Hello,
I am having an odd problem in a client's network and it is causing big issues. Please see the (simple) star topology below:
5x Cisco Small Business Switch SG220-50
1x Fortinet FortiWifi 60D firewall
A whole bunch of desktops and printers and servers
The problem we are having is that at very random times, no consistency whatsoever, internal clients lose connectivity to only the gateway which is at x.x.x.1. When this happens the entire office loses their internet connection. All internal resources such as servers and printers are still available and reachable, except the gateway.
When this problem occurs I ran an infinite ping -t to the gateway's IP and what I saw is intermittent replies and timeouts. I thought, because only the gateway is affected, that there would be a machine in the network assuming the gateway's IP address and so causing an IP conflict, but when checking the arp on a computer and checking the MAC address table on the switches, I do not see anything conflicting. Also, when I disconnect the internal interface of the firewall from the network, all pings timeout so there is no other device in the network that is assuming the gateway's IP address.
Now here comes the weird part I cannot explain. While working on this issue I was convinced there was a device in the network causing this. I disconnected cables one by one from the switches and then at some point the connectivity to the gateway is restored. After tracing the cable to the specific workstation I found a computer in sleep mode, so it wasn't even on. I turned it on and did an ipconfig. It had a normal IP address from the DHCP pool. Anyway, the connectivity to the gateway was restored and I called it a night. The next day the office's connection ran perfectly fine until the end of the day. Then the issue started occurring again. To fix it I had to do the exact same thing, but this time the connection got restored after disconnecting different cables on another switch. Again when tracing the cable to a workstation, there is no IP conflict on the computer. Also, after disconnecting the cables and the connection is restored to the gateway, I reconnected the workstations to the switch and everything was still working fine. However, the connection to the gateway keeps going down randomly and the only way to fix it is by disconnecting cables from the switches. I can't figure out what is going on and the times it happens is randomly and also every time I have to disconnect different cables in order to fix the problem.
Also, when this problem occurs I tried connecting my laptop straight into the inside interface of the fortinet firewall and that was working perfectly fine so I do not think the problem is caused by the firewall.
What can be the issue here?
Any help is greatly appreciated.