|Linux / Unix Command: arp|
NAMEarp - manipulate the system ARP cache
SYNOPSISarp [-evn] [-H type] [-i if] -a [hostname]
arp [-v] [-i if] -d hostname [pub]
arp [-v] [-H type] [-i if] -s hostname hw_addr [temp]
arp [-v] [-H type] [-i if] -s hostname hw_addr [netmask nm] pub
arp [-v] [-H type] [-i if] -Ds hostname ifa [netmask nm] pub
arp [-vnD] [-H type] [-i if] -f [filename]
DESCRIPTIONArp manipulates the kernel's ARP cache in various ways. The primary options are clearing an address mapping entry and manually setting up one. For debugging purposes, the arp program also allows a complete dump of the ARP cache.
- -v, --verbose
- Tell the user what is going on by being verbose.
- -n, --numeric
- shows numerical addresses instead of trying to determine symbolic host, port or user names.
- -H type, --hw-type type, -t type
- When setting or reading the ARP cache, this optional parameter tells arp which class of entries it should check for. The default value of this parameter is ether (i.e. hardware code 0x01 for IEEE 802.3 10Mbps Ethernet). Other values might include network technologies such as ARCnet (arcnet) , PROnet (pronet) , AX.25 (ax25) and NET/ROM (netrom).
- -a [hostname], --display [hostname]
- Shows the entries of the specified hosts. If the hostname parameter is not used, all entries will be displayed. The entries will be displayed in alternate (BSD) style.
- -d hostname, --delete hostname
- Remove any entry for the specified host. This can be used if the indicated host is brought down, for example.
- -D, --use-device
- Use the interface ifa's hardware address.
- Shows the entries in default (Linux) style.
- -i If, --device If
Select an interface. When dumping the ARP cache only entries matching
the specified interface will be printed. When setting a permanent or
ARP entry this interface will be associated with the entry; if this
option is not used, the kernel will guess based on the routing
entries the specified interface is the interface on which ARP requests will
NOTE: This has to be different from the interface to which the IP datagrams will be routed.
- -s hostname hw_addr, --set hostname
Manually create an ARP address mapping entry for host
with hardware address set to
class, but for most classes one can assume that the usual presentation
can be used. For the Ethernet class, this is 6 bytes in hexadecimal,
separated by colons. When adding proxy arp entries (that is those with
flag set a
may be specified to proxy arp for entire subnets. This is not good
practice, but is supported by older kernels because it can be
useful. If the
flag is not supplied entries will be permanent stored into the ARP
NOTE: As of kernel 2.2.0 it is no longer possible to set an ARP entry for an entire subnet. Linux instead does automagic proxy arp when a route exists and it is forwarding. See arp(7) for details.
- -f filename, --file filename
Similar to the
option, only this time the address info is taken from file
set up. The name of the data file is very often
but this is not official. If no filename is specified /etc/ethers
is used as default.
The format of the file is simple; it only contains ASCII text lines with a hostname, and a hardware address separated by whitespace. Additionally the pub, temp and netmask flags can be used.
In all places where a hostname is expected, one can also enter an IP address in dotted-decimal notation. As a special case for compatibility the order of the hostname and the hardware address can be exchanged.
SEE ALSOrarp(8), route(8), ifconfig(8), netstat(8)
Important: Use the man command (% man) to see how a command is used on your particular computer.