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PROBLEM: When I lose internet connectivity my internal network loses connectivity, meaning, I am unable to connect to any other device on my network while the internet connection is down.

I have an internal wired network in my home that consist of the following:

  • 12 Foscam IP cameras (wired)
  • Windows 2012 R2 Server (IIS FTP Server and IIS Web Server)
  • Windows 10 Professional (8 machines in total)
  • Ubuntu 20.04.1 (A minecraft server for my kids)
  • Two five port unmanaged switch
  • One five port managed switch
  • One 16 port unmanaged switch
  • Linksys Mesh Wifi Router
  • Netgear Cable Modem

Every device on this network has a statically assigned IP number in the 192.168.0.0/16 subnet. The only device directly connected to the Netgear Cable Modem is the Linksys Mesh Wifi Router.

When internet connectivity is down I open a command prompt on any computer and attempt to ping any other computer or any of the ip cameras and the ping times out. Each camera connects via FTP to my FTP server and uploads a continuous stream to the FTP server and connects via IP number only. When the internet connection is down, the cameras cannot reach the FTP server. (DNS is not involved). The kids (who am I kidding, I play too) cannot connect to the Minecraft server even though they attempt to connect using IP number only. In short, there is NO intranet connectivity at all if the internet connectivity goes down.

What I have tried: I have ensured that the only thing connected to the Linksys Mesh Wifi Router is the 16 port hub in an attempt to isolate the network from the hub if the router goes down or loses connectivity to the internet. If I disconnect the ethernet cable between the router and cable modem I am able to ping any device on my network. If I disconnect the ethernet cable between the 16 port hub and the router I am able to ping any device on my network (I have tested this while the router has connection to the internet and while it is unable to connect to the internet). This issue only occurs if the connection within the router goes down while it is still physically connected via ethernet cable to the rest of the network. When the connection is restored AND I reboot the router connectivity is reestablished within the internal network.

If anyone can shed light on this phenomenon, I would certain appreciate it.

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  • Upload the image somewhere and post the link, we can embed it for you.
    – Moab
    Jan 31, 2021 at 17:29
  • @Moab While there is a windows server 2012 R2 server on the network, it does not act as a domain controller. The only services running are IIS FTP and IIS Web
    – John Stottlemire
    Jan 31, 2021 at 17:40
  • When the net link goes down, do you see any activity on the switch port the router is connected to? My employer once had a broken switch that flooded the entire network with invalid Ethernet frames, slowing all computers to a crawl.
    – Daniel B
    Jan 31, 2021 at 17:51
  • (1) Do you know why the internet goes down? (2) What model is the cable modem? (3) Which box is the DHCP server? (4) Ditto for the DNS server? (5) Do you ping using IP or computer name? (6) Did you try another cable modem?
    – harrymc
    Jan 31, 2021 at 17:51
  • @harrymc 1) I have no idea why it goes down however, it normally always returns with a reboot of the router and cable modem. 2) NETGEAR Cable Modem CM1000 3) DHCP is disabled, the entire network has statically assigned IP numbers. 4) DNS should not be an issues since I am trying to connect via IP number and not DNS name but to answer your question the DNS servers point to Google (8.8.8.8, 8.8.4.4) 5) I never ping using computer name. 6) I have not tried another cable modem.
    – John Stottlemire
    Jan 31, 2021 at 18:00

3 Answers 3

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First try to connect each of your switches directly to the router LAN ports to see if that helps, your main 16 port switch/hub may be not be able to do Double NAT?

You can disconnect your modem to simulate the ISP/WAN failure

The obvious-non-obvious would be a router bug that stops the LAN working without the WAN/ISP connection. You know the LAN should work independently. (Check the gas supply before repairing the boiler) So google search your router for problems and ensure latest firmware is installed.

It is suggestive that your LAN settings may be looking out to the WAN in order to function somehow?

Are your static LAN assignments only configured in your router or individually in the network cards? Try to manually configure some of the PC network adaptors to the same settings as the router LAN setup (i.e. same static IP, Gateway, etc.) to see if that allows them to see each other?

Check that your device gateway setting is a LAN address and not the ISP's WAN gateway?

Assign your static IP's outside of your DHCP pool

If they are inside the pool range then check your DNS Lease is "Forever" for the static IP's

Hope that helps or triggers another idea for you!

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  • Thank you for your insight Zee: 1) All of the switches were connected directly to the router LAN ports when this issue first reared its ugly head. I moved them to the 16 port hub to isolate the network and only have one point of failure. 2) As stated above, I have disconnected the modem from the router to simulate the network going down and can ping every device on the network during that simulation. 3) Haven't checked for any bugs but I have the latest firmware in all devices.Nothing suggest the LAN settings are looking out to the WAN. Static assignments are in each individual network card
    – John Stottlemire
    Jan 31, 2021 at 19:17
  • 4) Device gateway on each device is 192.168.0.1, the address of the router. 5) All static IP addresses are outside the DHCP pool (I'm assuming you meant DHCP).
    – John Stottlemire
    Jan 31, 2021 at 19:18
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;-) Sorry, yes, I did mean DHCP...

Try setting your DHCP Server to start at 192.168.0.20 or higher and check the maximum is high or just set it to 192.168.0.254

Make sure nothing is accidentally set to use 192.168.0.1 as a static IP

then use 192.168.0.2 --> 192.168.0.19 for your static IP pool?

Also try assigning the static IP's in the router, This is sometimes called reservation because it may use the MAC address (unique network card ID) rather than the IP to achieve the function.

I wonder if the FTP server is causing conflicts, can you assign static IP's within the server and/or get an IP report table from it?

There are some details about host files and LAN conversation in this link... https://stevessmarthomeguide.com/name-resolution-and-dns-on-home-networks/

I assume you are familiar with the ipconfig command line request?

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  • 1) Where the DHCP starts/ends is irrelevant as long as it doesn't overlap with the static IP's. My DHCP server begins at 20 and ends at 150. My static IP's start at 198 and will end at 254 once I have the need. 2) The only device on the network set to use dot 1 is the router. if there were a conflict with dot 1, dot 1 would be unreachable. 3) There is no need to assign static IP's in the router as long as they are assigned in the device itself. Reservations are for DHCP and not static IP's
    – John Stottlemire
    Feb 2, 2021 at 15:36
  • 4) The FTP server is not causing any conflicts, windows would disable the network card if the IP number within that machine conflicted with any other IP number on the network 5) I am the previous CEO/President and Original Founder of Florida's Largest ISP (at the time) and maintained the largest commercially owned wide area network in the state. I am somewhat of an expert when it comes to Internet Protocol which is why I characterized this as a phenomenon.
    – John Stottlemire
    Feb 2, 2021 at 15:39
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I only have a little experience with networking and I was trying to help you within my own limitations. Your original description said "statically assigned IP number in the 192.168.0.0/16 subnet." which mistakenly worried me that your static pool was 0.0 - 0.16 and thus room for conflict. I was simply suggesting reversing the static assignments to the router as an experiment to see if it made any difference, to my mind you should not have the issue in the first place and I was searching for ANY possible remedy for you. Obviously I am hoping someone with deeper knowledge can help you find the solution to what seems an extraordinary problem, and had no idea of your own skill set. My other novice suggestion would be... why cannot Windows Server run your network?

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  • 192.168.0.0/16 with this notation the /16 is the subnet, the first 16 bits (a class B address space) and includes all IP numbers from 192.168.0.0 to 192.168.255.255
    – John Stottlemire
    Feb 4, 2021 at 4:15

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