Action principle of NAT

NAT Definition

NAT（Network Address Translator, The Internet address translation ） It is used to use private address in local network , Switch to global when connecting to the Internet IP Address technology .NAT Actually to solve IPv4 There is a shortage of addresses And developed technology .

1.2. NAT Working mechanism
With 192.168.1.2 The host and 1.1.1.2 Take the host of as an example to explain NAT How it works . utilize NAT, On the way NAT The router sends the source address from 192.168.1.2  Convert to global IP Address （12.1.1.1） Send data again . conversely , When response data from 1.1.1.2 When you send it , Destination address （12.1.1.1） First it's converted to private IP Address 192.168.1.2  It will be forwarded later .
 

In the whole process , The key points are as follows ：

Network access can only be initiated by private network side first , The public network cannot actively access the private network host

NAT The router completes two address conversions or translations in two access directions , Replace source information in outgoing direction , Replace the target information in the input direction ;

NAT Network address translation ：   On the border router -- Connect to the public network ip The interface configuration of the address

On the border router , Right in 、 The outgoing traffic enters the source or target ip Change of address ;

NAT In order to realize the function of two-way translation , Need to maintain an association table , Save the conversation information .
one-on-one    One to many     Many pairs     Port mapping

The experimental requirements

1、R2 by ISP equipment , Can only be configured on this device ip Address , No other configuration is allowed
2/1.1.1.0/24 Network segment represents all network segments of the whole Internet ;
3、Pc1 It's ok pingPC2
4、R1 Only one public ip Address , stay G0/0/1 On the interface
5、CLIENT Can pass http Visit two server
6、client Visiting another server By domain name

1.ip Division and configuration of addresses

  Configure the dynamic default route in the border router

 2 Route configuration

[r1]rip 
[r1-rip-1]version 2
[r1-rip-1]network 192.168.1.0
[r1-rip-1]network 12.1.1.0

[r2]rip 
[r2-rip-1]v 2	
[r2-rip-1]network 1.0.0.0
[r2-rip-1]network 12.0.0.0
[r2-rip-1]quit 
[r2]

3Pc1 It's ok pingPC2

 5、CLIENT Can pass http Visit two server

[r1]acl 2000	
[r1-acl-basic-2000]rule permit source any
[r1-acl-basic-2000]qu
[r1-GigabitEthernet0/0/1]nat outbound 2000

give the result as follows

 6、client Visiting another server By domain name

[r1]interface g0/0/1	
[r1-GigabitEthernet0/0/1]nat static global 12.1.1.3 inside 192.168.1.3
[r1-GigabitEthernet0/0/1]

give the result as follows