DNS domain name resolution

Preface

DNS(Domain Name System, The domain name system ), On the Internet as domain names and IP A distributed database with address mapping , It can make it easier for users to access the Internet , Instead of remembering what can be read directly by the machine IP Number string . By hostname , Finally, we get the corresponding IP The process of address is called domain name resolution ( Or hostname resolution ).DNS The protocol runs in UDP The agreement above , Use port number 53.

One .DNS The role of the system

positive A Record ： Domain name resolution ip
reverse P Record ：ip Domain name resolution
DNS The distributed data structure of the system
root .                                            Root region
.com .net .org .edu .cn .uk   Top-level domain
.com.cn .net.cn .edu.cn         The secondary domain
.zol.com.cn .sina.cn               Subdomain
www mail news                      Host name or tertiary domain

Two . Local parsing order

1. Local DNS cache
2./etc/hosts
3./etc/resolv.conf Find a local domain name server

3、 ... and . Iterative query

DNS Another query method of the server is iterative query , But when the client sends a query request ,DNS The server does not reply directly
Query results , Instead, tell the client another DNS Server address , The client is sending a message to this DNS The server submits the request , successively
Loop until the result of the query is returned .
The client's request needs to be queried one by one to get the result , When the server has no results, it will only provide you with other
Server address , It won't help you to ask for inquiry , This is the opposite of recursion
1. Find the root domain name server “.”
2. Find a top-level domain name server .cn.
3. Find a secondary domain name server .com.cn.\
4. Find a tertiary domain name server .baidu.com.cn
5. Find the host name www.baidu.com.cn.
6. Confirm understanding of the relationship ：192.168.226.129
7. Return to local DNS The server
8. Local DNS The server returns to the client
9. Client access baidu At the same time , Cache the resolution relationship locally

3、 ... and . recursive query

Recursive query is a kind of DNS The query mode of the server , In this mode DNS The server received a client request , You have to use one
The exact query results are replied 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 .
The client only needs to wait after sending the request , The middle part is specifically handed over to the server

Four .DNS To configure

1. install DNS

2.vim /etc/named.conf
Set the local listening port

3.vim /etc/named.rfc1912.zones
Set forward resolution as the primary region

4. Copy to the specified directory

5.vim gwk.com.zone 
Record the current DNS Server name

6. start-up DNS

7. test result
Another host will be the server's IP Add to DNS in