release/src/router/iproute2/doc/arpd.sgml

   1 <!doctype linuxdoc system>
   2
   3 <article>
   4
   5 <title>ARPD Daemon
   6 <author>Alexey Kuznetsov, <tt/kuznet@ms2.inr.ac.ru/
   7 <date>some_negative_number, 20 Sep 2001
   8 <abstract>
   9 <tt/arpd/ is daemon collecting gratuitous ARP information, saving
  10 it on local disk and feeding it to kernel on demand to avoid
  11 redundant broadcasting due to limited size of kernel ARP cache.
  12 </abstract>
  13
  14
  15 <p><bf/Description/
  16
  17 <p>The format of the command is:
  18
  19 <tscreen><verb>
  20        arpd OPTIONS [ INTERFACE [ INTERFACE ... ] ]
  21 </verb></tscreen>
  22
  23 <p> <tt/OPTIONS/ are:
  24
  25 <itemize>
  26
  27 <item><tt/-l/ - dump <tt/arpd/ database to stdout and exit. Output consists
  28 of three columns: interface index, IP address and MAC address.
  29 Negative entries for dead hosts are also shown, in this case MAC address
  30 is replaced by word <tt/FAILED/ followed by colon and time when the fact
  31 that host is dead was proven the last time.
  32
  33 <item><tt/-f FILE/  - read and load <tt/arpd/ database from <tt/FILE/
  34 in text format similar dumped by option <tt/-l/. Exit after load,
  35 probably listing resulting database, if option <tt/-l/ is also given.
  36 If <tt/FILE/ is <tt/-/, <tt/stdin/ is read to get ARP table.
  37
  38 <item><tt/-b DATABASE/  - location of database file. Default location is
  39 <tt>/var/lib/arpd/arpd.db</tt>.
  40
  41 <item><tt/-a NUMBER/ - <tt/arpd/ not only passively listens ARP on wire, but
  42 also send brodcast queries itself. <tt/NUMBER/ is number of such queries
  43 to make before destination is considered as dead. When <tt/arpd/ is started
  44 as kernel helper (i.e. with <tt/app_solicit/ enabled in <tt/sysctl/
  45 or even with option <tt/-k/) without this option and still did not learn enough
  46 information, you can observe 1 second gaps in service. Not fatal, but
  47 not good.
  48
  49 <item><tt/-k/ - suppress sending broadcast queries by kernel. It takes
  50 sense together with option <tt/-a/.
  51
  52 <item><tt/-n TIME/ - timeout of negative cache. When resolution fails <tt/arpd/
  53 suppresses further attempts to resolve for this period. It makes sense
  54 only together with option <tt/-k/. This timeout should not be too much
  55 longer than boot time of a typical host not supporting gratuitous ARP.
  56 Default value is 60 seconds.
  57
  58 <item><tt/-R RATE/ - maximal steady rate of broadcasts sent by <tt/arpd/
  59 in packets per second. Default value is 1.
  60
  61 <item><tt/-B NUMBER/ - number of broadcasts sent by <tt/arpd/ back to back.
  62 Default value is 3. Together with option <tt/-R/ this option allows
  63 to police broadcasting not to exceed <tt/B+R*T/ over any interval
  64 of time <tt/T/.
  65
  66 </itemize>
  67
  68 <p><tt/INTERFACE/ is name of networking inteface to watch.
  69 If no interfaces given, <tt/arpd/ monitors all the interfaces.
  70 In this case <tt/arpd/ does not adjust <tt/sysctl/ parameters,
  71 it is supposed user does this himself after <tt/arpd/ is started.
  72
  73
  74 <p> Signals
  75
  76 <p> <tt/arpd/ exits gracefully syncing database and restoring adjusted
  77 <tt/sysctl/ parameters, when receives <tt/SIGINT/ or <tt/SIGTERM/.
  78 <tt/SIGHUP/ syncs database to disk. <tt/SIGUSR1/ sends some statistics
  79 to <tt/syslog/. Effect of another signals is undefined, they may corrupt
  80 database and leave <tt/sysctl/ parameters in an unpredictable state.
  81
  82 <p> Note
  83
  84 <p> In order to <tt/arpd/ be able to serve as ARP resolver, kernel must be
  85 compiled with the option <tt/CONFIG_ARPD/ and, in the case when interface list
  86 is not given on command line, variable <tt/app_solicit/
  87 on interfaces of interest should be set in <tt>/proc/sys/net/ipv4/neigh/*</tt>.
  88 If this is not made <tt/arpd/ still collects gratuitous ARP information
  89 in its database.
  90
  91 <p> Examples
  92
  93 <enum>
  94 <item> Start <tt/arpd/ to collect gratuitous ARP, but not messing
  95 with kernel functionality:
  96
  97 <tscreen><verb>
  98    arpd -b /var/tmp/arpd.db
  99 </verb></tscreen>
 100
 101 <item> Look at result after some time:
 102
 103 <tscreen><verb>
 104    killall arpd
 105    arpd -l -b /var/tmp/arpd.db
 106 </verb></tscreen>
 107
 108 <item> To enable kernel helper, leaving leading role to kernel:
 109
 110 <tscreen><verb>
 111    arpd -b /var/tmp/arpd.db -a 1 eth0 eth1
 112 </verb></tscreen>
 113
 114 <item> Completely replace kernel resolution on interfaces <tt/eth0/
 115 and <tt/eth1/. In this case kernel still does unicast probing to
 116 validate entries, but all the broadcast activity is suppressed
 117 and made under authority of <tt/arpd/:
 118
 119 <tscreen><verb>
 120    arpd -b /var/tmp/arpd.db -a 3 -k eth0 eth1
 121 </verb></tscreen>
 122
 123 This is mode which <tt/arpd/ is supposed to work normally.
 124 It is not default just to prevent occasional enabling of too aggressive
 125 mode occasionally.
 126
 127 </enum>
 128
 129 </article>
 130