The London Perl and Raku Workshop takes place on 26th Oct 2024. If your company depends on Perl, please consider sponsoring and/or attending.


Net::SnoopLog - Read snoop network packet logs, from RFC1761 snoop ver 2. Perl implementation (not an interface).


use Net::SnoopLog;

$log = Net::SnoopLog->new(); $log->read("/tmp/out01");

@Indexes = $log->indexes;

foreach $index (@Indexes) { ($length_orig,$length_incl,$drops,$secs,$msecs) = $log->header($index); $data = $log->data($index);

     # your code here


This module can read the data and headers from snoop ver 2 logs (those that obey RFC1761 - try "man snoop").


new ()

Constructor, return a SnoopLog object.


Read the snoop file indicated into memory.

indexes ()

Return an array of index numbers for the packets loaded from the snoop file. The indexes start at 0.

maxindex ()

Return the number of the last index. More memory efficient than indexes(). Add 1 to get the packet count. The indexes start at 0.

header (INDEX)

Takes an integer index number and returns the packet header. This is: Length of original packet, Length actually included in the snoop log, Cumulative drops (since the snoop log began), Packet arrival time as seconds since Jan 1st 1970, Microseconds

data (INDEX)

Takes an integer index number and returns the raw packet data. (This is usually Ethernet/IP/TCP data).

version ()

Returns a string containing the numeric snoop log version, which is expected to be "2".

Returns a strings containing the numeric datalink type, see RFC 1761 for a table of these. (4 is Ethernet).


   perl Makefile.PL
   make test
   make install




Once you can read the raw packet data, the next step is read through the protocol stack. An Ethernet/802.3 example is,

($ether_dest,$ether_src,$ether_type,$ether_data) = unpack('H12H12H4a*',$data);

Keep an eye on CPAN for Ethernet, IP and TCP modules.


This reads snoop version 2 logs (the most common). There could be a new version in the distant future with a move to 64-bit timestamps - at which point this module will need updating.


Future versions should include the ability to write as well as read snoop logs. Also a memory efficient technique to process very large snoop logs (where the log size is greater than available virtual memory).


RFC 1761


Copyright (c) 2003 Brendan Gregg. All rights reserved. This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself


Brendan Gregg <> [Sydney, Australia]