RT-AC88U LAN to LAN access problem

[mekabe remain]

The following problem originally is noticed on my new RT_AC88U router with AsusWRT (original latest) firmware. Then I thought maybe it could be solved on AsusWrt-Merlin firmware, and since I would also change to AsusWRT-Merlin, I made the change.
I am very happy with the Merlin fw. But I still have the problem described below.

I could not access Asus official forum , maybe someone here can help me.
I'm sure I am doing something wrong in the configuration, although I don't know what it could be. Because I did not modify advanced settings of Wifi.

The problem:
My 2 LAN clients on same wifi SSID can not reach eachother. I tried with different client (2 Windows 10 PCs, 1 Windows 7 PC, 2 Android phones)
If I connect one client to 2.4Ghz and the other to 5Ghz then they can reach. If they are on same wifi frequency they can't.
I tried using ping and other network tools to test the access. It seems that the router is blocking access if we are on the same virtual interface.

how can I troubleshoot and solve this issue ?

Thanks.

 

[ColinTaylor]

Go to the Wireless > Professional and for each band make sure "Set AP Isolated" is "No".

 

[mekabe remain]

thnaks for your answer. but they are all set to "no" (I guess that's the default)
so that's not it.
what else should I check ?

 

[mekabe remain]

btw, I installed tcpdump and checked packet capture.
I see that the arp request is being sent but no reply is received.
what does that mean ?

 

[mekabe remain]

could this be related with windows clients ?
I had 3 windows clients at home and all of them has the problem.
but they did not have this issue before the Asus router (there was a Netgear r6700)

 

[mekabe remain]

seems there is a problem with my windows client connection to asus router.
because now it disconnected and could not connect until I disable/enable my network adapter.
but there was no problem with the old router (Netgear)

what is this incompatibility issue ?
how can I isolate it ?

 

[agilani]

Did you set the ssid as a guest ssid? Can you do wired to wired? wired to wireless and vice versa?

 

[mekabe remain]

one of my test clients was wired. So I tried wired and wireless as source and destination.
Btw, this problem does not occur on ALL destinations. With Some LAN clients as destination , I can ping/reach.

So , it's like some of the source client's arp requests are not welcome on the router ?

 

[mekabe remain]

now I installed a ping tool on my Android phone to isolate if the problem is on the source client. (Windows)
the same problem occurred on Android as the source.
So it's not a source issue.
Maybe the destination is not responding to arp request.
But there are many of these destinations (mainly Amazon Echo devices and Sonoff switch and some IP cameras)

 

[mekabe remain]

I just made another test.
Got the list of all connected devices from router.

Tested with ping from my windows client.
ALL wired devices are reachable
NONE of the wireless devices are reachable

So the problem is with the wireless destinations. (ALL of them)
The source does not matter. Either windows or android, either wired or wireless it can not ping wireless devices.

 

[mekabe remain]

I've gone through all the features in wireless professional settings.
ANd found out that "Airtime Fairness" feature is breaking.
if it is enabled, I can not ping wireless clients.
when I disable it , I can ping all of them.

does this make any sense ?

 

[ColinTaylor]

does this make any sense ?

Yes. It's known to cause problem with some devices.

https://www.snbforums.com/threads/guide-troubleshooting-wifi-issues.12825/#post-375354

 

[mekabe remain]

ok. now I have another issue. Sometimes, my connections drop and all of my clients on LAN (wired and wireless) disconnect from internet.
And they can not connect again until I reboot the router.
until I reboot, router seems normal (all leds OK) but no connection is possible.

is this a known issue ?
if yes, is there a workaround like the other one I had ? (disabling some feature)