Date: Wed, 16 Nov 2005 12:13:42 +0100 From: Michael Voucko <voucko@gmx.li> To: freebsd-stable@freebsd.org Subject: "message too long" when sending broadcasts Message-ID: <437B1466.8030202@gmx.li>
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This is a multi-part message in MIME format. --------------000304070202090800010101 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Hi, I'm trying to install the latest version of heartbeat (linux-ha), which unfortunately is not available from the ports tree yet. Setup is two boxes running (5.4-STABLE FreeBSD from Oct 17 2005) both connected to a hub with lnc NICs on a private 10.0.0.0/24 subnet (actually its only a 'simulated hub' provided by VMWare if this matters). After some initial struggles configuration, build and installations works as expected - but now the most basic parts of this application won't work anymore. When trying to use UDP broadcast messages for the heartbeat it would error out with "Message too long" for packets larger than 1472 bytes, in other words as soon as fragmentation of the package would be necessary (MTU is 1500). I received a code snippet from the heartbeat developers to isolate the problem (create sender and receiver socket, send broadcast packets of a certain size). To rule out VMware as the basic problem I tried real boxes but the problem persists. Is there any size restriction for UDP broadcast messages? Is there anything which prevents UDP broadcast from being fragmented? I searched RFCs, man pages for socket, setsockopt, ioctl, sendto and other places but did not find anything that could explain the behaviour (which seems to be no problem on other OS). Any pointers, comments? Thanks, Michael N.B: Code snippet is attached in case somebody cares to take a look - it works fine for me when using "./bcast-test -r -i lnc1 -p 1500" on the receiving box and "./bcast-test -r -i lnc1 -p XXX" on the sending box for XXX < 1473. --------------000304070202090800010101 Content-Type: text/plain; name="bcast.c" Content-Transfer-Encoding: base64 Content-Disposition: inline; filename="bcast.c" I2luY2x1ZGUgPHVuaXN0ZC5oPgojaW5jbHVkZSA8c3RkaW8uaD4KI2luY2x1ZGUgPHN0ZGxp Yi5oPgojaW5jbHVkZSA8c3lzL3R5cGVzLmg+CiNpbmNsdWRlIDxzeXMvc29ja2V0Lmg+CiNp bmNsdWRlIDxzdHJpbmcuaD4KI2luY2x1ZGUgPG5ldGluZXQvaW4uaD4KI2luY2x1ZGUgPG5l dC9pZi5oPgojaW5jbHVkZSA8ZXJybm8uaD4KI2luY2x1ZGUgPHN5cy9pb2N0bC5oPgoKI2Rl ZmluZSBQT1JUIDY5NAojZGVmaW5lIE1BWEJVRiAyMDQ4Cgp2b2lkCnVzYWdlKGludCBhcmdj LCBjaGFyICoqIGFyZ3YpCnsKCXByaW50ZigiVXNhZ2U6ICVzIFstc10gWy1yXSAtcCBwYWNr ZXRzaXplIC1pIGV0aDAvZXRoMS8uLi5cbiIsIGFyZ3ZbMF0pOwoJcHJpbnRmKCIjZGVmYXVs dCBpcyB0byByZWNlaXZlXG4iKTsKCXJldHVybjsKfQoKaW50CmNyZWF0ZV9yZWN2X3NvY2tl 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