Detailed explanation of why DNS uses UDP instead of TCP!

The main reason why DNS (Domain Name System) uses UDP (User Datagram Protocol) instead of TCP (Transmission Control Protocol) is for performance and efficiency considerations. The following explains in detail why DNS chooses to use the UDP protocol:

1. Small requests and fast responses: DNS queries are typically small requests, requiring only a few bytes of data transfer. UDP is a connectionless protocol that does not require establishing a connection before communicating, but instead sends packets to the destination address and waits for a response. This makes UDP more suitable for fast response scenarios than TCP.
2. Low latency: DNS queries usually require low latency to provide fast domain name resolution services. The simplicity and connectionless nature of UDP allows data packets to be transmitted with lower latency because it does not require the process of connection establishment and disconnection, reducing communication overhead.
3. Stateless: The DNS server is stateless when processing queries, that is, each query is independent and does not depend on the previous query status. As a connectionless protocol, UDP is more in line with this stateless feature. Each query and response is an independent data packet and does not need to maintain a connection state.
4. Save bandwidth: UDP has a smaller header overhead than TCP, which means that when transmitting the same data, UDP packet size is smaller and bandwidth resources can be saved. In DNS queries, especially large-scale queries, using UDP can reduce network traffic and improve network efficiency.

Although UDP has advantages in performance and efficiency, there are also some limitations and risks:

1. Reliability: UDP is connectionless, it does not provide reliable transmission and retransmission mechanism of data packets. This means that in the case of network instability or congestion, UDP packets may be lost or out of order, resulting in query failure or high latency.
2. Large responses: For large responses, such as DNS Zone Transfer (AXFR) or DNS Security Extensions (DNSSEC), UDP limitations may cause packets to be truncated or fragmented, requiring additional processing and management.
3. TCP fallback: In some cases, if the response to a DNS query exceeds the maximum length of the UDP packet (approximately 512 bytes), the DNS server can choose to use the TCP protocol for fallback transmission to ensure the integrity of the data. performance and reliability.

DNS chooses to use the UDP protocol mainly for performance and efficiency considerations. Although UDP may have some limitations, in the vast majority of cases, UDP has been proven to provide fast and reliable domain name resolution services. This is because the lightweight nature of the UDP protocol allows it to transmit data more quickly, reduce communication delays, and still maintain high efficiency when processing large numbers of queries. Although the TCP protocol can provide reliability, due to the large overhead of connection establishment and maintenance, it is not suitable for domain names

The above is the detailed content of Detailed explanation of why DNS uses UDP instead of TCP!. For more information, please follow other related articles on the PHP Chinese website!