Does the DSL Router provide the IP settings for all the PCs? In other words does it run as a DHCP server, proving automatic IP addresses to all the computers connected to it?
I suspect this might be the problem - you could set the 11 PCs IP address manually so long as you ensure they are on the same subnet as the DSL router - e.g. if the router's address is 192.168.0.254 then make the PCs 192.168.0.2 - 192.168.0.12 etc