Greetings,
I’m about to receive a new modem from my ISP, and I’m checking my configuration to make sure it will work. One of the things that came up is that the new modem is hard-coded to use the same IP address on its internal interface as I currently have set for the internal address of my Mikrotik router. My setup is pretty simple;
Modem-> hAPac2-> switches and AP’s-> client machines. My network is currently a single subnet in the 192.168.x.x range, with my router being the .1 address. Apparently this modem has to use that address so I’m working on a plan to change all of my DHCP scopes and server IP’s etc., but in thinking about it, I’m not sure any of that will be necessary. Since the modem is in bridge mode, I wont be actively using it’s IP for anything except perhaps troubleshooting, and since that IP will be on a different interface than the one on my router that has that IP, will that actually be a problem? I know I can just plug it in and find out but I’d much prefer to make all the changes (if required) before the new modem arrives so that everything is ready to go once it gets here.
As you describe it, it should be possible to ignore it. If it was only same subnet, but not directly in conflict with same address on any of your devices, it would be possible to make it accessible. Right now I’m not sure about a way with same address, I have some idea, but I’d have to test it.
Hi Sob, Thanks for the reply.
I’m thinking that since the port on the modem that is set to 192.168.100.1 is connected to different port on the router than the one with the same IP, they aren’t directly in conflict, which is really my main concern. Since the modem is in bridge mode, it’s technically invisible and the WAN port on the router will be a public IP address. If I need to access the modem I could just run a cable directly from my notebook to one of the modem ports and set it to an IP in that range. I’ve had a similar setup at home now for about 7 years and haven’t had to access the modem in that time (my current modem is in bridge but I think the IP on it is in the 10.x.x.x subnet), so hopefully it wont be something I need to do often.
Thinking out loud, could this potentially cause an issue with the ARP table? Dynamic routes?
It shouldn’t. Your router won’t be searching for 192.168.100.1 on its WAN port, modem has no reason to look for other 192.168.100.x either, and even if it does, router should ignore it.