What is the function of ARP?

Defects in the ARP protocol.

The ARP protocol is based on trusting all nodes in a local area network, and it is efficient, but it is not secure. It is a stateless protocol that does not check whether it has sent a request packet, and does not care (in fact) whether it is a legitimate reply, as long as it receives the target MAC is its ARP

Reply packets or ARP broadcast packets (including ARP

request and arp

reply), will be accepted and cached. This makes it possible for ARP spoofing, where malicious nodes can publish fake ARP packets to affect the communication of nodes in the network, and even act as a "middleman".

The answer is a. The address resolution protocol is an indispensable protocol in IPv4, and when sending IP packets over Ethernet, it is necessary to encapsulate the headers of Layer 3 (32-bit IP address) and Layer 2 (48-bit MAC address) first.

Layer 2 and 3, so you need to use the address resolution protocol.

The address resolution protocol can be used to parse the target hardware address (MAC address) information based on the IP address information in the IP packet header at the network layer to ensure smooth communication.

The main function of the ARP protocol is to resolve IP addresses to physical addresses.

The core idea of the ARP protocol is to establish a mapping table from IP addresses to MAC addresses. When a host sends a packet to another host, it first looks up its own ARP cache, and if it finds the IP address and corresponding MAC address of the destination host, it sends the packet directly and stealthily simulated. This saves the need to find the MAC address, which improves the communication speed.

If the IP address and MAC address of the destination host cannot be found in the ARP cache, the source host broadcasts an ARP request to all hosts on the network to ask for the MAC address of the destination host. When the target host receives an ARP request, it responds with an ARP reply that tells the source host its MAC address. This allows the source host to send packets to the destination host.

Disadvantages of ARP

There is still a possibility that there may be problems with the ARP cache table. When the network is large, it is necessary to hold more ARP cache tables to cope with more ARP requests and responses. However, if someone forges IP and MAC addresses in the network, the ARP protocol will not be able to handle this information properly, leading to communication failures or attacks.

Therefore, it is important to constantly update and monitor the ARP cache table to ensure the accuracy and timeliness of the cached table. The ARP protocol does not require all hosts to maintain an ARP cache or respond to all ARP requests. Typically, the host will only hold a small mapping table of IP addresses and MAC addresses around the network, and this cache table is updated based on the closest host with which the host communicates.

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