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Sat, Apr 10, 2021 4:07 AM

Packet drops between Comcast and Fastly?

Hey all, I'm posting this here because it's a little esoteric and is more annoying for me than anything else.

Over the past week, I've noticed about slowness and ~15% packet loss to certain websites and services. To be clear, I have no packet loss issues with the vast majority of the internet. I've done a little digging into the ones that have packet loss and have found one weird quirk -- they're all services hosted by Fastly. I did some trace routes and I've found that the packet loss always occurs between the final Comcast owned IP and the Fastly domain.

Here's an instance from reddit.com which is hostly by Fastly. I did some ping testing and found that I have 0% packet loss to 50.208.232.162 and ~15% packet loss to 151.101.1.140.

  7    10 ms     9 ms     8 ms  50.208.232.162
  8    47 ms    42 ms     *     151.101.1.140

Here's an instance from fastly.com.

  7     9 ms     9 ms     8 ms  75.149.231.94
  8     *       54 ms    47 ms  151.101.65.57

Again, I did some extended ping testing and found 0% packet loss to the Comcast owned 75.149.231.94 but ~15% packet loss to 151.101.65.57.

A third instance of a Fastly service with packet loss is stackoverflow.com. Same symptoms.

  7    12 ms    13 ms     9 ms  50.208.232.162
  8    45 ms     *       43 ms  151.101.65.69

I've also reproduced this against the New York Times (packet loss in the hop from 75.149.231.94 to 151.101.129.164). After finding 4 Fastly services that all run slow with high packet loss, I stopped trying to find more. I have not yet found packet loss to a non-Fastly service.

I tried to double-check that this might be Comcast related by tethering to a Verizon cellular connection and I found 0% packet loss to all of these Fastly services. This only happens on my Comcast Business line when I try to connect to sites hosted by Fastly.

My business doesn't really rely on having Stack Overflow, the NY Times, and Reddit load quickly but this is some pretty weird network behavior and I'm not sure what's causing it. It does seem to be related to the connection between Comcast and these Fastly servers, though, and it doesn't reproduce over non-Comcast connections. :\

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