What are the DNS port numbers? Summary of common port types and uses

in the network communication system, DNS is the core service of domain name and Internet Protocol Address conversion, and its operation relies on specific port numbers to realize data transmission. Many users will come into contact with DNS port numbers when configuring the network and troubleshooting domain name resolution failures, but their specific types and applicable scenarios are limited. This paper will systematically sort out the common DNS port numbers, interpret the function positioning of different ports, and apply logic in the actual network environment, providing a practical reference for network operation and maintenance personnel and ordinary users.

What are the basic DNS port numbers?

DNS services relies on standardized port numbers, among which the basic port is the core of the conventional parsing service, and it is also the type that users have the most contact with.

1, UDP 53 port

UDP 53 is the default port of DNS service, and it is also the most commonly used DNS port number. Since DNS resolution requests usually have small data volume and high transmission speed requirements, the connectionless characteristics of UDP protocol are just suitable for this demand, which can quickly complete the conversion of domain names to Internet Protocol Addresses, and are widely used in daily scenarios such as web page access and APP networking for ordinary users. Most public DNS servers will open UDP 53 port to receive resolution requests from clients.

2, TCP 53 port

TCP 53 is also the core DNS port number, mainly used for DNS interaction scenarios with large data volumes. When the client side needs to obtain complete domain name resolution records, such as zone transmission containing large quantum domain names, or when the response data of the resolution request exceeds the packet limit of the UDP protocol, it will switch to the TCP 53 port for transmission. The reliable transmission characteristics of the TCP protocol can ensure the complete transmission of large-scale resolution data, which is mostly used for synchronization operations between DNS servers.

Second, the DNS port number in special scenarios?

in addition to the basic port 53, under some special network requirements, other types of DNS port numbers will be used to meet individual needs such as security and privacy.

1, DNS over TLS port 853

853 port is a DNS port number dedicated to DNS over TLS services, which is mainly used to encrypt DNS resolution requests. Traditional DNS resolution transmits data in clear text, which has the risk of being eavesdropped and tampered with, while DNS over TLS encrypts the parsed data through the TLS protocol. All interactions are completed on port 853, which can effectively ensure the security of the parsing process. It is suitable for scenarios with high network privacy requirements, such as internal data transmission in enterprises, access to sensitive information, etc.

2, DNS over HTTPS port 443

DNS over HTTPS services usually reuse HTTPS port 443, which is also an encrypted DNS port number. It encapsulates DNS resolution requests in the HTTPS protocol for transmission, which not only avoids the theft of resolution data, but also bypasses DNS interception in some network environments to achieve more stable domain name resolution. At present, mainstream browsers and some network tools support encrypted DNS resolution through port 443, taking into account security and compatibility.

What is the DNS port number selection strategy?

different DNS port numbers adapt to different network scenarios, reasonable selection of port numbers can improve resolution efficiency and security, and avoid resolution failures.

1 Select the port according to the analysis requirements

If it is an ordinary user's daily Internet access, the default DNS port number of UDP 53 is preferred, which can not only meet the needs of fast resolution, but also adapt to most network environments. If it involves area synchronization and large-volume resolution record transmission between DNS servers, TCP 53 port should be used to ensure the integrity of data transmission.

2, according to the security requirements of the port

when there is a risk of privacy leakage in the network environment, or when you need to access sensitive information, it is recommended to use an encrypted DNS port number such as port 853 or port 443. Through encrypted transmission, it can effectively prevent attacks such as DNS hijacking and data eavesdropping, and ensure the security of the parsing process. However, this type of port requires both the client side and the server to support the corresponding encryption protocol, and the configuration is relatively complicated.

What are the key points of DNS port number troubleshooting?

when using DNS services, port number related failures are common causes of domain name resolution failures, and mastering troubleshooting points can quickly locate and solve problems.

1, check whether the port is occupied

if the DNS service cannot start normally, first check whether the corresponding DNS port number is occupied by other programs. You can check the occupancy of the port through network tools, such as the netstat command under the Windows system and the ss command under the Linux system to confirm whether the DNS port numbers such as 53 and 853 are occupied by other services or programs. If there is an occupancy, you can close the occupant program or replace the DNS port number.

2, check whether the firewall blocks the port

firewall rules may also cause DNS port numbers to fail to communicate normally. You need to check whether the local firewall and network firewall have opened the corresponding DNS port numbers, such as UDP 53, TCP 53, 853, etc. If the port is intercepted by the firewall, you need to add permission rules to ensure that DNS request and response data can be transmitted through the port normally.

To sum up, DNS port number is the core element to ensure the normal operation of domain name resolution service. Different types of DNS port numbers correspond to different functional scenarios and requirements. From basic UDP 53, TCP 53, to encrypted 853, 443 ports, each port has its own clear positioning. In practical applications, users need to reasonably choose DNS port number according to resolution needs and security requirements, and master troubleshooting methods to ensure the stability and security of domain name resolution services.