Obscure udp multicast issue/bug

[gds at chartertn.net (Gene Smith)]

Gene Smith wrote:
> When I send to a multicast address with TTL set to 1 (default, restrict 
> m/c to local subnet) and my gateway is set to NULL or to an invalid 
> address, I get destination unreachable (errno = 118) on sendto() call. 
> It fails in ip_output() before it even checks that the destination 
> address is multicast.
> 
> So if I want to multicast on only my local subnet and there is no 
> configured router/gateway to the outside world, I still have to specify 
> a reachable host as the gateway to get multicast to work.
> 
> I don't know if this is expected behavior or something broken in the BSD 
> stack.
> 
> -gene

See bug 1381 for proposed fix.