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We have a scenario where we cannot connect to our stunnel server running on port 443 on our network, which only allows access to Internet via a proxy server. On the contrary, when we tried a SSL VPN using Adito, we could connect to the HTTPS site and setup a SSL tunnel to our remote server.

Stunnel and SSL VPN were running on different hosts outside the restricted network. As for the symptoms of the stunnel failing, we simply got a "Connect failed" with stunnel, but no attempt was made to capture the raw traffic. But with Adito, the connection was smooth and works like a charm.

My questions, is how do connections to a stunnel differ from SSL-VPN, if both are running on the same port 443, and both use SSL to encrypt data?

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In all evidence, the two tunnels are not equal. Given that the port and (envelope) protocol are the same, the difference might be in either the endpoints, the access rules or the certificate setup.

Unless you shut down the stunnel server (and you say nothing to that effect), you shouldn't have been able to test Adito at all. Unless the stunnel server and the Adito server are running on separate hosts, and in that case, they might well have different firewall access rules.

Another possibility is that stunnel is compiled with TCP wrappers (or through [x]inetd) and the host unable to connect to it is not allowed to connect, while Adito has no such restrictions. So Adito works, and stunnel doesn't.

What are the symptoms of stunnel's connection failing (both at client and in the server logs, if any)?

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  • Thanks for the reply. Yes, I forgot to mention that both the stunnel and SSL VPN were running on different hosts outside the restricted network. As for the symptoms of the stuunel failing, we simply got a "Connect failed" with stunnel but no attempt was made to capture the raw traffic. But with Adito, the connection was smooth and works like charm :)
    – lamso
    Jun 6, 2013 at 21:20

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