Arpalert uses ARP protocol monitoring to prevent unauthorized connections on the local network. If an illegal connection is detected, a program or script could be launched, which could be used to send an alert message, for example.


-f config_file

Specify the config file.

-i interface

Comma separated network interfaces listen to.

-p pid_file

Use this pid file. this file containis a pid number of the arpalert session. If the file exist and his locked, the daemon do not run.

-e exec_script

Script launched when an alert is send.

-D log_level

The level logged. The levels are between 0 (emergency) and 7 (debug). If 3 is selected all levels bitween 0 and 3 are logged.

-l leases_file

This file contain a dump of the mac address in memory (see config file).

-m module file

Specify a module file to load


Run as daemon.


Run in foreground.


Watch on screen all the option selected (the options specified in config file and the default options)


The help command line.


Debug option: print a dump of packets captured.


Set the interface in promiscuous mode (don't set this if only the arp analyse is used).


Print version and quit.


The config file contains 3 types of data: integer, string and boolean. The boolean type can take values 'oui', 'true', 'yes', '1' for the true values or 'non', 'no', 'false', '0' for the falses values.

user = arpalert

Use privileges separation with this user

umask = 177

Uses this umask for file creation.

chroot dir = /home/thierry/arp_test/

Use this directory for program jail

If this option is commented out, the program does not use chroot.

The program read the config file and open the syslog socket before the chroot:

The kill -HUP does not work with chroot.

If the syslog program is restarted, the socket change and the arpalert syslog system can't be connect to the new socket: the logs with syslog are disabled. Prefere to use the log file.

The file pathes are relative to the chroot dir (except the config file)

log file = /var/log/arpalert.log

The program log into this file

If this option is commented out, the internal system log is not used.

The internal system logs can be used in same time that syslog.

log level = 6

The level logged. The levels are between 0 (emergency) and 7 (debug). If 3 is selected all levels between 0 and 3 are logged.

use syslog = true

If this option is false, the syslog system is disabled

maclist file = /etc/arpalert/maclist.allow

White list

maclist alert file = /etc/arpalert/maclist.deny

Black list

maclist leases file = /var/lib/arpalert/arpalert.leases

Dump file

dump inter = 5

Minimun time to wait between two leases dump

auth request file = /etc/arpalert/authrq.conf

List of authorized request

lock file = /var/run/

pid file

dump packet = false

Only for debugging: this dump packet received on standard output. The syntax "dump paquet" is also avalaible, but is deprecated

daemon = false

If is set to true, run the program as daemon

interface = ""

Comma separated network interfaces leisten to. If this value is not specified, the soft select the first interface.

catch only arp = TRUE

Configure the network for catch only arp request. The detection type "new_mac" is deactived. This mode is used for CPU saving if Arpalert is running on a router

mod on detect = ""

Module file loaded by arpalert. This module is launched on each valid alert. This system permit to avoid a costly fork/exec

mod config = ""

This chain is transfered to the init function of module loaded

action on detect = ""

Script launched on each detection. Parameters are:

- mac address of requestor,

- ip of requestor,

- supp. parm.,

- ethernet device listening on

- type of alert,

- optional: ethernet vendor

  • type of alert:

    0: IP change

    1: Mac address already detected but not in white list

    2: Mac address in black list

    3: New mac address

    4: Unauthorized arp request

    5: Abusive number of arp request detected

    6: Ethernet mac address different from arp mac address

    7: Flood detected

    8: New mac address whithout ip address

execution timeout = 10

Script execution timeout (seconds)

max alert = 20

Maximun simultaneous lanched script

dump black list = false

Dump the black listed mac address in leases file

dump white list = false

Dump the white listed mac address in leases file

dump new address = true

Dump the new mac address in leases file

mac timeout = 259200

After this time a mac address is removed from memory (seconds) (default 1 month)

max entry = 1000000

After this limit the memory hash is cleaned (protect to arp flood)

anti flood interval = 10

This permit to send only one mismatch alert in this time (in seconds)

anti flood global = 50

If the number of arp request in seconds exceeds this value, all alerts are ignored for "anti flood interval" time

mac vendor file = ""

This file contain the association from mac address to vendor name. This file can be downloaded here:

log mac vendor = false

Log vendor name

alert mac vendor = false

Give vendor name to script

mod mac vendor = false

Give vendor name to module

log referenced address, alert on referenced address, mod on referenced address = false

Log/launch script/call module if the address is referenced in hash but is not in white list

log deny address, alert on deny address, mod on deny address = true

Log/launch script/call module if the mac address is in black list

log new address, alert on new address, mod on new address = true

Log/launch script/call module if the address isn't referenced

log mac change, alert on mac change, mod on mac change = true

Log/launch script/call module if the mac address is different from the last arp request with the same ip address

log ip change, alert on ip change, mod on ip change = true

Log/launch script/call module if the ip address is different from the last arp request with the same mac address

log unauth request, alert on unauth request, mod on unauth request = true

Unauthorized arp request: launch if the request is not authorized in auth file

ignore unknown sender = true

Dont analyse arp request for unknow hosts (not in white list)

ignore self test = true

Ignore ARP self test generated by windows dhcp for unauthorized request detection

ignore me = true

Ignore arp request with mac addresse of the listing interfaces for the authorizations checks

unauth ignore time method = 2

Select suspend time method:

1: ignore all unauth alerts during "anti flood interval" time

2: ignore only tuple (mac address, ip address) during "anti flood interval" time

log request abus, alert on request abus, mod on request abus = true

Log/launch script/call module if the number of request per seconds are > "max request"

max request = 1000000

Maximun request authorized by second

log mac error, alert on mac error, mod on mac error = true

Log/launch script/call module if the ethernet mac address is different than the arp mac address (only for requestor)

log flood = true

alert on flood = true mod on flood = true Log/launch script/call module if have too many arp request per seconds


/etc/arpalert/maclist.allow and /etc/arpalert/maclist.deny:

All the line with # as a first caracter are ignored

The data on this file take this form


The available flags are:

ip_change: Ignore ip change alert for this mac address

black_listed: Ignore black list alerts for this mac address

unauth_rq: Ignore unauthorized requests for this mac address

rq_abus: Ignore request abuse for this mac address

mac_error: Ignore mac error for this mac address

mac_change: Ignore mac change for this mac address


All the words after # character are ignored

All the blank characters are ignored

The authorisations list for one mac address begins by the mac address into brackets

All the next values are ip hosts addresses or ip networks addresses (with /xx notion)




sbin/arpalert: binary file

etc/arpalert/arpalert.conf: default config file

var/run/ pid file

var/state/arpalert.leases: leases file