Address Resolution Protocol(ARP)

Address Resolution Protocol(ARP) - Address Resolution Protocol (ARP) is a low-level network protocol use IP address to find MAC address.

·         The Address Resolution Protocol (ARP) was developed to enable communications on a network.
·         Each and every device who is work on IP need ARP to map IP addresses to MAC addresses so that IP packets can be sent across networks.
·         ARP packet always broadcast on the network.
·         ARP table use to creates a data-link header and trailer that encapsulates the packet,
·         ARP cache use to storing MAC in memory for a period of time as the addresses are learned.
·         There are two types of ARP cache entry
·         1)static ARP cache entries
·         2)dynamic ARP cache entries.
·         Static entries are manually configured entry and kept in the cache table on permanent basis.
·         Dynamic entries are added by Cisco software and its kept for a period of time and then removed.
·         The ARP table is built and changed automatically
·         The default time limit is 4 hours.

              Take a look of ARP Cache Content: -

Protocol: - its define the TCP/IP Internet Layer.

Address: - Its define the Logical IP address that binding on define hardware address.

Age: - Its define MAC storage time in minutes

Hardware Address: - Its define the MAC address binding on Logical ip address.

Type: - In type field ARPA define the Ethernet frame which is currently used by the Internet Protocol.

Configure Static ARP Entry: -

            R1(config)#arp 00ac.a1f3.01ab arpa fastEthernet 0/1

Types of ARP: -

1) ARP                 : - It's mapping of Layer 3 address to a Layer 2 address.

2) Reverse ARP    : - it is mapping of Layer 2 address to a Layer 3 address.

3) Proxy ARP       : - Proxy ARP use to respond the ARP requests with wrong MAC Address for a destination which is not in same network.

4) Gratuitous ARP: - Gratuitous ARP use for Duplicate address detection.

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