What is reverse domain name resolution? Detailed explanation of the principle and function of reverse domain name resolution

in the Internet communication system, domain name resolution is the core link connecting users and servers, while reverse domain name resolution, as the reverse operation of forward resolution, plays an irreplaceable role in cyber security, mail services and other fields. Many users are familiar with forward domain name resolution, but their cognition of reverse domain name resolution is relatively vague. This article will deeply dissect the definition, principle, function and configuration method of reverse domain name resolution, and take you to fully understand this key technology that supports the reliable operation of the network. Provide practical reference for your network operation and maintenance or application deployment.

What is the reverse domain name resolution?

to understand the reverse domain name resolution, we first need to clarify the difference between it and the forward domain name resolution, and essentially grasp the core positioning of this technology.

1, the basic definition of reverse domain name resolution

forward domain name resolution is to convert the domain name into the corresponding Internet Protocol Address, which is convenient for users to access the server through the easy-to-remember domain name, while reverse domain name resolution is the reverse operation, which maps the Internet Protocol Address to the corresponding domain name. Simply put, forward resolution solves the problem of "which IP corresponds to the domain name", and reverse domain name resolution solves the problem of "which domain name does this IP belong to". Together, the two build a two-way mapping relationship between the domain name and the IP.

2, reverse domain name resolution application scenarios

different from forward domain name resolution for ordinary users, reverse domain name resolution serves more professional scenarios such as network background verification and mail system security. Ordinary users rarely directly contact reverse domain name resolution when visiting websites, but in scenarios such as enterprise mail server deployment and network device authentication, reverse domain name resolution is a necessary configuration to ensure service compliance and security.

The implementation principle of reverse domain name resolution

the operation of reverse domain name resolution depends on the specific network protocol and server architecture, understanding its principle can help us more clearly understand its operation logic.

1, the dependency system of reverse domain name resolution

reverse domain name resolution mainly relies on the reverse lookup area in the DNS system, also known as the PTR record area. Unlike the A record or AAAA record used for forward resolution, reverse domain name resolution stores the mapping relationship between the Internet Protocol Address and the domain name through the PTR record. When reverse resolution is required, the DNS server will query the reverse lookup area of the corresponding IP segment, find the matching PTR record and return the corresponding domain name information.

2, reverse domain name resolution execution process

reverse domain name resolution execution process is roughly divided into three steps: first, the device that initiates the resolution request submits the target Internet Protocol Address to the DNS server; then the DNS server converts the Internet Protocol Address into a reverse domain name format, such as converting the Internet Protocol Address 192.168.1.1 into 1.1.168.192 in-addr.arpa, and then querying the PTR record corresponding to the reverse domain name; finally, the DNS server returns the queried domain name information to the requesting device to complete the reverse domain name resolution operation.

Third, the core role of reverse domain name resolution

reverse domain name resolution is not an optional technical configuration, it assumes the key responsibility of ensuring cyber security and service reliability in multiple core scenarios.

1, to ensure the delivery of mail services security

this is the most extensive application scenario of reverse domain name resolution, the current mainstream mail servers will configure reverse domain name resolution verification mechanism. When a server sends mail to other mail servers, the recipient will perform reverse domain name resolution on the sender's Internet Protocol Address. If the resolution result is consistent with the domain name declared by the sender and there is a corresponding forward resolution record, the email will be received normally; if the reverse domain name resolution cannot be completed or the resolution result does not match, the email will be judged as email spam directly rejected, effectively intercepting malicious emails with forged domain names.

2, strengthen network access authentication

in some network scenarios with high security requirements, such as internal server access and network interaction of Financial Institution Group, reverse domain name resolution can be used to verify the true identity of the accessing device. Administrators can configure reverse domain name resolution to restrict only devices with a specific Internet Protocol Address corresponding to a legal domain name to access the core server, so as to prevent illegal devices from initiating unauthorized access through forged Internet Protocol Addresses and improve the security of network access.

3, auxiliary network operation and maintenance troubleshooting

in the process of network operation and maintenance, administrators often encounter situations where they only know the Internet Protocol Address but do not know the corresponding server or domain name. At this time, reverse domain name resolution can play a role. By performing reverse domain name resolution on the target Internet Protocol Address, administrators can quickly locate the service domain name and deployment subject corresponding to the IP, providing key information for network troubleshooting, traffic traceability and other work, and improving operation and maintenance efficiency.

Fourth, the basic configuration method of reverse domain name resolution

understand the configuration logic of reverse domain name resolution, which can help users in need to quickly complete the basic configuration and realize the corresponding functional requirements.

1 Confirm the administrative authority of the Internet Protocol Address

to configure reverse domain name resolution, you first need to confirm the ownership of the administrative authority of the target Internet Protocol Address. If you use the Internet Protocol Address provided by Cloud as a Service provider, you need to apply for reverse domain name resolution configuration permission in the console of Cloud as a Service provider; if it is a public Internet Protocol Address with its own server, you need to contact the corresponding operator to obtain the configuration permission of reverse resolution. Only by obtaining the corresponding permission can you add or modify PTR records.

2, add and verify PTR records

obtain permission, enter the corresponding DNS management interface and add the PTR record of reverse domain name resolution. The record content needs to fill in the target Internet Protocol Address and the corresponding domain name. After completing the addition, it usually takes 12-24 hours to synchronize the DNS records globally. After the synchronization is completed, you can use command-line tools such as nslookup or dig to verify. If the corresponding domain name can be returned after entering the target Internet Protocol Address, it means that the reverse domain name resolution is successfully configured.

sum up, reverse domain name resolution, as a reverse complementary technology to forward domain name resolution, plays a central role in email security, network verification, operation and maintenance investigation and other scenarios. It realizes the reverse mapping of IP and domain names through PTR records, and the execution process is clear and the configuration method is clear. Mastering the relevant knowledge of reverse domain name resolution can not only help us understand the underlying logic of network communication, but also improve the security and reliability of the network in actual network operation and maintenance and service deployment.