How do I get the destination IP of a received UDP packet?

Discussion in 'Ruby' started by Gavin Yap, Feb 7, 2009.

  1. Gavin Yap

    Gavin Yap Guest

    Hi There,

    I need to write a server which is able to identify client by

    My machine is listening to "", any IP addrs configured to it.
    Take for instance, the machine is configured with ",", also listening to "", allow listening to Broadcast
    queries, which is also important to my application

    Hence, if one of the clients send a UDP packet to it, the server program
    would check the destination address of the client request and reply the
    client with different "answers".

    I've not been lucky enough to google how to get the destination address
    of a incoming packet.

    Hope someone here could shed some light. Thanks :)
    Gavin Yap, Feb 7, 2009
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  2. Gavin Yap

    Tanaka Akira Guest

    How about using sockets for each IP address and ""?

    require 'socket'

    s0 =, Socket::SOCK_DGRAM, 0)
    s0.setsockopt(Socket::SOL_SOCKET, Socket::SO_REUSEADDR, 1)
    s0.bind(Socket.sockaddr_in(9999, ""))

    s1 =, Socket::SOCK_DGRAM, 0)
    s1.setsockopt(Socket::SOL_SOCKET, Socket::SO_REUSEADDR, 1)
    s1.bind(Socket.sockaddr_in(9999, ""))

    s2 =, Socket::SOCK_DGRAM, 0)
    s2.setsockopt(Socket::SOL_SOCKET, Socket::SO_REUSEADDR, 1)
    s2.bind(Socket.sockaddr_in(9999, ""))

    while true
    rs, =[s0, s1, s2])
    rs.each {|s|
    p [Socket.unpack_sockaddr_in(s.getsockname)[1], s.recv(100)]

    I'm not certain about the portability of the broadcast
    handling, though.
    Tanaka Akira, Feb 7, 2009
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  3. Gavin Yap

    Gavin Yap Guest

    Hi Tanaka Akira san,

    Thanks for the tip.

    I guess this is the only way get my destination address.
    I wonder if there's a way to recieve the packet, with layer 3(IP header)
    and layer 4(UDP header) info.
    I dun mind to write a wrapper to strip off or add, the IP header and UDP
    Gavin Yap, Feb 7, 2009
  4. Gavin Yap

    Tanaka Akira Guest

    Your OS may have another (non-portable) way.

    For example, IP_PKTINFO of GNU/Linux, IP_RECVDSTADDR of 4.4BSD.

    However they needs recvmsg which is not supported by Ruby, yet.
    Tanaka Akira, Feb 7, 2009
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