From owner-freebsd-net@freebsd.org Mon Mar 23 09:08:56 2020 Return-Path: Delivered-To: freebsd-net@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 28C0327D816 for ; Mon, 23 Mar 2020 09:08:56 +0000 (UTC) (envelope-from hausen@punkt.de) Received: from mail.punkt.de (mail.punkt.de [217.29.41.227]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 48m7pv0tyxz4SD4 for ; Mon, 23 Mar 2020 09:08:54 +0000 (UTC) (envelope-from hausen@punkt.de) Received: from [IPv6:2003:a:d59:3800:5cc8:2c6c:7020:8519] (unknown [IPv6:2003:a:d59:3800:5cc8:2c6c:7020:8519]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.punkt.de (Postfix) with ESMTPSA id C9C272A365; Mon, 23 Mar 2020 10:08:46 +0100 (CET) Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 12.4 \(3445.104.11\)) Subject: Re: IP MTU on gif and gre interfaces (with and without IPSec encryption) From: "Patrick M. Hausen" In-Reply-To: <20200323050012.GA50490@admin.sibptus.ru> Date: Mon, 23 Mar 2020 10:08:40 +0100 Cc: freebsd-net@freebsd.org Content-Transfer-Encoding: quoted-printable Message-Id: <7D560C6A-EB51-414A-A3A1-18587D40C218@punkt.de> References: <20200323050012.GA50490@admin.sibptus.ru> To: Victor Sudakov X-Mailer: Apple Mail (2.3445.104.11) X-Rspamd-Queue-Id: 48m7pv0tyxz4SD4 X-Spamd-Bar: / Authentication-Results: mx1.freebsd.org; dkim=none; dmarc=none; spf=pass (mx1.freebsd.org: domain of hausen@punkt.de designates 217.29.41.227 as permitted sender) smtp.mailfrom=hausen@punkt.de X-Spamd-Result: default: False [-0.64 / 15.00]; ARC_NA(0.00)[]; RCVD_VIA_SMTP_AUTH(0.00)[]; NEURAL_HAM_MEDIUM(-0.26)[-0.257,0]; FROM_HAS_DN(0.00)[]; TO_DN_SOME(0.00)[]; R_SPF_ALLOW(-0.20)[+ip4:217.29.32.0/20]; MV_CASE(0.50)[]; MIME_GOOD(-0.10)[text/plain]; DMARC_NA(0.00)[punkt.de]; NEURAL_HAM_LONG(-0.32)[-0.325,0]; TO_MATCH_ENVRCPT_SOME(0.00)[]; RCPT_COUNT_TWO(0.00)[2]; IP_SCORE(-0.26)[ipnet: 217.29.32.0/20(-0.71), asn: 16188(-0.56), country: DE(-0.02)]; FROM_EQ_ENVFROM(0.00)[]; R_DKIM_NA(0.00)[]; MIME_TRACE(0.00)[0:+]; ASN(0.00)[asn:16188, ipnet:217.29.32.0/20, country:DE]; MID_RHS_MATCH_FROM(0.00)[]; RCVD_TLS_ALL(0.00)[]; RCVD_COUNT_TWO(0.00)[2] X-BeenThere: freebsd-net@freebsd.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Networking and TCP/IP with FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 23 Mar 2020 09:08:56 -0000 Hi all, > Am 23.03.2020 um 06:00 schrieb Victor Sudakov : > I've noticed that a newly created gre0 interface has the expected "mtu = 1476" > value, but a newly created gif0 interface has "mtu 1280", why would = the > default be so low? gif is frequently used as the innermost encapsulation like in gif tunnel across host mode IPsec. Then there might be PPPoE, too. Possibly a VLAN tag ... So most probably the idea is to go as low as possible for arbitrary = additional encapsulations while still satisfying the minimum requirement for IPv6. For the others: no idea, I guess historical ;-) Patrick --=20 punkt.de GmbH Patrick M. Hausen .infrastructure Kaiserallee 13a 76133 Karlsruhe Tel. +49 721 9109500 https://infrastructure.punkt.de info@punkt.de AG Mannheim 108285 Gesch=C3=A4ftsf=C3=BChrer: J=C3=BCrgen Egeling, Daniel Lienert, Fabian = Stein