[t3ra]

Alongside probably whitelisting : Most speed test sites hit the ISP cache or peered traffic and hence are much faster.

you can inspect fast.com and see this in action: It will show up something like "ipv4-c209-sea001-ix.1.oca.nflxvideo.net" Which is their openconnect [1] location in Seattle IX.

In many cases you will probably see a prefix indicating your ISP - Most ISPs with some scale host their own caches or peer with an internet exchange directly.

Incase of speedtest - its the same story most ISPs host servers locally and speedtest's website generally tests from it

Most of my ISP screw ups are involve content which isnt cached and its difficult to convey that when your netflix is able to stream 4K content easily but struggling to download a 100mb file of some AWS region :/

I sometimes use proof.ovh.net and ping.online.net to test using iperf also ec2-reachability.amazonaws.com helps debug if ISP is having issues with connecting to AWS (more open than not thats the case with mine)

--- [1] https://openconnect.netflix.com