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)