CCNA Packet Tracer Labs – CCNA Vol 2, Chapter 10

The example begins with a show running-config command that confirms static NAT has already been configured, so the .pkt file has already configured the static NAT commands shown in the example.

The output in PT for the example’s second command, show ip nat translation, the output will match temporarily.  PT shows correct output before any user traffic is generated. However, if you generate traffic that uses the (simulated) NAT feature, the output expands to show output as if you had configured NAT/PAT. For instance, from PC1, issue a ping 170.1.1.1 command to ping the server in the Internet. Then repeat the show ip nat translation command to see the expanded (and incorrect) output.

The example lists only the output of a show running-config command that confirms dynamic NAT has already been configured, so the .pkt file begins with those commands pre-configured.

The example begins with dynamic NAT pre-configured per Example 10-2. The example shows the output in the state before any user traffic has been generated; PT happens to mostly mirror that output in compared to the output from real gear (as shown in the book’s example.)

In particular, note that the example’s first show command, show ip nat translation, lists null output because no translation table entries have been dynamically added yet. (PT should also list no lines initially, matching the example.)

The second command, show ip nat statistics, lists similar statistics and configuration settings as compared to the book example. However, the PT output has a few less lines, with a few less details, in comparison to the example in the book.

The example begins with dynamic NAT pre-configured per Example 10-2.

The example shows output after a user has generated traffic. The book shows the effects of using Telnet. To generate similar traffic in PT, use PC1, choose the web browser app instead of the command prompt, and browse to address 170.1.1.1 (the server in the Internet.) Then reload the page a few times. That should generate enough traffic to cause the command output to look more similar to the output in the example.

PT does diverge from real gear in this case, because the configuration enables NAT without PAT, but the show ip nat translation command lists port numbers, which it should only do if you had configured NAT with PAT. You may want to circle back to this example once you’ve finished all the examples for the chapter.

Note: Sometimes PT shows incorrect output in the show commands for inexplicable reasons. In our testing, a reload of the router, or a power cycle of the router, did not help, but closing the .pkt file and re-opening did.

This example works through a specific sequence of events – a sequence of events which may be difficult to replicate because of Cisco PT’s incorrect output when configured for NAT without PAT. It may not be worth trying, but if you want to attempt it, you can use the .pkt file for Example 10-2.

The example begins with dynamic NAT/PAT pre-configured per Example 10-6.

The command output from show ip nat translation lists port numbers, as it should. However, PT will not match the port numbers (listed after the : ) chosen by real gear.

Note that in real networks, most TCP-based apps keep their TCP connections open for a period of time, so that subsequent packets inside one TCP connection do not require a new NAT table entry. Cisco PT acts as if it stops each TCP connection almost immediately. As a result, if you generate test traffic multiple times, you will see multiple NAT table entries appear. For example, if you use PC1 to web browse to 170.1.1.1, and click “go” several times, you will create several NAT table entries.