Seth David Schoen writes:
> > Are there network devices that are neither point-to-point, nor do they
> > have broadcast support?
>
> We've talked about this question a bit in our project before. I don't
> believe so, but I can look into it further. It's logically conceivable
> that there could be such devices.
I found that there are several address family and/or interface types in the
Linux kernel now that always refuse the SIOCSIFBRDADDR ioctl (with EINVAL).
However, none of them are IPv4 and so they're all outside the scope of the
ip(7) man page. (They are x25, ax25, rose, netrom, and qrtr, each of
which has its own address family instead of AF_INET, namely AF_X25,
AF_AX25, AF_ROSE, AF_NETROM, and AF_QIPCRTR.)
I haven't found anywhere else in the kernel where setting a broadcast
address will be rejected as inapplicable. That is, you can always at
least complete the ioctl, so if it doesn't work because it's
inapplicable at a lower layer, that seems like a bug.
The existing man page for ip-link(8) seems to assume that an IP link is
either broadcast-capable or marked point-to-point:
broadcast LLADDRESS
brd LLADDRESS
peer LLADDRESS
change the link layer broadcast address or the peer address when
the interface is POINTOPOINT.
(These two cases seem to be taken as exhaustive and mutually exclusive
here.)
The more complete answer that I'm looking into now will depend on
whether you can get an interface that can run IPv4 but that has neither
IFF_BROADCAST nor IFF_POINTOPOINT in its flags.
--
Seth David Schoen <schoen@xxxxxxxxxxx> | Qué empresa fácil no pensar
http://www.loyalty.org/~schoen/ | en un tigre, reflexioné.
| -- Borges, "El Zahir"
