Airport Extreme reserves ip but ping fails

Hi,

I have an Airport Extreme 802.11ac which is connected to Internet via FIOS on the WAN port. The AEX is connected via a cable to a switch which connects two PCs running Win 10.

Using Airport Utility 134.22 on an iPad I am reserving two addresses (192.168.1.180 and 192.168.1.190) for the two PCs and naming them in the description field.

On each of the PCs ipconfig shows that the IP addresses are correctly assigned. However, when I try to ping one machine from the other using the ip address the ping times out. When using the machine name (the 'description' field in the Reserve screen) ping reports that the host name is not known ('Ping request could not find host ...').

What could I be missing?

Thanks,

Vladimir

P.S. When reserving another address (192.168.1.170) for a PC running Ubuntu and naming it, I can ping it from a Win machine using the IP address but not the name. I cannot ping the Win machine from the Ubuntu one though.