Solved Share folder outside own LAN

[bur]

We have some computers in a lab that are in a different LAN than the computers in the office:

Office LAN: 171.31.36.0/25
Lab LAN: 171.30.95.128/25


From the Office LAN I can access shared folders on the Lab LAN computers by mapping them as network drives.

Now I set up a new computer in the Office LAN and shared a folder. Everybody in the Office LAN can see and map that folder.

But the computers in the Lab LAN cannot.

How can I allow the computers in the Lab LAN to access the shared folder from the Office LAN computer?

I know this can somehow be done, since I can access the shares in the Lab LAN. Unfortunately the person who set that up is gone now...

 

[bur]

I probably solved it. Routing from Lab LAN to the Office works, Office -> Lab not.