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Cake day: February 2nd, 2025

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  • Couldn’t end up getting this to work for Discord (everything else works). Turns out, my IPv4 traffic leaving through wlp3s0 has a MTU of 1460. And I measured a MTU of 1407 for traffic going through the AirVPN tun (implying 53 bytes of overhead, or 25 bytes of OpenVPN overhead). I ended up just saying the VPN overhead was 40 bytes. Here’s my napkin math:

    1460 <- ISP MTU
    - 28 cost of IP/UDP <- ISP MSS
    - 40 cost of OpenVPN <- AirVPN MTU
    1392
    - 28 cost of IP/UDP <- AirVPN MSS
    1364
    - 40 cost of 2nd OpenVPN <- Home VPN MTU
    1339
    - 40 cost of IP/TCP
    1299 <- Home VPN MSS
    

    For Home and AirVPN I set those in the configs (tun-mtu and mssfix), then mirrored it on the client.