ARPD(8)			    System Manager's Manual		       ARPD(8)



NAME
       arpd - userspace arp daemon.


SYNOPSIS
       Usage: arpd [ -lkh? ] [ -a N ] [ -b dbase ] [ -B number ] [ -f file ]
       [-p interval ] [ -n time ] [ -R rate ] [ <INTERFACES> ]


DESCRIPTION
       The arpd daemon collects gratuitous ARP information, saving it on local
       disk and feeding it to the kernel on demand to avoid redundant
       broadcasting due to limited size of the kernel ARP cache.


OPTIONS
       -h -?  Print help

       -l     Dump the arpd database to stdout and exit. The output consists
	      of three columns: the interface index, the IP address of the
	      interface, and the MAC address of the interface. Negative
	      entries for dead hosts are also shown, in this case the MAC
	      address is replaced by the word FAILED followed by a colon and
	      the most recent time when the fact that the host is dead was
	      proven.

       -f <FILE>
	      Read and load an arpd database from FILE in a text format
	      similar to that dumped by option -l. Exit after load, possibly
	      listing resulting database, if option -l is also given. If FILE
	      is -, stdin is read to get the ARP table.

       -b <DATABASE>
	      the location of the database file. The default location is
	      /var/lib/arpd/arpd.db

       -a <NUMBER>
	      With this option, arpd not only passively listens for ARP
	      packets on the interface, but also sends broadcast queries
	      itself. NUMBER is the number of such queries to make before a
	      destination is considered dead. When arpd is started as kernel
	      helper (i.e. with app_solicit enabled in sysctl or even with
	      option -k) without this option and still did not learn enough
	      information, you can observe 1 second gaps in service. Not
	      fatal, but not good.

       -k     Suppress sending broadcast queries by the kernel. This option
	      only makes sense together with option -a.

       -n <TIME>
	      Specifies the timeout of the negative cache. When resolution
	      fails, arpd suppresses further attempts to resolve for this
	      period. This option only makes sense together with option '-k'.
	      This timeout should not be too much longer than the boot time of
	      a typical host not supporting gratuitous ARP. Default value is
	      60 seconds.

       -p <TIME>
	      The time to wait in seconds between polling attempts to the
	      kernel ARP table. TIME may be a floating point number. The
	      default value is 30.

       -R <RATE>
	      Maximal steady rate of broadcasts sent by arpd in packets per
	      second. Default value is 1.

       -B <NUMBER>
	      The number of broadcasts sent by arpd back to back. Default
	      value is 3. Together with the -R option, this option ensures
	      that the number of ARP queries that are broadcast does not
	      exceed B+R*T over any interval of time T.

       <INTERFACES> is a list of names of networking interfaces to watch. If
       no interfaces are given, arpd monitors all the interfaces. In this case
       arpd does not adjust sysctl parameters, it is assumed that the user
       does this himself after arpd is started.

SIGNALS
       When arpd receives a SIGINT or SIGTERM signal, it exits gracefully,
       syncing the database and restoring adjusted sysctl parameters. On a
       SIGHUP it syncs the database to disk. With SIGUSR1 it sends some
       statistics to syslog. The effect of any other signals is undefined. In
       particular, they may corrupt the database and leave the sysctl
       parameters in an unpredictable state.

NOTE
       In order for arpd to be able to serve as ARP resolver, the kernel must
       be compiled with the option CONFIG_ARPD and, in the case when interface
       list in not given on command line, variable app_solicit on interfaces
       of interest should be in /proc/sys/net/ipv4/neigh/*. If this is not
       made arpd still collects gratuitous ARP information in its database.

EXAMPLES
       arpd -b /var/tmp/arpd.db
	      Start arpd to collect gratuitous ARP, but not messing with
	      kernel functionality.

       killall arpd ; arpd -l -b /var/tmp/arpd.db
	      Look at result after some time.

       arpd -b /var/tmp/arpd.db -a 1 eth0 eth1
	      Enable kernel helper, leaving leading role to kernel.

       arpd -b /var/tmp/arpd.db -a 3 -k eth0 eth1
	      Completely replace kernel resolution on interfaces eth0 and
	      eth1. In this case the kernel still does unicast probing to
	      validate entries, but all the broadcast activity is suppressed
	      and made under authority of arpd.

       This is the mode in which arpd normally is supposed to work. It is not
       the default to prevent occasional enabling of too aggressive a mode.

				 28 June, 2007			       ARPD(8)