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131 lines
4.3 KiB
Plaintext
131 lines
4.3 KiB
Plaintext
<!doctype linuxdoc system>
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<article>
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<title>ARPD Daemon
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<author>Alexey Kuznetsov, <tt/kuznet@ms2.inr.ac.ru/
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<date>some_negative_number, 20 Sep 2001
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<abstract>
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<tt/arpd/ is daemon collecting gratuitous ARP information, saving
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it on local disk and feeding it to kernel on demand to avoid
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redundant broadcasting due to limited size of kernel ARP cache.
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</abstract>
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<p><bf/Description/
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<p>The format of the command is:
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<tscreen><verb>
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arpd OPTIONS [ INTERFACE [ INTERFACE ... ] ]
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</verb></tscreen>
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<p> <tt/OPTIONS/ are:
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<itemize>
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<item><tt/-l/ - dump <tt/arpd/ database to stdout and exit. Output consists
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of three columns: interface index, IP address and MAC address.
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Negative entries for dead hosts are also shown, in this case MAC address
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is replaced by word <tt/FAILED/ followed by colon and time when the fact
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that host is dead was proven the last time.
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<item><tt/-f FILE/ - read and load <tt/arpd/ database from <tt/FILE/
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in text format similar dumped by option <tt/-l/. Exit after load,
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probably listing resulting database, if option <tt/-l/ is also given.
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If <tt/FILE/ is <tt/-/, <tt/stdin/ is read to get ARP table.
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<item><tt/-b DATABASE/ - location of database file. Default location is
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<tt>/var/lib/arpd/arpd.db</tt>.
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<item><tt/-a NUMBER/ - <tt/arpd/ not only passively listens ARP on wire, but
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also send brodcast queries itself. <tt/NUMBER/ is number of such queries
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to make before destination is considered as dead. When <tt/arpd/ is started
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as kernel helper (i.e. with <tt/app_solicit/ enabled in <tt/sysctl/
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or even with option <tt/-k/) without this option and still did not learn enough
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information, you can observe 1 second gaps in service. Not fatal, but
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not good.
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<item><tt/-k/ - suppress sending broadcast queries by kernel. It takes
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sense together with option <tt/-a/.
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<item><tt/-n TIME/ - timeout of negative cache. When resolution fails <tt/arpd/
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suppresses further attempts to resolve for this period. It makes sense
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only together with option <tt/-k/. This timeout should not be too much
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longer than boot time of a typical host not supporting gratuitous ARP.
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Default value is 60 seconds.
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<item><tt/-R RATE/ - maximal steady rate of broadcasts sent by <tt/arpd/
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in packets per second. Default value is 1.
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<item><tt/-B NUMBER/ - number of broadcasts sent by <tt/arpd/ back to back.
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Default value is 3. Together with option <tt/-R/ this option allows
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to police broadcasting not to exceed <tt/B+R*T/ over any interval
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of time <tt/T/.
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</itemize>
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<p><tt/INTERFACE/ is name of networking inteface to watch.
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If no interfaces given, <tt/arpd/ monitors all the interfaces.
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In this case <tt/arpd/ does not adjust <tt/sysctl/ parameters,
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it is supposed user does this himself after <tt/arpd/ is started.
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<p> Signals
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<p> <tt/arpd/ exits gracefully syncing database and restoring adjusted
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<tt/sysctl/ parameters, when receives <tt/SIGINT/ or <tt/SIGTERM/.
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<tt/SIGHUP/ syncs database to disk. <tt/SIGUSR1/ sends some statistics
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to <tt/syslog/. Effect of another signals is undefined, they may corrupt
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database and leave <tt/sysctl/ parameters in an unpredictable state.
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<p> Note
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<p> In order to <tt/arpd/ be able to serve as ARP resolver, kernel must be
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compiled with the option <tt/CONFIG_ARPD/ and, in the case when interface list
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is not given on command line, variable <tt/app_solicit/
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on interfaces of interest should be set in <tt>/proc/sys/net/ipv4/neigh/*</tt>.
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If this is not made <tt/arpd/ still collects gratuitous ARP information
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in its database.
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<p> Examples
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<enum>
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<item> Start <tt/arpd/ to collect gratuitous ARP, but not messing
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with kernel functionality:
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<tscreen><verb>
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arpd -b /var/tmp/arpd.db
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</verb></tscreen>
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<item> Look at result after some time:
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<tscreen><verb>
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killall arpd
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arpd -l -b /var/tmp/arpd.db
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</verb></tscreen>
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<item> To enable kernel helper, leaving leading role to kernel:
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<tscreen><verb>
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arpd -b /var/tmp/arpd.db -a 1 eth0 eth1
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</verb></tscreen>
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<item> Completely replace kernel resolution on interfaces <tt/eth0/
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and <tt/eth1/. In this case kernel still does unicast probing to
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validate entries, but all the broadcast activity is suppressed
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and made under authority of <tt/arpd/:
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<tscreen><verb>
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arpd -b /var/tmp/arpd.db -a 3 -k eth0 eth1
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</verb></tscreen>
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This is mode which <tt/arpd/ is supposed to work normally.
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It is not default just to prevent occasional enabling of too aggressive
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mode occasionally.
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</enum>
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</article>
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