1ARP(8)                Linux System Administrator's Manual               ARP(8)
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NAME

6       arp - manipulate the system ARP cache
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SYNOPSIS

9       arp [-vn] [-H type] [-i if] [-ae] [hostname]
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11       arp [-v] [-i if] -d hostname [pub]
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13       arp [-v] [-H type] [-i if] -s hostname hw_addr [temp]
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15       arp [-v] [-H type] [-i if] -s hostname hw_addr [netmask nm] pub
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17       arp [-v] [-H type] [-i if] -Ds hostname ifname [netmask nm] pub
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19       arp [-vnD] [-H type] [-i if] -f [filename]
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21

NOTE

23       This program is obsolete. For replacement check ip neigh.
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25

DESCRIPTION

27       Arp  manipulates or displays the kernel's IPv4 network neighbour cache.
28       It can add entries to the table, delete one or display the current con‐
29       tent.
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31       ARP  stands  for Address Resolution Protocol, which is used to find the
32       media access control address of a network neighbour for  a  given  IPv4
33       Address.
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MODES

36       arp with no mode specifier will print the current content of the table.
37       It is possible to limit the number of entries printed, by specifying an
38       hardware address type, interface name or host address.
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40       arp  -d  address will delete a ARP table entry. Root or netadmin privi‐
41       lege is required to do this. The entry is found by  IP  address.  If  a
42       hostname  is  given, it will be resolved before looking up the entry in
43       the ARP table.
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45       arp -s address hw_addr is used to set up a new table entry. The  format
46       of  the  hw_addr  parameter is dependent on the hardware class, but for
47       most classes one can assume that the usual presentation  can  be  used.
48       For  the  Ethernet  class, this is 6 bytes in hexadecimal, separated by
49       colons. When adding proxy arp entries (that is those with  the  publish
50       flag  set)  a netmask may be specified to proxy arp for entire subnets.
51       This is not good practice, but is supported by older kernels because it
52       can  be useful. If the temp flag is not supplied entries will be perma‐
53       nent stored into the ARP cache. To simplify setting up entries for  one
54       of  your own network interfaces, you can use the arp -Ds address ifname
55       form. In that case the hardware address is  taken  from  the  interface
56       with the specified name.
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OPTIONS

60       -v, --verbose
61              Tell the user what is going on by being verbose.
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63       -n, --numeric
64              shows  numerical  addresses  instead of trying to determine sym‐
65              bolic host, port or user names.
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67       -H type, --hw-type type, -t type
68              When setting or reading the ARP cache, this  optional  parameter
69              tells  arp  which  class  of  entries  it should check for.  The
70              default value of this parameter is  ether  (i.e.  hardware  code
71              0x01  for  IEEE  802.3  10Mbps  Ethernet).   Other  values might
72              include network technologies such as ARCnet  (arcnet)  ,  PROnet
73              (pronet) , AX.25 (ax25) and NET/ROM (netrom).
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75       -a     Use alternate BSD style output format (with no fixed columns).
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77       -e     Use default Linux style output format (with fixed columns).
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79       -D, --use-device
80              Instead  of  a  hw_addr,  the  given  argument is the name of an
81              interface.  arp will use the MAC address of that  interface  for
82              the  table  entry.  This  is usually the best option to set up a
83              proxy ARP entry to yourself.
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85       -i If, --device If
86              Select an interface. When dumping the  ARP  cache  only  entries
87              matching the specified interface will be printed. When setting a
88              permanent or temp ARP entry this interface  will  be  associated
89              with  the  entry;  if  this  option is not used, the kernel will
90              guess based on the routing table. For pub entries the  specified
91              interface  is  the  interface  on  which  ARP  requests  will be
92              answered.
93              NOTE: This has to be different from the interface to  which  the
94              IP  datagrams will be routed.  NOTE: As of kernel 2.2.0 it is no
95              longer possible to set an ARP entry for an entire subnet.  Linux
96              instead  does  automagic proxy arp when a route exists and it is
97              forwarding. See arp(7) for  details.  Also  the  dontpub  option
98              which  is available for delete and set operations cannot be used
99              with 2.4 and newer kernels.
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101       -f filename, --file filename
102              Similar to the -s option, only this time  the  address  info  is
103              taken from file filename.  This can be used if ARP entries for a
104              lot of hosts have to be set up.  The name of the  data  file  is
105              very often /etc/ethers, but this is not official. If no filename
106              is specified /etc/ethers is used as default.
107
108              The format of the file is simple; it only  contains  ASCII  text
109              lines  with  a  hostname,  and  a  hardware address separated by
110              whitespace. Additionally the pub, temp and netmask flags can  be
111              used.
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113       In  all  places  where a hostname is expected, one can also enter an IP
114       address in dotted-decimal notation.
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116       As a special case for compatibility the order of the hostname  and  the
117       hardware address can be exchanged.
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119       Each  complete  entry  in the ARP cache will be marked with the C flag.
120       Permanent entries are marked with M and published entries  have  the  P
121       flag.
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EXAMPLES

124       /usr/sbin/arp -i eth0 -Ds 10.0.0.2 eth1 pub
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126       This will answer ARP requests for 10.0.0.2 on eth0 with the MAC address
127       for eth1.
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129       /usr/sbin/arp -i eth1 -d 10.0.0.1
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131       Delete the ARP table entry for 10.0.0.1 on interface  eth1.  This  will
132       match published proxy ARP entries and permanent entries.
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FILES

135       /proc/net/arp
136       /etc/networks
137       /etc/hosts
138       /etc/ethers
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SEE ALSO

141       ip(8)
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AUTHORS

144       Fred   N.  van  Kempen  <waltje@uwalt.nl.mugnet.org>,  Bernd  Eckenfels
145       <net-tools@lina.inka.de>.
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149net-tools                         2008-10-03                            ARP(8)
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