Look up rfc1918, it details the private networks.  Three major classes 
of private ipv4 as Kevin listed.  In large networks, you will tend to 
see all 3 uses, typically with physical or security differences in them. 
  They usually only touch in internal network peering relationships with 
a routing protocol.

Don't mix and match lightly (or do, but look up gns3 first), and learn 
CIDR subnet/supernet masking.  Don't go by class a/b/c/d anymore, it's 
all cidr now, and with ipv6 it only gets worse.

-mb


On 03/08/2012 10:46 AM, Kevin Fries wrote:
> Mike,
>
> Just for your information, there is also a third lesser known range
> 172.[16-31].x.y
>
> Each of the three ranges are available for private use, and are illegal
> on the Internet.  Which you use is completely up to you and is generally
> based upon your own individual needs.
>
> If you take the first part of any address, and represent it in binary,
> it will tell you the address "class".
>
> 0.... ->  Class A address
> 10... ->  Class B address
> 110.. ->  Class C address
> 1110. ->  Class D address
> 11110 ->  Class E address
>
> 10  ->  0000 1010 ->  Class A - Default mask is 255.0.0.0 - CIDR /8
> 172 ->  1010 1100 ->  Class B - Default mask is 255.255.0.0 - CIDR /16
> 192 ->  1100 0000 ->  Class C - Default mask is 255.255.255.0 - CIDR /24
>
> Class D was reserved for multi-cast addresses.  Most of these you will
> see in the 224.x.y.z range
>
> 224 ->  1110 0000 ->  Class D - Default mask is 255.255.255.255 - CIDR /32
>
> Class E was reserved, but never used, and never will be now that IPv6 is
> here.
>
> Using a class A address reserves 8 bits for the network address (i.e.
> 10) and 24 bits for the hosts, which leaves you with 2^24 or 16,777,216
> hosts - 2 (network broadcast, and network addresses)
>
> Using a class B address reserves 16 bits for the network (i.e. 172.16)
> and 16 bits for the hosts, which leaves you with 2^16 or 8,65,536 hosts
> - 2 (network broadcast, and network address)
>
> Using a class C address reserves 24 bits for the network (i.e.
> 192.168.1) and 8 bits for the host, which leaves you with 2^8 or 256 -
> the same 2 addresses.
>
> Your broadcast address is where all bits in the host part are 1, and
> your network address is where all host bits are 0.
>
> I hope this helps you understand the difference between addresses, and
> helps you pick the right one for your needs.
>
> Kevin Fries
>
>
>
> On Thu, 2012-03-08 at 10:18 -0700, Michael Havens wrote:
>> What is the difference between the 192.168.x.y and the 10.x.y.z range?
>> They are both the private network ranges but why would one decide to
>> use one but not the other?
>>
>> --
>> :-)~MIKE~(-:
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