arp-fingerprint (1)

Leading comments

Copyright (C) Roy Hills, NTA Monitor Ltd.

Copying and distribution of this file, with or without modification,
are permitted in any medium without royalty provided the copyright
notice and this notice are preserved.

$Id: arp-fingerprint.1 12365 2007-12-27 13:23:40Z rsh $

(The comments found at the beginning of the groff file "man1/arp-fingerprint.1".)

NAME

arp-fingerprint - Fingerprint a system using ARP

SYNOPSIS

arp-fingerprint [options] target

The target should be specified as a single IP address or hostname. You cannot specify multiple targets, IP networks or ranges.

If you use an IP address for the target, you can use the -o option to pass the --numeric option to arp-scan, which will prevent it from attempting DNS lookups. This can speed up the fingerprinting process, especially on systems with a slow or faulty DNS configuration.

DESCRIPTION

arp-fingerprint fingerprints the specified target host using the ARP protocol.

It sends various different types of ARP request to the target, and records which types it responds to. From this, it constructs a fingerprint string consisting of "1" where the target responded and "0" where it did not. An example of a fingerprint string is 01000100000. This fingerprint string is then used to lookup the likely target operating system.

Many of the fingerprint strings are shared by several operating systems, so there is not always a one-to-one mapping between fingerprint strings and operating systems. Also the fact that a system's fingerprint matches a certain operating system (or list of operating systems) does not necessarily mean that the system being fingerprinted is that operating system, although it is quite likely. This is because the list of operating systems is not exhaustive; it is just what I have discovered to date, and there are bound to be operating systems that are not listed.

The ARP fingerprint of a system is generally a function of that system's kernel (although it is possible for the ARP function to be implemented in user space, it almost never is).

Sometimes, an operating system can give different fingerprints depending on the configuration. An example is Linux, which will respond to a non-local source IP address if that IP is routed through the interface being tested. This is both good and bad: on one hand it makes the fingerprinting task more complex; but on the other, it can allow some aspects of the system configuration to be determined.

Sometimes the fact that two different operating systems share a common ARP fingerprint string points to a re-use of networking code. One example of this is Windows NT and FreeBSD.

arp-fingerprint uses arp-scan to send the ARP requests and receive the replies.

There are other methods that can be used to fingerprint a system using arp-scan which can be used in addition to arp-fingerprint. These additional methods are not included in arp-fingerprint either because they are likely to cause disruption to the target system, or because they require knowledge of the target's configuration that may not always be available.

arp-fingerprint is still being developed, and the results should not be relied on. As most of the ARP requests that it sends are non-standard, it is possible that it may disrupt some systems, so caution is advised.

If you find a system that arp-fingerprint reports as UNKNOWN, and you know what operating system it is running, could you please send details of the operating system and fingerprint to arp-scan@nta-monitor.com so I can include it in future versions. Please include the exact version of the operating system if you know it, as fingerprints sometimes change between versions.

OPTIONS

-h

Display a brief usage message and exit.

-v

Display verbose progress messages.

-o <option-string>

Pass specified options to arp-scan. You need to enclose the options string in quotes if it contains spaces. e.g. -o "-I eth1". The commonly used options are --interface (-I) and --numeric (-N).

EXAMPLES

$ arp-fingerprint 192.168.0.1
192.168.0.1   01000100000     Linux 2.2, 2.4, 2.6

$ arp-fingerprint -o "-N -I eth1" 192.168.0.202
192.168.0.202 11110100000     FreeBSD 5.3, Win98, WinME, NT4, 2000, XP, 2003

NOTES

arp-fingerprint is implemented in Perl, so you need to have the Perl interpreter installed on your system to use it.

AUTHOR

Roy Hills <Roy.Hills@nta-monitor.com>

SEE ALSO

arp-scan(1)

www.nta-monitor.com/wiki The arp-scan wiki page.