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Module 6: NAT for IPv4, image, image, image, image, image, image - Coggle…

- - - - This command shows active NAT translations. Because the example is a static NAT configuration, the translation is always present in the NAT table regardless of any active communications.
      - Another useful command is show ip nat statistics, which displays information about the total number of active translations, NAT configuration parameters, the number of addresses in the pool, and the number of addresses that have been allocated.
      - After the client establishes a session with the web server, the show ip nat statistics displays an increase to four hits on the inside (Serial0/1/0) interface. This verifies that the static NAT translation is taking place on R2.
- - - - Port Address Translation (PAT), also known as NAT overload, maps multiple private IPv4 addresses to a single public IPv4 address or a few addresses.
        With PAT, multiple addresses can be mapped to one or to a few addresses, because each private address is also tracked by a port number.
    - - In the previous example, the client port numbers, 1331 and 1555, did not change at the NAT-enabled router. This is not a very likely scenario, because there is a good chance that these port numbers may have already been attached to other active sessions.
        When packets are returned from outside the network, if the source port number was previously modified by the NAT-enable router, the destination port number will now be changed back to the original port number by the NAT-enabled router.
    - - What about IPv4 packets carrying data other than a TCP or UDP segment? These packets do not contain a Layer 4 port number. PAT translates most common protocols carried by IPv4 that do not use TCP or UDP as a transport layer protocol. The most common of these is ICMPv4. Each of these types of protocols is handled differently by PAT.
- - - - 6.6.4 Analyze PAT - PC to Server
        The process of NAT overload is the same whether a pool of addresses is used, or a single address is used. In this figure, PAT is configured to use a single public IPv4 address, instead of a pool of addresses. PC1 wants to communicate with the web server, Svr1. At the same time another client, PC2, wants to establish a similar session with the web server Svr2. Both PC1 and PC2 are configured with private IPv4 addresses, with R2 enabled for PAT.
        
        6.6.5 Analyze PAT - Server to PC
        Although PC1 and PC2 are using the same translated address, the inside global address of 209.165.200.225, and the same source port number of 1444; the modified port number for PC2 (1445) makes each entry in the NAT table unique. This will become evident with the packets sent from the servers back to the clients,
        
        6.6.6 Verify PAT
        Router R2 has been configured to provide PAT to the 192.168.0.0/16 clients. When the internal hosts exit router R2 to the internet, they are translated to an IPv4 address from the PAT pool with a unique source port number
        The same commands used to verify static and dynamic NAT are used to verify PAT, as shown in the example output. The show ip nat translations command displays the translations from two different hosts to different web servers. Notice that two different inside hosts are allocated the same IPv4 address of 209.165.200.226 (inside global address). The source port numbers in the NAT table differentiate the two transactions