arpd



SYNOPSIS
       Usage: arpd [ -lkh? ] [ -a N ] [ -b dbase ] [ -B number ] [ -f file ] [
       -n time ] [ -R rate ] [ interfaces ]


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


OPTIONS
       -h -?  Print help

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

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

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

       -a <NUMBER>
              arpd not only passively listens ARP on wire, but also send brod-
              cast  queries  itself.  NUMBER is number of such queries to make
              before destination is considered as 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  kernel.  It  takes  sense
              together with option -a.

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

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

       Signals
       arpd exits gracefully syncing database and  restoring  adjusted  sysctl
       parameters,  when  receives SIGINT or SIGTERM. SIGHUP syncs database to
       disk. SIGUSR1 sends some statistics to syslog. Effect of  another  sig-
       nals  is  undefined, they may corrupt database and leave sysctl praame-
       ters in an unpredictable state.

       Note
       In order for arpd to be able to serve as ARP resolver, 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  ker-
              nel 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 kernel still does unicast probing to validate
              entries,  but  all the broadcast activity is suppressed and made
              under authority of arpd.

       This is mode which arpd is supposed to work normally. It is not default
       just  to  prevent  occasional enabling of too aggressive mode occasion-
       ally.



                                 28 June, 2007                         ARPD(8)
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