Current Modem: TM I-240G-P (the oldest one)
Current Router: TP-Link Archer AX90
Switches: D-link DGS-1005A Gigabit Switch
Internet Plan: unifi advanced plus 500Mbps

Last month I started experiencing internet completely down issue where previous router ASUS RT-AC68U AC1900 totally cannot access internet at all. Called TM and they sent a technician over and immediately the internet worked, but stopped working as soon as he left. They blamed it on my router, and since I was having video steaming issues ever since I switched to previous router, I decided to get a new one listed above after 3 years. Today, the same issue appeared again with my new router. The router light turned red, and my main PC (connected via LAN) was unable to access the router login page. With many devices, only my iPhone was able to access it. I borrow a LAN cable and removed it from my TV, and boom the internet worked again. Is there a maximum limit of LAN devices connected to a router? Currently running 2 switches, each with 3 devices connected per switch, plus 2 devices (one extender and one NAS).

Very very odd. From my main PC connected via LAN to a switch, I wasn't able to access the router page via tplinkwifi.net or 192.168.0.1 and was assigned a completely different IP address that is not even 192.168. The only way to make the internet suddenly recover again is to unplug my SONY Smart TV in my bedroom, which I was just using the night before both downs (it's a smart TV and I was streaming content from my NAS).

I tried searching online but couldn't seem to find any solutions or answers to this, maybe someone here can shed a light on this matter. I get it if it happened to 1 router but 2 routers now.

Cheers!

Oh ya, not all of the LAN devices are all operating at the same time.

Most good routers can handle at least 200 devices so I don't think that is your problem.

Are those managed switch or unmanaged switch? (Maybe IP clash, Just guessing if the problem doesn't comes from TM.)

If PC, can try goto device manager, network card (or on-board), properties, untick allow this device to power off to save power.

Another is to set static ip and try see if there's any difference. Set dhcp range to start from .100 and then you can manual set those between .2 to .99 as static ip for your nas, tv, pc etc.

Maybe can try check or replace the LAN cable to SONY smart TV to see if its a faulty cable issue.

sound like your network got more than 1 DHCP server.

I believe the DGS-1005A is unmanaged switch

i can't seem to set static ip from the pc side for some reason. it immediately goes into unidentified network.

i had to use address reservation from the router's menu.

havent tried messing with dhcp range

Basically same problem as mine. The switch kena ARP poisoning and need to reboot.

The solution is to replace the dumb switch with a managed switch. It is smart enough to filter out the bad traffic.

Looks like is dhcp problem.

I think TS need 1 software to scan the whole network.

So it will show all devices which connect in the network with all ip address. That is easy to tackle which device got crash with your currect DHCP.

Nope it wont happen onviously is tm themselves now

One of your devices is drawing too much bandwidth. Mining? Malware bot?

Switches smart or "dumb" don't do "bad traffic" filtering. That's already in the realm of firewall.

TS, try the static IP solution first and inform the results here..

Try limiting the number of your DHCP server IP assignment range to like around the number of your devices connected to your switches and routers somewhere like 50? Change your netmask to something smaller like 255.255.255.0.

Assign fixed IPs to each device one by one.

Disable IGMP Snooping and Pingback.