ARP on main control board SCUN, SCUH, MPLA is am important element when engineer choose OLT

ARP on main control board SCUN and SCUH on Huawei MA5600T, MPLA on MA5800 is am important element when engineer choose OLT, then what is ARP?

The Address Resolution Protocol (ARP) is an Internet protocol used to map IP addresses to MAC addresses.

Purpose
To communicate with each other, the sending device must know the network-layer IP address of the receiving device. IP datagrams, however, must be encapsulated with MAC addresses before they can be transmitted over the physical network. Therefore, a resolution from the known IP address to a MAC address is required.
ARP was developed to enable communication between devices.

Dynamic ARP: Devices dynamically learn and update the mapping between IP addresses and MAC addresses by exchanging ARP messages. Real-time communication is a priority, or network resources are insufficient.

Static ARP: The mapping between IP addresses and MAC addresses is manually created and cannot be dynamically modified. Communication security is a priority, and network resources are sufficient.

Gratuitous ARP:A device broadcasts gratuitous ARP packets that carry the local IP address as both the source and destination IP addresses to notify the other devices on the same network segment of its address information. Gratuitous ARP is used to check whether the local IP address conflicts with that of another device, to notify other devices on the same network segment of the new MAC address after the local network interface card is replaced, or to notify master/slave switchovers in a Virtual Router Redundancy Protocol (VRRP) backup group.

Benefits
ARP ensures Ethernet communication by mapping IP addresses at the network layer to MAC addresses at the link layer on Ethernet networks.

Principles
ARP involves the following concepts:
Address Resolution Protocol (ARP) messages
An ARP message can be an ARP request or reply message. Figure below shows the ARP message format.

ARP table

An ARP table, for example SCUN on Huawei MA5603T ARP table is 8192, contains the latest mapping between IP addresses and MAC addresses. If a host always broadcasts an ARP Request message for a MAC address before it sends an IP datagram, network communication traffic will greatly increase. Furthermore, all other hosts on the network have to receive and process the ARP Request messages, which lowers network efficiency. To solve this problem, an ARP table is maintained on each host to ensure efficient ARP operations. The mapping between an IP address and a MAC address is called an ARP entry.

ARP entries can be classified as dynamic or static.

− Dynamic ARP entries are automatically generated and maintained by using ARP messages. Dynamic ARP entries can be aged and overwritten by static ARP entries.
− Static ARP entries are manually configured and maintained by a network administrator. Static ARP entries can neither be aged nor be overwritten by dynamic ARP entries.
Before sending IP datagrams, a host searches the ARP table for the MAC address corresponding to the destination IP address.
− If the ARP table contains the corresponding MAC address, the host directly sends the IP datagrams to the MAC address instead of sending an ARP Request message.
− If the ARP table does not contain the corresponding MAC address, the host broadcasts an ARP Request message to request the MAC address of the destination host.
Reverse Address Resolution Protocol (RARP)
If only the MAC address of a host is available, the host can send and receive RARP messages to obtain its IP address.
To do so, the network administrator must establish the mapping between MAC addresses and IP addresses on a gateway. When a new host must be configured, its RARP client requests the host's IP address from the RARP server on the gateway.