Emilie Meyer
Network Address Translation (NAT) is a process that allows multiple devices to use the same public IP address to access the internet. This is useful when the number of users who want to access the internet is limited, as is the case with organizations that want to monitor their employees' online activity. NAT also offers a cost-effective solution, as it conserves legally registered IP addresses. There are three types of NATs: static IP, dynamic IP, and NAT overload. Static IP involves a one-to-one mapping between local and global addresses, while dynamic IP translates the source IP address. NAT overload, also known as PAT (Port Address Translation), maps multiple local IP addresses to a single public one. NAT is a standard feature in most home routers and can be configured through PAN-OS, which uses rules to determine the type of translation to be performed on the source and destination addresses.
| Characteristics | Values |
|---|---|
| Network Address Translation (NAT) | Multiple devices can use the same public IP address and access the internet. |
| NAT device | Changes the source IP addresses and the source ports to its own address and port number, then sends the packets to the destination. |
| Dynamic IP and Port | Translates a private subnet or multiple private subnets to one or more internet routable IP addresses. |
| Dynamic IP | Translates only the source IP address. |
| Dynamic IP (with session distribution) | Destination NAT allows you to translate the original destination address to a destination host or server that has a dynamic IP address. |
| Port Address Translation (PAT) | A type of dynamic NAT that bands several local IP addresses to a single public one. |
| Static IP | Configurable one-to-one, static translation in several formats. |
| Destination NAT | Translates a destination address to a different destination address, for example, a public destination address to a private destination address. |
| Port Forwarding | Translates a public destination address and port number to a private destination address but keeps the same port number. |
| Port Translation | Translates a public destination address and port number to a private destination address and a different port number, keeping the actual port number private. |
| Source Address Translation | Determines the type of translation to perform on the source, the address, and possibly the port to which the source is translated. |
| Destination Address Translation | Makes an internal host accessible by a public IP address. |
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What You'll Learn
Port Address Translation (PAT)
PAT is often used in combination with NAT to make internet routing more efficient. For example, a corporate network may use NAT to allow multiple devices to share a single public IP address, and then use PAT to allow those devices to communicate with the internet using unique port numbers. This combination of NAT and PAT is particularly useful for addressing the shortage of IPv4 addresses.
PAT generates a mapping table that stores the private IP address and port number associated with each public IP address and port number. This table is maintained by the router, which performs the translation of IP addresses and port numbers into their corresponding formats using the mapping table. When a device sends a request to the internet, PAT assigns it a unique port number and translates the private IP address into the public IP address. The destination server on the internet receives the request and responds to the unique port number, allowing the device to receive the response.
To configure PAT, specific commands are required to set up the router's inside and outside interfaces, create an access list of inside source addresses to be translated, and enable PAT with the appropriate global configuration command. PAT can also include advanced settings such as specific port ranges, prioritising certain traffic, and handling a large number of connections simultaneously.
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Source Address Translation
Source NAT (Network Address Translation) is typically used by internal users to access the internet. The source address is translated and kept private. There are three types of source NAT: Static IP, Dynamic IP, and Dynamic IP and Port (DIPP).
Static IP allows a 1-to-1 static translation of a source IP address but leaves the source port unchanged. This is often used for an internal server that must be available on the internet. Dynamic IP allows a one-to-one dynamic translation of a source IP address only (no port number) to the next available address in the NAT address pool. The size of the NAT pool should equal the number of internal hosts requiring address translations.
Dynamic IP and Port (DIPP) allows multiple hosts to have their source IP addresses translated to the same public IP address with different port numbers. The dynamic translation is to the next available address in the NAT address pool, which can be configured as a Translated Address pool with an IP address, range of addresses, a subnet, or a combination of these.
Source NAT is supported on PAN-OS, and it is important to configure the correct NAT policy for source and destination zones. For example, if you are translating traffic that is incoming to an internal server reached via a public IP address, the NAT policy must be configured using the zone in which the public IP address resides.
Source NAT is an important tool for organizations and individuals to maintain privacy when accessing the internet, ensuring that internal IP addresses remain private and are not exposed to external hosts.
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Destination Address Translation
One of the key applications of Destination NAT is in facilitating connections between external, untrusted networks and internal, secured networks. By using DNAT, any host on the internet can communicate with a specific host on the Local Area Network (LAN). This is achieved by modifying the destination address in the IP header of the packets being transmitted.
Destination NAT can be configured for static or dynamic IP addresses. When dealing with static IP addresses, the translation involves mapping a single destination IP address, a range of IP addresses, or an IP netmask. The firewall ensures that the original and translated packets maintain the same format and number of IP addresses. On the other hand, dynamic IP configurations enable the translation of multiple pre-NAT destination IP addresses to multiple post-NAT destination IP addresses.
Additionally, Destination NAT provides the option for port forwarding or port translation. This feature allows for the translation of destination ports in TCP/UDP headers, enhancing the flexibility of network communications.
Destination NAT also plays a crucial role in improving session distribution. By utilising Dynamic IP with session distribution, firewalls can distribute incoming NAT sessions across multiple addresses, optimising traffic flow and ensuring efficient load balancing.
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Dynamic IP and Port
In a Dynamic PAT setup, when a device initiates communication with an external server, PAT dynamically assigns a unique source port number to the communication session. This port number is chosen from a pool of available ports. The combination of the device's private IP address and the assigned source port number serves as a unique identifier for the session. This allows multiple devices to share the same public IP address while maintaining their individual identities.
The dynamic nature of PAT comes into play when the router determines the mapping between the pre-translation and post-translation attributes. In contrast, static PAT involves explicitly defining this mapping. Dynamic PAT is the most common type of address translation, especially in home networks and small to medium-sized businesses. It is also known as NAT overload due to its ability to handle multiple devices with a single public IP address.
One challenge with Dynamic PAT is the potential for packet loss when two hosts pick the same source port. To address this, routers ensure that each packet sent through Dynamic PAT uses a unique source port number, allowing return packets to be distinguishable and forwarded to the appropriate host.
Dynamic PAT offers benefits such as improved security, efficient resource utilization, and scalability. It is an innovative solution for optimizing address allocation and enhancing the performance of certain applications, such as online gaming and video streaming. However, it is important to note that Dynamic PAT is unidirectional, allowing only internal hosts to initiate connections with external hosts.
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Static IP
Static NAT is commonly employed when a device within a network needs to be consistently reachable from outside the network using a dedicated IP address. It is particularly useful for external access to specific devices, such as web servers. Static NAT provides a one-to-one mapping between private and public IP addresses, ensuring that the device can be reliably accessed from both inside and outside the network.
In contrast to Dynamic NAT, where translations are created on-demand and have a timeout period, Static NAT configurations are permanent and do not expire. This makes Static NAT ideal for scenarios where consistent external access to a specific device is required. For example, if you have a web server hosting a website, using Static NAT allows external users to access the website by connecting to the associated public IP address, which consistently maps to the server's private IP address.
Static NAT also has security implications. By using a Static NAT configuration, the external public IP address remains constant, making it easier for security policies and access controls to be implemented. This static mapping allows network administrators to define specific rules and firewall configurations for the public IP address, enhancing the security posture of the network.
Additionally, Static NAT can be used in combination with Port Address Translation (PAT), also known as NAT Overload. PAT allows multiple private IP addresses to share a single public IP address by utilising unique port numbers. In a Static PAT configuration, the IP address is translated, and specific ports are explicitly defined, allowing for granular control over network traffic. Static PAT enables multiple services to be hosted on different internal servers using a single public IP address, providing flexibility and efficient utilisation of IP addresses.
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Frequently asked questions
NAT stands for Network Address Translation. It is a way to map multiple private addresses inside a local network to a public IP address before transferring the information onto the internet.
Static IP allows you to configure a one-to-one static translation. Dynamic IP, on the other hand, translates only the source IP address.
PAT stands for Port Address Translation. It is a type of dynamic NAT that binds several local IP addresses to a single public one.
Destination NAT is performed on incoming packets when the firewall translates a destination address to a different destination address. For example, it can translate a public destination address to a private destination address.
PAN-OS uses rules to configure NAT. These rules are separate entities and are not configured as part of the allow/drop security rules. NAT rules are configured to match on the source and destination zones on the NAT policy.
