NAME¶
network streams - a tcpdump output analyzer
SYNOPSIS¶
nstreams [ -v ] [ -c
nstreams-services ] [ -n
nstreams-networks_file ] [ -N [ -i ] [ -I ]] [ -r ] [ -O output [ -D
iface ] [ -Y ]] [ -u ] [ -U ] [ -B ] [ -f
tcpdump_file ] [ -l <iface>
] [ tcpdump output ]
DESCRIPTION¶
nstreams is a utility designed to identify the IP streams that are
occuring on a network from a non-user friendly tcpdump output of several
megabytes.
This is especially useful when you plan to install a firewall but if you do not
know the nstreams that the network users are generating (http, real audio, and
more...).
nstreams can read the tcpdump output directly from stdin, or
from a file. It can even generate the configuration file of your firewall,
using the -O option.
OPTIONS¶
- -c <nstreams-services-file>
- The path to an alternate nstreams service file. This file
is used to identify each protocol. See the services file section
later in this manual page.
- -n <nstreams-networks-file>
- The path to an alternate nstreams network file. This file
is used to identify which hosts belong to which network. See the
networks file section later in this manual page.
- -f <tcpdump output file>
- The path to the file to read data from. This file must have
been generated using 'tcpdump -w filename'.
- -l <iface>
- Listen directly on interface <iface>. This avoids the
use of tcpdump.
- -N
- print the networks names instead of the hosts IP addresses.
The intra-network traffic will not be shown. Use this option twice to show
the networks IP address instead of their names.
- -i
- Also show the intra-network traffic (must be used with -N)
- -I
- Only show the intra-network traffic (must be used with -N)
- -r
- be redundant. That is, the same streams will be printed
each time they appear in the dump.
- -v
- print version number and exit.
- -O <type>
- output type. You can use this option to generate your
firewall startup script. Do nstreams -h to see the supported output types.
- -D <iface>
- interface to apply to output onto. Must be used with -O.
- -Y
- The firewall rules that will be generated will deny all
packets coming from the outside trying to establish connections to the
inside. If you system is not serving anything, then it's safe to turn on
this option.
- -u
- Do not print the unknown streams
- -U
- Only print the unknown streams
- -B
- Show broadcasts and networks
USAGE¶
Let tcpdump(1) run some time on your network (like one week), and save its
output in a file, by doing :
tcpdump -l -n > output
or
tcpdump -w filename
Then, feed
nstreams with this output file, and it will turn it into a
easily-readable file which will help you to write efficient firewall filters.
You may also do :
tcpdump -l -n | nstreams
or
nstreams -f filename (if you used tcpdump -w)
THE SERVICES FILE¶
The service file contains the description of each protocol, as well as their
name. Its syntax is :
protocol_name:server_port(s)/{udp,tcp}:client_ports(s)
or :
protocol_name:type(s)/icmp:code(s)
Whereas :
- protocol_name
- is the name of the protocol described. This name may
contain any character, including space, except ':'.
- server_port(s)
- is the range of ports used by the server. Usually, you will
want to define one server port only, but you may enter any range you want.
- ip_protocol
- is the IP protocol that this protocol is lying onto.
Acceptable values are tcp and udp
- client_port(s)
-
is the range of ports that the client may use. You can set this to
any or, for more accurate results, to ports ranges, like
'1-1024,2048-4096'.
The rules are : 'first match, first taken'.
SERVICE FILE EXAMPLE¶
Using this syntax, you would declare the ssh protocol by :
ssh-unix:22/tcp:1000-1023
Because the Unix version of the ssh client uses a privileged port to connect
onto the ssh server which listens on port 22.
THE NETWORKS FILE¶
The networks file is used to define sets and subsets of hosts (also known as
networks). This avoids redundancy in the output file. The syntax format for
this file is :
network name:ip/mask
Whereas the network name is whatever you want, the IP is the ip of the network,
and the mask is the CIDR netmask of the network. The rule is 'first match,
first taken'.
NETWORKS FILE EXAMPLE¶
admin:192.168.19.0/29
whole_subnet:192.168.0.0/16
internet:0.0.0.0/0
LIMITS¶
• nstreams can only parse the output of 'tcpdump -n'
• Even though the output of nstreams is easier to read than the one of
tcpdump, it is still not easily readable. Use
sort(1) on the nstream output to
get a more readable file.
• This program could have been written in perl
FILES¶
/etc/nstreams-services
/etc/nstreams-networks
SEE ALSO¶
tcpdump(1)
AUTHORS¶
Concept : Herve Schauer Consultants -
http://www.hsc.fr
Coding : Renaud Deraison <deraison@cvs.nessus.org>
BUG REPORTS¶
Please send all your bug reports with the detail of your configuration to Renaud
Deraison <deraison@cvs.nessus.org>