Mix intern and extern network
 

I have a home network with the ip-address 192.168.0.* and in my area of the city network we have the ip 217.31.176.*

Now I want to just use the router to control the network, each host behind it should have it's own 217.31.176.*-ip and should be in reach from other boxes.

For example two hosts on my network should have 217.31.176.101 and 217.31.176.102 and both can have ftp servers on port 21.

How can I do that?

You need a bridge