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We have the following setup at the office:

Some of the clients (laptops) have static mapping, some of them (mostly the cellphones) are using IPs from the dynamic pool.

What happens is that random devices about once in 1-2 weeks loose network connection - i.e they cannot connect to any other device, nor the internet.

Common things across devices:

  • the IP address looks fine
  • DHCP renew does not help - they fail to contact the DHCP server, while other clients have no problem doing so at the same time
  • DHCP server logs say that the device managed to renew its address properly
  • the AP status page says that the client is associated
  • no such problem has been known to happen to wired clients

For the laptops that are running Windows 8.1/10:

  • it is enough that we switch the wifi adapter off and on (from Windows, not the kill switch on the keyboard) - they get back connectivity right after reconnecting to the network

For the Android devices (5.0+ too), it seems more persistent:

  • tried restarting the phones & the APs, nothing works - they just sit on the wifi, without being able to use it (small exclamation mark next to the wifi icon).
  • looking at the routing table, the office gateway is there, but it is set not to be used
    • tried pinging the cellphone from another office machine - and it responds
    • tried pinging anything in the office from the phone - does not work
    • traceroute tries to go via the cellphone network (because of the wrong routing table I guess)
    • going home, the cellphone works perfectly with my own wifi - back at the office, same problem
    • it goes away after some time - few days/weeks/months... and then it appears again

Happens to iPhones too, but have not tried debugging there.

According to colleagues, they had problems with the wifi when they used another kind of access point. Not sure if it was the same problem.

I am going a bit crazy because of this - any ideas? Where should I look, which device, what tool, what log...?

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  • Try different wireless gear. As much as I want to like Ubnt devices, we have nearly constant problems with them, especially in high-use, high-noise environments. We did see issues like you describe and were never able to resolve it or truly find a root cause other than knowing it was something to do with the UniFi wireless gear. The problem resolved itself after living to Ruckus equipment. – EEAA Oct 27 '15 at 11:57
  • Did a quick check on the prices - they do seem to suggest there is a difference. Ubiquiti: $79, Ruckus: $730. I'll try to get one of the Ruckus APs if I can :) – sfThomas Oct 27 '15 at 20:15
  • The RF section on the Ubiquiti APs is garbage, and the software is unreliable as well. I always dreaded when I needed to perform firmware upgrades on them, as there was a about a 50% chance that any firmware update would actually reduce performance and break functionality. – EEAA Oct 27 '15 at 20:17
  • In general with WiFi gear, you get what you pay for. Anyone can write software to manage wireless, but designing a reliable RF section requires real dollars to be spent on experienced RF/EE engineers. – EEAA Oct 27 '15 at 20:18
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  1. tried pinging the cellphone from another office machine - and it responds
  2. tried pinging anything in the office from the phone - does not work
  3. traceroute tries to go via the cellphone network (because of the wrong routing table I guess)

The above items relating to the smartphone would tell me that the DHCP server is offering IP addresses that are already in use, so the cellphone does not actually get one. After pinging the cellphone from another office machine, do an arp -a and see if the MAC address associated with the IP address that was just pinged matches the MAC address on the expected phone. If it does not match, some other device besides the cellphone is responding to the ping. Maybe a device with a static IP? Exclude that IP address from the DHCP pool.

Have you done a network trace to make sure there is not another DHCP server on the LAN? Maybe the firewall or UniFi itself?

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