arp-scan - Man Page

Send ARP requests to target hosts and display responses

Examples (TL;DR)

Scan the current local network: arp-scan --localnet
Scan an IP network with a custom bitmask: arp-scan 192.168.1.1/24
Scan an IP network within a custom range: arp-scan 127.0.0.0-127.0.0.31
Scan an IP network with a custom net mask: arp-scan 10.0.0.0:255.255.255.0

Synopsis

arp-scan [options] [hosts...]

Target hosts must be specified on the command line unless the --file or --localnet option is used.

Targets can be IPv4 addresses or hostnames. You can also use CIDR notation (10.0.0.0/24) (network and broadcast included), ranges (10.0.0.1-10.0.0.10), and network:mask (10.0.0.0:255.255.255.0).

arp-scan sends ARP request packets to the specified hosts and displays any responses received. The network interface can be specified with the --interface option. If no interface is specified, arp-scan will pick the lowest numbered, configured up interface (excluding loopback).

arp-scan uses raw sockets, which requires privileges on some systems:

Linux with POSIX.1e capabilities support using libcap:: arp-scan is capabilities aware. It requires CAP_NET_RAW in the permitted set and only enables that capability for the required functions. use setcap cap_net_raw+p /path/to/arp-scan to add CAP_NET_RAW to the permitted set of the arp-scan executable. Capabilities support also makes SUID root much safer because arp-scan will drop all capabilities except CAP_NET_RAW and will not run with full root privileges.
BSD and macOS:: You need read/write access to /dev/bpf*
Any operating system:: Running as root or SUID root will work on any OS but other methods are preferable where possible.

ARP only operates on the local network, and cannot be routed. Although the ARP protocol uses IPv4 addresses, it is not an IP protocol and arp-scan can be used on interfaces without an IPv4 address.

One ARP request is sent for each target. If a host does not respond, the request will be re-sent once more. The number of retries can be changed with the --retry option. Reducing the number of retries will reduce the scanning time at the risk of missing some results due to packet loss.

You can specify the bandwidth that arp-scan will use with the --bandwidth option. The default is 256000 bits per second. Increasing the bandwidth will reduce scanning time, but setting the bandwidth too high may cause a high broadcast packet rate. Another way to specify the packet rate is with the --interval option.

The time for a single-pass scan (i.e. with --retry=1) is:

$t i m e = n \times i + t + o$

Where n is the number of hosts, i is the interval (given with --interval or calculated from --bandwidth), t is the timeout (specified with --timeout) and o is the overhead time taken to load the target list and read the MAC/Vendor mapping files. The overhead is normally negligible (typically around 100ms) but can be reduced further by the --quiet option. For small lists of hosts, the timeout value will dominate, but for large lists the packet interval is the most important value.

Any part of the ARP request may be modified through the use of the --arpXXX options as shown in the table below:

ARP Request Packet Options
Field	Bits	Option	Default
ar$hrd	16	--arphrd	1 (ARPHRD_ETHER)
ar$pro	16	--arppro	0x0800
ar$hln	8	--arphln	6 (ETH_ALEN)
ar$pln	8	--arppln	4 (IPv4)
ar$op	16	--arpop	1 (ARPOP_REQUEST)
ar$sha	48	--arpsha	interface h/w address
ar$spa	32	--arpspa	interface IPv4 address
ar$tha	48	--arptha	00:00:00:00:00:00
ar$tpa	32	None	target host IPv4 address

The most common option is --arpspa, which sets the source IPv4 address in the ARP request, allowing the ARP request to use a different source address from the interface address. This allows the use of arp-scan on interfaces with no IPv4 address. Note: Setting ar$spa to the target's IP address causes some operating systems to report an address clash when they receive an ARP request for their own address.

You can also change the values in the Ethernet frame header as shown below:

Ethernet Header Options
Field	Bits	Option	Default
Dest Address	48	--destaddr	ff:ff:ff:ff:ff:ff
Source Address	48	--srcaddr	interface address
Protocol Type	16	--prototype	0x0806 (ARP)

The --destaddr option which sets the destination Ethernet address is the only one that is commonly used.

By default, ARP responses are displayed in the following format:

Where IPv4 Address is the IP address of the responding target, MAC Address is its link-layer address and Vendor Details are the vendor details decoded from the hardware address. The output fields are separated by a single tab character. You can change the output format with the --format option.

The responses are displayed in the order they are received, which can be different from the order the requests were sent because some hosts may respond quicker than others.

The vendor decoding uses the files ieee-oui.txt and mac-vendor.txt. ieee-oui.txt is generated from the IEEE MA-L (OUI), MA-M, MA-S (OUI36) and IAB registries. mac-vendor.txt contains additional MAC to Vendor mappings, and can be used to add custom mappings. get-oui can be used to update ieee-oui.txt with the latest data from the IEEE registries.

All IPv4 hosts should respond to ARP request packets, including hosts with packet filtering such as firewalls. This makes arp-scan a useful tool to discover all active IPv4 hosts on the local network.

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>: Character string.
: Decimal integer, or hex if preceeded by 0x e.g. 2048 or 0x800.
<f>: Floating point decimal number.
<m>: MAC address, e.g. 01:23:45:67:89:ab or 01-23-45-67-89-ab (case insensitive)
<a>: IPv4 address e.g. 10.0.0.1
<h>: Hex encoded binary data. No leading 0x. (case insensitive).
<x>: Something else - see option description.

General Options

--help or -h: Display this usage message and exit.
--verbose or -v: Display verbose progress messages. Can be used than once to increase verbosity. Max=3.
--version or -V: Display program version and exit. Displays the version, license details, libpcap version, and whether POSIX.1e capability support is included.
--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).

Host Selection

--file=<s> or -f <s>: Read hostnames or addresses from the specified file. One name or address pattern per line. Use "-" for stdin.
--localnet or -l: Generate addresses from interface configuration. Generates list from interface address and netmask (network and broadcast included). You cannot use the --file option or give targets on the command line. Use --interface to specify the interface.

MAC/Vendor Mapping Files

--ouifile=<s> or -O <s>: Use IEEE registry vendor mapping file <s>. Default is ieee-oui.txt in the current directory. If that is not found /usr/share/arp-scan/ieee-oui.txt is used.
--macfile=<s> or -m <s>: Use custom vendor mapping file <s>. Default is mac-vendor.txt in the current directory. If that is not found /etc/arp-scan/mac-vendor.txt is used.

Output Format Control

--quiet or -q

Display minimal output for each responding host. Only the IP address and MAC address are displayed. Reduces memory usage by about 5MB because the vendor mapping files are not used. Only the ${ip} and ${mac} fields are available for the --format option if --quiet is specified.

--plain or -x

Supress header and footer text. Only display the responding host details. Useful if the output will be parsed by a script.

--ignoredups or -g

Don't display duplicate packets. By default duplicate packets are flagged with (DUP: n) where n is the number of times this host has responded.

--rtt or -D

Calculate and display the packet round-trip time. The time is displayed in milliseconds and fractional microseconds. Makes the ${rtt} field available for --format.

--format=<s> or -F <s>

Specify the output format string. The format is a string that will be output for each responding host. Host details can be included by inserting references to fields using the syntax "${field[;width]}". Fields are displayed right- aligned unless the width is negative in which case left alignment will be used. The following case- insensitive field names are recognised:

IP	Host IPv4 address in dotted quad format
Name	Host name if --resolve option given
MAC	Host MAC address xx:xx:xx:xx:xx:xx
HdrMAC	Ethernet source addr if different
Vendor	Vendor details string
Padding	Padding after ARP packet in hex if nonzero
Framing	Framing type if not Ethernet_II
VLAN	802.1Q VLAN ID if present
Proto	ARP protocol if not 0x0800
DUP	Packet number for duplicate packets (>1)
RTT	Round trip time if --rtt option given

Only the ${ip} and ${mac} fields are available if the --quiet option is specified.

Any characters that are not fields are output verbatim. "\" introduces escapes:

\n	newline
\r	carriage return
\t	tab
\	suppress special meaning for following character

You should enclose the --format argument in 'single quotes' to protect special characters from the shell.

Example: --format='${ip}\t${mac}\t${vendor}'

Host List Randomisation

--random or -R: Randomise the target host list.
--randomseed=: Seed the pseudo random number generator. Useful if you want a reproducible --random order.

Output Timing and Retry

--retry= or -r : Set total number of attempts per host to , default=2.
--backoff=<f> or -b <f>: Set backoff factor to <f>, default=1.50. Multiplies timeout by <f> for each pass.
--timeout= or -t : Set initial per host timeout to  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 packet rate. If you want to use up to a given bandwidth it is easier to use the --bandwidth option instead. The interval is in milliseconds, or microseconds if "u" is appended.
--bandwidth=<x> or -B <x>: Set outbound bandwidth to <x>, default=256000. The value is in bits per second. Append K for kilobits or M for megabits (decimal multiples). You cannot specify both --interval and --bandwidth.

DNS Resolution

--numeric or -N: Targets must be IP addresses, not hostnames. Can reduce startup time for large target lists.
--resolve or -d: Resolve responding addresses to hostnames. The default output format will display the hostname instead of the IPv4 address. This option makes the ${name} field available for the --format option.

Output ARP Packet

--arpsha=<m> or -u <m>: Set the ARP source Ethernet address. Sets the 48-bit ar$sha field but does not change the hardware address in the frame header, see --srcaddr for how to change that address. Default is the Ethernet address of the outgoing interface.
--arptha=<m> or -w <m>: Set the ARP target Ethernet address. Sets the 48-bit ar$tha field. The default is zero, because this field is not used for ARP request packets.
--arphrd= or -H : Set the ARP hardware type, default=1. Sets the 16-bit ar$hrd field. The default is 1 (ARPHRD_ETHER). Many operating systems also respond to 6 (ARPHRD_IEEE802).
--arppro= or -p : Set the ARP protocol type, default=0x0800. Sets the 16-bit ar$pro field. Most operating systems only respond to 0x0800 (IPv4).
--arphln= or -a : Set the hardware address length, default=6. Sets the 8-bit ar$hln field. The lengths of the ar$sha and ar$tha fields are not changed by this option; it only changes the ar$hln field.
--arppln= or -P : Set the protocol address length, default=4. Sets the 8-bit ar$pln field. The lengths of the ar$spa and ar$tpa fields are not changed by this option; it only changes the ar$pln field.
--arpop= or -o : Specify the ARP operation, default=1. Sets the 16-bit ar$op field. Most operating systems only respond to the value 1 (ARPOP_REQUEST).
--arpspa=<a> or -s <a>: Set the source IPv4 address. The address should be in dotted quad format, or the string "dest" which sets the source address to the target host address. The default is the outgoing interface address. Sets the 32-bit ar$spa field. Some operating systems only respond if the source address is within the network of the receiving interface. Setting ar$spa to the destination IP address can cause some operating systems to report an address clash.

Output Ethernet Header

--srcaddr=<m> or -S <m>: Set the source Ethernet MAC address. Default is the interface MAC address. This sets the address in the Ethernet header. It does not change the address in the ARP packet: use --arpsha to change that address.
--destaddr=<m> or -T <m>: Set the destination MAC address. Sets the destination address in the Ethernet header. Default is ff:ff:ff:ff:ff:ff (broadcast) Hosts also respond if the request is sent to their unicast address, or to a multicast address they are listening on.
--prototype= or -y : Sets the Ethernet protocol type, default=0x0806. This sets the protocol type field in the Ethernet header.
--llc or -L: Use RFC 1042 LLC/SNAP encapsulation for 802.2 networks. arp-scan will decode and display ARP responses in both Ethernet-II and IEEE 802.2 formats irrespective of this option.
--vlan= or -Q : Use 802.1Q tagging with VLAN id . The id should be in the range 0 to 4095. arp-scan will decode and display ARP responses in 802.1Q format irrespective of this option.

Misc Options

--limit= or -M : Exit after the specified number of hosts have responded. arp-scan will exit with status 1 if the number of responding hosts is less than the limit. Can be used in scripts to check if fewer hosts respond without having to parse the output.
--pcapsavefile=<s> or -W <s>: Write received packets to pcap savefile <s>. ARP responses will be written to the specified file as well as being decoded and displayed.
--snap= or -n : Set the pcap snap length to . Default=64. Specifies the frame capture length, including the Ethernet header. The default is normally sufficient.
--retry-send= or -Y : Set number of send attempts, default=20.
--retry-send-interval= or -E : Set interval between send attempts. Interval is in milliseconds or microseconds if "u" is appended. default=5.
--padding=<h> or -A <h>: Specify padding after packet data. Set padding after the ARP request to hex value <h>.

Exit Status

arp-scan will exit with 0 on successful completion or >0 if an error was encountered.

If the --limit option is specified, arp-scan will also exit with a non-zero exit code if the number of responding hosts is less than the specified limit.

Files

/usr/share/arp-scan/ieee-oui.txt: List of IEEE OUI (Organisationally Unique Identifier) to vendor mappings.
/etc/arp-scan/mac-vendor.txt: List of other Ethernet MAC to vendor mappings, including local additions.

Examples

Simple Scan

Scan the default network using the interface IPv4 configuration to generate the list of hosts to scan.

$ arp-scan --localnet
Interface: eth0, type: EN10MB, MAC: 50:65:f3:f0:6d:7c, IPv4: 10.0.0.106
Starting arp-scan 1.9.9 with 256 hosts (https://github.com/royhills/arp-scan)
10.0.0.14       a4:1f:72:7f:25:bb       Dell Inc.
10.0.0.22       10:60:4b:73:43:de       Hewlett Packard
10.0.0.74       00:0c:29:90:07:e9       VMware, Inc.
10.0.0.75       00:0c:29:66:9e:c2       VMware, Inc.
10.0.0.76       00:0c:29:d0:e1:ea       VMware, Inc.
10.0.0.82       9c:b6:54:bb:f3:ec       Hewlett Packard
10.0.0.84       00:21:9b:fd:b9:b3       Dell Inc.
10.0.0.85       00:02:b3:eb:5a:f8       Intel Corporation
10.0.0.91       00:9c:02:a5:7b:29       Hewlett Packard
10.0.0.92       d4:ae:52:d0:07:6f       Dell Inc.
10.0.0.93       d4:ae:52:d0:04:9b       Dell Inc.
10.0.0.96       9c:b6:54:bb:f5:35       Hewlett Packard
10.0.0.97       00:0c:29:0e:95:20       VMware, Inc.
10.0.0.104      50:65:f3:f0:70:a4       Hewlett Packard

15 packets received by filter, 0 packets dropped by kernel
Ending arp-scan 1.9.9: 256 hosts scanned in 1.532 seconds (167.10 hosts/sec). 14 responded

Output Formatting

Scan all hosts in 10.0.0.0/24 using interface eth0. Calculate round-trip time and display in aligned columns using a custom format.

$ arp-scan -I eth0 --rtt --format='|${ip;-15}|${mac}|${rtt;8}|' 10.0.0.0/24
Interface: eth0, type: EN10MB, MAC: 50:65:f3:f0:6d:7c, IPv4: 10.0.0.106
Starting arp-scan 1.9.9 with 256 hosts (https://github.com/royhills/arp-scan)
|10.0.0.14      |a4:1f:72:7f:25:bb|   0.280|
|10.0.0.22      |10:60:4b:73:43:de|   0.293|
|10.0.0.74      |00:0c:29:90:07:e9|   0.380|
|10.0.0.75      |00:0c:29:66:9e:c2|   0.311|
|10.0.0.76      |00:0c:29:d0:e1:ea|   0.326|
|10.0.0.82      |9c:b6:54:bb:f3:ec|   0.216|
|10.0.0.84      |00:21:9b:fd:b9:b3|   0.244|
|10.0.0.85      |00:02:b3:eb:5a:f8|   0.244|
|10.0.0.91      |00:9c:02:a5:7b:29|   0.209|
|10.0.0.92      |d4:ae:52:d0:07:6f|   0.289|
|10.0.0.93      |d4:ae:52:d0:04:9b|   0.278|
|10.0.0.96      |9c:b6:54:bb:f5:35|   0.255|
|10.0.0.97      |00:0c:29:0e:95:20|   0.288|
|10.0.0.104     |50:65:f3:f0:70:a4|   0.263|

14 packets received by filter, 0 packets dropped by kernel
Ending arp-scan 1.9.9: 256 hosts scanned in 2.032 seconds (125.98 hosts/sec). 14 responded

CSV Output

--plain removes extraneous output.

$ arp-scan -I eth0 --plain --format='${ip},${mac},"${vendor}"' 10.0.0.0/24
10.0.0.14,a4:1f:72:7f:25:bb,"Dell Inc."
10.0.0.22,10:60:4b:73:43:de,"Hewlett Packard"
10.0.0.74,00:0c:29:90:07:e9,"VMware, Inc."
10.0.0.75,00:0c:29:66:9e:c2,"VMware, Inc."
10.0.0.76,00:0c:29:d0:e1:ea,"VMware, Inc."
10.0.0.82,9c:b6:54:bb:f3:ec,"Hewlett Packard"
10.0.0.84,00:21:9b:fd:b9:b3,"Dell Inc."
10.0.0.85,00:02:b3:eb:5a:f8,"Intel Corporation"
10.0.0.91,00:9c:02:a5:7b:29,"Hewlett Packard"
10.0.0.92,d4:ae:52:d0:07:6f,"Dell Inc."
10.0.0.93,d4:ae:52:d0:04:9b,"Dell Inc."
10.0.0.96,9c:b6:54:bb:f5:35,"Hewlett Packard"
10.0.0.97,00:0c:29:0e:95:20,"VMware, Inc."
10.0.0.104,50:65:f3:f0:70:a4,"Hewlett Packard"

Referenced By

arp-fingerprint(1), get-oui(1), mac-vendor(5).

November 9, 2022