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A coworker is having an issue where a certain XHR call is not completing on their computer. The rest of us are unable to repro the issue. The only differences between their computer and ours:

  • Because of the special Internet connection they use, they need to connect through a corporate proxy
  • When examining the XHR call in Chrome's "Dev Tools --> Networking" tab, the hostname resolves to a different IP address

The "wrong IP" appears to be the issue - when I force the hostname to resolve to that IP on my machine, I see the same problem.

The weird thing is, doing a ping on their machine shows it resolving to the correct IP!

Here is what I've tried:

  • Changing their DNS to 8.8.8.8
  • Forcibly adding the correct address to their hosts file(!?!)
  • ipconfig /flushdns
  • chrome://net-internals/#dns -> Flush
  • Restart their PC

None of it made a difference - Chrome still resolves the call to the wrong address, while ping resolves to the correct address. How is this possible!?

My guess would be it has something to do with the proxy, but I don't see how that could true, since using the hosts file should prevent it from even sending out a DNS request, right?

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  • Seems like a strange suggestion, but this appears to be a strange problem: did you try a private browsing window? What about clearing the entire cache? I've seen weird redirects get cached and those causing seemingly similar headaches. Also, what about other browsers? Are you all running the same version of Chrome?
    – FCTW
    Commented Jun 5, 2017 at 20:15
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    cleaning the entire cache should work. Make sure you not clean for 1 hour, but everything.
    – LPChip
    Commented Jun 5, 2017 at 20:21
  • @LPChip: We just tried it in Firefox with a clean cache, same issue.
    – BlueRaja - Danny Pflughoeft
    Commented Jun 5, 2017 at 21:07
  • Hmmm very interesting... Have you tried tracerouting the address? Also if things get tough I would resolve to wireshark
    – Genesis_GDK
    Commented Jun 5, 2017 at 23:23
  • Most likely, it is the proxy's fault. You can try to go around it by using cryptdns, here: dnscrypt.org, or by using a VPN
    – MariusMatutiae
    Commented Jun 6, 2017 at 6:31

1 Answer 1

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"How is this possible?"

The chrome proxy is also proxying DNS requests for the chrome browser. As a result, all of the requests made by chrome are being resolved on the proxy system, which is providing the wrong IP address.

All of your local DNS modifications are being ignored by chrome, as chrome DNS lookups are being handled by the proxy.

The proxy doesn't effect the ping command, so that resolves with local (correct) DNS response.

Have the user try disabling the proxy, or you can try using their proxy to confirm or deny this explanation.

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  • Unfortunately the office connection is setup such that any requests not routed through the proxy are blocked. I'm not sure how this is done, but that makes it impossible to test without the proxy. We'd have to physically move the machine, or find a wireless card for it in order to connect to the other network.
    – BlueRaja - Danny Pflughoeft
    Commented Jun 6, 2017 at 20:38
  • Understood. Can you make your working machine use the office proxy? If that starts to fail for you too, it at least proves the proxy is the problem. Can you contact the proxy maintainer and check for their DNS set up for the problem domain?
    – JesseM
    Commented Jun 6, 2017 at 20:42

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