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NAT how it is works?

Hello all!!!

It is more theoretical question...

I have follow configuration:

LAN network with addresses 192.168.0.0/24

WAN ADSL interface with two sub interface

Sub Interface 1 have globally assigned ip address (for example ? not really) 217.107.182.22

Sub Interface 2 have locally assigned ip address 172.16.182.22

ISP has recommended to access internet use address 217.107.182.22

And to access ISP resources (include resources with globally assigned ip address) use address 172.168.182.22. For this I should add some static routes to my router.

I use dynamic NAT with overload:

192.168.0.0/24 =>217.107.182.22

192.168.0.0/24 =>172.16.182.22

All works fine

But when I have configure static NAT:

217.107.182.22 25 => 192.168.0.1 25 (MS Exchange)

I have some trouble with Networks defined in static route (for example 217.107.50.0/24)

When user from this Network try telnet to 217.107.182.22 25 packet destination translated to 192.168.0.1 25?

But telnet session does not established? because when packet going back it routed first to 172.16.182.22 and after what translated to 172?

Please can anybody explain:

NAT works incorrectly??? (I think that NAT works fine)

Or

NAT configured incorrectly???

Or

ISP does not provide this issue???

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