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arp ? manipulate the system ARP cache |
arp [?vn] [?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] |
Arp 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, ??umeric |
shows numerical addresses instead of trying to determine symbolic host, port or user names. |
?H type, ??hw-type 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. |
?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. |
?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 temp ARP entry this
interface will be associated with the entry; if this option
is not used, the kernel will guess based on the routing
table. For pub entries the specified interface is the
interface on which ARP requests will be answered. |
?s hostname hw_addr, ??set hostname |
Manually create an ARP address mapping entry for host
hostname with hardware address set to hw_addr
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 the publish flag set
a netmask 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 temp
flag is not supplied entries will be permanent stored into
the ARP cache. |
?f filename, ??file filename |
Similar to the ?s option, only this time the address info is taken from file filename set up. The name of the data file is very often /etc/ethers, 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. Each complete entry in the ARP cache will be marked with the C flag. Permanent entries are marked with M and published entries have the P flag. |
/proc/net/arp, |
rarp(8), route(8), ifconfig(8), netstat(8) |
Fred N. van Kempen, <waltje@uwalt.nl.mugnet.org> with a lot of improvements from net-tools Maintainer Bernd Eckenfels <net-tools@lina.inka.de>. |