Public and Private IP Addresses

[sinja]

I would like to know what are these public and private IP's?

A friend of mine is connected to a different LAN and I want to access his system directly, but what he knows is his internal IP and using which I cannot connect to it.

So how do these so called Remote Tools work across the Internet?

[Will.Spencer]

Private IP address space is defined in RFC1918: Address Allocation for Private Internets.

The three address ranges reserved for private address space are:

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 address spaces are special, in that they can be re-used over and over again by every private network. However, because of this, these address spaces are also unroutable.

What this means is that your router cannot know how to get to 10.1.1.1 -- because it could never know which 10.1.1.1 you are trying to reach.

The work-around to this is Network Address Translation (NAT).

NAT converts between public addresses and private addresses.

To connect to your friends machine, he is going to have to use NAT to map his private IP address to a public IP address.

Because of the shortage of public IP addresses, most NAT implementations allow you to map many private IP addresses to one public IP address. In these systems, each port on the public IP address can be assigned to a different private IP address.

So, your buddy should be able to configure his router to map port 5646 (for example) of his public IP address to one of his private IP addresses.

[imported_krish]

This might sound silly, but is NAT a software or hardware?

[Will.Spencer]

NAT is a concept which may be implemented in software or in hardware.

Most commonly, NAT is implemented in routers and firewalls.

[compnut]

I've often wondered the same thing, and I just got my question answered. Thanks for the information, and now I can stop looking for that same answer.