Section: Linux Programmer's Manual (8)
Updated: 5 Jan 1999Index
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arp - manipulate the system ARP cache
-s hostname hw_addr
-s hostname hw_addr
-Ds hostname ifa
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
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
When setting or reading the ARP cache, this optional parameter tells
which class of entries it should check for. The default value of
this parameter is
(i.e. hardware code 0x01 for IEEE 802.3 10Mbps Ethernet).
Other values might include network technologies such as
- -a [hostname], --display [hostname]
Shows the entries of the specified hosts. If the
parameter is not used,
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
- -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
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
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
- -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
is expected, one can also enter an
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
flag. Permanent entries are marked with
and published entries have the
Fred N. van Kempen, <firstname.lastname@example.org
> with a lot of improvements
from net-tools Maintainer Bernd Eckenfels <email@example.com
- SEE ALSO