Why did the internet speed drop?

Question

linux

There is a connection to the provider through the Keenetic Lite III router. L2TP protocol. Speed ​​according to the tariff 50 Mb/s.
Three systems are also installed: Windows 10, Fedora and openSUSE. Basically, the computer is used for the Internet and the main OS for this is openSUSE.
Yesterday and today I noticed a sharp drop in the incoming speed by 10 times - up to 5 Mbps. Outgoing speed is about the same. Ping 17 - 18 ms, but for measurements I connect to a non-provider server (the native server is not located).
The drop in speed is also clearly visible when downloading torrents.
However, this phenomenon has so far only been observed on openSUSE; I reboot into Windows and into Fedora and the same tests show normal speed. This is the first time I've seen this, although I've been using openSUSE for several years.
Shortly before that, I installed plasma-nm5-l2tp, NetworkManager-l2pt, strongswan-ipsec, strongswan-libso, xl2tp packages on it. I set up an l2tp connection in NetworkManager to use the Internet directly, without a router, but then reconnected the router. Now I removed this connection from NetworkManager - I thought this might be the reason - but even after rebooting, the speed is still low.
I also noticed that if you restart the router, then the incoming speed increases noticeably, up to 35 - 38 Mbps. However, in other operating systems, the speed without reboot is more than 50 Mbps.

Answer 1

Well, for example, incorrect network settings, leading to a large amount of spurious traffic, IP packet fragmentation enabled (or vice versa, disabled), incorrect MTU, MSS, triggering of some conditions at the provider, under which the restriction is enabled etc.
I think you need to contact the provider's support. With numbers, graphs, pings etc