Date: Fri, 4 Aug 2006 06:02:25 +0200 From: Benjamin Lutz <benlutz@datacomm.ch> To: questions@freebsd.org Subject: IP broadcasts Message-ID: <200608040602.29799.benlutz@datacomm.ch>
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--nextPart1327891.zGBWxTohYJ Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Hello, I've been playing around with IP packets tonight, and I've noticed a peculi= ar=20 behaviour in FreeBSD that I can't explain. Can someone provide some insight? Specifically, I've been sending IP packets to broadcast addresses, once to= =20 10.0.0.255, which is the local subnet's broadcast address, and once to=20 255.255.255.255, which as I understand it, is a general broadcast address.= =20 The first broadcast (to 10.0.0.255) works, the second (to 255.255.255.255)= =20 doesn't. Looking at it with tcpdump on the sending machine, I see this: 05:46:52.057994 00:12:17:5a:b3:b6 > ff:ff:ff:ff:ff:ff, ethertype IPv4=20 (0x0800), length 136: 10.0.0.1 > 10.0.0.255: ip-proto-255 102 05:47:16.472315 00:12:17:5a:b3:b6 > 00:40:63:d9:a9:28, ethertype IPv4=20 (0x0800), length 136: 10.0.0.1 > 255.255.255.255: ip-proto-255 102 In other words, the packet to 10.0.0.255 is has a destination MAC address o= f=20 ff:ff:ff:ff:ff:ff, so all machines on the subnet receive it. The second=20 packet has the destination MAC of my gateway, so only that machine receives= =20 it, the other machines on the net don't see it (the ethernet uses a switch). Things work as expected when sending the packets from a Linux machine. Mayb= e=20 there's some socket option or sysctl I need to set? Cheers Benjamin --nextPart1327891.zGBWxTohYJ Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (GNU/Linux) iD8DBQBE0sbVgShs4qbRdeQRAlLZAJ93RW5febIlktpNMia5Y6MiqhOSiACdGT26 kIsGlsmb8I+4/qXRwFaewqc= =RQL2 -----END PGP SIGNATURE----- --nextPart1327891.zGBWxTohYJ--
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