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From: "Jason A. Donenfeld" <Jason@zx2c4.com>
To: Ismael Bouya <ismael@bouya.org>
Cc: wireguard@lists.zx2c4.com
Subject: Re: Incorrect computation of the MTU in wg-quick
Date: Wed, 21 May 2025 23:08:43 +0200	[thread overview]
Message-ID: <aC5A29Qmn-5uoCC0@zx2c4.com> (raw)
In-Reply-To: <cvlwdlcato6fv5ih7qcib2tyzjltvfnq3l4flfcfrqqltl32j7@2mae3zkuvmuw>

> I would like to report a behavior that seems to be incorrect in the way
> wg-quick computes the MTU to assign to a wireguard interface:
> https://git.zx2c4.com/wireguard-tools/tree/src/wg-quick/linux.bash#n125
> In this block, wg-quick goes through every endpoint it knows about,
> gets the mtu of the route to reach the endpoint, and takes the highest
> value among all the computed values.
> However it appears to me that the chosen value should instead be the
> lowest among all endpoints rather than the highest.
> 
> As an example, if I declare myself (localhost) as an endpoint (it may or
> may not be supported, but that’s how I found about this issue), then the
> mtu will be set to 65456 (65536-80) which is higher than what the other
> endpoints are able to manage, and I’ll only be able to contact myself
> properly.

Thanks for the report. Fixed:
https://git.zx2c4.com/wireguard-tools/commit/?id=5150cd647073be1f1c12688aef291bdf17970154

Let me know if that looks okay to you.

Jason

  reply	other threads:[~2025-05-21 21:08 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-02-02 23:47 Incorrect computation of the MTU in wg-quick Ismael Bouya
2025-05-21 21:08 ` Jason A. Donenfeld [this message]
2025-05-25 22:51   ` Ismael Bouya

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