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Network Address Translation(NAT)

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Network Address Translation (NAT) is a technique used in computer networking to allow multiple devices on a local network to share a single public IP address. It operates at the network layer of the OSI model.

When devices on a local network communicate with the internet, NAT translates their private IP addresses into a single public IP address before sending the data packets to the internet. This helps conserve public IP addresses and adds a layer of security by hiding the internal network structure.

There are different types of NAT, such as Static NAT (one-to-one mapping), Dynamic NAT (maps private addresses to public addresses dynamically), and Port Address Translation (PAT), which is a form of dynamic NAT where multiple private IP addresses are mapped to a single public IP address using different ports.

Let's delve a bit deeper into how NAT works and the different types:

  1. Static NAT:

    • In Static NAT, a one-to-one mapping is established between a private IP address and a public IP address. This mapping is typically manually configured and remains constant.
  2. Dynamic NAT:

    • Dynamic NAT allows a pool of public IP addresses to be shared among multiple devices on the internal network.
    • When a device from the internal network wants to communicate with the internet, it is assigned an available public IP address from the pool dynamically.
  3. Port Address Translation (PAT):

    • PAT, also known as NAT overload, allows multiple private IP addresses on the local network to be mapped to a single public IP address.
    • It uses different ports to distinguish between the internal devices. This is the most common type of NAT used today.
  4. NAT Process:

    • When an internal device sends a packet to an external destination, the NAT device replaces the source IP address and port of the packet with its own public IP address and a unique port number.
    • When the external system receives the packet and sends a reply, the NAT device uses its translation table to determine which internal device to forward the reply to.
  5. Benefits:

    • Address Conservation: NAT helps conserve public IP addresses as multiple devices can share a single public IP.
    • Security: It acts as a firewall by hiding internal network structure. External entities only see the public IP address, adding a layer of security.
  6. Drawbacks:

    • Limitations for Inbound Connections: Traditional NAT can complicate hosting services from within the private network as it doesn't easily allow external devices to initiate connections to internal devices.
    • Complexity in Application Layer Protocols: Some protocols embedded in application layer data, like FTP and SIP, might not work seamlessly with NAT without additional configuration.

Inconclusion these nuances helps in configuring NAT effectively based on the specific needs of a network.