general question about DNAT-rule

[Stefan Bauer <stefan.bauer@xxxxxxxxxxx>]

Dear Users,

please help me to understand the processing of packages when a DNAT-rule is setup.
With DNAT on a Router the destination address is changed so a package with 
SRC: 1.2.3 and DST 4.5.6 
will become
SRC: 1.2.3 and DST 7.8.9

If the receiver answers it is

SRC: 7.8.9 and DST 1.2.3

so if this packages is arriving on 1.2.3 it will get dropped as the sender was talking to 4.5.6 and not 7.8.9.

Now to my question - is a SNAT-rule mandatory on the Router or is there some other process of "reverse-NAT" the answer packages to the initial sender?

I want to understand what is happening with the packages and answer-packages in detail.

thank you in advance

Stefan
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