[Description]

When setting a new network address and changing the subnet in the advanced settings, if it is set to 255.0.0.0 without using the "custom" option but the "255.0.0.0" in the drop down menu, the web management GUI is not reachable and cannot be pinged/nmap shows no 80 port open/host down.

[Steps to reproduce]

1) Follow standard setup all of the way through until it brings you to the home page of the web GUI.

2) Go to advanced settings and then select the LAN sub menu in the network menu.

3) Change the ip to 10.0.0.1 and choose the subnet 255.0.0.0 with its option, not inputting it manually using the "custom" option.

4) Let the device save the settings.

5) Set a static ip of 10.0.0.2 with a 255.0.0.0 subnet.

6) Try connecting with either 10.0.0.1 or the tplinkwifi.net to connect to the web GUI.

[Standard setup used]

Timezone: Pacific time

WAN: No

Wifi radios: Disabled *have tried with enabled but showed no difference

[Expected results]

The web GUI should open to its home page and allow for normal operations.

[Actual results]

The page gives "Unable to connect" error, it does not matter if it is the 10.0.0.1 or tplinkwifi.net for the address entered in the browser. Ping results give "Network is unreachable" and nmap shows "Host seems down".

[Times seen]

5/5 times I tested using the repro steps I was able to see the same issue.

[Additional info]

OS: Linux Manjaro

Version: 5.10.31-1-MANJARO

Connection: Ethernet cable Cat5e

Network card/manufacturer: Qualcomm Atheros QCA8171 Gigabit Ethernet REV 10

Browser: Firefox

Version: 88.0.1

Build: 20210506154205

*I have tried disabling the DHCP server before setting the ip/subnet and it does not show any differences

*I was able to set it up correctly if I set the subnet with the "custom" option, still setting it with the same ip/subnet, just not if you use the "255.0.0.0" option.