A coworker was experiencing a strange problem with their Internet connection at home. Large downloads from most sites worked fine. The exception was that downloads from a Amazon S3 would get up to a good speed (500Mbps), stall completely for a few seconds, restart for a while, stall again, and eventually hang completely. The problem seemed to be specific to S3, downloads from generic AWS VMs were ok.
What could be going on? It shouldn't be a problem with the ISP, or anything south of that: after all, connections to other sites were working. It should not be a problem between the ISP and Amazon, or there would have been problems with AWS too. But it also seems very unlikely that S3 would have a trivially reproducible problem causing large downloads to hang. It's not like this is some minor use case of the service.
If it had been a problem with e.g. viewing Netflix, one might suspect some kind of targeted traffic shaping. But an ISP throttling or forcibly closing connections to S3 but not to AWS in general? That's just silly talk.
The normal troubleshooting tips like reducing the MTU didn't help either. This sounded like a fascinating networking whodunit, so I couldn't resist butting in after hearing about it through the grapevine.
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