Provided by: arp-scan_1.8.1-2ubuntu1_amd64 
NAME
arp-scan - The ARP scanner
SYNOPSIS
arp-scan [options] [hosts...]
Target hosts must be specified on the command line unless the --file option is given, in which case the
targets are read from the specified file instead, or the --localnet option is used, in which case the
targets are generated from the network interface IP address and netmask.
You will need to be root, or arp-scan must be SUID root, in order to run arp-scan, because the functions
that it uses to read and write packets require root privilege.
The target hosts can be specified as IP addresses or hostnames. You can also specify the target as
IPnetwork/bits (e.g. 192.168.1.0/24) to specify all hosts in the given network (network and broadcast
addresses included), IPstart-IPend (e.g. 192.168.1.3-192.168.1.27) to specify all hosts in the inclusive
range, or IPnetwork:NetMask (e.g. 192.168.1.0:255.255.255.0) to specify all hosts in the given network
and mask.
DESCRIPTION
arp-scan sends ARP packets to hosts on the local network and displays any responses that are received.
The network interface to use can be specified with the --interface option. If this option is not present,
arp-scan will search the system interface list for the lowest numbered, configured up interface
(excluding loopback). By default, the ARP packets are sent to the Ethernet broadcast address,
ff:ff:ff:ff:ff:ff, but that can be changed with the --destaddr option.
The target hosts to scan may be specified in one of three ways: by specifying the targets on the command
line; by specifying a file containing the targets with the --file option; or by specifying the --localnet
option which causes all possible hosts on the network attached to the interface (as defined by the
interface address and mask) to be scanned. For hosts specified on the command line, or with the --file
option, you can use either IP addresses or hostnames. You can also use network specifications
IPnetwork/bits, IPstart-IPend, or IPnetwork:NetMask.
The list of target hosts is stored in memory. Each host in this list uses 28 bytes of memory, so
scanning a Class-B network (65,536 hosts) requires about 1.75MB of memory for the list, and scanning a
Class-A (16,777,216 hosts) requires about 448MB.
arp-scan supports Ethernet and 802.11 wireless networks. It could also support token ring and FDDI, but
they have not been tested. It does not support serial links such as PPP or SLIP, because ARP is not
supported on them.
The ARP protocol is a layer-2 (datalink layer) protocol that is used to determine a host's layer-2
address given its layer-3 (network layer) address. ARP was designed to work with any layer-2 and layer-3
address format, but the most common use is to map IP addresses to Ethernet hardware addresses, and this
is what arp-scan supports. ARP only operates on the local network, and cannot be routed. Although the ARP
protocol makes use of IP addresses, it is not an IP-based protocol and arp-scan can be used on an
interface that is not configured for IP.
ARP is only used by IPv4 hosts. IPv6 uses NDP (neighbour discovery protocol) instead, which is a
different protocol and is not supported by arp-scan.
One ARP packet is sent for each for each target host, with the target protocol address (the ar$tpa field)
set to the IP address of this host. If a host does not respond, then the ARP packet will be re-sent once
more. The maximum number of retries can be changed with the --retry option. Reducing the number of
retries will reduce the scanning time at the possible risk of missing some results due to packet loss.
You can specify the bandwidth that arp-scan will use for the outgoing ARP packets with the --bandwidth
option. By default, it uses a bandwidth of 256000 bits per second. Increasing the bandwidth will reduce
the scanning time, but setting the bandwidth too high may result in an ARP storm which can disrupt
network operation. Also, setting the bandwidth too high can send packets faster than the network
interface can transmit them, which will eventually fill the kernel's transmit buffer resulting in the
error message: No buffer space available. Another way to specify the outgoing ARP packet rate is with
the --interval option, which is an alternative way to modify the same underlying parameter.
The time taken to perform a single-pass scan (i.e. with --retry=1) is given by:
time = n*i + t + o
Where n is the number of hosts in the list, i is the time interval between packets (specified with
--interval, or calculated from --bandwidth), t is the timeout value (specified with --timeout) and o is
the overhead time taken to load the targets into the list and read the MAC/Vendor mapping files. For
small lists of hosts, the timeout value will dominate, but for large lists the packet interval is the
most important value.
With 65,536 hosts, the default bandwidth of 256,000 bits/second (which results in a packet interval of
2ms), the default timeout of 100ms, and a single pass ( --retry=1), and assuming an overhead of 1 second,
the scan would take 65536*0.002 + 0.1 + 1 = 132.172 seconds, or about 2 minutes 12 seconds.
Any part of the outgoing ARP packet may be modified through the use of the various --arpXXX options. The
use of some of these options may make the outgoing ARP packet non RFC compliant. Different operating
systems handle the various non standard ARP packets in different ways, and this may be used to
fingerprint these systems. See arp-fingerprint(1) for information about a script which uses these
options to fingerprint the target operating system.
The table below summarises the options that change the outgoing ARP packet. In this table, the Field
column gives the ARP packet field name from RFC 826, Bits specifies the number of bits in the field,
Option shows the arp-scan option to modify this field, and Notes gives the default value and any other
notes.
┌───────────────────────────────────────────────────────────────┐
│ Outgoing ARP Packet Options │
├───────┬──────┬──────────┬─────────────────────────────────────┤
│Field │ Bits │ Option │ Notes │
├───────┼──────┼──────────┼─────────────────────────────────────┤
│ar$hrd │ 16 │ --arphrd │ Default is 1 (ARPHRD_ETHER) │
│ar$pro │ 16 │ --arppro │ Default is 0x0800 │
│ar$hln │ 8 │ --arphln │ Default is 6 (ETH_ALEN) │
│ar$pln │ 8 │ --arppln │ Default is 4 (IPv4) │
│ar$op │ 16 │ --arpop │ Default is 1 (ARPOP_REQUEST) │
│ar$sha │ 48 │ --arpsha │ Default is interface h/w address │
│ar$spa │ 32 │ --arpspa │ Default is interface IP address │
│ar$tha │ 48 │ --arptha │ Default is zero (00:00:00:00:00:00) │
│ar$tpa │ 32 │ None │ Set to the target host IP address │
└───────┴──────┴──────────┴─────────────────────────────────────┘
The most commonly used outgoing ARP packet option is --arpspa, which sets the source IP address in the
ARP packet. This option allows the outgoing ARP packet to use a different source IP address from the
outgoing interface address. With this option it is possible to use arp-scan on an interface with no IP
address configured, which can be useful if you want to ensure that the testing host does not interact
with the network being tested.
Warning: Setting ar$spa to the destination IP address can disrupt some operating systems, as they assume
there is an IP address clash if they receive an ARP request for their own address.
It is also possible to change the values in the Ethernet frame header that precedes the ARP packet in the
outgoing packets. The table below summarises the options that change values in the Ethernet frame header.
┌───────────────────────────────────────────────────────────────────┐
│ Outgoing Ethernet Frame Options │
├───────────────┬──────┬─────────────┬──────────────────────────────┤
│Field │ Bits │ Option │ Notes │
├───────────────┼──────┼─────────────┼──────────────────────────────┤
│Dest Address │ 48 │ --destaddr │ Default is ff:ff:ff:ff:ff:ff │
│Source Address │ 48 │ --srcaddr │ Default is interface address │
│Protocol Type │ 16 │ --prototype │ Default is 0x0806 │
└───────────────┴──────┴─────────────┴──────────────────────────────┘
The most commonly used outgoing Ethernet frame option is --destaddr, which sets the destination Ethernet
address for the ARP packet. --prototype is not often used, because it will cause the packet to be
interpreted as a different Ethernet protocol.
Any ARP responses that are received are displayed in the following format:
<IP Address> <Hardware Address> <Vendor Details>
Where IP Address is the IP address of the responding target, Hardware Address is its Ethernet hardware
address (also known as the MAC address) and Vendor Details are the vendor details, decoded from the
hardware address. The output fields are separated by a single tab character.
The responses are displayed in the order they are received, which is not always the same order as the
requests were sent because some hosts may respond faster than others.
The vendor decoding uses the files ieee-oui.txt, ieee-iab.txt and mac-vendor.txt, which are supplied with
arp-scan. The ieee-oui.txt and ieee-iab.txt files are generated from the OUI and IAB data on the IEEE
website at http://standards.ieee.org/regauth/oui/ieee-oui.txt and
http://standards.ieee.org/regauth/oui/iab.txt. The Perl scripts get-oui and get-iab, which are included
in the arp-scan package, can be used to update these files with the latest data from the IEEE website.
The mac-vendor.txt file contains other MAC to Vendor mappings that are not covered by the IEEE OUI and
IAB files, and can be used to add custom mappings.
Almost all hosts that support IP will respond to arp-scan if they receive an ARP packet with the target
protocol address (ar$tpa) set to their IP address. This includes firewalls and other hosts with IP
filtering that drop all IP traffic from the testing system. For this reason, arp-scan is a useful tool to
quickly determine all the active IP hosts on a given Ethernet network segment.
OPTIONS
Where an option takes a value, that value is specified as a letter in angle brackets. The letter
indicates the type of data that is expected:
<s> A character string, e.g. --file=hostlist.txt.
<i> An integer, which can be specified as a decimal number or as a hexadecimal number if preceded with
0x, e.g. --arppro=2048 or --arpro=0x0800.
<f> A floating point decimal number, e.g. --backoff=1.5.
<m> An Ethernet MAC address, which can be specified either in the format 01:23:45:67:89:ab, or as
01-23-45-67-89-ab. The alphabetic hex characters may be either upper or lower case. E.g.
--arpsha=01:23:45:67:89:ab.
<a> An IPv4 address, e.g. --arpspa=10.0.0.1
<h> Binary data specified as a hexadecimal string, which should not include a leading 0x. The
alphabetic hex characters may be either upper or lower case. E.g. --padding=aaaaaaaaaaaa
<x> Something else. See the description of the option for details.
--help or -h
Display this usage message and exit.
--file=<s> or -f <s>
Read hostnames or addresses from the specified file instead of from the command line. One name or
IP address per line. Use "-" for standard input.
--localnet or -l
Generate addresses from network interface configuration. Use the network interface IP address and
network mask to generate the list of target host addresses. The list will include the network and
broadcast addresses, so an interface address of 10.0.0.1 with netmask 255.255.255.0 would generate
256 target hosts from 10.0.0.0 to 10.0.0.255 inclusive. If you use this option, you cannot
specify the --file option or specify any target hosts on the command line. The interface
specifications are taken from the interface that arp-scan will use, which can be changed with the
--interface option.
--retry=<i> or -r <i>
Set total number of attempts per host to <i>, default=2.
--timeout=<i> or -t <i>
Set initial per host timeout to <i> ms, default=100. This timeout is for the first packet sent to
each host. subsequent timeouts are multiplied by the backoff factor which is set with --backoff.
--interval=<x> or -i <x>
Set minimum packet interval to <x>. This controls the outgoing bandwidth usage by limiting the
rate at which packets can be sent. The packet interval will be no smaller than this number. If
you want to use up to a given bandwidth, then it is easier to use the --bandwidth option instead.
The interval specified is in milliseconds by default, or in microseconds if "u" is appended to the
value.
--bandwidth=<x> or -B <x>
Set desired outbound bandwidth to <x>, default=256000. The value is in bits per second by
default. If you append "K" to the value, then the units are kilobits per sec; and if you append
"M" to the value, the units are megabits per second. The "K" and "M" suffixes represent the
decimal, not binary, multiples. So 64K is 64000, not 65536. You cannot specify both --interval
and --bandwidth because they are just different ways to change the same underlying parameter.
--backoff=<f> or -b <f>
Set timeout backoff factor to <f>, default=1.50. The per-host timeout is multiplied by this
factor after each timeout. So, if the number of retries is 3, the initial per-host timeout is
500ms and the backoff factor is 1.5, then the first timeout will be 500ms, the second 750ms and
the third 1125ms.
--verbose or -v
Display verbose progress messages. Use more than once for greater effect:
1 - Display the network address and mask used when the --localnet option is specified, display any
nonzero packet padding, display packets received from unknown hosts, and show when each pass
through the list completes.
2 - Show each packet sent and received, when entries are removed from the list, the pcap filter
string, and counts of MAC/Vendor mapping entries.
3 - Display the host list before scanning starts.
--version or -V
Display program version and exit.
--random or -R
Randomise the host list. This option randomises the order of the hosts in the host list, so the
ARP packets are sent to the hosts in a random order. It uses the Knuth shuffle algorithm.
--numeric or -N
IP addresses only, no hostnames. With this option, all hosts must be specified as IP addresses.
Hostnames are not permitted. No DNS lookups will be performed.
--snap=<i> or -n <i>
Set the pcap snap length to <i>. Default=64. This specifies the frame capture length. This length
includes the data-link header. The default is normally sufficient.
--interface=<s> or -I <s>
Use network interface <s>. If this option is not specified, arp-scan will search the system
interface list for the lowest numbered, configured up interface (excluding loopback). The
interface specified must support ARP.
--quiet or -q
Only display minimal output. If this option is specified, then only the minimum information is
displayed. With this option, the OUI files are not used.
--ignoredups or -g
Don't display duplicate packets. By default, duplicate packets are displayed and are flagged with
"(DUP: n)".
--ouifile=<s> or -O <s>
Use OUI file <s>, default=/usr/local/share/arp-scan/ieee-oui.txt This file provides the IEEE
Ethernet OUI to vendor string mapping.
--iabfile=<s> or -F <s>
Use IAB file <s>, default=/usr/local/share/arp-scan/ieee-iab.txt This file provides the IEEE
Ethernet IAB to vendor string mapping.
--macfile=<s> or -m <s>
Use MAC/Vendor file <s>, default=/usr/local/share/arp-scan/mac-vendor.txt This file provides the
custom Ethernet MAC to vendor string mapping.
--srcaddr=<m> or -S <m>
Set the source Ethernet MAC address to <m>. This sets the 48-bit hardware address in the Ethernet
frame header for outgoing ARP packets. It does not change the hardware address in the ARP packet,
see --arpsha for details on how to change that address. The default is the Ethernet address of
the outgoing interface.
--destaddr=<m> or -T <m>
Send the packets to Ethernet MAC address <m> This sets the 48-bit destination address in the
Ethernet frame header. The default is the broadcast address ff:ff:ff:ff:ff:ff. Most operating
systems will also respond if the ARP request is sent to their MAC address, or to a multicast
address that they are listening on.
--arpsha=<m> or -u <m>
Use <m> as the ARP source Ethernet address This sets the 48-bit ar$sha field in the ARP packet It
does not change the hardware address in the frame header, see --srcaddr for details on how to
change that address. The default is the Ethernet address of the outgoing interface.
--arptha=<m> or -w <m>
Use <m> as the ARP target Ethernet address This sets the 48-bit ar$tha field in the ARP packet The
default is zero, because this field is not used for ARP request packets.
--prototype=<i> or -y <i>
Set the Ethernet protocol type to <i>, default=0x0806. This sets the 16-bit protocol type field
in the Ethernet frame header. Setting this to a non-default value will result in the packet being
ignored by the target, or sent to the wrong protocol stack.
--arphrd=<i> or -H <i>
Use <i> for the ARP hardware type, default=1. This sets the 16-bit ar$hrd field in the ARP
packet. The normal value is 1 (ARPHRD_ETHER). Most, but not all, operating systems will also
respond to 6 (ARPHRD_IEEE802). A few systems respond to any value.
--arppro=<i> or -p <i>
Use <i> for the ARP protocol type, default=0x0800. This sets the 16-bit ar$pro field in the ARP
packet. Most operating systems only respond to 0x0800 (IPv4) but some will respond to other
values as well.
--arphln=<i> or -a <i>
Set the hardware address length to <i>, default=6. This sets the 8-bit ar$hln field in the ARP
packet. It sets the claimed length of the hardware address in the ARP packet. Setting it to any
value other than the default will make the packet non RFC compliant. Some operating systems may
still respond to it though. Note that the actual lengths of the ar$sha and ar$tha fields in the
ARP packet are not changed by this option; it only changes the ar$hln field.
--arppln=<i> or -P <i>
Set the protocol address length to <i>, default=4. This sets the 8-bit ar$pln field in the ARP
packet. It sets the claimed length of the protocol address in the ARP packet. Setting it to any
value other than the default will make the packet non RFC compliant. Some operating systems may
still respond to it though. Note that the actual lengths of the ar$spa and ar$tpa fields in the
ARP packet are not changed by this option; it only changes the ar$pln field.
--arpop=<i> or -o <i>
Use <i> for the ARP operation, default=1. This sets the 16-bit ar$op field in the ARP packet.
Most operating systems will only respond to the value 1 (ARPOP_REQUEST). However, some systems
will respond to other values as well.
--arpspa=<a> or -s <a>
Use <a> as the source IP address. The address should be specified in dotted quad format; or the
literal string "dest", which sets the source address to be the same as the target host address.
This sets the 32-bit ar$spa field in the ARP packet. Some operating systems check this, and will
only respond if the source address is within the network of the receiving interface. Others don't
care, and will respond to any source address. By default, the outgoing interface address is used.
WARNING: Setting ar$spa to the destination IP address can disrupt some operating systems, as they
assume there is an IP address clash if they receive an ARP request for their own address.
--padding=<h> or -A <h>
Specify padding after packet data. Set the padding data to hex value <h>. This data is appended
to the end of the ARP packet, after the data. Most, if not all, operating systems will ignore any
padding. The default is no padding, although the Ethernet driver on the sending system may pad the
packet to the minimum Ethernet frame length.
--llc or -L
Use RFC 1042 LLC framing with SNAP. This option causes the outgoing ARP packets to use IEEE 802.2
framing with a SNAP header as described in RFC 1042. The default is to use Ethernet-II framing.
arp-scan will decode and display received ARP packets in either Ethernet-II or IEEE 802.2 formats
irrespective of this option.
--vlan=<i> or -Q <i>
Use 802.1Q tagging with VLAN id <i>. This option causes the outgoing ARP packets to use 802.1Q
VLAN tagging with a VLAN ID of <i>, which should be in the range 0 to 4095 inclusive. arp-scan
will always decode and display received ARP packets in 802.1Q format irrespective of this option.
--pcapsavefile=<s> or -W <s>
Write received packets to pcap savefile <s>. This option causes received ARP responses to be
written to the specified pcap savefile as well as being decoded and displayed. This savefile can
be analysed with programs that understand the pcap file format, such as "tcpdump" and "wireshark".
FILES
/usr/local/share/arp-scan/ieee-oui.txt
List of IEEE OUI (Organisationally Unique Identifier) to vendor mappings.
/usr/local/share/arp-scan/ieee-iab.txt
List of IEEE IAB (Individual Address Block) to vendor mappings.
/usr/local/share/arp-scan/mac-vendor.txt
List of other Ethernet MAC to vendor mappings.
EXAMPLES
The example below shows arp-scan being used to scan the network 192.168.0.0/24 using the network
interface eth0.
$ arp-scan --interface=eth0 192.168.0.0/24
Interface: eth0, datalink type: EN10MB (Ethernet)
Starting arp-scan 1.4 with 256 hosts (http://www.nta-monitor.com/tools/arp-scan/)
192.168.0.1 00:c0:9f:09:b8:db QUANTA COMPUTER, INC.
192.168.0.3 00:02:b3:bb:66:98 Intel Corporation
192.168.0.5 00:02:a5:90:c3:e6 Compaq Computer Corporation
192.168.0.6 00:c0:9f:0b:91:d1 QUANTA COMPUTER, INC.
192.168.0.12 00:02:b3:46:0d:4c Intel Corporation
192.168.0.13 00:02:a5:de:c2:17 Compaq Computer Corporation
192.168.0.87 00:0b:db:b2:fa:60 Dell ESG PCBA Test
192.168.0.90 00:02:b3:06:d7:9b Intel Corporation
192.168.0.105 00:13:72:09:ad:76 Dell Inc.
192.168.0.153 00:10:db:26:4d:52 Juniper Networks, Inc.
192.168.0.191 00:01:e6:57:8b:68 Hewlett-Packard Company
192.168.0.251 00:04:27:6a:5d:a1 Cisco Systems, Inc.
192.168.0.196 00:30:c1:5e:58:7d HEWLETT-PACKARD
13 packets received by filter, 0 packets dropped by kernel
Ending arp-scan: 256 hosts scanned in 3.386 seconds (75.61 hosts/sec). 13 responded
This next example shows arp-scan being used to scan the local network after configuring the network
interface with DHCP using pump.
# pump
# ifconfig eth0
eth0 Link encap:Ethernet HWaddr 00:D0:B7:0B:DD:C7
inet addr:10.0.84.178 Bcast:10.0.84.183 Mask:255.255.255.248
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:46335 errors:0 dropped:0 overruns:0 frame:0
TX packets:1542776 errors:0 dropped:0 overruns:0 carrier:0
collisions:1644 txqueuelen:1000
RX bytes:6184146 (5.8 MiB) TX bytes:348887835 (332.7 MiB)
# arp-scan --localnet
Interface: eth0, datalink type: EN10MB (Ethernet)
Starting arp-scan 1.4 with 8 hosts (http://www.nta-monitor.com/tools/arp-scan/)
10.0.84.179 00:02:b3:63:c7:57 Intel Corporation
10.0.84.177 00:d0:41:08:be:e8 AMIGO TECHNOLOGY CO., LTD.
10.0.84.180 00:02:b3:bd:82:9b Intel Corporation
10.0.84.181 00:02:b3:1f:73:da Intel Corporation
4 packets received by filter, 0 packets dropped by kernel
Ending arp-scan 1.4: 8 hosts scanned in 0.820 seconds (9.76 hosts/sec). 4 responded
AUTHOR
Roy Hills <Roy.Hills@nta-monitor.com>
SEE ALSO
get-oui(1) get-iab(1) arp-fingerprint(1) RFC 826 - An Ethernet Address Resolution Protocol http://www.nta-monitor.com/wiki/ The arp-scan wiki page. http://www.nta-monitor.com/tools/arp-scan/ The arp-scan homepage. January 31, 2011 ARP-SCAN(1)