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In port forwarding, is the ultimate destination to connect to solely decided by the intermediary entity which provides port forwarding, not by an application client?

Although the page mentions dynamic port forwarding (such as provided by SSH), is it correct that dynamic port forwarding isn't port forwarding, because its ultimate destination is decided by application client itself not by the intermediary entity? Is dynamic port forwarding not port forwarding, but proxy?

Thanks.

A complement to https://unix.stackexchange.com/questions/498849/what-are-the-relations-and-differences-between-port-forwarding-and-proxy to help me understand their differences.

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  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you can provide and accept your own answer.
    – Ron Maupin ♦
    Commented Dec 14, 2019 at 20:02

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Basically, port forwarding is creating a manual, static entry in the NAPT table. The table will build dynamic entries as traffic is sent from inside to outside (these entries will eventually close or time out) so that traffic can return to the original sender. If the original sender is on the outside, the table will not have an entry for that. To allow outside initiated traffic, you manually create a static entry in the NAPT table, and that is called port forwarding.

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  • Thanks. (1) How can I check the NAPT table on Ubuntu to verify the port forwarding created by ssh? (2) is it correct that dynamic port forwarding isn't port forwarding, because its ultimate destination is decided by application client itself not by the intermediary entity? Is dynamic port forwarding not port forwarding, but proxy?
    – Tim
    Commented Feb 6, 2019 at 23:50
  • Unfortunately, hosts/servers are off-topic here. We can help with on-topic, enterprise grade devices, like routers and firewalls. What you call port forwarding is really subjective. There is no standard that says this is port forwarding and that is not port forwarding. To most people, port forwarding is when you manually configure the NAPT device to forward outside-initiated traffic, and the dynamic table entries are considered just part of the NAPT process, even though both accomplish the same type of thing.
    – Ron Maupin ♦
    Commented Feb 7, 2019 at 0:04
  • WHere is the NAPT table on Ubuntu?
    – Tim
    Commented Feb 7, 2019 at 0:11
  • I don't know, but hosts/servers are off-topic here. You can ask about those on Server Fault for a business network, or on Ask Ubuntu or Unix & Linux.
    – Ron Maupin ♦
    Commented Feb 7, 2019 at 0:14

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