I have it wired.

Anyone know why this is and how I can change it?

[microchip8]

Which servers are you talking about? DNS? Speed Test?

Which router model do you have?

Which firmware version?

Which modem & ISP?

[Mike404xx]

NETGEAR XR1000 AX5400 ROUTER
CM700 DOCSIS 3.0 High Speed Cable Modem
Xfinity
Latest firmware.

Speedtest.net for example. When I have the router connected it chooses a different server by default to test my speed.

I have both my computer and my router set to the same dns server.

[microchip8]

Do you use DNS servers from your ISP or thrid party ones on all/most of your devices? If you plug a modem-only into a PC, the PC will get the DNS of your ISP (you can't set custom DNS on a modem-only device, only on the PC in question). If your router is set to a different DNS than the ones from your ISP, that could explain things