DNS Client related configuration

Since the internet protocol (ip) address structure (consisting of 32 bits) is not easy to remember, most organizations use abbreviations or meaningful names to represent addresses instead of using ip addresses such as dns.qy .com.cn. However, how do you map a non-ip-identified domain name to an ip address? The mapping between the ip address and its domain name is done by means of a parser and a domain name server. //This article transferred from www.45it.com computer software and hardware application network

Domain Name System (DNS) is a distributed database for tcp /ip applications, it provides between the host name and ip address Conversion and email routing information. In terms of application, access to the dns server is done through a resolver. The dns client mainly completes the function of the resolver. Its main function is to complete the conversion between the ip address and the host's domain name.

Generally, the working process of a dns system is that the application first sends a request to the dns client. After receiving the request, the dns client first queries the local database. If it is not found, it sends a query message to the name server, and receives the request. After the response, the response message sent by the name server is parsed, and the next step is determined according to the content of the response message.

The user program sends a query to the parser according to its needs (requires domain name or ip address). The parser first queries the local buffer (cache), if the mapping item is found in the buffer. , directly respond to the user's request. If there is no buffer, it will organize the query message according to the type of the query (ip address or domain name). The message can be in tcp or udp format, and then issue udp to the default domain name server according to the dns configuration on the local device. Or tcp) querying the message, and after obtaining the response from the server, parsing the response message and answering the user's request.

The buffer relationship on the application, parser and domain name server and parser is shown in the figure above, where the parser and buffer are integrated to form the dns client, which is used to accept the application's dns. Consult and respond to it. Generally, the "application" and "domain name resolver" are on the same host, and the "domain name servers" can be on the same host or on different hosts.

The configuration of dns client includes the following configurations:

1. Start dns parsing

To use dns client function, you need to open dns parsing switch on the device, use The dns resolve command can start dns parsing. By default, dns domain name resolution is disabled.

2. Configure the ip address of the dns server

To perform dns domain name resolution, you need to know the address of the domain name server, so that the query request message can be sent to the correct server for resolution, configuration and The commands for deleting the ip address of the dns server are: "dns server ip-address" and "undo dns server ip-address".

3. Configure the dns domain suffix search list

When users visit some websites, the suffixes are often the same. Such as sina.com.cn, huawei-3com.com.cn, sohu.com.cn and so on.

For the convenience of users, you can set a domain to com.cn, so when the user types the command ping sina, dns will first find the ip corresponding to the string "sina.com.cn". Address, if not received, send sina to resolve to find the ip address corresponding to "sina". Repeat the following command to configure the domain suffix search list.

The command to configure the DNS domain search suffix is: "dns domain domain-name". The default is delete operation. According to the provisions of rfc1034, if the user inputs "ping sina.", then the ip address corresponding to "sina" will be searched first. If there is no response, the ip address resolution request message corresponding to "sina.com.cn" will be sent.

After the configuration is complete, you can use the debugging dns to enable the DNS Client debugging switch for debugging.