netpacket(3pm) [debian man page]
NetPacket(3pm) User Contributed Perl Documentation NetPacket(3pm) NAME
NetPacket - assemble/disassemble network packets at the protocol level VERSION
version 1.3.0 SYNOPSIS
# NetPacket is a base class only DESCRIPTION
"NetPacket" provides a base class for a cluster of modules related to decoding and encoding of network protocols. Each "NetPacket" descendent module knows how to encode and decode packets for the network protocol it implements. Consult the documentation for the module in question for protocol-specific implementation. Note that there is no inheritance in the "NetPacket::" cluster of modules other than each protocol module being a "NetPacket". This was seen to be too restrictive as imposing inheritance relationships (for example between the IP, UDP and TCP protocols) would make things like tunneling or other unusual situations difficult. WRITING YOUR OWN ";NetPacket::" MODULE You are encouraged to write additional "NetPacket::" modules as well as improve existing ones. Contact the maintainer of the module in question with your suggestions or changes. The following sections are a list of suggestions and conventions for writing a "NetPacket::" module. Naming Conventions When creating a module in the "NetPacket::" namespace, it is suggested that you stick to a couple of conventions when naming packet contents. This will hopefully lead to a consistent namespace making the "NetPacket::" easier to use. Content names are all lowercase, with underscores separating multiple words. The following abbreviations are recommended: Word Abbreviation -------------------------------- source src destination dest checksum cksum identifier id version ver protocol proto Required Methods encode(), decode(), strip() Required Fields Every NetPacket:: object should have the following fields. _parent A link to the parent "NetPacket::" object in which this "NetPacket::" object is encaulated. This field is undefined if there is no parent object. _frame A copy of the raw data of the packet. data This field should contain the data encapsulated in the packet (i.e any headers or trailers stripped off) or undef if the packet contains no data. Note that in this sense, "data" is taken to mean information not relevant to the particular protocol being decoded. For example, an ARP packet contains many header fields but no data. A UDP datagram, however contains header fields and a payload. SEE ALSO
Joel Knight has a patch for NetPacket for IPv6 support available at http://www.packetmischief.ca/code/netpacket/. COPYRIGHT AND LICENSE
Copyright (c) 2001 Tim Potter and Stephanie Wehner. Copyright (c) 1995,1996,1997,1998,1999 ANU and CSIRO on behalf of the participants in the CRC for Advanced Computational Systems ('ACSys'). This module is free software. You can redistribute it and/or modify it under the terms of the Artistic License 2.0. This program is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose. AUTHORS
Tim Potter <tpot@samba.org> Stephanie Wehner <atrak@itsx.com> Yanick Champoux <yanick@cpan.org> perl v5.14.2 2011-11-20 NetPacket(3pm)
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NetPacket::UDP(3pm) User Contributed Perl Documentation NetPacket::UDP(3pm) NAME
NetPacket::UDP - Assemble and disassemble UDP (User Datagram Protocol) packets. VERSION
version 1.3.0 SYNOPSIS
use NetPacket::UDP; $udp_obj = NetPacket::UDP->decode($raw_pkt); $udp_pkt = NetPacket::UDP->encode($ip_obj); $udp_data = NetPacket::UDP::strip($raw_pkt); DESCRIPTION
"NetPacket::UDP" provides a set of routines for assembling and disassembling packets using UDP (User Datagram Protocol). Methods "NetPacket::UDP->decode([RAW PACKET])" Decode the raw packet data given and return an object containing instance data. This method will quite happily decode garbage input. It is the responsibility of the programmer to ensure valid packet data is passed to this method. "NetPacket::UDP->encode($ip_obj)" Return a UDP packet encoded with the instance data specified. Needs parts of the IP header contained in $ip_obj, the IP object, in order to calculate the UDP checksum. The length field will also be set automatically. Functions "NetPacket::UDP::strip([RAW PACKET])" Return the encapsulated data (or payload) contained in the UDP packet. This data is suitable to be used as input for other "NetPacket::*" modules. This function is equivalent to creating an object using the "decode()" constructor and returning the "data" field of that object. Instance data The instance data for the "NetPacket::UDP" object consists of the following fields. src_port The source UDP port for the datagram. dest_port The destination UDP port for the datagram. len The length (including length of header) in bytes for this packet. cksum The checksum value for this packet. data The encapsulated data (payload) for this packet. Exports default none exportable udp_strip tags The following tags group together related exportable items. ":strip" Import the strip function "udp_strip". ":ALL" All the above exportable items. EXAMPLE
The following example prints the source IP address and port, the destination IP address and port, and the UDP packet length: #!/usr/bin/perl -w use strict; use Net::PcapUtils; use NetPacket::Ethernet qw(:strip); use NetPacket::IP; use NetPacket::UDP; sub process_pkt { my($arg, $hdr, $pkt) = @_; my $ip_obj = NetPacket::IP->decode(eth_strip($pkt)); my $udp_obj = NetPacket::UDP->decode($ip_obj->{data}); print("$ip_obj->{src_ip}:$udp_obj->{src_port} -> ", "$ip_obj->{dest_ip}:$udp_obj->{dest_port} ", "$udp_obj->{len} "); } Net::PcapUtils::loop(&process_pkt, FILTER => 'udp'); The following is an example use in combination with Net::Divert to alter the payload of packets that pass through. All occurences of foo will be replaced with bar. This example is easy to test with netcat, but otherwise makes little sense. :) Adapt to your needs: use Net::Divert; use NetPacket::IP qw(IP_PROTO_UDP); use NetPacket::UDP; $divobj = Net::Divert->new('yourhost',9999); $divobj->getPackets(&alterPacket); sub alterPacket { my ($data, $fwtag) = @_; $ip_obj = NetPacket::IP->decode($data); if($ip_obj->{proto} == IP_PROTO_UDP) { # decode the UDP header $udp_obj = NetPacket::UDP->decode($ip_obj->{data}); # replace foo in the payload with bar $udp_obj->{data} =~ s/foo/bar/g; # re-encode the packet $ip_obj->{data} = $udp_obj->encode($ip_obj); $data = $ip_obj->encode; } $divobj->putPacket($data,$fwtag); } COPYRIGHT
Copyright (c) 2001 Tim Potter. Copyright (c) 1995,1996,1997,1998,1999 ANU and CSIRO on behalf of the participants in the CRC for Advanced Computational Systems ('ACSys'). This module is free software. You can redistribute it and/or modify it under the terms of the Artistic License 2.0. This program is distributed in the hope that it will be useful, but without any warranty; without even the implied warranty of merchantability or fitness for a particular purpose. AUTHOR
Tim Potter <tpot@samba.org> Stephanie Wehner <atrak@itsx.com> Yanick Champoux <yanick@cpan.org> perl v5.14.2 2011-11-20 NetPacket::UDP(3pm)