RFC 919 compliance (broadcasts to 255.255.255.255)

[Mohacsi Janos]

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
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