Hi.
I'm using the FreeBSD network stack (on top of the eCos embedded OS),
and I want to send a limited broadcast (a broadcast with destination IP
of 255.255.255.255).
Normally (I believe) the stack will only send a broadcast like this if
there is no subnet mask set on the interface, or an all zeros mask (this
is how bootp/dhcp work). Once I set a normal subnet mask, the stack will
change my broadcasts into subnet broadcasts, eg. 192.168.0.255. In my
situation the interface is active, so I can't just remove the netmask -
I must find another way to send the limited broadcast.
When the interface gets setup with IP and netmask it creates a default
broadcast address. If I override this and set it to 255.255.255.255
(using SIOCSIFBRDADDR), then it will try to send my limited broadcast as
is, rather then changing it into a subnet braodcast. Unforunately this
fails, because there is no route available that matches this destination.
Okay, so just add a route? But when I try to add a route that would
match 255.255.255.255 it gets rejected – it is not valid for the
interface as currently configured.
The next step – which I would rather avoid - is modify the ip code. If
the SO_DONTROUTE/IP_ROUTETOIF flag is set then you only need a route in
order to pick an interface, not for any actual routing. So, I could add
some code to manually pick an interface (even though none really match
my destination address). But I’d rather avoid changing the code.
So, can anyone suggest how I can send a limited broadcast (on an
interface that has been initalized with an IP and a subnet)?
Thanks for any suggestions.
Tom.
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