From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.zx2c4.com (lists.zx2c4.com [165.227.139.114]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 190B0C433F5 for ; Mon, 4 Apr 2022 06:56:01 +0000 (UTC) Received: by lists.zx2c4.com (OpenSMTPD) with ESMTP id 82a091e2; Mon, 4 Apr 2022 06:55:59 +0000 (UTC) Received: from tampoco.espindola.nl (tampoco.espindola.nl [149.210.133.191]) by lists.zx2c4.com (OpenSMTPD) with ESMTPS id 19955088 (TLSv1.3:AEAD-AES256-GCM-SHA384:256:NO) for ; Mon, 4 Apr 2022 06:55:58 +0000 (UTC) Received: from [192.168.68.249] (drawbridge.espindola.nl [62.251.122.20]) (using TLSv1.3 with cipher TLS_AES_128_GCM_SHA256 (128/128 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (Client did not present a certificate) (Authenticated sender: frank-deze) by tampoco.espindola.nl (Postfix) with ESMTPSA id B1B123C0184; Mon, 4 Apr 2022 08:55:57 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=deze.org; s=default; t=1649055357; bh=ZKFrmFd+xyaKrFSfSz1mZWmm16Q0NQqtDkJ0LDvapIc=; h=Date:Subject:To:References:From:In-Reply-To; b=HY70roX2uNYVr0Rjnl/j3rRtkhJ+38f+DHz2YXQ26a01HoGavJ/TFNHqXXr+Pspmz J5iHvv+hed5pqEGsUe/XKIBl9D+fpy8jIeFMzUrwlc2SYrqBxU0Qgz9C3nPqDo9U0P 7qMTv/qQILCenIjLzacYvvHDCvWLWjN6rsTzt1/Ew0tz21RskvKiaQILobzYX15c88 bHztvPnxGdgNohg4cG7Jnp28osqldx1o92eef66osnMeRzGxRlxMRM3E74RQHIrij2 ZT1CUapv5ZyR6LwFEa4EMjNlMf5jE0IGswxlAOa/KjlfjeAsQaA2uGwheZBnhV6Ysj PIZJw9+t0yLsA== Message-ID: <88efb74e-39ec-99e5-98a8-244e0af70724@deze.org> Date: Mon, 4 Apr 2022 08:55:58 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:91.0) Gecko/20100101 Thunderbird/91.7.0 Subject: Re: MTUs go strange ways - ? Content-Language: en-US To: lejeczek , wireguard@lists.zx2c4.com References: From: Frank Volf In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: wireguard@lists.zx2c4.com X-Mailman-Version: 2.1.30rc1 Precedence: list List-Id: Development discussion of WireGuard List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: wireguard-bounces@lists.zx2c4.com Sender: "WireGuard" Hi, The "-s" option provides the length of the ICMP data in the packet, not the total packet length. To the data size you need to add 8 bytes for the ICMP header and 20 bytes for the IP header. So, you are sending 1328 bytes (which is noted between the brackets in your output). If you change to "-s 1292" then you are actually sending packets with total length of 1320. Kind regards, Frank Op 2-4-2022 om 19:41 schreef lejeczek: > Hi guys > > I thought there was no better place to ask but here so - both ends are > centOS and end up having different MTUs for 'wg' interfaces and that I > thought, was wrong. > 1370 (server) VS 1320 (client) > I expected that would be negotiated between nodes without user > involved, right? > Moreover if I from the client do: > > -> $ ping server -M do -s 1300 > PING 10.3.3.1 (10.3.3.1) 1300(1328) bytes of data. > ping: local error: message too long, mtu=1320 > > Could some expert or two shed more light on what & why is happening? > many thanks, L. >