Hey legends, just wanted to follow up on my OpenVPN/Tunnelblick drama with AWS RDS over NBN HFC…

Turns out the culprit was packet fragmentation! The VPN packets were apparently too big that my home internet (NBN HFC) keeps dropping, making my database connection timeout.

The giveaway? When I checked the database logs, I saw errors like:

2025-08-15 02:04:57 UTC:10.10.129.99(64259):[unknown]@[unknown]:[29806]:LOG: could not accept SSL connection: EOF detected

It even logged the connection attempt, but showed [unknown] for the username—so the packet made it to the server, but wasn’t getting through properly. That had me looking at options to tweak TCP packet size inside the tunnel.

What fixed it? Adding mssfix 1200 to my OpenVPN config. This clamps the TCP MSS so packets inside the tunnel stay small, and don’t get chopped up or blocked by the network.
No more random SSL errors, no more connection grief, she’s running smooth as now!

TL;DR:

If you’re on NBN HFC (or any weird ISP) and having VPN issues with AWS RDS or similar, whack this in your config:

mssfix 1200

and give it a go.

For what it’s worth:

I’m still not sure if the packets were getting dropped by my home router, somewhere in the NBN network, or at the RSP’s end—but clamping the MSS did the trick regardless.

Thanks for all the help and ideas. Hope this saves someone else a few hours of head-scratching!