Ytdyklly

I am using Linksys EA 6900 in home setup. There are multiple devices like TV, Phones, Tablet, Wireless speakers connected to router via 2.4 & 5 GHz channel.

I started to observe problems with setup - like few devices not being able to access others - when I enabled guest access on 2.4 channel.

When the guest network is turned off, all works fine.

I checked the setup in WiFi analyzer, it shows that the two networks (main 2.4 & guest 2.4) are operating on same channel (4). And I think its root of all problems.

I cannot find any option on the admin pages of router that would allow me to set separate channels for the two networks.

Any idea how to do this?

EDIT:
As pointed out, this is most probably not issue with wifi channels.
I was looking around and found : http://forum.xda-developers.com/showthread.php?t=1371794
Somehow MAC and IP of gateway was somehow confused by device.

As I observed, the MAC address of the two SSIDs(main & guest) differ by only last digit, so could it be the case? The problem was observed twice, once when Android tablet was not ping'able and other time when only the tablet was ping'able from an wired desktop.

After turning off the guest wifi, the problem resolved in few seconds, everything was working well.
The 5 GHz devices are unaffected by the problem.

This is not possible because this devices typically only have one radio transmitter. So all clients use the same physical interface and are separated with VLANs.
But I don't think this is the cause of your problem.
The clients interfere with each other at device level, not network level. If you have 10 clients connected they interfere with each other potentially. If you conncet 5 to your main Wifi and 5 to your guest Wifi it is still the same.

This smells like your guest Wifi is misconfigured in some way or like albal said it is a coincidence.

I think it might be a matter of coincidence that things are better with Guest Wi-Fi turned on or off - do you have some empirical evidence?

Normally on a domestic Wi-Fi access points it is not possible to use separate channels for different base stations on the same band (i.e. 2.4GHz or 5GHz). You may have the have an SSID bound to one band (i.e. 2.4GHz) and another SSID bound another (i.e. 5GHz). Much of the 2.4GHz range overlaps anyway so unless you were able to use distinct channels actually having the SSIDs on the same frequency would be better than being separate.

The first thing to do is check you have the latest firmware - often new firmware is release to address Wi-Fi performance issues.

Wi-Fi analyzer should show you all the other access points in the area and what channel they are using. I would recommend you choose from either 1, 6 or 13 (in the 2.4GHz band) - sometimes the automatic option on a Wi-Fi router does not perform well.

To asses which band to use as a first stab (and this does not take into account signal strength or use) just total up the number of access points using channels 1, 6 and 11. If you have access points using say 2 or 8 then you will have to count them twice for the channels they overlap - i.e. 2 overlaps the signals for both 1 and 6.

If you have a draw or close draw then choose the channel that has the least stronger signals in there.