[RT-N66U] slow internet speed only on some protocols/servers?

[Fire-Dragon-DoL]

Greetings! I'm looking for some suggestions on how to diagnose the following problem.

I'm on a gigabit internet here (Vancouver, Canada), and I can run speedtests against some servers and get 900/900 mbit/s easily.

Then, I try to download a file over http on a server under my control on AWS (an EC2 instance, an m4.xlarge, quite beefy) and I get 800 KB/s. That shouldn't happen. I asked a different person in the same town to download from that server and he gets 30 MB/s, so it doesn't seem to be a server problem.

I tried with this same machine today at work and was able to get 9MB/s (only 100 mbit available at the office), so it's not the machine.
I would love to understand where the problem is, but I'm really struggling to diagnose. I can network dumps with wireshark, but not sure what to look for then. I ran some latency tests using `mtr` against the server and I get 27ms latency, which is definitely ok.

There must be something, but I can't understand if it's on the ISP side or on router side. Considering I can get that 900/900 speed on the speedtest, I assume my router is healthy, but I don't know if there is some kind of protocol monitor feature that maybe it's slowing down the speed.

Any suggestion on how to diagnose this? I'm able to use shell (bash) without any problems or setup scripts or do any work on linux (using kubuntu 17.10), but I have 0 experience in diagnosing network problems.

P.S.
I'm able to download a file from a non-aws server at 15MB/s, so it really seem like an ISP problem?

 

[MichaelCG]

If you can download at appropriate speeds just fine from other servers, it is less likely to be a problem on your end and more than likely related to the route path between your ISP and AWS.

 

[Fire-Dragon-DoL]

If you can download at appropriate speeds just fine from other servers, it is less likely to be a problem on your end and more than likely related to the route path between your ISP and AWS.

I think so, today I'll try directly connected to the ethernet cable though, I might have some setting on my end with stuff slowing down other stuff (however, it's really weird if that's the case)

 

[Fire-Dragon-DoL]

If you can download at appropriate speeds just fine from other servers, it is less likely to be a problem on your end and more than likely related to the route path between your ISP and AWS.

I ran hundreds of test and they are all inconsistent with results.

Different speed without router, sometimes same speed with router. Different speed with O.S., sometimes the same (ubuntu consistently slower than windows though, weird).
Overall, it looks like a ISP problem, but they can't confirm that because I don't have the same problem with everything.
Sigh.