linux - UDP-Broadcast on all interfaces -


on linux system wired , wireless interface (e.g. 192.168.1.x , 192.168.2.x subnets) want send udp broadcast goes out via available interfaces (i.e. both through wired , wireless interface).

currently sendto() inaddr_broadcast, seems broadcast sent through 1 of interfaces (not same , subsequent broadcasts may use other interface).

is there way can send udp broadcast goes out through every single interface?

first of all, should consider broadcast obsolete, specially inaddr_broadcast (255.255.255.255). question highlights 1 of reasons broadcast unsuitable. should die along ipv4 (hopefully). note ipv6 doesn't have concept of broadcast (multicast used, instead).

inaddr_broadcast limited local link. nowadays, it's visible use dhcp auto-configuration, since @ such time, client not know yet in network connected to.

with single sendto(), single packet generated, , outgoing interface determined operating system's routing table (ip route on linux). can't have single sendto() generate more 1 packet, have iterate on interfaces, , either use raw sockets or bind socket device using setsockopt(..., sol_socket, so_bindtodevice, "ethx") send each packet bypassing os routing table (this requires root privileges). not solution.

instead, since inaddr_broadcast not routed anyway, can achieve same thing iterating on each interface, , sending packet broadcast address. example, assuming networks have 255.255.255.0 (/24) masks, broadcast addresses 192.168.1.255 , 192.168.2.255. call sendto() once each of these addresses , have accomplished goal.

edit: fixed information regarding inaddr_broadcast, , complementing answer information so_bindtodevice.


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