Perhaps the reason there is an interface for setting the broadcast address is so that it can be explicitly set to the lowest address (e.g. for compatability with 4.2BSD)? The ability to set an arbitrary broadcast address does seem rather useless otherwise. Sounds like a good email discussion to pull some historical info out of netdev participants and/or the Internet-History mailing list. Hmm -- after our patch, when the lowest address is no longer reserved for broadcast, you can still make the lowest address into a second broadcast address by setting it with ifconfig! That actually argues that our patch is even more innocuous; if anybody in the world actually needs the lowest address to be broadcast, they already have a userspace way to specify that. (By the way, the kernel code looks to me that if the interface broadcast address is set to 255.255.255.255 then it is NOT enabled, so only the default broadcast addresses are enabled. That doesn't seem to be documented either.) I don't know that the documentation that we added about how Linux support for reserved addresses varies from the RFCs needs to wait for these broadcast-related questions to be resolved. We can further improve that documentation once we know if and when "setting the broadcast address on an interface" has or used to have any usefulness. John
