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)