NAT

NAT/PAT

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This material was developed with funding from the National Science Foundation

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This work is licensed with a Creative Commons Attribution 4.0 International LicenseEndFragment

Network Address Translation/ Port Address Translation

IPv4 is a 32-bit address space that supports a total of four billion addresses worldwide. With the proliferation of devices that can connect to the Internet, there was a growing need to exceed the 4-billion address capacity. In 2002, the Internet Engineering Task Force (EITF) proposed a solution—network address translation (NAT).

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190.157.16.200 102.222.1.8 20.17.250.233 188.176.100.5 13.16.19.1 56.100.150.17 160.30.200.8 99.88.17.1 105.96.122.116 233.204.1.16 154.45.92.124 78.99.100.5 77.177.17.1

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NAT uses two types of IPv4 addresses: public and private. To create private IP addresses, the IETF proposed the implementation of RFC 2663 establishing three PRIVATE pools of IPv4 addresses. These private IP addresses are only used inside a private network such as a home or office since they are not allowed on the Internet. This means that private IP addresses can be reused by any private network whereas a public IP address can be used only once.

All devices on the Internet must use a public IP address that falls into the traditional Class A, B, or C range.

192.168.0.9

192.168.0.1

192.168.0.2

192.168.0.10

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192.168.0.3

192.168.0.4

192.168.0.5

192.168.0.6

My computer needs the latest security updates The latest episode for my streaming show is available.

192.168.0.7

Isaac only has one Internet connection and one public IP address assigned by his ISP. NAT allows devices with a private IP address to communicate outside the private network. Multiple devices can access the same Internet connection at the same time.

192.168.0.8

Device sends request to router for remote server

Outside Public Address 65.97.14.76

Default Gateway Address 192.168.0.1

When the device needs access to a network, it sends a request to the router. The router converts the private address to the public one. The private network has only one public address assigned by the ISP, so the router also adds a unique port number and saves this information to its NAT forwarding table.

sending from 65.97.14.76/1007

Click to continue

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Router checks NAT translation table

Used in the local area network side of the network.

Paid

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Public IP Addresses are:

Provided by the ISP and used in the wide area network side of the network

Helps to conserve the IP address space

Allows mutliple numbers of private addresses to access one Internet connection

Free

Advantages of Using NAT

Able to be reused on different LANs

Required to access the Internet

Hides the real IP address of an internal network devices from the public network and acts as a firewall

Unique and cannot be reused on any network

Private IP Addresses are:

Not routable

Each device within Isaac’s private network recieves a private IP address, and the devices can communicate with each other using these addresses. But what happens when one of these devices needs to communicate outside the private network? Remember, private IP addresses are not pemitted on the Internet.

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Outside public address: 65.97.14.76

Offer is 192.168.0.3

Default Gateway Address: 192.168.0.1

Isaac has a home network with a wireless router. His Internet Service Provider (ISP) provides a public IP address for the router’s outside interface.Isaac is responsible for configuring his home network. First he assigns the router (the default gateway) a private address to its inside interface. Next he creates an IP address pool with a range of addresses that the router uses to automatically assign a private address to each device that requests one. Finally, he enables NAT on his router.

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192.168.0.3

Inside Private Address Range: 192.168.0.1 - 192.168.0.255

Requesting an IP address

NAT enabled

Click to configure the network

The remote server sends back the reply. The router checks the NAT translation table to send the data to the requesting device.

replying to 192.168.0.8

replying to 65.97.14.76/1007

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Device sends a second request for a different remote server

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When multiple requests come from one device, which content needs to be displayed on which page? NAT was enough to handle a single request, but what about multiple requests? Enter Port Address Translation (PAT). With PAT, the port is also noted. The tablet has only one IP address with multiple browsing sessions. The router tracks which packets are for each request.

sending from 65.97.14.76/1001

sending from 65.97.14.76/1004

Router checks translation table

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replying to 192.168.0.3:9000

replying to 65.97.14.76/1004

The remote server sends back the reply. The router checks the translation table to send the data to the proper application on the requesting device.