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Cisco e3200 can't have more than 4 wired devices on switch

I have recently set up the internet at my house. It was complicated because we can't get the cables to the house, so we had to use a wireless p2p bridge to get the internet to us. So we have the ISP cable, and modem in one house, and the LAN and all users in another.

The ISP connection is fiber optics, into a box which is a modem and a router. The ISP modem/router connects to the internet, and than through eth port1 sends 100mbs connection to a wireless PTP bridge set up using mikrotik SXT Lite5.

On the other end of the wireless bridge is a Cisco E3200 router, running the latest official firmware. The cisco router connects to the internet using Automatic configuration - DHCP. So the ISP modem/router assigns the cisco an IP. Which is

[i]Up to here it all works. The internet works flawlessly, and I've tested it by plugging the bridge ethernet cable directly into a computer, and the computer got it's IP 192.168.1.x assigned instantly, and without an issue. So the ISP modem/router, and PTP bridge work perfectly.[/i]

The cisco than has its own DHCP for the LAN, which is on

From the cisco e3200 goes a single 1GB cat5e eth cable to the TP-link [url=]16-Port Gigabit Switch TL-SG1016[/url] unmanaged switch.

From the switch go 6 connections currently:

Samsung TV, ETA Central heating, PC1, PC2, PC3, Wireless AP (onto which connect numerous smartphones, laptops, and tablets, mac and android)

When it works, it works flawlessy. All the PC's are on 1gbps connections, can ping eachother, can transfer files, DLNA works the internet is smooth etc. etc., so in short it works.

But there are huge problems! The router behaviour is very erratic. Sometimes everything works, sometimes it doesn't. The problems mostly occur on the PC's. The problem is basically that the PC gets an IP assigned by the cisco router DHCP (in the range), and can see other PC's and devices on the network, and can ping other devices, and can transfer files from other devices, HOWEVER CAN NOT ping the router. So it gets IP from dhcp, but can not ping. There's no internet connectivity, and the PC can't connect to the cisco web setup (

So I've started troubleshooting. And there is only one common point. Whenever there are only 4 ETHERNET devices connected to the Cisco router it works fine.

So for example: I can connect 1 cable from the cisco to the tplink switch, and in the switch I can connect 3 PC's and 1 wireless AP, and it will work. Onto that AP I can connect a lot of devices and it will work.

HOWEVER, as soon as I connect additional devices to the switch/or router, for example the central heating unit, the PC's loose connectivity. However this also is erratic. The PC's loose connectivity BUT ONLY AFTER RESTART. The wireless AP still works, but only sometimes.

So the whole thing is weird and very very very hard to troubleshoot.

I have tried so many things, that I might have missed something, so if you have ANY ideas, everything's appreciated.

ATTACHED: I've attached a scheme of my network. The brown blue rectangle shows up to what point things work well.

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