arpd man page on Debian

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ARPD(8)								       ARPD(8)

NAME
       arpd - userspace arp daemon.

SYNOPSIS
       Usage: arpd [ -lk ] [ -a N ] [ -b dbase ] [ -f file ] [ 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.

       -B <NUMBER>
	      Number  of  broadcasts  sent  by <tt/arpd/ back to back. Default
	      value is 3. Together with option <tt/-R/ this option  allows  to
	      police  broadcasting  not	 to  exceed B+R*T over any interval of
	      time T.

       <INTERFACE> is the name of networking interface to watch. If no	inter‐
       faces  given,  arpd monitors all the interfaces. In this case arpd does
       not adjust sysctl parameters, it is supposed  user  does	 this  himself
       after arpd is started.

       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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