What is NAT? Guide to configuring NAT types

In the context of booming digital services, managing network resources—especially IP addresses—becomes extremely crucial. As a provider of VPS infrastructure and network services, VPTS Company needs to ensure that thousands of servers and devices can communicate stably and securely with the Internet.

One of the indispensable techniques in the network system ofVPTSis NAT (Network Address Translation). This article will help you clearly understand what NAT is, its benefits, and how to apply each appropriate NAT type in a company's modern network infrastructure model.

What is NAT?

Definition:NAT (Network Address Translation) is a technique that enables devices in a private network (using private IPs) to communicate with the Internet (requiring public IPs). NAT "translates" between private IPs and public IPs as data passes through a routing device (such as a router or firewall).

NAT is particularly useful for enterprises like VPTS, where hundreds of VPSs or devices access the Internet simultaneously with only a limited pool of public IP addresses.

Benefits of NAT for VPTS

• Conserve public IPs: Multiple devices share 1 outbound IP.

• Enhance security: Hides the real IP address of the internal system.

• Allows internal servers to be accessed externally if needed.

How NAT works

NAT (Network Address Translation) operations involve modifying the IP address and/or port of a data packet as it traverses a NAT device on the network. The primary NAT operations are as follows:

1. Receive Input Data

NAT starts working when it receives a data packet from an internal network that needs to reach the Internet or an external network.

2. Check NAT Table

The NAT device checks the NAT table to see if there is any record corresponding to this data packet. The NAT table contains information about established connections within the local network, including the internal IP address, internal port, public IP address, and corresponding public port.

3. Create NAT records if needed

If there is no matching entry, NAT creates a new entry in the NAT table. This entry maps the data packet's internal IP address to the external network's public IP address and the internal port to the corresponding public port.

4. Change IP address and/or port

NAT modifies the IP address and/or port of the data packet based on the generated or existing NAT entry. This ensures the data packet has the appropriate IP address and port to travel outside the external network without conflicting with other connections.

5. Forward data packets to external network

After modification, data packets are routed to external networks or the Internet via the NAT device.

6. Monitor connections

NAT tracks connections established in the NAT table. When response packets return from the external network, NAT uses the NAT table information to determine the matching internal IP address and port to route them to the corresponding device.

Applications of NAT

1. Share Internet Connection

NAT allows multiple devices in an internal network to use the same public IP address to access the Internet. This conserves public IP addresses and utilizes them efficiently, while protecting the internal network from external attacks.

2. Internal Network Security

NAT acts as a natural firewall because it prevents connections from the Internet from directly reaching internal network devices. Only connections initiated from within the internal network can reach the Internet.

3. Network performance

NAT can help improve network performance by maintaining a NAT table to track connections. It helps manage ports and distribute network resources more effectively.

4. Multi-port IPv4 support (NAT44)

In the context of IPv4 address exhaustion, NAT44 allows multiple devices on an internal network to share a single public IPv4 address through port mapping. This helps alleviate the pressure of providing a unique IP address for each device.

5. Distribute multiple services on the same IP address

NAT allows multiple services (e.g., web servers, email servers) to share a single public IP address via port mapping. This saves IP addresses and reduces network configuration complexity.

6. Internal network isolation

NAT can create isolation between the internal network and external Internet networks. This ensures internal network devices cannot directly access external devices without NAT authorization.

7. Port forwarding (Port Forwarding)

NAT can be configured to forward connections addressed to a specific port in the internal network to a designated device or service, such as a web server or game server. This allows remote access to these services from the Internet.

Main differences between SNAT and DNAT

SNAT (Source NAT – Network Address Translation)

• SNAT modifies the source IP address of data packets. It is commonly used when data packets travel from an internal network to an external network or the Internet.

• The main objective of SNAT is to hide internal IP addresses and replace them with the NAT device's public IP address.

• Example: If a computer on the internal network has the local IP 192.168.1.2 and wants to access the Internet, SNAT translates the source IP address of packets to the router/firewall's public IP address before sending it out to the Internet.

DNAT (Destination NAT – Network Address Translation)

• DNAT modifies the destination IP address of data packets. It is commonly used when data packets from the Internet or external networks are forwarded to a specific service or server within an internal network.

• The primary objective of DNAT is to redirect data packets from the NAT device's public IP address to the private IP address of a specific server or service.

• Example: If there is a web server on the local network with internal IP 192.168.1.20 and you want to allow Internet users to access this web server, DNAT translates the destination IP address of packets from the router/firewall's public IP to the web server's internal IP.

Differences between Private IP and Public IP addresses

Private IP addresses are addresses used within the local area network (LAN) of an organization, enterprise, or household. These addresses are not used directly on the Internet and can be reused across different local networks without causing conflicts. For example, IP addresses such as 192.168.x.x, 172.16.x.x to 172.31.x.x, or 10.x.x.x are commonly assigned to devices such as personal computers, printers, or internal VPS within a private network. Devices using Private IPs generally cannot access the Internet directly without going through an intermediary device such as a router or NAT.

In contrast, Public IP addresses are unique addresses assigned by Internet Service Providers (ISPs) and used to identify a device globally. Every device wishing to connect directly to the Internet requires a Public IP address to send and receive data with other devices across the Internet. Services like websites, mail servers, or remotely accessed VPS systems must have a Public IP assigned to operate properly.

In short, Private IPs are used within local networks and do not access the Internet directly, while Public IPs are unique addresses used for devices to connect directly to the global Internet.

CONCLUSION

NAT (Network Address Translation) is an essential networking solution that translates IP addresses between internal and external networks, ensuring flexible, economical, and secure Internet connectivity. With popular types like SNAT, DNAT, PAT, or Static NAT, NAT enables efficient and secure control of network data flow.

At the companyVPTS, NAT is widely deployed for multiple purposes: from granting Internet access to VPS instances in the system to exposing internal services to the outside, such as SSH, HTTP, or VPN. Understanding and correctly configuring different NAT types not only helps optimize IP resources, but also ensures the network operates stably, flexibly, and effectively meets business growth demands.

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