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Barracuda Load Balancer

Network Address Translation (NAT)

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Network Address Translation (NAT) maps outbound IP addresses to prevent exposing internal IP addresses.

NAT allows you to:

  • Conceal the internal IP address from external exposure or access.
  • Reduce the demand for registered IP addresses because internal IP addresses are not revealed to the outside world.

Incoming IP addresses can be translated to correct internal IP addresses.

Source Network Address Translation (SNAT)

Source Network Address Translation (SNAT) maps internal IP (private IP) addresses to an external IP (public IP) address. SNAT re-writes the IP address of the computer that originated the packet. SNAT is composed of two steps:

  • The process of translating an internal IP address into an external IP address;
  • The process of undoing the translation for returning traffic, that is, rewriting the IP address of the computer that originated the packet.

On the NETWORK > NAT page, you can define an SNAT rule to allow Real Servers to forward traffic to the Internet.

Create a Source NAT Rule 

To create a source NAT rule, complete the following steps:

  1. Log into the Barracuda Load Balancer ADC as the administrator, and go to the NETWORK > NAT page.
  2. In the ADD NAT RULE section, enter values for the following:
    • Pre SNAT Source - Enter the internal IP address or source network that is to be translated.
    • Pre SNAT Source Mask - Enter the subnet for the entered network; you can use a 32-bit netmask if required for single IP NAT.
    • Protocol - Specify TCP or UDP.
    • Destination Port: Either enter an individual port number (for example, 80) or a range of port numbers (for example, 100-200). The default value of 1-65535 allows all ports.
    • Post SNAT Source: Enter the source IP address after the translation. If you specified a range in the Pre SNAT Source Mask, this is the first IP address in the translated range.

      There must already be a virtual interface configured on this system with the IP address (and range, if applicable) specified in Post SNAT Source. If not, the NAT rule will not be added and you will get an error message.


    • Outgoing Interface: The network connection that the outgoing traffic passes through.
  3. Click Save.
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