Ask Leo! #718 – Your Router’s Two IP Addresses

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Featured: Did you know your router has two IP addresses? Also this week: tools that promise to fix everything! Also, what it really means to scan a document.

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Your Router's Two IP Addresses

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 I was completely unaware that your router has two IP addresses.

Indeed it does.

It's an important part of understanding how information travels between your computer and the internet services you use.

It's also important to know when asking questions and interpreting answers.

Your router's primary job

Routers perform many different functions, but their primary role, at least in the home, is to act as a gateway to the internet.

You can think of your router as having two “sides”: one side is connected to the internet, and another to all of your computers and other devices. The router sits in-between, passing data traffic back and forth.

A Router's Role

The internet side is a connection provided by your ISP. All traffic to and from internet sites and services travel over this connection.

The “local” side, often referred to as a LAN, for Local Area Network, consists of all of the devices connected to the network at your home or place of business. Be it through a wired or wireless connection, these devices connect not to the internet, but to your router, through which the internet is made available.

The router's two networks

These two networks — the internet on one side and your local network on the other — are completely separate. That data crosses between them is only due to the workings of your router, which is connected to both.

Two different networks imply two different IP addresses.

On the internet side, your router is typically assigned an IP address by your ISP when it boots up or first connects. This is your “true” internet address. You can see what yours is by using several online services, or by consulting my article, What's My IP Address?

On the local side, your router is configured to use a specific IP address: often something like 192.168.1.1, 10.1.10.1, or something similar. You can see what yours is by running the command “IPCONFIG /ALL” in a Windows Command Prompt and looking for the Default Gateway address.

Default Gateway

The number using periods as the separator — it's IPv4 address — is the IP address of your router.

Router IP Addresses

Your router's other job

Another job performed by your router is to manage the local network.

When the router connects to the internet, it requests an IP address, which is then provided by the ISP. This is your internet IP address. You very likely have only one of these, and it's assigned to your router.

When your computer (or other device) connects to your local network, it also requests an IP address. This IP address is provided by your router. It looks a lot like the router's own local IP address, though the last two numbers will be different. This is that computer's local IP address. Each device connected to the local network has its own unique local IP address.

When a device on your local network wants to communicate with a device on the internet, it is the router's job to “translate” between the two types of addresses. In fact, that's what it's called: Network Address Translation, or NAT. NAT makes it appear as if all of your devices (each with a unique local IP address) are coming from the same internet IP address — because they are. All the traffic going to and from the internet is handled by your router through its internet-side connection and IP address.

Determining the IP address

As we've seen above, there are two ways to see the two different IP addresses:

  • Using an online service (or page like my What's My IP Address? article) will tell you the internet IP address of your router. When someone asks you for your IP address — say when trying to diagnose an issue you're having in accessing a website — this is the number you provide.
  • Using the “ipconfig” command in a Windows Command Prompt will tell you the local IP address of that computer. In practice, you rarely need to know this one, except perhaps when diagnosing local network connectivity problems.

Specific IP addresses

One final note: a “local” IP address begins with either:

  • 10.x.x.x
  • 172.16.x.x through 172.31.x.x
  • 192.168.x.x

You will never see these addresses on the internet. They are called “non-routable” IP addresses and are reserved exclusively for local networks. That's how, if you provide the wrong kind of IP address to your support person, they can tell immediately and ask you for “the other one.”

Related Links & Comments: Your Router's Two IP Addresses
https://askleo.com/61473

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Do "Fix All Your Windows Problems" Utilities Work?

I have a number of knotty problems with error messages at present and there are several programs on the net which “guarantee” to fix them. When the offered free scan is invited, they always come up with lots of faults which they will only fix if you subscribe. My usual reaction is that it's all a con to get subscribers, but is this true in all cases or are there some programs which really are the cure-alls they claim to be?

To quote the old aphorism: “If it seems too good to be true, it probably is.”

I'm sure there are good programs out there, but like you, I'm very skeptical. Beyond skeptical. Downright suspicious, even.

As a result, I've never purchased such a program. Instead, I've tackled my problems head-on, lived with them, or, if things are bad enough and unsolvable, reformatted and re-installed.

But there are some ways to at least stack the deck in your favor if you want to try one or more of these types of tools.

Continue Reading: Do "Fix All Your Windows Problems" Utilities Work?
https://askleo.com/2815

Why Does a Scan of a Simple Text Document Result in Such a Large File?

 I scanned a copy of my W2 form and tried to email it to someone but I was told the file was too big – over 25 MB. How does a simple text document acquire such a huge volume?

The short answer is very simple: a scan of a document creates a picture. It's exactly as if you had pointed your camera at the paper and snapped a photo of it, except your scanner is better at capturing large, flat surfaces.

And pictures can be big.

Let's look at why, and what some of the alternatives might be.

Continue Reading: Why Does a Scan of a Simple Text Document Result in Such a Large File?
https://askleo.com/6165

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