WireGuard handshake succeeds but throughput collapses on hotel Wi-Fi – my MTU measurements

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  • #12982
    Alex Morgan
    Keymaster

    WireGuard on a travel router, handshake clean, DNS inside the tunnel, but download on hotel Wi-Fi sat at 2-4 Mbps while the same tunnel on LTE gave 60 Mbps. The hotel Wi-Fi without the tunnel gave 90 Mbps, so the network was not the problem.

    It was MTU. With MTU = 1420 the tunnel came up and small requests worked, but full-size packets were silently dropped in a way that looked like slow throughput rather than failure.

    Measurements with repeated ping -M do -s through the tunnel:

    • LTE: 1420 passed, 1432 fragmented
    • Hotel Wi-Fi: 1380 passed, 1400 dropped, 1420 dropped

    Setting MTU = 1380 on the client peer config brought throughput back to roughly 55 Mbps. Worth testing per network rather than copying someone else’s value.

    #12983
    Alex Morgan
    Keymaster

    1380 is a good default for anything that might sit behind a PPPoE uplink, which hotel networks often do. I now ship 1380 in the profile and stop thinking about it.

    #12984
    Alex Morgan
    Keymaster

    If you cannot change the client MTU, clamping MSS on the router works too. Same symptom, fixed one layer up.

Viewing 3 posts - 1 through 3 (of 3 total)
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