The Key to Static NAT Configuration on Routers

Which command is used to configure a static NAT mapping on a router?

• A. (config)#ip nat source static PRIVATE IP ADDRESS AND PUBLIC IP ADDRESS
• B. (config)#ip nat inside source list ACCESS LIST NUMBER
• C. (config)#access-list ACL NUMBER permit host PRIVATE IP ADDRESS
• D. (config)#ip nat pool POOL NAME

Answer: (A)

The command to configure a static NAT mapping on a router is indeed the one that specifies both the private IP address and the public IP address. This command creates a direct mapping between a specific private IP address (typically used within a local internal network) and a public IP address (used for external access on the internet). By using this command, the router is instructed to always translate the given private IP address into the specified public IP address every time traffic is sent from the private network to the internet. This is essential for scenarios where a specific internal server (like a web server) needs to be reliably accessible from external networks with a consistent public address. The other options represent different commands or configurations used in the context of NAT but do not directly configure static NAT mappings. One of them is related to defining a NAT access list, while another deals with defining a NAT pool for dynamic mappings. The access list command serves to permit certain traffic rather than establishing a static mapping, and the command for NAT pool focuses on a range of addresses rather than direct one-to-one mappings.

When it comes to networking, understanding how to configure static NAT on a router is not just a box to check on your certification journey; it’s a fundamental skill that can significantly simplify how your internal network connects to the outside world. So, have you ever found yourself pondering, “What’s the best way to ensure my web server is reliably accessible without changing IPs all the time?” Well, let’s unpack that.

The command you’re looking for is (config)#ip nat source static PRIVATE IP ADDRESS AND PUBLIC IP ADDRESS. This straightforward command creates a steadfast bridge—almost like a reliable handshake—between a private IP address on your local network and a public IP address used for external communications on the internet. Think of it this way: if your private IP is the home address of a cozy café (your internal web server), the public IP is the address on the main street where customers can always find you. And we wouldn’t want your customers to have to search for your café every time they want to sip a cup of your fine espresso, right?

So, what you’re doing here is telling the router, “Hey, whenever someone from the outside world wants to reach my café at its public addresses, direct them to my private address.” This is particularly crucial in scenarios where you need consistent access. It’s not just a good practice; it’s essential for businesses that depend on reliable access to their servers.

Now, let’s take a moment to consider the other options you might encounter. For instance, option B—(config)#ip nat inside source list ACCESS LIST NUMBER—might sound tempting, but it's more about permitting traffic than creating that one-to-one mapping. It’s like saying, “You can come in, but I’m not giving you the exact address.” While useful, it doesn’t meet your specific need for static NAT mapping.

The command in option C—(config)#access-list ACL NUMBER permit host PRIVATE IP ADDRESS—serves a different purpose altogether. This is about controlling access rather than mapping addresses. It’s more like setting up a bouncer (the access list) at your café’s front door to decide who gets in based on certain rules.

And then there’s option D: (config)#ip nat pool POOL NAME, which is quite different as well. This command aims to define a range for dynamic IP mappings instead of establishing a fixed relationship like static NAT does. Imagine it as setting up a whole hotel for guests who want to stay in town—but again, not your café where you want a specific guest to have a specific table.

Grasping these distinctions is crucial, especially when preparing for your CCNA exam. You want to not only memorize the commands but also understand the underlying principles. So, the next time you hear someone talking about NAT configurations, you can confidently share, “Oh, I know just the command for that!”

Let’s face it—having a solid grasp of these topics pays off in the long run, both in your exam success and in your networking career. It’s the difference between being just another face in the crowd versus being the networking whiz who knows exactly how to keep things running smoothly. So, keep practicing, and make that NAT magic happen!