NAT (network address translation)

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One 、NAT What is it?

NAT(Network Address Translation) Also known as network address translation , It is used to realize mutual visits between private networks and public networks .
Private network address and public network address
Public network address ( Hereinafter referred to as the public network address ) It refers to the only in the world on the Internet IP Address .2019 year 11 month 26 Japan , It is a memorable day in the era of human Internet , almost 43 One hundred million IPV4 Address officially exhausted .
Private network address ( Hereinafter referred to as private network address ) It refers to the internal network or host IP Address .

1.NAT How it works

NAT It is used to convert the intranet address and port number into a legal public address and port number , Set up a conversation , Communicate with the public network host
NAT An external host cannot actively follow NAT Internal host communication ,NAT The internal host wants to communicate , Must be active and one of the public networks IP signal communication , The router is responsible for establishing a mapping relationship , So as to realize data forwarding

2.NAT The function of

NAT Not only can it solve IP The problem of insufficient address , And it can also effectively avoid intrusion from outside the network , Hide and protect computers inside the network .
Broadband sharing : This is a NAT The biggest function of the host .
Safety protection :NAT Within PCc Online to Internet. Up there , What he showed IP yes NAT Host's public network IP, therefore client Terminal PC It has a certain degree of security , The outside world is portscan ( Port scanning ) When , You can't detect the source client Terminal PC.

advantage : Saving is legal IP Address 、 Handle address overlap 、 Increase flexibility 、 Security 20
shortcoming : Delay increases 、 The complexity of configuration and maintenance 、 Some applications are not supported ( such as VPN)21

3. static state NAT

static state NAT Realize one-to-one conversion between private network address and public network address . You need to configure as many public addresses as you have private addresses . static state NAT Can't save the public address , But it can hide the internal network .

When the internal network sends a message to the external network , static state NAT The source of the message IP Replace the address with the corresponding public network address . When the external network sends a response message to the internal network , static state NAT Replace the destination address of the message with the corresponding private network address .

4. dynamic NAT

Multiple private networks IP The address corresponds to multiple public networks IP Address , One to one mapping based on address pool .
1. Configure the configuration of external network port and internal network port IP Address
2. Define legal iP Address pool

5.PAT Port multiplexing

PAT Also known as NAPT (Network Address PortTranslation), It realizes the mapping between a public network address and multiple private network addresses , Therefore, the public network address can be saved .PAT The basic principle of is to source messages with different private network addresses IP Address conversion to the same public network address , But they are converted to different port numbers for that address , So you can still share the same address .

6. PAT The role of

Change the of the packet ip Address and port number :
2. Can affect a large number of public networks IP Address .
PAT There are the following types of :
dynamic PAT, Include NAPT and IEasy IP
NAT It's a one-to-one conversion
NAPT Many to one conversion
2. static state PAT, Include NAT Server.