IP address

as i know, there are 3 class of ip (A,B and C)
class A start with 1.x.y.z to 126.x.y.z and subnet is 255.0.0.0
and i always see that people use 10.x.y.z as the private ip..
why they not use 1.x.y.x or 2.x.y.z as the private ip etc..
can u decribe to me..i really don't know it..

as i know, there are 3 class of ip (A,B and C)
class A start with 1.x.y.z to 126.x.y.z and subnet is 255.0.0.0
and i always see that people use 10.x.y.z as the private ip..
why they not use 1.x.y.x or 2.x.y.z as the private ip etc..
can u decribe to me..i really don't know it..

--Class D for MultiCasting
--Class E For Scientific Purposes.

--Class A looks something like this

Network.Node.Node.Node

--I don't think there is anything wrong with using IP's as you mentioned above. Anyone correct me if I am wrong.
Check the below link.

www.faqs.org/rfcs/rfc791.html

As long as you use the ip on a private network you can use any ip you want. If you access the internet you must have either a unique ip or a private ip

If you access the internet you must have either a unique ip or a private ip

--Did you mean Unique IP or Public IP?

that mean i can use 1.x.y.z at my office network..
why people always use 10.x.y.z, 170.x.y.z and 192.x.y.z ?
is the standard or other reason?

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)

These are all RFC1918 private IP addresses. In other words these are not routeable on the Internet. They were initially put in place to avoid the exhaustation of the IPv4 address space, and now they are used by most organisations for the internal network and then NAT'd (see our NAT tutorial) to a public IP for internet access.

You *can* however use just about any IP address you choose on your network, however this can cause a lot of problems for you if somehow your IP routes manage to leak, or by coincidence you need to communicate with a host that actually resides in that netblock. For this reason, its recommended you stick to the RFC1918 IP addresses -- its good network hygiene.

Its actually a very easy to read RFC, and quite interesting too.. check it out
www.faqs.org/rfcs/rfc1918.html

Cheers,