ARPD(8)                  (28 June, 2007)                  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 ker-
          nel 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 for-
               mat 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

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     ARPD(8)                  (28 June, 2007)                  ARPD(8)

               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 reso-
               lution 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 sec-
               onds.

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

          -R <RATE>
               Maximal steady rate of broadcasts sent by arpd in pack-
               ets 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 parame-
          ters, it is assumed that the user does this himself after
          arpd is started.

     SIGNALS
     fully, syncing the database and restoring adjusted sysctl parame-
     ters. 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.
          When arpd receives a SIGINT or SIGTERM signal, it exits grace-

     NOTE
     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 col-
     lects gratuitous ARP information in its database.
          In order for arpd to be able to serve as ARP resolver, the kernel

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     ARPD(8)                  (28 June, 2007)                  ARPD(8)

     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.

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