1 .TH ARP 8 "2008\-10\-03" "net\-tools" "Linux System Administrator's Manual"
3 arp \- manipulate the system ARP cache
68 manipulates or displays the kernel's IPv4 network neighbour cache. It can add
69 entries to the table, delete one or display the current content.
72 stands for Address Resolution Protocol, which is used to find the media
73 access control address of a network neighbour for a given IPv4 Address.
76 with no mode specifier will print the current content of the table. It is
77 possible to limit the number of entries printed, by specifying an hardware
78 address type, interface name or host address.
82 will delete a ARP table entry. Root or netadmin privilege is required to do
83 this. The entry is found by IP address. If a hostname is given, it will be
84 resolved before looking up the entry in the ARP table.
88 is used to set up a new table entry. The format of the
90 parameter is dependent on the hardware class, but for most classes one can
91 assume that the usual presentation can be used. For the Ethernet class,
92 this is 6 bytes in hexadecimal, separated by colons. When adding proxy arp
93 entries (that is those with the
97 may be specified to proxy arp for entire subnets. This is not good
98 practice, but is supported by older kernels because it can be
101 flag is not supplied entries will be permanent stored into the ARP
102 cache. To simplify setting up entries for one of your own network interfaces, you can use the
105 form. In that case the hardware address is taken from the interface with the
111 .B "\-v, \-\-verbose"
112 Tell the user what is going on by being verbose.
114 .B "\-n, \-\-numeric"
115 shows numerical addresses instead of trying to determine symbolic host, port
118 .B "\-H type, \-\-hw\-type type, \-t type"
119 When setting or reading the ARP cache, this optional parameter tells
121 which class of entries it should check for. The default value of
124 (i.e. hardware code 0x01 for IEEE 802.3 10Mbps Ethernet).
125 Other values might include network technologies such as
126 .RB "ARCnet (" arcnet ")"
128 .RB "PROnet (" pronet ")"
130 .RB "AX.25 (" ax25 ")"
132 .RB "NET/ROM (" netrom ")."
135 Use alternate BSD style output format (with no fixed columns).
138 Use default Linux style output format (with fixed columns).
140 .B "\-D, \-\-use-device"
141 Instead of a hw_addr, the given argument is the name of an interface.
143 will use the MAC address of that interface for the table entry. This is usually the best option to set up a proxy ARP entry to yourself.
145 .B "\-i If, \-\-device If"
146 Select an interface. When dumping the ARP cache only entries matching
147 the specified interface will be printed. When setting a permanent or
149 ARP entry this interface will be associated with the entry; if this
150 option is not used, the kernel will guess based on the routing
153 entries the specified interface is the interface on which ARP requests will
157 This has to be different from the interface to which the IP
158 datagrams will be routed.
160 As of kernel 2.2.0 it is no longer possible to set an ARP entry for an
161 entire subnet. Linux instead does automagic proxy arp when a route
162 exists and it is forwarding. See
164 for details. Also the
166 option which is available for delete and set operations cannot be
167 used with 2.4 and newer kernels.
169 .B "\-f filename, \-\-file filename"
172 option, only this time the address info is taken from file
174 . This can be used if ARP entries for a lot of hosts have to be
175 set up. The name of the data file is very often
177 but this is not official. If no filename is specified /etc/ethers
180 The format of the file is simple; it
181 only contains ASCII text lines with a hostname, and a hardware
182 address separated by whitespace. Additionally the
183 .BR "pub" , " temp" " and" " netmask"
186 In all places where a
188 is expected, one can also enter an
190 in dotted-decimal notation.
192 As a special case for compatibility the order of the hostname and
193 the hardware address can be exchanged.
195 Each complete entry in the ARP cache will be marked with the
197 flag. Permanent entries are marked with
199 and published entries have the
203 .B /usr/sbin/arp -i eth0 -Ds 10.0.0.2 eth1 pub
205 This will answer ARP requests for 10.0.0.2 on eth0 with the MAC address for
208 .B /usr/sbin/arp -i eth1 -d 10.0.0.1
210 Delete the ARP table entry for 10.0.0.1 on interface eth1. This will match
211 published proxy ARP entries and permanent entries.
221 rarp(8), route(8), ifconfig(8), netstat(8)
223 Fred N. van Kempen <waltje@uwalt.nl.mugnet.org>, Bernd Eckenfels <net\-tools@lina.inka.de>.