DHCP clients are having netmask 0.0.0.0

[ppfoong]

I just noticed all my DHCP clients are having netmask of 0.0.0.0 instead of 255.255.255.0 for my 192.168.0.x network.

Firmware 3004.388.11 on RT-AX86U with YazDhcp 1.2.5

Is this normal?

Subnet mask in LAN IP setting page is 255.255.255.0

There is no subnet mask setting in DHCP page.

DHCP IP pool range is 192.168.0.101 to 192.168.0.199

 

[ColinTaylor]

Is this normal?

No. Check the contents of /etc/dnsmasq.conf for corruption.

 

[ppfoong]

In dnsmasq.conf, there are 3 interfaces: local, br1 and br2, all having a line of dhcp-range respectively.

In dhcp-range, I can see it is 255.255.255.0

I notice that my Windows desktop and laptop are showing the expected class C subnet mask.

However, all my Android devices, including Samsung tab running on Android 14, and Honor phones running on Android 16, are showing netmask of 0.0.0.0

Maybe it is Android related...

 

[PaddraighOS]

Hey, The Android-only behaviour narrows it down. Android 14 changed how it handles DHCP responses and there are known display glitches where the subnet mask shows as 0.0.0.0 in some network info screens even when the underlying routing is correct. First thing worth checking is whether the Android devices actually have any connectivity issues - if they can reach other devices on the same subnet and browse the internet normally, the problem may be purely cosmetic in the display layer. To verify what is actually happening at the DHCP level, you can capture DHCP packets on the router with: tcpdump -i br0 -v port 67 and watch the offer packet sent to an Android device when it connects. Look for option 1 (subnet mask) in the output - if 255.255.255.0 is in the offer, Android is receiving it correctly but ignoring or mishandling it. If that is the case it is a known Android 14 quirk that some YazDhcp or dnsmasq versions trigger, and the workaround in some cases is to explicitly set the subnet mask via a dnsmasq option in YazDhcp settings.

Should sort you out.

 

[ppfoong]

OK. I use adb to check, the subnet mask is correct.

Command: adb shell ip addr show wlan0
Result: inet 192.168.0.123/24 brd 192.168.0.255 scope global dynamic wlan0