nstreams(1) Users Manuals nstreams(1)NAME
network streams - a tcpdump output analyzer
SYNOPSISnstreams [ -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 ]
DESCRIPTIONnstreams is a utility designed to identify the IP streams that are
occuring on a network from a non-user friendly tcpdump output of sev‐
eral 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 configu‐
ration 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 syn‐
tax 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 ALSOtcpdump(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>
nstreams July 1999 nstreams(1)
