When setting up my internet connection, my router asks for the upstream and downstream bandwidth. What does this really do?
Is this only for limiting bandwidth to proritze between networks? So if you don’t have other networks you can theoretically just always leave it at a way higher number than your actual speed and nothing really changes?
The bandwidth setting is meant to aid with Quality of Service.
If you set it too high, the upstream can go too high which clogs up the speed which can slow down the download speed which then slows down the upload stream, similarly the reverse is true, except that usually you don't reach the download max.
In theory, a speed too high will work, but you can get a better performance when you find the sweet spot.
If you set the bandwidth too low, it is artificially capped.
Ideally you set the bandwidth to whatever your connection is, and if you feel like the speed fluctuates a lot or you have high pings, you often want to lower the values a little bit and test again.
Keep in mind that if a connection itself is very slow (for example a malfunction somewhere outside) your QoS settings would still be good. So rule of thumb is, the lowest bandwidth settings you would want to set is 10% lower of your connection speed, but preferably set it close to what you should get.
On an old Draytek router, I found out that even if QoS is disabled, changing the bandwidth will still had an effect.
This setting exists to fix an issue called "bufferbloat", and exhibits as very slow response times when all the bandwidth is in use (eg you download a large file, and then try to play an online game while it's downloading). By artificially limiting to a speed, all upstream buffers should generally remain empty.
This router can identify bulk connections (like large downloads) and put them in a separate buffer, allowing all other traffic to have low latency. Note however that this only works if the router is the only one restricting the speed along the path; If (for example) you set the router to limit the speed to 100mbps, but your ISP limits the speed to 50mbps, then the buffer (and thus latency) will build at the ISP out of your control.
You should set this setting by experiment; Start with the speed your ISP claims, and then run a large download and see what your ping times look like. Repeat at various values until you find a nice trade-off between ping times and speed.
