arp

 

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 ARP(8)              Linux Programmer's Manual              ARP(8)
 
 
 
NAME
        arp - manipulate the system ARP cache
 
SYNOPSIS
        arp [-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]
 
 
DESCRIPTION
        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.
 
OPTIONS
        -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 (arc­
               net) , 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 alter­
               nate (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.
 
        -e     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  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.
               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  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  ker­
               nels  because it can be useful. If the temp flag is
               not supplied entries will be permanent stored  into
               the ARP cache.
               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  -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  file­
               name 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 host­
        name 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 pub­
        lished entries have the P flag.
 
FILES
        /proc/net/arp,
        /etc/networks
        /etc/hosts
        /etc/ethers
 
SEE ALSO
        rarp(8), route(8), ifconfig(8), netstat(8)
 
AUTHORS
        Fred N. van Kempen,  <waltje@uwalt.nl.mugnet.org>  with  a
        lot of improvements from net-tools Maintainer Bernd Ecken­
        fels <net-tools@lina.inka.de>.
 
 
 
 net-tools                   5 Jan 1999                     ARP(8)

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