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ARPALERT(8) arp traffic monitoring ARPALERT(8)


arpalert - ARP traffic monitoring


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.


Specify the config file.
Comma separated network interfaces listen to.
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.
Script launched when an alert is send.
The level logged. The levels are between 0 (emergency) and 7 (debug). If 3 is selected all levels bitween 0 and 3 are logged.
This file contain a dump of the mac address in memory (see config 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.

Use privileges separation with this user
Uses this umask for file creation.
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 paths are relative to the chroot dir (except the config file)
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.
The level logged. The levels are between 0 (emergency) and 7 (debug). If 3 is selected all levels between 0 and 3 are logged.
If this option is false, the syslog system is disabled
White list
Black list
Dump file
Minimum time to wait between two leases dump
List of authorized request
pid file
Only for debugging: this dump packet received on standard output. The syntax "dump paquet" is also avalaible, but is deprecated
If is set to true, run the program as daemon
Comma separated network interfaces leisten to. If this value is not specified, the soft select the first interface.
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
Module file loaded by arpalert. This module is launched on each valid alert. This system avoids a costly fork/exec
This chain is transferred to the init function of module loaded
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 without ip address
Script execution timeout (seconds)
Maximun simultaneous lanched script
Dump the black listed mac address in leases file
Dump the white listed mac address in leases file
Dump the new mac address in leases file
After this time a mac address is removed from memory (seconds) (default 1 month)
After this limit the memory hash is cleaned (protect to arp flood)
This sends only one mismatch alert in this time (in seconds)
If the number of arp request in seconds exceeds this value, all alerts are ignored for "anti flood interval" time
This file contain the association from mac address to vendor name. This file can be downloaded here:
Log vendor name
Give vendor name to script
Give vendor name to module
Log/launch script/call module if the address is referenced in hash but is not in white list
Log/launch script/call module if the mac address is in black list
Log/launch script/call module if the address isn't referenced
Log/launch script/call module if the mac address is different from the last arp request with the same ip address
Log/launch script/call module if the ip address is different from the last arp request with the same mac address
Unauthorized arp request: launch if the request is not authorized in auth file
Don't analyse arp request for unknown hosts (not in white list)
Ignore ARP self test generated by windows dhcp for unauthorized request detection
Ignore arp request with mac addresse of the listing interfaces for the authorizations checks
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/launch script/call module if the number of request per seconds are > "max request"
Maximun request authorized by second
Log/launch script/call module if the ethernet mac address is different than the arp mac address (only for requestor)
Log/launch script/call module if have too many arp request per seconds
Log/launch script/call module if the ethernet mac address expire
Allow authorized mac addresses to expire


/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
mac_expire: Never expire this mac address. Useful if the option "expire authorized mac addresses" is used
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