Date: Tue, 09 Feb 2010 13:12:21 +0100 From: Harald Schmalzbauer <h.schmalzbauer@omnilan.de> To: freebsd-questions@freebsd.org Subject: MTU, fragmentation and Jumbo Frames question Message-ID: <4B715125.8070809@omnilan.de>
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This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigB4BB7E910E5D4D5BD007D7D5 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: quoted-printable Hello all, I have 3 machines connected to an JumboFrame enabled switch. One FreeBSD 8-stable and two windows machines. I can send echo requests with payload of 8972 between the windows=20 machines, but I don't get an answer from the FreeBSD machine. At the=20 edge of 8130 bytes, the FreeBSD machine eats the packets without any=20 error notification. A payload <=3D 8130 bytes works! All MTUs are set to 9000, interfaces are all intel em. Like mentioned, the ping between the two windows machines work like=20 expected, beyond 8972 bytes payload the OS is fragmenting (resp. tells=20 me that DF bit was set but fragmentation was needed) FreeBSD seems to never fragment packets, since I don't get an answer if=20 I define payload greater than MTU. But this should work, shouldn't it=20 (`ping -s 10000 host`) Does anybody have any explanation why pings are working up to 8130 bytes = payload and are silently droped beyond that even my MTU ist set to 9000=20 (and route get confirms the MTU 9000)? Thanks for any help, -Harry --------------enigB4BB7E910E5D4D5BD007D7D5 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.13 (FreeBSD) iEYEARECAAYFAktxUSUACgkQLDqVQ9VXb8gvMgCcC52QIP/ENPX4phXazLXtQscO dWwAoIT72cbbxHFw61rvGnZmu3JhRlWt =KNRY -----END PGP SIGNATURE----- --------------enigB4BB7E910E5D4D5BD007D7D5--
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