phpman > man > arpd(8)

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 ] [ <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 inter‐
              face. 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 to‐
              gether 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 particu‐
       lar, 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, vari‐
       able 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)