NAT

February 12, 2021
Network Address Translation (NAT) refers to a method in which one or several local IP addresses are translated into one or several global IP addresses and vice versa to give local hosts access to the internet.

NAT operates behind a routing device or firewall.

One of NATs’ main functionality in the modern world is the conservation of the global IPv4 space to prevent exhaustion.

How Does NAT Work?

NAT requests are one of the most complex forms of network translations, usually involving large private networks with ranges between 10.0.0.0 to 10.255.255.255, 172.16.0.0 to 172.31.255.255, or 192.168.0 0 to 192.168.255.255, 100.64.0.0 to 100.127.255.255.

Picture this. Your smartphone connected to a home router needs to stream one of your favorite shows. This request is forwarded from your phone to your router, then to the web. But before sending the packet to the web, your router changes the outgoing packet from a private to a public IP address. This is to make sure that the receiving server can get the packet and forward the information back to your device. This is where NAT comes in: it makes sure that the information comes back to your device as a public address and not a private address.

Types of NAT

1. Static NAT

A NAT router in this case maintains a table that logs internal IP addresses with registered IP addresses. This type of NAT is mainly used by devices existing in a private network and need internet access.

2. Dynamic NAT

In this type, several private addresses are mapped in a pool of public IP addresses. The mapping may vary depending on the public IP addresses existing in a NAT pool.

3. PAT (Port Address Translation)

This is a form of dynamic NAT that can map several private IP addresses to a single IP address by leveraging PAT technology. Port Address Translation (PAT) is a NAT extension that facilitates mapping of multiple devices on a LAN to a single IP address for the purpose of IP address conservation.

Applications Of NAT

By using Carrier-Grade NAT, ISPs can share one IP address with multiple subscribers, hence prolonging the use of IPv4, while paving way for an easy transition to IPv6.

NAT also plays a critical role in strengthening security as it’s impossible to establish a connection from outside, with the subscriber behind the NAT.

Another application of NAT is to avoid IP overlapping. This occurs when different hosts with similar IP space try to access the same destination host.

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