A Cisco solution that’s perfectly NAT-ural

Home > Blogs > Cisco > A Cisco solution that’s perfectly NAT-ural

A Cisco solution that’s perfectly NAT-ural

Like This Blog 0 Mark Jacob
Added by February 25, 2015

If you are reaching for your CCNA Routing and Switching certification, you probably already know that configuring NAT is on the list of stuff to know. In the CCNA world, this is accomplished using dynamic NAT, or NAT pools, as one solution, or Port Address Translation (PAT) for the other solution. Static NAT is mentioned in the official CCNA curriculum for the CCNA classes, but the labs do not require a student to actually configure it. What I want to show today is an alternate method to configure NAT which works just fine, but is NOT the method used in CCNA R&S.

This blog assumes that you already have a basic understanding of NAT configuration. If you want to brush up on your understanding of NAT before diving in, feel free to take a look at my previous blog on the topic Troubleshooting NAT pools on Cisco routers. The main point here is to enable NAT on an interface (or several interfaces) without specifying an inside or outside interface. Let’s take a look at the topology which will be used in this discussion:

001-Cisco-CCNA-network-topology

The objective is to permit the two clients to access the (fake) Internet hosted on the WWW router, or more precisely, to be able to reach the target address of 8.8.8.8 (borrowed from Google). The two clients are actually Cisco routers in client clothing, so I have disabled ip routing on each of them using the command no ip routing from global configuration mode. I have then configured a default-gateway on each which is 192.168.1.254 for Client1 and 192.168.2.254 for Client2. What remains is to configure NAT on the NAT-RTR.

First, let’s make sure that NAT-RTR can hit the 8.8.8.8 address, because if it can’t get there, our clients are not going to have much success either:

002-Cisco-CCNA-NAT_RTR

Yay! Success. Now let’s configure the f0/0 interface so that it can speak trunk (802.1q) with SW1. Note that this topology was created using GNS3 1.2.1 and that SW1 is a vanilla ethernet switch which has been preconfigured with port 1 in VLAN 10, port 2 in VLAN 20, and port 8 configured as a trunk link. The steps on NAT-RTR:

003-Cisco-CCNA-NAT-RTR-VLAN

Now to repeat the steps for our second subinterface:

004-Cisco-CCNA-NAT-RTR-subinterface

Let’s include int f0/1 in the NAT process:

005-Cisco-CCNA-NAT-RTR-process

We still need to create an access-list to allow our traffic of choice.

006-Cisco-CCNA-NAT-RTR-traffic-access

Now to actually fire up the NAT process:

007-Cisco-CCNA-NAT-RTR-launch

If everything is working as expected, I should be able to hit the 8.8.8.8 address from each of my clients. Let’s check:

008-Cisco-CCNA-NAT-RTR-check

All is well on Client1. The last verification step is to try Client2:

009-Cisco-CCNA-NAT-RTR-client

So both clients can now hit an external IP address using the NAT-RTR as the initial objective stipulated. We can see that the NAT process is working even though I have not configured NAT inside or NAT outside. You may find it interesting to note that even after a successful ping from one of the clients, the command show ip nat translations will return no results. This is because using the command ip nat enable creates a NAT Virtual Interface (nvi) so if you want to see the NAT activity, you must type show ip nat nvi translation like so:

010-Cisco-CCNA-NAT-RTR-nvi-virtual-interface

As mentioned, this is not an expectation if you are studying for your CCNA R&S, but it is way cool to know other ways of accomplishing similar tasks! If you have suggestions or comments, I would love to hear them.

Until next time…

Mark Jacob
Cisco and CompTIA Network + Instructor – Interface Technical Training
Phoenix, AZ

Videos You May Like

A Simple Introduction to Cisco CML2

0 3877 0

Mark Jacob, Cisco Instructor, presents an introduction to Cisco Modeling Labs 2.0 or CML2.0, an upgrade to Cisco’s VIRL Personal Edition. Mark demonstrates Terminal Emulator access to console, as well as console access from within the CML2.0 product. Hello, I’m Mark Jacob, a Cisco Instructor and Network Instructor at Interface Technical Training. I’ve been using … Continue reading A Simple Introduction to Cisco CML2

Creating Dynamic DNS in Network Environments

0 641 1

This content is from our CompTIA Network + Video Certification Training Course. Start training today! In this video, CompTIA Network + instructor Rick Trader teaches how to create Dynamic DNS zones in Network Environments. Video Transcription: Now that we’ve installed DNS, we’ve created our DNS zones, the next step is now, how do we produce those … Continue reading Creating Dynamic DNS in Network Environments

Cable Testers and How to Use them in Network Environments

0 724 1

This content is from our CompTIA Network + Video Certification Training Course. Start training today! In this video, CompTIA Network + instructor Rick Trader demonstrates how to use cable testers in network environments. Let’s look at some tools that we can use to test our different cables in our environment. Cable Testers Properly Wired Connectivity … Continue reading Cable Testers and How to Use them in Network Environments

Write a Comment

Share your thoughts...

Please fill out the comment form below to post a reply.