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Publisher| arp |
addresses into media access control (MAC)
addresses and caches them for reuse.
Syntax
arp -s IPaddress MACaddress [interfacenumber]
arp -d IPaddress [interfacenumber]
arp -a [IPaddress] [-N interfacenumber]
Options
- -a [IPaddress]
Resolves the specified IP address into its associated MAC address by
querying the Address Resolution Protocol (ARP)
cache on the local
machine. (If no address is specified, all cached IP-to-MAC address
mappings are displayed.)- -g [IPaddress]
Same as -a.- -N interfacenumber
Specifies the network adapter whose ARP cache is to be queried. (Each
network adapter has its own ARP cache on a multihomed machine.) Use
arp -a to determine the number
of each interface. If arp is used without
-N on a multihomed machine, the first interface
found is used.- -d IPaddress [interfacenumber]
Removes the IP-to-MAC address mapping from the local ARP cache for
the specified IP address and interface. If no
IPaddress is specified, the top entry in
the ARP cache is removed.- -s IPaddress MACaddress [interfacenumber]
Adds a static IP-to-MAC address mapping to the local ARP cache for
the specified interface. The MAC address must be expressed in
hexidecimal form as 12 characters, in groups of 2, separated by
dashes. Static ARP mappings are persistent until the system reboots.
Examples
View the ARP cache on the local machine:
arp -a
Interface: 172.16.11.104 on Interface 0x2
Internet Address Physical Address Type
172.16.11.100 00-40-95-d1-29-6c dynamic
Ping the host named Leonardo to determine its IP
address, and add a mapping for it to the local ARP cache:
ping -n 1 leonardo
Pinging leonardo [172.16.11.39] with 32 bytes of data:
Reply from 172.16.11.39: bytes=32 time<10ms TTL=32
Ping statistics for 172.16.11.39:
Packets: Sent = 1, Received = 1, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 0ms, Maximum = 0ms, Average = 0ms
Verify that an IP-to-MAC address mapping for
Leonardo (172.16.11.39) has been added to the
local ARP cache:
arp -a
Interface: 172.16.11.104 on Interface 0x2
Internet Address Physical Address Type
172.16.11.39 00-40-95-d1-32-90 dynamic
172.16.11.100 00-40-95-d1-29-6c dynamic
Add a static mapping for Leonardo to the local
ARP cache:
arp -s 172.16.11.39 00-40-95-d1-32-90
Verify the static mapping:
arp -a
Interface: 172.16.11.104 on Interface 0x2
Internet Address Physical Address Type
172.16.11.39 00-40-95-d1-32-90 static
172.16.11.100 00-40-95-d1-29-6c dynamic
Notes
- For one host to communicate with another on a TCP/IP network, the
first host uses arp to resolve the second
host's IP address into its corresponding MAC
address. This MAC address then provides a destination address for
Ethernet or token ring frames sent from the first host to the second.
arp caches these IP-to-MAC address mappings for a
short time (from 2 to 10 minutes) to reduce the number of ARP
broadcasts needed. - arp is a useful tool for troubleshooting TCP/IP
networks because it can be used to find the MAC address of any host
on the local subnet, provided that the IP address for the host is
known. - arp can be used to view the ARP cache only on the
local machine, not on remote ones. - To reduce broadcast traffic and speed up TCP/IP communications, you
can add static mappings to the ARP cache on client machines. This
lets clients resolve IP addresses of commonly used servers on the
network from the clients' local ARP caches instead
of using ARP broadcasts. - To make static ARP cache mappings persistent across reboots, add
arp commands to a batch file and run the file at
system startup. - Gratuitous ARP (or "courtesy ARP")
is a TCP/IP mechanism used by hosts to announce their IP address,
which avoids duplicate IP addresses on the network. You can disable
gratuitous ARP by editing the registry and specifying 1 for the
following value:HKLM\System\CurrentControlSet\Services\TcpIp\Parameters\ArpRetryCount
See Also
ipconfig, pathping,
ping, TCP/IP ,
tracert
