Date: Sat, 5 Aug 2006 07:18:54 +0200 (CEST) From: Mohacsi Janos <mohacsi@niif.hu> To: Benjamin Lutz <benlutz@datacomm.ch> Cc: freebsd-hackers@freebsd.org Subject: Re: RFC 919 compliance (broadcasts to 255.255.255.255) Message-ID: <20060805071620.D83852@mignon.ki.iif.hu> In-Reply-To: <200608041712.11939.benlutz@datacomm.ch> References: <200608041712.11939.benlutz@datacomm.ch>
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On Fri, 4 Aug 2006, Benjamin Lutz wrote: > Hello, > > I've noticed that FreeBSD does not by default comply to RFC 919, Chapter 7 > (http://tools.ietf.org/html/rfc919). Specifically, it does not handle IP > packets with a destination address of 255.255.255.255 properly. > > 255.255.255.255 is a "limited broadcast address" (the term is not mentioned in > the RFC, but seems to be in use everywhere else). An IP packet send to that > address should be broadcast to the whole IP subnet of the broadcasting > device. However, in FreeBSD (4.11, 5.5, 6.1) this does not work, as is > evident by this tcpdump output: > > 17:00:59.125132 00:12:17:5a:b3:b6 > 00:40:63:d9:a9:28, ethertype IPv4 > (0x0800), length 98: 10.0.0.1 > 255.255.255.255: ICMP echo request, id 33319, > seq 0, length 64 > > The destination MAC address is that of my gateway, but it should be > ff:ff:ff:ff:ff:ff. You can reproduce this by running "tcpdump -en ip proto 1" > and "ping 255.255.255.255". > > I found a discussion from 2003 about this, but it seems to have trailed off > without coming to a conclusion: > http://lists.freebsd.org/pipermail/freebsd-net/2003-July/000921.html > > I've noticed that the ip(7) manpage lists a SO_ONESBCAST option. The intention > seems to be to enable packets to 255.255.255.255. However a test with a small > program showed that this option seems to have no effect, outgoing packets > still carried the gateway's MAC address as destination. > > Btw, Linux and NetBSD both handle packets to 255.255.255.255 as broadcasts. > > Now, is this behaviour intentional? Is there a way to turn on RFC 919 > compliance? If not, would someone be willing to add this to the kernel? Should > I submit a PR? Does this feature really necessary? For waht purpose? I believe this feature is more harmful than useful. Regards, Janos Mohacsi Network Engineer, Research Associate, Head of Network Planning NIIF/HUNGARNET, HUNGARY Key 00F9AF98: 8645 1312 D249 471B DBAE 21A2 9F52 0D1F 00F9 AF98 > > Cheers > Benjamin > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org" >
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