Date: Mon, 23 Mar 2020 14:17:15 +0700 From: Victor Sudakov <vas@sibptus.ru> To: freebsd-net@freebsd.org Subject: Re: IP MTU on gif and gre interfaces (with and without IPSec encryption) Message-ID: <20200323071715.GB54231@admin.sibptus.ru> In-Reply-To: <20200323050012.GA50490@admin.sibptus.ru> References: <20200323050012.GA50490@admin.sibptus.ru>
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--KsGdsel6WgEHnImy Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Victor Sudakov wrote: >=20 > If the MTU on the external Ethernet interface is 1500, it should be safe > to configure the gif(4) interfaces with mtu=3D1480 and gre(4) > interfaces with mtu=3D1476, correct? >=20 > I've noticed that a newly created gre0 interface has the expected "mtu 14= 76" > value, but a newly created gif0 interface has "mtu 1280", why would the > default be so low? >=20 > A second question. If the gif and gre tunnels will be wrapped in > IPSec transport mode, does it make sense to set the MTU on the > corresponding gif and gre interfaces to some lower value? And to make the matter even more mysterious, if_ipsec(4) which is essentially the same as gif, is created by default with mtu=3D1400 for some reason. --=20 Victor Sudakov, VAS4-RIPE, VAS47-RIPN 2:5005/49@fidonet http://vas.tomsk.ru/ --KsGdsel6WgEHnImy Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iQEcBAEBAgAGBQJeeGJ7AAoJEA2k8lmbXsY0CyoH/3Rtm1q5B3WuthzkTX0/1+B0 SjHIAaUxUyajiIN7+E4DuqHRvnLoMwM5omnGFgek7hmbJFhpgIzSKuHjmsCNNHX6 BpmeRS2YFlnucq365nr/5yaRJh3VM0DT+K1LPJ9csa8jkl+SMoheEMPGlRQR5lMY 79rvqCYn4lZ3wZ6dAJw0PhY9nEbsXpIp0RuA87Wa0x+zdZg7pcnXEyGdJxc2u2qz 7D4G8Cw8RdN9lcUDeqvUCc7hG1pl9AP6iz7pTo5WGFbmYJ9c+qSYkb8smFcnx04G IdAN4kR4FBrttamrM/UqhuMkAjNCTAmWwmmVtBmETMftrZCkpp5R7KGQfuIi+ro= =PmYG -----END PGP SIGNATURE----- --KsGdsel6WgEHnImy--
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