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Special IP Addresses#

Let's look at a few examples of IP address spaces and talk about their characteristics.


So what's interesting about these IP addresses? Two of them are for private networks, for internal communications (you should be able to identify one of these at this point); one of them is a public facing IP address; and another is a special range of IP addresses.

Hopefully you can I identify as being for internal use as we've been using and in some of our examples. This range, along with are private address spaces. They're not what we call "Internet routable", so they cannot be used to communicate with other systems outside of their own network.

So if we have a system with an IP address of and another with an IP address of they cannot talk directly to each other without a router to operate between them.

The IP address is a public facing IP. It's owned by Google and they use it to offer free, public DNS resolution, something you'll learn about in this chapter. What "public facing" means is "Internet routable", which in turn means it can be connected to over the public Internet from another system or network.

Finally, the IP address is for "documentation" purposes. It has been assigned to, "MCAST-TEST-NET, documentation and examples." I'll confess that I don't fully understand what it's used for, but all we need to understand is we cannot use it as a valid set of IP addresses in our own networks.