How single Internet connection shared with multiple PCs ?

How single Internet connection shared with multiple PCs ?

Have you ever wondered how a single home or office broadband internet line connected to multiple computers. Corporate office have more than one internet connection, that acts as a backup if any of the ISP is down, it is called Multi-Homing.

It is through NAT(Network Address Translation) we are able to connect multiple PCs to a single internet connection. NAT is implemented at ISP, corperate offices, home network by using routers or Wi-Fi devices.

To understand NAT in simple way, NAT is like the receptionist in a large office managing and connecting extensions for the phone calls coming from the board number(Office telephone). Let's say you have left instructions with the receptionist not to forward any calls to you unless you request it. Later on, you call a potential client and leave a message for them to call you back. You tell the receptionist that you are expecting a call from this client and to put them through.

Internet has grown larger than every one has imagined, as per the recent estimate there are 100 million hosts and 350 million users activity on the internet.

So what does the size of the internet do with the NAT.

An IP address (IP stands for Internet Protocol) is a unique 32-bit number that identifies the location of your computer on a network. Basically it works just like your street address: a way to find out exactly where you are and deliver information to you. Theoretically IPv4 can have 4,294,967,296 unique addresses (2 ^ 32). The actual number of available addresses is smaller (somewhere between 3.2 and 3.3 billion) because of the way that the addresses are separated into Classes and the need to set aside some of the addresses for multicasting, testing or other specific uses. 

With the explosion of the Internet and the increase in home networks and business networks, the number of available IP addresses is simply not enough. The obvious solution is to redesign the address format to allow for more possible addresses. This is being developed IPv6 but will take several years to implement because it requires modification of the entire infrastructure of the Internet and support (2^128) unique address.


Advantages of NAT
1. Reduce the need of public addresses.
2. Extends the longevity of IPv4 by optimizing the current number of IP addresses.
3. Adds security by blanketing an entire network to appear as a single client.


Understand, Public and Private IP by selecting this.


In internet terminology all the communications are performed using Data Packets. Each packet consist of Destination IP, Sender IP, control information and data. 
As your computer is assigned Private IP, others can't reply your request by taking "Sender IP" from the data packet that you have sent.


The NAT router translates traffic coming into and leaving the private network by storing the data inside the routing table.It basically alters the "Sender IP" address inside the data packet, in the same way it memorize and changes the inbound data packet "Destination IP" to what it has changed earlier.

IP masquerading, also called as Network address and port translation (NAPT), port address translation (PAT). 

NAT - Flash Animation Demo. (Select GREEN and RED lights at the bottom of the video on both sides).




Understand, how data packets are sent through different hots to reach the destination server.


Probably your next question would be "Bharath why are you explaining network related stuff in your blog?".
Better having knowledge on networks and protocols for a performance test engineer, so that he can trouble shoot and create better test scenarios. It would be difficult to test, if you don't understand the underlying architecture.



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