Hello to everybody,
I am a very proud Plex user and since a few days ago I am not able to use Plex from one of my access points. I explain.
I have my main FFTH router connected with Cat5E Ethernet cable with another router working as an access point, both with their respective wireless networks and separated each one by a dozen meters roughly. Plex App in mobile devices has been working perfectly with both wireless networks until a few days ago, when suddenly Plex App has stopped working when is connected to the main router, but incredibly works well when connected to the second access point.
I’m getting crazy because everything seems to be fine in that access point, that is to say, when connected to it I am able to ping Plex server, Internet and so on, but when I start Plex App in a device connected to that wireless network, Plex App can’t find Plex server. Also external access is enabled and working well with all my mobile devices outside my home. So, do you have an approximate idea about what is happening?
Thank you very much for your help!
I’d double-check that “Client isolation” or “Guest mode” has not been enabled on the router.
Hi Peter_W,
Thank you for answering. No “Client Isolation” nor “Guest Mode” in my routers, notice that both routers are Livebox from Orange ISP (very simple routers) so they have not advanced functions like those.
Please be careful when reusing routers with Wifi as Wifi-only. I did the same thing and got into ‘trouble’. Step 1: Make certain it’s in Bridge mode and you’re not trying to skirt it by connecting to the backside (peer) LAN ports of the router and having that cross over to the Wifi. Sometimes you get luck, sometimes you don’t.
With it in bridge mode, ALL router function will be off. Your LAN will be completely “Flat” (everything on the same subnet). I’m certain you set it up that way but something changed so please verify again. You might have had an ISP firmware update that’s now causing things to behave differently (as I did).
My resolution was to remove the ‘reused’ modem/router/wifi and get a pure (AP-only) device with no router function. Even an Apple Airport Extreme in ‘Bridge mode’ (meaning it has no IP) works perfect for this. The drawback here is it must be managed from tablet or phone via wifi.
Hi ChuckPA,
Thanks a lot for your answer. When I configured my router as an Access Point, I just connected LAN ports nor WAN port, so I think it’s working correctly, and it has been like this always (installation was made a long time ago and it’s been working very well). However, remind that my problem is not with the Access Point but with the main router, which is working as a FFTH router from Orange ISP. That is to say, when I connect Plex App to the Access Point wireless network, it works like a charm, but when connected to the main router it looses connection with the server and reproduction never starts.
I have tried many things with no success, for instance disabling main router firewall and restoring a full backup of the KVM virtual machine where Plex Server is installed. I have also thought about the possibility of the issue to be in the Plex Mobile App due to a new update, but downgrading to a previous version is not an easy matter thanks to Google.
Thank you very much again.
Provide a topology of your network and I will see if I can assist.
Be careful of that KVM. IF it has a NAT network connection to the actual host’s network, now you’ve got double NAT. All stop right there.
You must make the Guest OS run as a peer host on the same LAN segment.
e.g.
Host : 192.168.1.3
Guest: 192.168.1.13
Hi again,
@ChuckPA, of course, KVM virtual machine has a bridged IP, so the machine is in the same LAN segment as the other devices, physical and virtual machines. As I said before, Plex has been working like a charm with this configuration until a few days ago, either inside or outside my home.
@Ach!lles, All right, I will try it 
As my home is quite long, and in order to provide wireless coverage to the whole home, I have two wireless access points (first a FFTH router, second a router working as an access point) connected by a Cat5E Ethernet cable. Plex App connected to the second access point works well, but when connected to the main router looses connection with the Plex server and the reproduction never starts. Honestly, main router is not directly connected to the second access point, but there are some L2 managed switches across the path, but I’m sure they are not the problem (obviously no firewall or similar, and no modification was made there). As I said, Plex server is running in a KVM virtual machine without firewall enabled, and this virtual machine is running in a HP Proliant Microserver host (without firewall again), both running Debian Stretch. If you need some more details, please ask me.
Additionally, and to complicate things even more, one of the things I tried yesterday was to restart (not reset) my ONT, when suddenly my “dear” ISP took off forever my public IPv4 and gave me a brand new IPv6, so my whole “infrastructure” has stopped working, like port forwarding and so on, and now my Plex server is not visible from outside my LAN, and neither my VPN… All the misfortunes come together :neutral:
Thanks a lot again.
EDIT: I forgot… When I am connected to the wireless network of the main router, I am able to see and to ping all the devices in the network, including Plex server.
I am somewhat confused because initially you said it is fine from the access point but not from the main router wireless. Then your edit states its fine from the main router wireless. Which is it? Are you running different SSIDs?
@Ach!lles, sorry for having confused you. Which is fine from the main router wireless is simply the other tasks which can be done within a network, for instance browse the web, make ping to the rest of the machines in the LAN (including virtual machine where Plex server is running), connect via SSH with all the machines, etc. But as I said, Plex App cannot connect to the server, so when I start the mobile App, I can login well and access my libraries, but when I try to reproduce some media, it never starts and in a few seconds an alert message appears telling me that Plex App has lost connection with the server.
And concerning the SSIDs, the answer is no, SSIDs are the same, and so with the encryption protocol and password (but not the channels, both are separated enough in order to avoid overlap). Initially I set up same SSIDs to leverage the advantage of pre-authentication in WPA2 networks when moving between access points.
