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Tngld avatar Server

Issues with telnet to external web service from azure vm

ck flag
Tngld

I have an Azure VM running Windows server. There is a job running on this server that fetches data from an external web service on port 80. This job has suddenly stopped working after a reboot (I know this is vague...).

The provider of the webservice says that as long as we can telnet their service on port 80 everything should work fine. The problem is that I cannot telnet their service on port 80 from the VM. I can access it via web (http and https), but not telnet to port 80 or 443.

When trying to telnet it says "Connecting To the.webservice.com for a minute or two, and aborts with "Could not open connection to the host, on port 80: Connect failed"

I can telnet other external services on port 80 from this VM, I can telnet this service on port 80 from any other computer outside of Azure, AND from a nginx proxy in the same Azure resource group as the Windows VM.

So, telnet to the external service in question on port 80 from a proxy server within the same RG, and from any computer outside Azure works fine. Telnet other web services on port 80 from the Windows VM works fine. Accessing the service in question via web (http and https) works fine from the Windows VM.

There are no outbound NSG rules blocking port 80 from the Windows VM. I have tried turning Windows firewall off on the Windows VM just in case this was acting up, this didn't have any effect on this issue.

So I find this kind of strange. As long as I can browse the address with http and https, telnet to port 80 and 443 should work, shouldn't it?

Appreciate all help :)

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joeqwerty avatar
cv flag
joeqwerty
How does the job connect to this server? Does it use telnet? If not, then stop trying to troubleshoot telnet and troubleshoot the actual problem. It sounds like you're getting hung up on chasing a red herring. Now I could be wrong, so post details about how your job actually connects to this server.
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cn flag
Greg Askew
`As long as I can browse the address with http and https, telnet to port 80 and 443 should work, shouldn't it?` No. You need to remove references to port 443. The provider stated port 80. Tossing in a second port is unnecessary. You need to perform a netmon packet capture when you connect to port 80. It should be very helpful because it is on tcp/80 unencrypted. Since you cannot connect the capture should be small and easy to analyze.
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ws flag
symcbean
If you want to test from the command line then there are tools in powershell - but I prefer curl https://curl.se/windows/
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