dnf download capped to ~100kbps, why?

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Hello,

I am reinstalling my home server using Fedora Server 29 and there is one mysterious problem I was not able to figure out - dnf downloads are very very slow. All downloads (both meta data and packages) are runnig at stable rate of 13kB/s, which is about 100kbps. Just the initial metadata download and update took me several hours at this rate.

I can't figure out what is the problem. What I tried:

• I verified my internet connection / router, another system connected to same router downloads at 20Mbps
• I tried wget from the problematic system and it downloads at 20Mbps
• I tried to enable fastestmirror
• I tried to specify minrate to 100kB/s - it kept switching mirrors, because all of them were downloading at 13kB/s
• I tried to force IPv4 via -4
• I tried to enable throttling on dnf and set it to 1MB/s

And nothing. The only situation where I get better speed is when dnf downloads 3 packages at the same time, then it is approx 40kB/s which equals to 3x13kB/s.

Based on my tests I can say:

• the problem is not in the internet connection (works fine from another system)
• the problem is not in connection of the system to my router (works fine via wget)
• the problem is probably isolated to dnf (again, wget works fine)
• the problem is not limited to specific mirrors (with minrate it tried a dozen of mirrors, all with same results)
• the problem is not caused by dnf's throttling (I tried both disabled state and throttling set to high value)
• the throttled speed appears to be stable, set to around 100kbps per connection

What else could I try? What on Fedora Server 29 could throttle dnf's http(s) connections and why?