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allow to change MTU for all VPNs #2044

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ak370 opened this issue Jan 13, 2024 · 3 comments · May be fixed by #2221
Open

allow to change MTU for all VPNs #2044

ak370 opened this issue Jan 13, 2024 · 3 comments · May be fixed by #2221
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Category: Foolproof settings 👼 Category: OpenVPN 🔐 Complexity: 🟩 Easy to do Status: 🗯️ Waiting for feedback

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@ak370
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ak370 commented Jan 13, 2024

What's the feature 🧐

In certain circumstances MTU needs to be smaller as some networks have issues. Wireguard side seems to have now(link below) MTU parameter but not OpenVPN. Can there be a feature that allows setting lower MTU irrespective of if it is Wireguard or OpenVPN.
I resolve OpenVPN MTU limit problem simply executing below after starting the container, however this should be configurable parameter.
docker exec f86573009ed6 /sbin/ip link set dev tun0 up mtu 1300

#1650

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@PseudoResonance PseudoResonance linked a pull request Apr 13, 2024 that will close this issue
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@qdm12
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qdm12 commented Apr 29, 2024 •
edited

Does using OPENVPN_MSSFIX=1272 fixes it (1300-28)?

@qdm12 qdm12 mentioned this issue Apr 29, 2024
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@ak370
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ak370 commented Apr 29, 2024

Does using OPENVPN_MSSFIX=1300 fixes it?

This flag doesn't to change the MTU is still 1500, however unable to verify as it works at the moment without any flags anyway.

2: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN mode DEFAULT group default qlen 500
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@qdm12
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qdm12 commented May 2, 2024

See the mssfix documentation at https://openvpn.net/community-resources/reference-manual-for-openvpn-2-6/

Basically the mtu is unchanged, but internal TCP connections will have packets at most as MTU-MSSFIX. I guess your issues are related to TCP (tunneled over UDP), if you have issues with UDP tunneled over UDP, then using the --fragment option might be of interest but that's rather rare so far and I would prefer to no add this option.

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Category: Foolproof settings 👼 Category: OpenVPN 🔐 Complexity: 🟩 Easy to do Status: 🗯️ Waiting for feedback
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feat(openvpn): Add OPENVPN_MTU env to change default tun-mtu PseudoResonance/gluetun
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@qdm12 @ak370