How to Break Up Large tcpdump Files

Wireshark is probably the best, but if you want/need to look at the payload without loading up a GUI you can use the -X or -A options

tcpdump -qns 0 -X -r serverfault_request.pcap

14:28:33.800865 IP 10.2.4.243.41997 > 69.59.196.212.80: tcp 1097
        0x0000:  4500 047d b9c4 4000 4006 63b2 0a02 04f3  E..}..@.@.c.....
        0x0010:  453b c4d4 a40d 0050 f0d4 4747 f847 3ad5  E;.....P..GG.G:.
        0x0020:  8018 f8e0 1d74 0000 0101 080a 0425 4e6d  .....t.......%Nm
        0x0030:  0382 68a1 4745 5420 2f71 7565 7374 696f  ..h.GET./questio
        0x0040:  6e73 2048 5454 502f 312e 310d 0a48 6f73  ns.HTTP/1.1..Hos
        0x0050:  743a 2073 6572 7665 7266 6175 6c74 2e63  t:.serverfault.c
        0x0060:  6f6d 0d0a 5573 6572 2d41 6765 6e74 3a20  om..User-Agent:.
        0x0070:  4d6f 7a69 6c6c 612f 352e 3020 2858 3131  Mozilla/5.0.(X11
        0x0080:  3b20 553b 204c 696e 7578 2069 3638 363b  ;.U;.Linux.i686;

tcpdump -qns 0 -A -r serverfault_request.pcap

14:29:33.256929 IP 10.2.4.243.41997 > 69.59.196.212.80: tcp 1097
E..}..@.@.c.
...E;...^M.P..^w.G.......t.....
.%.}..l.GET /questions HTTP/1.1
Host: serverfault.com

There are many other tools for reading and getting stats, extracting payloads and so on. A quick look on the number of things that depend on libpcap in the debian package repository gives a list of 50+ tools that can be used to slice, dice, view, and manipulate captures in various ways.

For example.

• tcpick
• tcpxtract

I hope somebody is still interested in the solution to the problem. ;) We had the same issue in our company and I started writing a script for this.

I wrote a blog post about it with the source code and a screenshot.

I've also shared it below...

And the code: (Be sure to check my site for future updates)

#!/bin/bash
#===================================================================================
#
# FILE: dump.sh
# USAGE: dump.sh [-i interface] [tcpdump-parameters]
# DESCRIPTION: tcpdump on any interface and add the prefix [Interace:xy] in front of the dump data.
# OPTIONS: same as tcpdump
# REQUIREMENTS: tcpdump, sed, ifconfig, kill, awk, grep, posix regex matching
# BUGS:  ---
# FIXED: - In 1.0 The parameter -w would not work without -i parameter as multiple tcpdumps are started.
#        - In 1.1 VLAN's would not be shown if a single interface was dumped.
# NOTES: ---
#        - 1.2 git initial
# AUTHOR: Sebastian Haas
# COMPANY: pharma mall
# VERSION: 1.2
# CREATED: 16.09.2014
# REVISION: 22.09.2014
#
#===================================================================================

# When this exits, exit all background processes:
trap 'kill $(jobs -p) &> /dev/null && sleep 0.2 &&  echo ' EXIT
# Create one tcpdump output per interface and add an identifier to the beginning of each line:
if [[ $@ =~ -i[[:space:]]?[^[:space:]]+ ]]; then
    tcpdump -l $@ | sed 's/^/[Interface:'"${BASH_REMATCH[0]:2}"'] /' &
else
    for interface in $(ifconfig | grep '^[a-z0-9]' | awk '{print $1}')
    do
       tcpdump -l -i $interface -nn $@ | sed 's/^/[Interface:'"$interface"']    /' &
    done
fi
# wait .. until CTRL+C
wait