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Recieving Raw IP packets.

by Jimmmy Features (Initiate)
on Dec 07, 2005 at 23:27 UTC ( #515070=perlquestion: print w/replies, xml ) Need Help??
Jimmmy Features has asked for the wisdom of the Perl Monks concerning the following question:

Hi. I made a small script in perl that uses the Net::RawIP module to send a tcp packet with the syn flag set to another computer. How would I go about listening for the return packet?

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Re: Recieving Raw IP packets.
by Celada (Monk) on Dec 08, 2005 at 04:04 UTC
    Since you are dealing with raw packets, you have to listen to everything and filter yourself for the packets you are interested in. You will probably want to consider the packets that are received on the port you used to send packets from, and discard all others. This code will listen to every TCP packet and show you the IP addresses and port numbers involved.
    #!/usr/bin/perl use strict; use Socket; socket S, PF_INET, SOCK_RAW, 6; my $result; while (my $sender = recv(S, $result, 2000, 0)) { print "got a ", length($result), " byte TCP packet...\n"; if (length($result) < 20) { print " ...which is too small to be an IP packet\n"; } else { printf " from %d.%d.%d.%d to %d.%d.%d.%d\n", map { unpack("C", substr($result, $_, 1)) } (12..19); if (length($result) < 40) { print " ...and is too small to be a TCP packet\n"; } else { printf " from port %d to port %d\n", map { unpack("n", substr($result, $_, 2)) } (20, 22); } } }

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