Explanation and Difference between Port Overloading and Port Translation

Though port-overloading and port-translation seems to be almost equivalent, this article focuses on a minute difference between these two.
Below example will bring out the difference between two:


Client ( —— ( SRX ( ——– ISP ——- Servers (,,

Consider SRX has interface based NAT configured on it.
This means if my client sends a packet to each of the server,,, it would take a source IP as

Scenario 1:

Scenario 2:

Now, in both scenarios mentioned above there is a PAT, because I do see a change in the port numbers after NAT.
Here comes the difference:
In scenario 1, port-overloading is at work but not in scenario 2. The reason is because I am using the same port 5000 for interface NAT’d IP, for 3 different sessions but not in scenario 2.

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James Palmer

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