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Linux 2.6 - man page for arpd (linux section 8)

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 brodcast 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 informa-
	      tion, 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  time-
	      out  should  not be too much longer than boot time of a typical host not supporting
	      gratuitous 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 interfaces 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 signals is undefined, they may corrupt database and leave
       sysctl praameters 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 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 ker-
	      nel 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 occasionally.

					  28 June, 2007 				  ARPD(8)


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