ARP header

ARP header

The layer at which ARP operates is at the same network layer as IP. Defined in RFC826.

　Here is the ARP header for Ethernet. This structure uses packets of this structure not only for ARP, but also for the RARP protocol, which will be introduced later.

●Hardware type (0x0001)
A 16-bit number that indicates the type of network media. Ethernet is set to “0x0001”.

●Protocol (0x0800)
　Indicates the type of upper protocol handled by the ARP protocol. The TCP/IP protocol is set to “0x0800”.

●HLEN (0x06)
　HLEN (hardware address length) indicates the length of the MAC address.Since the MAC address is 6 bytes, this value is “6”.

●PLEN (0x04)
　PLEN (protocol address length) indicates the length of the IP address. An IPv4 address is 4 bytes, so the value of this field is ‘4’.

●Operation code (ARP/RARP)
A code to indicate the type of ARP operation is entered.

●Source
MAC address Enter the MAC address of the source. Store your own MAC address in this field.

●Source
IP address Enter the IP address of the source. Store your own IP address in this field.
* Since it is unknown at the time of RARP request transmission, it remains “0”.

● Destination (target) MAC address
The MAC address of the destination is stored.
* When sending an ARP request, it remains “0” because it is unknown.
* Enter the MAC address (your own MAC address) that you want to resolve with RARP.

● Destination (target) IP address
The IP address of the destination is stored.
* Since it is unknown at the time of RARP request transmission, it remains “0”.