The broadcast address is apparently misconfigured on some (old) Linux embedded device that I setup (but that I don't own anymore) because it doesn't match the expected value given the IP address and the netmask (for example, it has a broadcast of 192.168.70.255 instead of 192.168.71.255 for 192.168.70.243/255.255.254.0). It runs a kernel 2.4.31 with busybox 0.60.5. The network configuration is simply done with that shell snippet:
ifconfig eth0 $IPADDR netmask $NETMASK if [ -n "$GATEWAY" ]; then route add default gw $GATEWAY fi
Thus the broadcast address is not explicitely configured. The question is: what is responsible of this bad behaviour? Is it busybox's ifconfig that doesn't set the broadcast address correctly or is it the kernel that set it up badly?
Note: it's possible that none of them are responsible but something else gets in the way in the boot process (and reconfigures it badly) as the device runs user-specific software that I don't know. I will follow up with more info once I have them.