userspace arp daemon.
Usage: arpd [
-lkh? ] [ -a N ] [ -b dbase ] [ -B number ] [ -f file ] [-p
interval ] [ -n time ] [ -R rate ] [ <INTERFACES>
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
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.
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.
the location of the database
file. The default location is /var/lib/arpd/arpd.db
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
Suppress sending broadcast queries by the kernel. This
option only makes sense together with option -a.
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.
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.
Maximal steady rate of
broadcasts sent by arpd in packets per second. Default value
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 parameters, it is
assumed that the user does this himself after arpd is
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
statistics to syslog. The effect of any other signals is
particular, they may corrupt the database and leave the
parameters in an unpredictable state.
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
list in not given on command line, variable app_solicit on
of interest should be in /proc/sys/net/ipv4/neigh/*. If this
made arpd still collects gratuitous ARP information in its
Start arpd to collect
gratuitous ARP, but not messing with kernel
killall arpd ; arpd -l -b
Look at result after some
arpd -b /var/tmp/arpd.db -a 1
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