c - How do I identify the source of a UDP packet in an access point? -

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i'm creating kind of access point.

i capture packets, of types, machine, in order prioritize them before forwarding them, according default quality of service (qos) classes.

by calling socket eth_p_all parameter , can incoming packets of protocol type:

    if ((sockfd = socket(af_packet, sock_raw, htons(eth_p_all))) == error)  {         perror("socket");         exit(1);     }

by using ethhdr, iphdr, tcphdr , udphdr structs can't retrieve information on application sent each packet.

however, both voip , snmp use udp, , don't know of 2 sent me udp package.

i'd know applications sending udp packets, may follow qos classes , forward packets (e.g. conversational voice) before others (e.g. e-mail).

in order recognize protocol, should use list of tcp , udp port numbers?

you cannot tell for sure application sent packet - sender knows this. if understand correctly, want detect protocol being used. have 2 possibilities:

  1. assume application based on destination port set on tcp/udp packet - list of tcp/udp port numbers or /etc/services (if you're on linux/unix/osx/etc) might of help;

  2. analyse packet contents , match against known protocol signatures (like ids - see snort rules example). note may need form of conntrack make work reliably;


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