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The Protocol ARP—A Beginner Must Master (1)

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The Protocol ARP—A Beginner Must Master

When it comes to ARP, you should be familiar with it. It is a common protocol in IPv4 Ethernet networks. Address Resolution Protocol (ARP) is a Protocol used to resolve IP addresses into MAC addresses. ARP can be learned dynamically or configured manually. Why is ARP required?

Assume that there are two devices on the network, PC1 and PC2, and PC1 and PC2 belong to the same broadcast domain.

However, before PC1 communicates with PC2, PC1 needs to know the IP address of PC2. However, the IP address alone cannot realize the communication between PC1 and PC2. IP packets must be encapsulated at the data link layer before they can be transmitted at the physical layer. However, in Ethernet networks, packets cannot be encapsulated at the data link layer without MAC addresses. This requires PC1 to resolve the MAC address of PC2 through its IP address.

So, how does ARP resolve? Generally, there are two ways of static analysis and dynamic analysis:

In dynamic mode, ARP is automatically generated and maintained by ARP packets. It can be aged out, updated by new ARP packets, and overwritten by static ARP entries. Dynamic ARP is applicable to the network with complex topology and high real-time communication requirements.

Static ARP refers to the fixed mapping between IP addresses and MAC addresses manually established by the network administrator. Static ARP entries are not aged and cannot be overwritten by dynamic ARP entries.

Generally, you can use ARP to dynamically learn ARP entries and generate dynamic ARP entries. However, when ARP attacks occur on the network, dynamic ARP entries on the device may be updated to incorrect entries or aged out, resulting in abnormal communication between legitimate users.

In order to guarantee the security of network communication, the static ARP table entries can restrict the end equipment and specify the IP address to end communication equipment use only the specified MAC address, the attack packets can’t modify the device’s IP address and MAC address in the ARP table mapping relation, thus protect the equipment and the normal communication between the terminal equipment.

The Protocol ARP—A Beginner Must Master

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