Address Resolution Protocol (ARP)

Address Resolution Protocol is a network layer protocol used to convert an IP address into a physical address, such as an Ethernet address. A host wishing to obtain a physical address broadcasts an ARP request onto the TCP/IP network. The host on the network that has the IP address in the request then replies with its physical hardware address.

Basics

When you try to ping an IP address on your local network, say 192.168.1.1, your system has to turn the IP address 192.168.1.1 into a MAC address. This involves using ARP to resolve the address.

ARP Table

Comand in Linux and MacOS :  arp -an 

Example:

# arp -an | grep 10
? (10.241.1.114) at 00:25:90:3e:dc:fc [ether] on vlan241
? (10.252.1.8) at 00:c0:b7:76:ac:19 [ether] on vlan244
? (10.252.1.9) at 00:c0:b7:76:ae:56 [ether] on vlan244
? (10.241.1.111) at 00:30:48:f2:23:fd [ether] on vlan241
? (10.252.1.6) at 00:c0:b7:74:fb:9a [ether] on vlan244
? (10.241.1.121) at 00:25:90:2c:d4:f7 [ether] on vlan241
[...]

See also

• Address Resolution Protocol (ARP): arp (command), arping, arp spoofing, MAC, CAM, show ip arp, ARP table, Proxy ARP, Address
• Ethernet: MII, MDI, bonding, etherchannel, STP, ARP, MAC, STP, Jumbo frames, 802.1X, MTU, Ethernet In-Band Access (IBA), LACP, Multicast, Broadcast, SPI