What should I do about the DNS reverse resolution failure? Common problems and solutions

in the network service structure, DNS reverse resolution is the key technology to map Internet Protocol Address to the corresponding domain name, which is widely used in mail server verification, cyber security audit and other scenarios. Once the DNS reverse resolution fails, it will not only lead to mail delivery failure, abnormal service access, but also may cause security risks. This paper will combine the actual operation and maintenance scenarios to sort out the common causes, troubleshooting ideas and landing solutions of DNS reverse resolution failures to help readers quickly locate and solve problems and ensure the normal operation of network services.

What are the common causes of DNS reverse resolution failure?

want to quickly solve the DNS reverse resolution failure, it is necessary to identify the core cause of the problem, which is the first step of troubleshooting.

1, reverse parsing record configuration error

this is the most common cause of DNS reverse resolution failures, including incorrect record type selection, mismatch between Internet Protocol Address and domain name mapping, and lack of PTR records. For example, misconfiguring A records as PTR records, or Internet Protocol Address segments and reverse resolution regions do not correspond, will cause DNS servers to fail to properly complete IP to domain name mapping.

2, DNS server running abnormally

DNS the running state of the server itself will also affect the reverse resolution function. For example, the server process crashes, the memory occupation is too high, and the network port is occupied, which will cause the DNS server to fail to respond to the reverse resolution request. In addition, the firewall rules of the server limit the UDP or TCP traffic of port 53, which will also block the normal interaction of reverse resolution.

3, network link and permission issues

network link interruption, routing configuration errors will lead to DNS reverse resolution request can not reach the target server; and the domain name service provider or IP provider does not open reverse resolution permissions, will also make it impossible for users to configure or modify PTR records, and then cause failure.

How to quickly troubleshoot DNS reverse resolution failure?

master the scientific troubleshooting method, which can greatly shorten the positioning time of DNS reverse resolution fault and avoid the expansion of the problem caused by blind operation.

1. Initial verification

can directly test DNS reverse resolution results through command-line tools such as nslookup and dig. For example, enter "dig -x target Internet Protocol Address" at the end point. If the PTR record is missing or "NXDOMAIN" is displayed in the return result, it indicates that there is a problem with the reverse resolution configuration. At the same time, you can also verify the correspondence between the domain name and the IP through the ping command to assist in judging the fault range.

2, check DNS server and record configuration

log in to the DNS server management background to check the configuration status of the reverse resolution area, confirm whether the Internet Protocol Address and domain name recorded by PTR are accurate, and whether the record type is PTR. At the same time, check the running log of the server to see if there are process crashes, port occupancy or permission error messages, and locate server-level problems.

3, check the network and permission restrictions

use the traceroute command to test the connectivity of the network link to confirm whether the reverse resolution request can reach the target DNS server; contact the IP provider or domain name service provider to verify whether the reverse resolution permission has been opened, and whether there is a mismatch between the Internet Protocol Address attribution and the domain name service provider.

Third, DNS reverse resolution fault targeted solutions

take corresponding solutions according to the troubleshooting causes, and can efficiently restore the DNS reverse resolution function.

1, fix reverse analysis record configuration

If the troubleshooting is found to be a record configuration error, log in to the domain name or IP management background, delete the wrong PTR record, and recreate the correct mapping relationship. Make sure that the Internet Protocol Address matches the domain name exactly, select the record type PTR, and confirm that the IP segment range of the reverse resolution area is the same as the target IP. After the configuration is completed, wait 10 to 30 minutes for the record to take effect, and then verify it through the command line tool.

2, repair DNS server running abnormally

for the server process crash problem, you can restart the DNS service process or the entire server; if the memory occupation is too high, you need to clean up the server redundant process or expand the memory; for the port occupation problem, you can locate the process occupying port 53 through the netstat command, close the irrelevant process or modify the DNS server listening port. At the same time adjust the firewall rules to open UDP and TCP traffic on port 53.

3 Solve network and permission restrictions

If it is a network link problem, you need to contact the network service provider to repair the link or adjust the routing configuration; if the authority is insufficient, you need to submit a reverse resolution application to the IP provider, provide domain name filing information, IP attribution certificate and other materials, and then obtain the authority to configure. If there is a mismatch between the IP and the domain name service provider, you can transfer the domain name to the IP corresponding service provider, or apply for reverse resolution authorization across service providers.

4. How to prevent the recurrence of DNS reverse resolution failure?

solve the current fault, do a good job of daily maintenance and preventive measures, can reduce the recurrence probability of DNS reverse resolution fault, to ensure long-term stable operation.

1, establish a configuration audit and backup mechanism

before modifying the DNS reverse resolution records, establish a double audit mechanism to ensure that the configuration information is accurate; at the same time, regularly back up the configuration files and resolution records of the DNS server, when there is a configuration error, it can quickly return to the normal state and reduce the scope of failure.

2, regularly monitor the server and parse the status

build a DNS monitoring system to monitor the running status, port connectivity and resolution success rate of DNS servers in real time. Once the reverse resolution request timed out or failed, an alarm will be triggered immediately. At the same time, DNS reverse resolution results are randomly checked through command line tools every week to find potential problems in time.

3, optimize the network and rights management process

establish a regular communication mechanism with network service providers and IP providers to keep abreast of network adjustment or authority change information; when changing Internet Protocol Address or domain name service providers, do a good job in the migration and verification of DNS reverse resolution records in advance to avoid failure due to changes.

To sum up, the solution of DNS reverse resolution failure needs to form a complete closed loop from incentive investigation, targeted repair to daily prevention. By clarifying common incentives, mastering scientific investigation methods, landing accurate solutions, and cooperating with daily monitoring and maintenance, DNS reverse resolution function can be quickly restored, effectively prevent failure recurrence, and provide a solid guarantee for the stability and security of network services.