Re: [Openvpn-users] Monitoring client traffic

[Leroy T. <ler...@ve...>]

Through the VPN?  If not then you're asking the wrong group.

If through the VPN, keep in mind that, unless you force all traffic to go through the VPN once a client connects, you have no control over how they get to the web.  And even if you attempt to do this, if the client has enough technical skill, they can circumvent it.

Second point, you have unencrypted traffic at the OpenVPN server (the web traffic can't go out OpenVPN-encrypted to a web server).  However, doing what you want is non-trivial.  Unless you can find a package which can monitor traffic and filter for http or https (assuming a web site hasn't set up a different port for access) you're going to need more sophisticated firewall rules.  Something like "if source IP address is 'the client' and destination port is either 80 or 443 and 'who knows what else' (so that you don't capture all web traffic)".  This assumes the client always uses the same source IP address.  Hopefully this makes the point that, without a specialized package, you're signing up for an enormous (if even possible) task.

If someone knows an elegant solution I'd be very interested to hear about all possibilities.

If you're trying to block "illegitimate" web access (and this is only a wild guess) probably the better approach is to find a blacklisting tool that tracks "evil" website identities and can block them.  However, even this is problematic because their "list" or "criteria" for defining what to block has to be maintained and probably will never be complete.


On Tuesday, July 22, 2025 at 01:13:42 PM CDT, Peter Davis via Openvpn-users <ope...@li...> wrote: 





Hello,
How can I find out which websites a client has visited? Does this require traffic decryption?

Thank you.
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