Nighthawk RAX15 -LAN setup change subnet mask but it does not get change

[cordycep]

    Under Netgear LAN menu setup, I change the subnet mask  from 255.255.255.0 to 255.0.0.0   and click apply.

   But checking network setting using "ipconfig/all" the subnet mask never got change -still the old 255.255.255.0.  Re-Checking the LAN menu setup it show the new subnet 255.0.0.0.    I tried hard reset power on the router and perform  ipconfig/all it still shows 255.555.555.0   even though the LAN menu setup has the correct 255.0.0.0 .     I also tried disabling DHCP but still not change.

thanks

[FURRYe38]

Netgear has set up a community forum specifically for the NightHawk RAX WiFi 6 Router products. Most of the people who watch that forum are more likely to have experience with NH router products and know how to work it better than those of us who follow this router forum. Might be more likely to find someone who has a solution if the question is posted there:
https://community.netgear.com/t5/Nighthawk-Routers-with-WiFi-6-AX/bd-p/en-home-routers-nighthawk-wif...

Please use this link to the main forum product list to review and choose where to make your posts. 
https://community.netgear.com/t5/NETGEAR-Forum/ct-p/en-netgear

Thank you.