I'm trying to reach an external site using the curl command: curl https://external.site.com -x my.proxy:PORT. In order to figure out my issue I try to curl some local services in my environment, e.g:

  • I can curl a local web service directly using curl, curl web1.local.com
  • I can curl a local web service using proxy, ONLY ON SOME HOSTS, not all, why? curl -x my.poxy:PORT web1.local.com (This works on just a few hosts of mine).

I have tried to look at the network and I cannot find any huge differences, however, could there be anything running locally on these machines that is blocking?

  • Did you check the error returned from the curl command, but more importantly, did you check the logs on your proxy server? Without such information (emphasis on the proxy server's) it's only guessing what can go wrong among a lot of possibilities.
    – A.B
    Nov 1, 2022 at 14:29
  • That's a good point, however, I can not find anything in the proxy logs referring to my host instances that cannot reach my proxy. The following message from curl curl: (7) Failed connect to my.proxy:PORT; Connection timed out
    – N. J
    Nov 1, 2022 at 14:43
  • With this it falls to me on the "a lot of possibilities". You should use tools like tcpdump to check what's going on.
    – A.B
    Nov 1, 2022 at 14:46

1 Answer 1


This might be related to the need for the "proxytunnel" option.

Curl post about proxies

The sites that succeed might be normal ssl, and the ones that fail might be tls.

The difference is the "CONNECT" keyword sent to the proxy, vs the modified "GET" keyword.

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