Concerns about changing router's subnet

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Patrick9876

Regular Contributor
I'm running Merlin 386.1.2 on an RT-AC86U. The router's default config had it using subnet 192.168.50.0/24. I changed that to 192.168.1.0/24 just because that is what I was used to. Now I have a device (a USB modem that I'd like to try as a backup WAN connection) that has an admin HTTP server hardcoded to 192.168.1.1 - the current address of my router. I don't know if this will cause any problem other than not accessing the modem's admin function, but I can't imagine having the same IP address on a LAN - even on separate LAN segments - is a good idea. So I'm considering changing router's subnet back to 192.168.50.0/24. But I have some concerns.
  1. The subnet is references on at least 2 different pages in the Merlin admin GUI, each with it's own Apply function :
    LAN - LAN IP specifies the router's IP addr and subnet mask.
    LAN - DHCP Server specifies the starting and ending address of the DHCP pool. (I assume this pool has to be in the router's subnet, but I guess I don't know that for sure.)

    What happens between the 2 Applys?
  2. All devices on my LAN get their addrs via DHCP, but their leases will almost certainly not have expired when I change the router. Will I have to take some action on each device (such as rebooting) to get it to ask for a new address? (No problem for 4 computers. More problematic for 3 NAS devices. Very difficult for an IOT thermostat.)

 

ColinTaylor

Part of the Furniture
1. When you change the LAN IP it will automatically change the DHCP range (to 192.168.50.2 - 254). There's no need to change it separately.

2. Any devices directly connected to the router, either by WiFi or Ethernet, will loose their network connection. This will force them to reconnect at which time they will pick up a new IP address. Any devices indirectly connected (e.g. via a switch) will need to be rebooted.
 

eibgrad

Very Senior Member
Anytime I change the IP network, it's a basic assumption I'll need to reboot *all* my devices. I also stay away from assigning static IPs on devices as well, and use static leases as much as possible (yes, even for NAS and servers). In some rare instances, I've even had to power off entire circuits or the mains for a few seconds for problematic devices.

P.S. It's a very good idea to NOT use either 192.168.1.x or 192.168.0.x for your home network in case you decide to use an OpenVPN server. There's a very real possibility that your remote OpenVPN client might end up on one of those same IP networks given how common they are used by default. And when both sides of the tunnel have the same IP network, your home network will become inaccessible!
 

Patrick9876

Regular Contributor
Thank you both. The NAS devices are on a switch so I guess I'll have to reboot them ... and won't be able to do that through their admin GUIs since I'll loose access to those. That's sort of a pain.

I DO occasionally use an OpenVPN server on my router, but I think the remote clients are on some 10.x.y.z subnet. At any rate, that won't be a problem if I change the router to the 192.168.50.0/24 subnet.

I guess I'll give that a try and see what dies. I can always change it back. I hope.
 

ColinTaylor

Part of the Furniture
Thank you both. The NAS devices are on a switch so I guess I'll have to reboot them ... and won't be able to do that through their admin GUIs since I'll loose access to those. That's sort of a pain.
If they use DHCP you could just try unplugging their Ethernet cable, waiting a minute and then plugging it back in. You should be able to see what IP address they get from the router's syslog.
 

Patrick9876

Regular Contributor
If they use DHCP you could just try unplugging their Ethernet cable, waiting a minute and then plugging it back in....
I thought about that and suspect it would have worked, but I decided to go ahead and reboot those devices that didn't automatically get the new addresses. Surprisingly, one Windows PC that (I'm almost certain) is cabled through a switch automatically picked up its new address. I'll chase cables later to confirm (or refute) that.

All went much more smoothly than I expected.
 

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