||FreeBSD General Commands Manual
arp-scan - The ARP scanner
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
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.
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,
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
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
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 500ms,
and a single pass ( --retry=1), and assuming an overhead of 1 second,
the scan would take 65536*0.002 + 0.5 + 1 = 132.57 seconds, or about 2
minutes 13 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
||Default is 1 (ARPHRD_ETHER)
||Default is 0x0800
||Default is 6 (ETH_ALEN)
||Default is 4 (IPv4)
||Default is 1 (ARPOP_REQUEST)
||Default is interface h/w address
||Default is interface IP address
||Default is zero (00:00:00:00:00:00)
||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
||Default is ff:ff:ff:ff:ff:ff
||Default is interface address
||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
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/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.
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:
- A character string, e.g. --file=hostlist.txt.
- An integer, which can be specified as a decimal number or as a hexadecimal
number if preceeded with 0x, e.g. --arppro=2048 or --arpro=0x0800.
- A floating point decimal number, e.g. --backoff=1.5.
- 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.
- An IPv4 address, e.g. --arpspa=10.0.0.1
- 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
- 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
- --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
- --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=500. 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
- --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
- 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
- 2 - Show each packet sent and received, when entries are removed from the
list, the pcap filter string, and counts of MAC/Vendor mapping
- 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.
- Use <i> to seed the pseudo random number generator. This option
seeds the PRNG with the specified number, which can be useful if you want
to ensure that the random host list is reproducable. By default, the PRNG
is seeded with an unpredictable value. This option is only effective in
conjunction with the --random (-R) option.
- --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
- --quiet or -q
- Only display minimal output. No protocol decoding. If this option is
specified, then only the IP address and MAC address are displayed for each
responding host. No protocol decoding is performed and the OUI mapping
files are not used.
- --plain or -x
- Display plain output showing only responding hosts. This option supresses
the printing of the header and footer text, and only displays one line for
each responding host. Useful if the output will be parsed by a
- --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 IEEE Ethernet OUI to vendor mapping file <s>. If this option is
not specified, the default filename is ieee-oui.txt in the current
directory. If that is not found, then the file
/usr/local/share/arp-scan/ieee-oui.txt is used.
- --iabfile=<s> or -O <s>
- Use IEEE Ethernet IAB to vendor mapping file <s>. If this option is
not specified, the default filename is ieee-iab.txt in the current
directory. If that is not found, then the file
/usr/local/share/arp-scan/ieee-iab.txt is used.
- --macfile=<s> or -O <s>
- Use custom Ethernet MAC to vendor mapping file <s>. If this option
is not specified, the default filename is mac-vendor.txt in the current
directory. If that is not found, then the file
/usr/local/share/arp-scan/mac-vendor.txt is used.
- --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
- --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"
- --rtt or -D
- Display the packet round-trip time.
The example below shows arp-scan being used to scan the network
192.168.0.0/24 using the network interface eth0.
- List of IEEE OUI (Organisationally Unique Identifier) to vendor
- List of IEEE IAB (Individual Address Block) to vendor mappings.
- List of other Ethernet MAC to vendor mappings.
$ 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-resources/security-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
# 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
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-resources/security-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
Roy Hills <Roy.Hills@nta-monitor.com>
RFC 826 - An Ethernet Address Resolution Protocol
http://www.nta-monitor.com/wiki/ The arp-scan wiki
https://github.com/royhills/arp-scan The arp-scan
Visit the GSP FreeBSD Man Page Interface.
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