Can't reach ubuntu desktop, but desktop can ping other machines

[Hunterkiller306]

The main computer cannot ping the Ubuntu desktop, but the desktop can ping other machines. I've tried the normal restart server and connection, but am at a loss for how to fix it. any ideas?

Edit 1: After configuring the firewall on the ubuntu desktop, I can now get a reply. Problem is, is that its a "destination net unreachable" from another IP (my guess is the router but idk).

 

[failboat]

Have you nested one of them behind a router/NAT? The same applies with the firewall.
Either could be blocking inbound but allowing outbound.

Ubuntu doesn't turn on the UFW by default. type UFW status in terminal.

https://help.ubuntu.com/community/UFW