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arpd -

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 ] [  ]

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 
              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 
              the location of the database file. The default location is /var/lib/arpd/arpd.db

       -a 
              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 
              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 
              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 
              Maximal steady rate of broadcasts sent by arpd in packets per second. Default value
              is 1.

       -B 
              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.

         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
       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  unpre‐
       dictable 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 activ‐
              ity 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 pre‐
       vent occasional enabling of too aggressive a mode.

                                          28 June, 2007                                   ARPD(8)

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