On Fri, 6 Dec 2002, Joshua Graessley wrote: > I am aware of the issues with broadcast, and I strongly urge people to > use multicast instead of broadcast for a variety of reasons. All the > same, I've been asked to address this issue and I wanted to understand > why FreeBSD doesn't allow broadcast on the loopback interface. > Conceptually, it sort of makes sense to allow it. Using a broadcast > should result in everyone on some link receiving your packet. If > loopback is your only interface that's up, then why not use that? In > the case of loopback, you are the only one on your link, so you should > still receive your broadcast. > > Is there a technical reason this was done (i.e. if I set the broadcast > flag on loopback I'll be chasing down other bugs until my hair turns > grey or falls out) or is it a conceptual reason (i.e. broadcast, on > loopback, are you out of your mind?). >
With any kind of broadcast media, unless this is specific to Ethernet, or there are some exceptions, a broadcast packet sent by a station is received on every port other than the port that the packet came from. As far as I know, a station should never receive it's own broadcast packets unless you have a loop somewhere in your Layer 2 infrastructure. I believe that the above applies to IP broadcasts (or any other Layer 3 protocols) as well. > Other platforms out there will handle broadcast on the loopback > interface. Is it desirable to make changes to the FreeBSD stack to get > this behavior? Any examples? I cannot think of a practical case where this would be required. I would think that an application will know if it sent a broadcast or not, so it shouldn't have to receive that broadcast itself. Anyone disagree? To Unsubscribe: send mail to [EMAIL PROTECTED] with "unsubscribe freebsd-net" in the body of the message
