Date: Mon, 23 Mar 2020 10:08:40 +0100 From: "Patrick M. Hausen" <hausen@punkt.de> To: Victor Sudakov <vas@sibptus.ru> Cc: freebsd-net@freebsd.org Subject: Re: IP MTU on gif and gre interfaces (with and without IPSec encryption) Message-ID: <7D560C6A-EB51-414A-A3A1-18587D40C218@punkt.de> In-Reply-To: <20200323050012.GA50490@admin.sibptus.ru> References: <20200323050012.GA50490@admin.sibptus.ru>
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Hi all, > Am 23.03.2020 um 06:00 schrieb Victor Sudakov <vas@sibptus.ru>: > 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
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