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Up to now, all the networks that we mentioned were assumed to be a public network, and all of the

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IP addresses were public IP addresses.

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Right?

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In the Internet addressing architecture.

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A private network is a network that uses private IP address space.

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Whoa, whoa, whoa, whoa, whoa, whoa, wait.

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I'll try to explain an unknown with another one.

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But first, I should explain what the private IP address space is.

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Tell you what.

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Let's take a break here and I'll talk about the special use IP addresses, including the private IP

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address space.

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So the authorities, IETF and Iana, please don't ask.

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You can google it if you really want to know who they are.

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But they've restricted from general use various reserved IP addresses for special purposes.

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So that means you cannot use any IP address in these reserved blocks as the public IP addresses of your

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devices.

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So here we have some of these reserved blocks.

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Now, these are the most important blocks for us to know because pretty much anybody who's not familiar

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with the networking concept gets confused about the difference between public and private IP addresses.

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So these IP blocks are reserved for private networks.

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They're commonly used for home office and Enterprise, local Area Networks or LANs.

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Private IP address.

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Spaces were originally defined in an effort to delay IPv4 address exhaustion.

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But there are also a feature of IPv6 where exhaustion is not an issue.

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Bear with me.

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Packets.

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Addresses in these ranges are not routable in the public internet because they are ignored by all public

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routers.

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Therefore, private hosts cannot directly communicate with public networks but require network address,

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translation or Nat at a routing gateway for this purpose.

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But no worries.

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We'll talk about Nat coming up next.

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So without getting too deep, the only thing about the loopback is that 127.0.0.1 is the most common

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IPv4 address which is mapped to the local host.

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So let me give you an example.

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The IP address of your host machine is.

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172.16.99.222 and a web application is served in your host.

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Now in that machine you can use the web address.

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HP Colon slash slash 127.0.0.1 to access the web app as well as Http colon slash slash.

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172.16.99.222.

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Both IP addresses point to the same machine, which is your host.

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Generally an IP address that starts with 169 means that your computer wasn't able to obtain an IP address

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from your Dhcp server.

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Usually that means that your router is wedged and needs to be rebooted or that your Wi-Fi isn't working

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at all.

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So now let's have a look at the private IP address blocks closely.

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As I mentioned a few minutes ago, a private network is a network that uses private IP address space.

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Administrators of private networks can assign networks and subnets from the above ranges.

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If an administrator decides to use the IP range.

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192.168.0.0 slash 16 and then decides to have a single subnetwork assigning 255.255.0.0 as a subnet

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mask.

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Then he or she will have a subnet with a max of 65,536 devices.

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Make sense.