Different Types of NAT (Network Address Translation)

Introduction

Network Address Translation (NAT) is a fundamental concept in networking that plays a crucial role in allowing communication between different devices on a network. It allows multiple devices to share a single public IP address, conserving the limited IPv4 address space. NAT is widely used in both residential and enterprise networks, making it essential for network administrators and professionals to understand its types and functions. In this blog, we will explore the concept of NAT, types of NAT, and key related terms. At the end of this blog, you will clearly understand how NAT works, its importance, and how it can be implemented in different network scenarios.

Before getting into different types of network address translation, let us first understand what NAT is.

What is NAT?

NAT stands for Network Address Translation. It is a process used to translate IP addresses within a network. In simple terms, NAT allows multiple devices on a private network to share a single public IP address when communicating with the outside world. This is achieved by modifying the source or destination IP addresses of packets as they pass through a router or firewall.

Let us now discuss the different types of NAT in detail.

Different Types of NAT in Networking

There are three types of NAT broadly categorized based on how NAT translates IP addresses. Let us look into these types in detail.

1. Static NAT

Static NAT is one of the types of NAT. The simplest NAT implementation comes through Static NAT. A unique public IP address from the external network is mapped to every private IP address from the internal network when using static NAT. The mapping stays fixed since each communication between internal devices and external networks maintains identical public IP addresses.

Working of Static NAT

When using static NAT, the router establishes a one-to-one mapping between every private and external IP network address. The following example explains static NAT implementations.

Here, private IP addresses in an internal network are mapped to unique public IP addresses on a one-to-one basis. The process begins with devices in the internal network, each assigned a private IP address (e.g., 192.168.0.1, 192.168.0.2, etc.), which are not routable on the internet. These devices send data packets to the switch (SW), which forwards the traffic to the router (R). The router, configured with Static NAT, translates each private IP address into its corresponding public IP address (e.g., 200.200.200.1, 200.200.200.2, etc.) based on a predefined mapping.

This one-to-one mapping ensures that each private IP has a fixed public IP, allowing external devices on the internet to communicate with specific internal devices. The NAT translation table at the bottom of the image summarizes this mapping, showing how each Inside Local IP (private) is paired with an Inside Global IP (public). This process enables seamless communication between the internal network and the internet while maintaining a consistent public identity for each internal device.

Use Cases for Static NAT

Static NAT is mainly used to provide outside-world access to a particular device located on your internal network. For example:

• Web Servers: Static NAT allows web server access from the internet by connecting server private IP addresses to public IP addresses.
• VPN Servers: The external accessibility of your VPN server depends on static NAT because this translation system assigns the desired public IP for server reachability.
• VoIP Servers: The use of static NAT in VoIP Server environments supports continuous communication operations.

Advantages of Static NAT

• Simplicity: You can implement Static NAT because its configuration methods and management are straightforward.
• Predictable Communication: Static NAT allows reliable communication management through its predictable mapping, which remains static.
• No Overhead: The translating process creates minimal processing overhead because the translation is done once and remains static.

Disadvantages of Static NAT

• Limited Address Conservation: The use of static NAT provides no benefits for conserving IP addresses because each internal IP requires its own individual public IP address.
• Costly: Static NAT becomes expensive to employ because public IP addresses are limited and costly for managing multiple devices.

2. Dynamic NAT

Other types of NAT include dynamic NAT. The advanced version of NAT is the NAPT (Network Address Port Translation) which is also known as Dynamic NAT. Multiple internal IP addresses get dynamic translation through a public IP address pool when implementing dynamic NAT. The router assigns public IP addresses from its allocated pool after internal network devices start their connection to the external network. After the connection terminates, the public IP address is returned to the pool for potential reassignment.

Working of Dynamic NAT

Dynamic NAT requires a translation table for maintaining records of present active network connections. A request generated from an internal network device gets its source IP address translated into an available public IP from the pool by the router. The translation table maintains records of the mapping of internal IP addresses to their public counterparts, along with the used port numbers. After an external device responds, the router makes use of the translation table to locate both the public IP address and port so it can locate and retrieve the corresponding internal IP address and port.

Here, private IP addresses in an internal network are dynamically mapped to a pool of public IP addresses. The process begins with devices in the internal network, each assigned a private IP address (e.g., 192.168.0.1, 192.168.0.2, etc.), which are not routable on the internet. These devices send data packets to the switch (SW), which forwards the traffic to the router (R). The router, configured with Dynamic NAT, selects an available public IP address from a predefined Public IP Pool (e.g., 200.200.200.1 to 200.200.200.8) and temporarily assigns it to the private IP address.

This mapping is dynamic, meaning the public IP assigned to a private IP can change based on availability. For example, 192.168.0.1 might be mapped to 200.200.200.2 at one moment and to another public IP later. The NAT Translation Table at the bottom of the image shows the current mapping between Inside Local IPs (private) and Inside Global IPs (public). This dynamic allocation ensures efficient use of the public IP pool, as only active devices are assigned public IPs. Once the communication ends, the public IP is returned to the pool for reuse. This process enables many-to-many communication between internal devices and the internet while conserving public IP addresses.

Use Cases for Dynamic NAT

The deployment of Dynamic NAT provides an appropriate solution for multiple devices that access a limited set of public IP addresses. Examples include:

• Home Networks: Most home routers implement dynamic NAT for multiple devices to share one public IP address.
• Small Office Networks: Small businesses with numerous devices can benefit from dynamic NAT for conserving public IP address usage.
• Temporary Connections: Dynamic NAT provides an excellent solution for short-term connection requirements like VPNs and remote access because devices utilize public IP addresses in a temporary manner.

Advantages of Dynamic NAT

• IP Address Conservation: Dynamic NAT allows multiple devices to share a few public IP addresses, which directly conserves the available IPv4 address space.
• Flexibility: Devices that use dynamic NAT benefit from flexible translations because they require no predefined rules for device connection and disconnection.
• Cost-Effective: Dynamic NAT allows shared public IP addresses, which lowers expenses for obtaining numerous public IP addresses.

Disadvantages of Dynamic NAT

• Complexity: The implementation of dynamic NAT needs a more intricate setup and management compared to how static NAT operates.
• Overhead: The translation process involves the operation of a translation table, which results in processing overhead.

3. Port Address Translation (PAT)

Port Address Translation (PAT), also known as NAPT, is an extension of dynamic NAT. In PAT, multiple internal IP addresses are translated to a single public IP address using different port numbers. This allows many devices on the internal network to share a single public IP address.

Working of PAT

In PAT, the router not only translates the source IP address but also modifies the source port number. When a device on the internal network initiates a connection to the external network, the router assigns a unique source port number from the pool of available ports. This allows multiple devices to share the same public IP address without conflicts.

PAT or NAT overload allows multiple devices in a private network to share a single public IP address for internet communication. The process begins with devices in the internal network, each assigned a private IP address (e.g., 192.168.0.1, 192.168.0.2, etc.), which are not routable on the internet. These devices send data packets to the switch (SW), which forwards the traffic to the router (R). The router, configured with PAT, translates the private IP addresses into a single public IP address (e.g., 200.200.200.1) by appending unique port numbers to each connection.

For example, the private IP 192.168.0.1 is mapped to the public IP 200.200.200.1 with port 18, while 192.168.0.2 is mapped to the same public IP with port 19. This many-to-one mapping is achieved by using different port numbers for each connection, ensuring all devices can communicate simultaneously using the same public IP. The NAT Translation Table at the bottom of the image shows the mapping between Inside Local IP:Port (private) and Inside Global IP:Port (public).

Use Cases for PAT

PAT is widely used in scenarios where many devices need to connect through one public IP address. Some common use cases include:

• Residential Networks: Home routers implement PAT to allow their users to connect multiple devices with a single public Internet Protocol address.
• Large Enterprise Networks: In large enterprise networks, PAT functions to maintain public IP address conservation as it allows multiple devices to access the internet.
• Mobile Networks: Mobile networks implement PAT to allow a large number of devices to utilize a limited number of public IP addresses.

Advantages of PAT

• Maximal IP Address Conservation: IP Address Conservation reaches its maximum potential through PAT when devices can use a single public IP address to create connections for hundreds or thousands of devices.
• Efficiency: The PAT makes use of available port numbers effectively so multiple connections remain free of interference.
• Scalability: The PAT offers excellent scalability because it works effectively with large networks that contain many devices.

Disadvantages of PAT

• Complexity: Configuration and management of PAT becomes challenging because PAT performs both IP address and port translation.
• Security Considerations: Security threats arise from PAT because the protocol hides internal devices’ actual IP addresses, which makes tracking malicious activities more difficult.

These are the three types of NAT.

Key Terms Related to NAT

One needs a good knowledge of specific terms to understand Network Address Translation (NAT).

• Inside Local Address: The Inside Local Address refers to the private IP address that belongs to devices operating within the internal network. A network device must maintain its Inside Local Address from within one of the reserved private IP addresses (such as 10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16). The Inside Local Address remains hidden from external devices because it is mainly used for communication purposes within the internal network.
• Inside Global Address: A device located inside the internal network obtains its representation for external access through the Inside Global Address, which functions as the public IP address. This address is mainly configured on the NAT-enabled router to become visible to external devices. Service providers provide a registered public IP address to their clients who require the Inside Global Address.
• Outside Local Address: The Outside Local Address is the public IP address of a device on the external network. This address is mainly visible to the internal network, which allows the NAT router to communicate with external devices. For example, an internal device opening a website that uses the public IP address 200.200.200.200 will show this IP as the Outside Local Address.
• Outside Global Address: The Outside Global Address is the private IP address of a device on the external network. Inside networks cannot see this address since it handles all external network communications. For example, if a website is hosted on a server with the private IP address 192.168.2.100, this is the Outside Global Address.

Frequently Asked Questions

Q1. What is NAT and its types?

NAT is a mechanism with which it is possible to conserver IP addresses and helps in communicating between private and public networks. Different types of NAT include static NAT, dynamic NAT, and PAT.

Q2. What are the three NAT types?

Three types of types of network address translation are:

• Static NAT
• Dynamic NAT
• PAT or NAT overload

Q3. What is type 2 NAT type?

Type 2 NAT type is moderate NAT type.

Q4. What are the different types of NAT in Cisco?

Four types of NAT in Cisco are:

• Static NAT
• Dynamic NAT
• Static PAT
• Dynamic PAT

Conclusion

In conclusion, NAT is one of the significant processes in modern networking. It helps in conserving IP addresses, enhancing security, and allowing communication between private and public networks. In this blog, we have discussed different types of NAT, including static NAT, Dynamic NAT, and PAT or NAT overload. We have explained types of network address translation, their functioning, and use cases, along with their advantages and disadvantages.

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