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I've seen the following forms for network addresses:

  • 10.1.1.0
  • 172.16.1.0
  • 192.168.1.0

I usually see 192.168.1.0 for my home network address. Sometimes I've seen the other two forms listed above. What do setups with the other two network addresses indicate?

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6 Answers

up vote 14 down vote accepted

All of these are private network IP adresses, the last one is typically used for home networks, but as it offers the smallest number of sub-adresses, the other ones might be preferred for larger networks like e.g. company intranet.

IP address range              number of addresses   classful description
10.0.0.0 – 10.255.255.255     16,777,216            single class A
172.16.0.0 – 172.31.255.255   1,048,576             16 contiguous class Bs
192.168.0.0 – 192.168.255.255 65,536                256 contiguous class Cs
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The 172 ranges and the 192 ranges there are also unrouted since they are "Private" IP address ranges. Duh and the 10 lol. –  OG Chuck Low Dec 19 '11 at 20:21
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All 3 designate private non routeable IP addresses.

With IP addresses you must be assigned one by the managing authority, unless you use a non routable address. What that means if your address is in

10.x.x.x
192.168.x.x
172.16.x.x – 172.31.x.x

when your request goes to a router that bridges your network and the internet the request can not cross the router. What will happen because you can not use that private IP on a public network is at the router it will do something like Network Address Translation (NAT) and it will use the single IP it was given by the ISP and map the internal IP addresses to that single public IP.

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Nothing. See RFC 1918

The Internet Assigned Numbers Authority (IANA) has reserved the following three blocks of the IP address space for private internets:

 10.0.0.0        -   10.255.255.255  (10/8 prefix)
 172.16.0.0      -   172.31.255.255  (172.16/12 prefix)
 192.168.0.0     -   192.168.255.255 (192.168/16 prefix)

We will refer to the first block as "24-bit block", the second as "20-bit block", and to the third as "16-bit" block. Note that (in pre-CIDR notation) the first block is nothing but a single class A network number, while the second block is a set of 16 contiguous class B network numbers, and third block is a set of 256 contiguous class C network numbers.

An enterprise that decides to use IP addresses out of the address space defined in this document can do so without any coordination with IANA or an Internet registry. The address space can thus be used by many enterprises. Addresses within this private address space will only be unique within the enterprise, or the set of enterprises which choose to cooperate over this space so they may communicate with each other in their own private internet.

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These are defined in RFC 1918 as private (aka non-routable) IPv4 addresses.

  • The 10.0.0.0 – 10.255.255.255 range if a single class A address space.
  • The 172.16.0.0 – 172.31.255.255 range is 16 separate class B address spaces.
  • The 192.168.0.0 – 192.168.255.255 range is 256 separare class C address spaces.
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You're allowed to use them however you want on your internal network as long as you don't expect them to cross a public router (like the gateway to your ISP). –  kbyrd Dec 19 '11 at 20:15
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They're class A, B & C private networks

class A 10.0.0.0 – 10.255.255.255 have a subnet mask of 255.0.0.0 and support 16,777,214 hosts

Class B 172.16.0.0 – 172.31.255.255 have a subnet mask of 255.255.0.0 and support 65,534 hosts

Class C 192.168.0.0 – 192.168.255.255 have a subnet mask of 255.255.255.0 and support 254 hosts

As you can see Class C is the most suitable for a home network, in fact its suitable for most networks, as a good network architect should be able to split the network up to sections so that the broadcasts don't slow down the network.

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This answer seems unaware that we ditched classes and went to CIDR decades ago. –  Spiff Dec 19 '11 at 21:37
    
@Spiff I'd advise you to do a course on networking before publicly displaying your lack of knowledge on subnetting. –  Shutupsquare Dec 20 '11 at 10:01
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As the others have mentioned more accurately than I, these IP addresses you mention are all Private IP addresses. You'll find these on local private, personal, home, or some small business networks.

What none of the other answers have mentioned though is that with certain exceptions, any number formatted xxx.xxx.xxx.xxx could be a valid IP address. That means nearly every combination from 0.0.0.0 to 255.255.255.255 could be an IP address. That's over 4 billion possible combinations (which isn't all that many, when you compare it with the number of devices that connect to the internet).

The 255.xxx.xxx.xxx are reserved for subnet numbers, and the three ranges you specified are reserved for private networks, most of the rest of the possible ranges are purchased by or assigned to organizations or corporations for their own networks. These may be ISPs which will assign a public IP address to any modem connecting to them (the modems then assign private IP addresses to the clients connecting through them, so you may have a completely random looking ip address at your modem, but the three computers you have on your home network would have 192.168.0.xxx addresses), or they may be huge corporations which assign public IP addresses to each of their client computers. You can see how the sheer number of devices connecting to the internet very quickly exceeds 4 billion, and thus why people talk about running out of IP addresses. They're talking about what is called IPv4, or version 4 of the Internet Protocol. IPv6 uses longer addresses which I believe are hexidecimal (allowing not just 0-9 characters, but 0-f, where f is equivalent in decimal to 16, hence the name hexi- (six) decimal (ten)). The possible addresses in IPv6 are said to be enough to address nearly every particle in the universe, which I think underestimates the universe. Suffice it to say, it's a lot, and we're not as likely to run out so soon.

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