Configuration case of CISCO router NAT Function (1)

NAT technology is a commonly used technology in the vro configuration process. How do I configure and implement its functions? How does it work? The following article will give you a detailed answer.

NAT (Network Address Translation) is the Translation of Network IP addresses. NAT is designed to address the increasing shortage of IP addresses. It maps multiple internal addresses to a few or even one public IP address. In this way, computers in our Intranet can access INTERNET resources through pseudo IP addresses.

The vro that sets the NAT Function must have at least one internal port (Inside) and one external port (Outside ).

The user of the network connected by an internal port uses an illegal IP address.) The external port connects to an external network and uses the IP address assigned to us by the Telecommunications Department. Generally, the internal port should use the ETHERNET port and the external port should use the SERIAL port. In addition, to use the NAT Function, IOS of the router must support the NAT Function.

NAT settings can be divided into static address translation, dynamic address translation, and multiplexing dynamic address translation. The following example uses a Cisco router.

1. Static address translation

Static address translation performs one-to-one conversion between the internal local address and the internal legal address, and specifies the legal address to which the conversion is required. If there are WWW servers or FTP servers in the internal network that can provide services to external users, the IP addresses of these servers must adopt static address translation so that external users can use these services.

2. Dynamic Address Translation

Dynamic Address Translation also converts an internal local address and an internal legal address one to one, however, dynamic address translation dynamically selects an unused address from the internal valid address pool to convert the internal local address.

3. Reuse Dynamic Address Translation

Multiplexing dynamic address translation is a kind of dynamic address translation, but it allows multiple internal local addresses to share one internal legal address. This type of conversion is extremely useful when only a small number of IP addresses are applied but multiple users are on the external network at the same time.

PAT (Port Address Translation), also known as NAPT, maps multiple internal addresses into a public Address, but corresponds to different internal addresses using different protocol Port numbers. This method is usually used for dialing Internet.
The following uses the 2611 router as an example. The configuration list is as follows:
Current configuration:
!
Version 12.0:
Service timestamps debug uptime
Service timestamps log uptime
No service password-encryption
!
Hostname 2611
!
Enable secret 5 $1 $ JIeG $ UZJNjKhcptJXHPc/BP5GG0
Enable password 2323 ipro
!
Ip subnet-zero
No ip source-route
No ip finger
!
!
!
Interface Ethernet0/0
Ip address 192.168.10.254 255.255.255.0 secondary
Ip address 218.27.84.249 255.255.255.255.248
No ip directed-broadcast
Ip accounting output-packets
No ip mroute-cache
No cdp enable
!