Development discussion of WireGuard
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From: tlhackque <>
Subject: Re: Question about MTU and Wireguard and the current changes
Date: Mon, 10 Jan 2022 15:56:07 -0500	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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On 10-Jan-22 15:37, wrote:
> Hi,
> I run in some connection troubles between two wireguards host (one 
> running fedora 35, one arch linux). If I tried to transfer large files 
> through SSH (SCP or btrfs send/receive thorugh ssh through wireguard 
> tunnel) it stucks after a few byte and nothing transfered anymore.
> This happens in the last days, so probably an update on one or both 
> machines. I also saw, that there some changes on the MTU thing (If I 
> remember correctly, a per peer MTU is configurable)
> However. My first try was just set the MTU to a lower number (MTU = 
> 1200) and yes, scp works again.
> Okay, so I did the good old ping test. "ping -M do -s $SIZE -c 1 
>" with $SIZE increasing. And that surprised me. It works 
> until an Size of 36932 Bytes. Checked with wireguard and "MTU = 36932" 
> and yes, scp still working.
> Can somebody explain, why the old default setting of "65456" doesn't 
> work anymore but the MTU can set to much higher values as typical ones?
> Thanks
> Henning
Guess: Fragmentation happens somewhere and fragments are blocked at your 
router/firewall/host.  Blocking fragments is a common, if misguided, 
"security enhancement".

A packet trace would provide the necessary clues in any case.

Wireshark is a convenient way to get one.

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      reply	other threads:[~2022-01-10 20:57 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-01-10 20:37 henning.reich
2022-01-10 20:56 ` tlhackque [this message]

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