How to configure DNS recursion? DNS recursive deployment steps and precautions

in the Internet domain name resolution system, DNS recursion is the key link to improve the resolution efficiency and reduce the load of the root server. Many enterprises and technicians will choose to build local DNS recursive services to optimize the speed and stability of the domain name resolution of the internal network. However, the configuration and deployment of DNS recursion involves multiple links, from environmental preparation to operation and maintenance. There are strict requirements. Improper operation may cause problems such as resolution delay and service failure. This article will comprehensively explain the key points of DNS recursion construction and maintenance from the dimensions of configuration premise, deployment steps, optimization methods and operation and maintenance precautions, and provide readers with practical guidance that can be implemented.

What preparations should be done before DNS recursive configuration?

before the formal deployment of DNS recursive services, adequate preparation is the basis for ensuring the stable operation of services, which needs to be confirmed one by one from multiple dimensions such as software and hardware environments and network permissions.

1, hardware and software environment preparation

server hardware, it is recommended to choose at least 2-core CPU and 4G memory devices. If the service covers a large number of users, the configuration can be appropriately upgraded to avoid resolution cards in high-concurrency scenarios. The system prefers mainstream Linux distributions such as CentOS and Ubuntu. Such systems have stronger compatibility with DNS recursive service software and better community support. At the same time, it is necessary to install Bind, Unbound and other commonly used DNS recursive service software in advance, and choose the appropriate tools according to your own needs. For example, Bind functions are fully suitable for complex scenarios, and Unbound is lightweight and efficient for small networks.

2, Network and Authority Confirmation

need to ensure that the server has stable public network access and can normally connect to the global root domain name server, which is the core premise of DNS recursive service to complete the resolution request. At the same time, the 53 ports of the server should be opened, including UDP and TCP protocols, the former is used for regular domain name resolution, and the latter is used for large-size DNS message transmission. In addition, to plan the access scope of the service in advance, if only for the internal network, it is necessary to configure firewall rules to restrict external IP access to avoid DNS recursive service abuse.

Second, the specific deployment steps of DNS recursive service?

complete the preparation work, you can enter the actual deployment of DNS recursive service, this stage needs to strictly follow the configuration process to ensure that each step is accurate.

1, software installation and basic configuration

take the Bind software as an example, in the CentOS system, the installation can be completed through the yum install bind -y command. After the installation is completed, enter the/etc/named.conf configuration file, turn on the recursion function, turn on the recursion yes option, and set the client side IP segment that allows access, such as allowing devices 192.168.1.0/24 network segments to use the DNS recursive service. At the same time, to configure the root domain server address, you can directly use the system default root domain configuration file to ensure that the service can initiate recursive resolution requests normally.

2, service start-up and basic authentication

configuration is completed, start the DNS recursive service through the systemctl start named command, and set the boot to avoid service interruption after the server restarts. Then you can use the nslookup or dig command to verify on the local server, such as performing dig www.baidu.com @127.0.0.1. If you can return the correct Internet Protocol Address, it means that the DNS recursive service is basically running normally. At the same time, modify the DNS server address to the deployed DNS recursive service IP on the client side device to test the speed and stability of the client's domain name resolution.

How to optimize the resolution efficiency of DNS recursion?

DNS the recursive service deployment is completed, it is necessary to improve the parsing efficiency by optimizing the configuration, further reduce the parsing delay, and improve the user experience.

1, configure cache policy

cache is the core means to improve the efficiency of DNS recursive resolution. You can adjust the cache size and expiration time in the configuration file, such as setting max-cache-size to 512M to increase the cache capacity, and at the same time set the cache expiration time reasonably. For commonly used domain names, the cache time can be appropriately extended to reduce the number of repeated recursive requests. In addition, the prefetch function can be turned on. When the cache is about to expire, it will automatically initiate a recursive request to update the cache in advance to avoid resolution delays when users request.

2, optimize recursive query parameters

can adjust the timeout time and retry times of recursive requests, such as setting timeout to 2 seconds and retry to 2 times to avoid the overall resolution delay caused by a single request timed out. At the same time, the EDNS0 extension function can be enabled to support larger DNS packets to improve the data transmission efficiency during the recursive resolution process. In addition, multiple upstream DNS servers can be configured as standby, and when the main recursive request fails, it can automatically switch to the standby server to ensure the availability of resolution services.

4, DNS recursive operation and maintenance need to pay attention to what matters?

DNS recursive service is launched, daily operation and maintenance is the key to ensure the long-term stable operation of the service, and it is necessary to pay attention to the service status, security protection and other aspects.

1, real-time monitoring service status

need to build a monitoring system to track the running status of DNS recursive services in real time, including core metrics such as request volume, response time, cache hit rate, etc., which can be visually monitored by Prometheus combined with Grafana and other tools. When there are abnormal situations such as sudden increase in request volume and long response time, check the cause in time to avoid service collapse. At the same time, check the service logs regularly, and check the analysis failure and recursion timeout through log files such as/var/log/messages.

2, do a good job of safety protection measures

DNS recursive services are vulnerable to security threats such as cache poisoning and DDoS attacks, it is necessary to turn on the DNSSEC function to verify the digital signature of the resolution results to prevent cache poisoning. At the same time, it is necessary to configure strict firewall rules to allow only authorized IP to access DNS recursive services to avoid services being used to initiate DNS amplification attacks. In addition, it is necessary to regularly update the service software version to fix known security bugs and improve the security of the service.

To sum up, the construction and maintenance of DNS recursive services is a systematic project. From the preparation of the environment in the early stage to the implementation of deployment, and then to the optimization and operation and maintenance in the later stage, each link needs to be strictly operated. By doing the preparation work before configuration, following the standard deployment steps, optimizing the resolution efficiency and doing a good job in daily operation and maintenance protection, we can create an efficient, stable and secure DNS recursive service, provide reliable support for the domain name resolution of the internal network, and improve the overall network access experience.