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NAME | SYNOPSIS | DESCRIPTION | OPTIONS | SIGNALS | NOTE | EXAMPLES | COLOPHON |
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ARPD(8) System Manager's Manual ARPD(8)
arpd - userspace arp daemon.
Usage: arpd [ -lkh? ] [ -a N ] [ -b dbase ] [ -B number ] [ -f
file ] [-p interval ] [ -n time ] [ -R rate ] [ <INTERFACES> ]
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.
-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
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.
-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 together 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.
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 particular, they may corrupt the
database and leave the sysctl 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
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.
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.
This page is part of the iproute2 (utilities for controlling
TCP/IP networking and traffic) project. Information about the
project can be found at
⟨http://www.linuxfoundation.org/collaborate/workgroups/networking/iproute2⟩.
If you have a bug report for this manual page, send it to
[email protected], [email protected]. This page was
obtained from the project's upstream Git repository
⟨https://git.kernel.org/pub/scm/network/iproute2/iproute2.git⟩ on
2024-06-14. (At that time, the date of the most recent commit
that was found in the repository was 2024-06-11.) If you
discover any rendering problems in this HTML version of the page,
or you believe there is a better or more up-to-date source for
the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original
manual page), send a mail to [email protected]
28 June, 2007 ARPD(8)
Pages that refer to this page: arp(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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