1ARP(8) Linux Programmer's Manual ARP(8)
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6 arp - manipulate the system ARP cache
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9 arp [-evn] [-H type] [-i if] -a [hostname]
10 arp [-v] [-i if] -d hostname [pub]
12 arp [-v] [-H type] [-i if] -s hostname hw_addr [temp]
14 arp [-v] [-H type] [-i if] -s hostname hw_addr [netmask nm] pub
16 arp [-v] [-H type] [-i if] -Ds hostname ifa [netmask nm] pub
18 arp [-vnD] [-H type] [-i if] -f [filename]
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23 Arp manipulates the kernel's ARP cache in various ways. The primary
24 options are clearing an address mapping entry and manually setting up
25 one. For debugging purposes, the arp program also allows a complete
26 dump of the ARP cache.
27
29 -v, --verbose
30 Tell the user what is going on by being verbose.
31 -n, --numeric
33 shows numerical addresses instead of trying to determine sym‐
34 bolic host, port or user names.
35 -H type, --hw-type type, -t type
37 When setting or reading the ARP cache, this optional parameter
38 tells arp which class of entries it should check for. The
39 default value of this parameter is ether (i.e. hardware code
40 0x01 for IEEE 802.3 10Mbps Ethernet). Other values might
41 include network technologies such as ARCnet (arcnet) , PROnet
42 (pronet) , AX.25 (ax25) and NET/ROM (netrom).
43 -a [hostname], --display [hostname]
45 Shows the entries of the specified hosts. If the hostname
46 parameter is not used, all entries will be displayed. The
47 entries will be displayed in alternate (BSD) style.
48 -d hostname, --delete hostname
50 Remove any entry for the specified host. This can be used if
51 the indicated host is brought down, for example.
52 -D, --use-device
54 Use the interface ifa's hardware address.
55 -e Shows the entries in default (Linux) style.
57 -i If, --device If
59 Select an interface. When dumping the ARP cache only entries
60 matching the specified interface will be printed. When setting a
61 permanent or temp ARP entry this interface will be associated
62 with the entry; if this option is not used, the kernel will
63 guess based on the routing table. For pub entries the specified
64 interface is the interface on which ARP requests will be
65 answered.
66 NOTE: This has to be different from the interface to which the
67 IP datagrams will be routed.
68 -s hostname hw_addr, --set hostname
70 Manually create an ARP address mapping entry for host hostname
71 with hardware address set to hw_addr class, but for most classes
72 one can assume that the usual presentation can be used. For the
73 Ethernet class, this is 6 bytes in hexadecimal, separated by
74 colons. When adding proxy arp entries (that is those with the
75 publish flag set a netmask may be specified to proxy arp for
76 entire subnets. This is not good practice, but is supported by
77 older kernels because it can be useful. If the temp flag is not
78 supplied entries will be permanent stored into the ARP cache.
79 NOTE: As of kernel 2.2.0 it is no longer possible to set an ARP
80 entry for an entire subnet. Linux instead does automagic proxy
81 arp when a route exists and it is forwarding. See arp(7) for
82 details.
83 -f filename, --file filename
85 Similar to the -s option, only this time the address info is
86 taken from file filename set up. The name of the data file is
87 very often /etc/ethers, but this is not official. If no filename
88 is specified /etc/ethers is used as default.
89 The format of the file is simple; it only contains ASCII text
91 lines with a hardware address and a hostname separated by white‐
92 space. Additionally the pub, temp and netmask flags can be used.
93 In all places where a hostname is expected, one can also enter an IP
95 address in dotted-decimal notation.
96 As a special case for compatibility the order of the hostname and the
98 hardware address can be exchanged.
99 Each complete entry in the ARP cache will be marked with the C flag.
101 Permanent entries are marked with M and published entries have the P
102 flag.
103
105 /proc/net/arp,
106 /etc/networks
107 /etc/hosts
108 /etc/ethers
109
111 rarp(8), route(8), ifconfig(8), netstat(8)
112
114 Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org> with a lot of improve‐
115 ments from net-tools Maintainer Bernd Eckenfels <net-
116 tools@lina.inka.de>.
117net-tools 5 Jan 1999 ARP(8)