* Seth David Schoen:

Both things you noted are true: you can change broadcast addresses with
ifconfig or ip (e.g. ip addr add x/y broadcast z dev d), and /31 subnets
indeed don't have them.  This is defined at

There is also the questions of netmask that aren't in the CIDR style
(so 255.255.0.255 instead of 255.255.255.0).  Are they still
supported?

I'm not familiar with a way in which it depends on the network device
other than the /31 issue.  At least, this particular logic isn't
affected by other aspects of the network device type.

Are there network devices that are neither point-to-point, nor do they
have broadcast support?

Could you suggest a way that these details could usefully be described
here?  The ability to change the broadcast address is very little-used,
so I'm not sure many readers would benefit from details about it here,
but I also wouldn't want to mislead them about that.  Maybe just
changing it to "are both designated, by default, as broadcast
addresses"?

My main concern is that the language should not imply that something
cannot happen if it actually can.  Otherwise programmers will end up
using this guidance and create software that won't work in such
configurations.