What is the difference between SNAT and DNAT for an interface ?

Question

There is a concept of NATing using which interface modifies IP addresses. I want to understand real use case of source natting and destination natting.

Comments

For basic understanding :

Source NAT changes the source address in IP header of a packet. It may also change the source port in the TCP/UDP headers. The typical usage is to change the a private (rfc1918) address/port into a public address/port for packets leaving your network.

Destination NAT changes the destination address in IP header of a packet. It may also change the destination port in the TCP/UDP headers.The typical usage of this is to redirect incoming packets with a destination of a public address/port to a private IP address/port inside your network.

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