DNS domain name resolution service

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Preface

Domain name resolution is to point domain name to website space IP, Let people through the registered domain name can easily access a website service .IP The address is the digital address on the network that identifies the site , For the convenience of memory , Use domain names instead of IP Address identification site address . Domain name resolution is domain name to IP Address conversion process . Domain name resolution work by DNS The server completes .

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One 、BIND Domain name service foundation

1.DNS Concept

DNS The domain name system （Domain Name System abbreviation DNS,Domain Name Translated as domain name ） It is a core service of the Internet , It can be used to IP A distributed database with address mapping , Can make people more convenient access to the Internet , Instead of remembering what can be read directly by the machine IP Number string

2.DNS Protocol and port number used

DNS The default port is 53,DNS Ports are divided into TCP and UDP

2.1TCP It is used for area transmission , Mostly used for master-slave synchronization

In a district DNS The server reads the data file of this area DNS Data and information , And auxiliary DNS The server is from the master of the zone DNS The server reads the DNS Data and information

2.2UDP Is used to do DNS Analytic

Client to DNS Server query domain name , Generally, no more than 512 byte , use UDP Just transfer . Without three handshakes , such DNS Server load is lower , More responsive . In theory, , The client can also refer to the direction DNS Server query time TCP, But in fact , quite a lot DNS When the server is configured , Support only UDP Query package

3. Domain name Architecture

The desired domain name must end with a dot
for example ：www.baidu.com.
Root domain name "."
First level domain name ：.cn（ China ）.us（ The United States ）.tw（ Taiwan ）.kr（ South Korea ）.jp（ Japan ）.hk（ Hong Kong ）.uk（ The British ）
Two level domain name ：.com.cn（ Chinese business organizations ）.edu.cn（ educational services ）.org.cn（ uncommercially ）.net.cn（ Chinese operators ）
Three level domain name / Subdomain ： sina.com.cn baidu.com.cn
Host name ： www mail ftp

4.DNS Distributed Internet parsing library

large 、 Distributed Internet DNS Parsing library
Root domain name DNS The server ： Responsible for root domain name
Class A DNS The server ： Responsible for the resolution of primary domain names （ It generally represents a type of organization or country or region ）
second level DNS The server ： Responsible for secondary domain name resolution
Level three / subdomain DNS The server ： Responsible for sub domain name resolution , Also known as tertiary domain name
Host site ： www、mail、ftp

5.DNS The role of the system

• Forward analysis ： Search for the corresponding IP Address
• Reverse DNS ： according to IP Address to find the corresponding domain name

6.DNS A query

6.1 recursive query

Recursive query is a kind of DNS The query method of the server , In this mode DNS The server received a client request , You must use an accurate query result to return to the client . If DNS The server does not store queries locally DNS Information , Then the server will ask other servers , And submit the returned query results to the client
Just wait for the client to send the request , The middle specific process is handed over to the server to realize

6.2 Iterative query

DNS Another query method of the server is iterative query , When the client sends a query request ,DNS The server does not reply directly to the query results , Instead, tell the client another DNS Server address , The client will go to this DNS The server submits the request , Cycle in turn until you return the result of the query directly
That is, the client requests need to be queried one by one to get the results , When the server has no results, it will only provide you with the address of other servers , Instead of asking for information for you , This is the opposite of recursion

7.DNS The query process

（1） First check the cache address of this machine
（2） Inquire about /etc/hosts file
（3） Inquire about dns Domain name server , hand DNS Domain name server processing
The above process is recursive query
（4） This dns The server may be a local domain name server , There is also this cache , If there is , Direct return , If not, proceed to the next step
（5） Help the root domain server , The root domain server returns the top-level server that may know the result and asks him to find the top-level domain server
（6） Help the top-level domain server , The top-level domain server returns the secondary domain server that may know the result and asks him to find the secondary domain server
（7） Turn to the secondary domain server , The secondary domain server found that it is my host , Find out ip The address is returned to the local domain name server
（8） The local domain name server logs the results to the cache , Then put the domain name and ip The corresponding relationship is returned to the client
The above is Iterative query

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Two 、DNS To configure

To configure DNS The server

1. install bind

2. Query profile

3. Modify global profile （/etc/named.conf）


4. Modify area profile (/etc/named.rfc1912.zone)


5. Configuration area data profile （/var/named/named.localhost）



6. This completes the configuration , Turn off firewall , Turn off core protection , Turn on dns service

verification

1. Open another machine

2. modify DNS The configuration file , Point to the configured DNS Server's IP


3. Use nslookup Command view

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