Date: Sun, 23 Nov 2008 19:24:48 +0200 From: "Eitan Shefi" <eitans@mellanox.co.il> To: <freebsd-net@freebsd.org> Cc: Eitan Shefi <eitans@mellanox.co.il> Subject: IP fragmentation Message-ID: <5D49E7A8952DC44FB38C38FA0D758EAD0105450B@mtlexch01.mtl.com>
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Hi, =20 The IP fragmentation is not like in Linux, and is not clear to me. =20 I'm using 2 FreeBSD-6.3 hosts, connected directly. If I change the MTU of both hosts to 5000, and send "ping" with message size 4972 bytes ( 4972 =3D 5000 - 8(which is ICMP Header size) - 20 = (which is IP Header size) ) from one host to the other, the message is passed as one packet: packet size 5000 bytes. (as expected) But if I send "ping" with message size 4973 bytes, the IP fragmentation to 2 packets is not clear to me: The first packet is with size: 4116 bytes The second packet is with size: 905 bytes =20 I expected the first packet size to be: 4996 =3D 5000 - ((5000-20) Mod = 8) and the second packet size to be: 25 =3D 5021 - 4996 =20 What is the formula being used in FreeBSD to compute the IP fragments size? =20 =20 Thanks, Eitan =20
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