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Alexey Kuznetsov, email@example.com
some_negative_number, 20 Sep 2001
The format of the command is:
- -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
- -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
information, you can observe 1 second gaps in service. Not fatal, but
- -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 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 arpd back to back.
Default value is 3. Together with option -R this option allows
to police broadcasting not to exceed B+R*T over any interval
of time T.
INTERFACE is name of networking inteface 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.
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 parameters in an unpredictable state.
In order to arpd be able to serve as ARP resolver, kernel must be
compiled with the option CONFIG_ARPD and, in the case when interface list
is not given on command line, variable app_solicit
on interfaces of interest should be set in /proc/sys/net/ipv4/neigh/*.
If this is not made arpd still collects gratuitous ARP information
in its database.
- Start arpd to collect gratuitous ARP, but not messing
with kernel functionality:
- Look at result after some time:
- To enable kernel helper, leaving leading role to kernel:
- 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
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