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I'm having an issue with my home network. I'm a software dev but have somewhat limited network knowledge.

I always used my own router to provide internet to my home network but, last year, I "upgraded" our TV/Internet experience to Videotron's Helix setup (same as Comcast X1, in Quebec). That meant that I needed to use their modem/router to connect the wireless devices on each television. But I needed to keep my "old" router (Asus RT-AC68U) because many devices were connected to it via LAN.

So, the provider signal comes in the modem/router via a coax cable, then a network cable goes to my other router to provide internet to other wired devices.

The new router was setup as the DHCP server (192.168.1.1) and my old new, not (192.168.1.2).

This worked fine for a year until there was an apparent update to the modem/router because it's ip changed to 10.0.0.1.

Now, I cannot access my old router, which I'm guessing is still using the same ip as before.

BTW, every device connected to this router is still connected to the internet. No issues here.

I've tried looking at the modem/router "connected devices" page to see if I could find my router's address, and also tried a few commands:

Ipconfig shows that my main computer, which is connected via LAN to the old router, has a default gateway of 10.0.0.1, and not my old router (which I thought it would show).

Tried tracert to any devices connected via LAN or WAN to my old router to see if I would see it, but nothing.

Route print also... nothing that I see/understand ;)

If I reset my old router, I'm guessing it will revert to the default IP, which would be 192.168.1.1 which I'm guessing I cannot access from a 10.0.0.x ip range.

I thought about changing the modem/router ip range back to 192.168.1.1, with it's original range but, that would only mean that it might change back to 10.0.0.1 with a future update.

Really don't know where to go from here...

Any help would be greatly appreciated.

Eric
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  • You said the arrangement worked for about a year, so I suggest returning the new router to the settings it had before. In other words, in terms of IP addressing, get back to where you used to be. – John Jun 19 '21 at 13:14
  • The technician told my that this was their default address range, and since it changed by itself, I don't want to put it back the way it was only for this to happen again. I was able to switch the ip address on my other router by changing my computer's so, it's all good now. – Eric Jun 22 '21 at 11:47

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If the old router was statically configured to be 192.168.1.2, that means it is still 192.168.1.2 today. It can't have been affected by the DHCP server's change, because it wasn't using DHCP to obtain the address in the first place. (Which is also most likely why it doesn't show up in the "connected devices" list.)

You cannot access it currently, because neither your computer nor your main router (gateway) know where the address is supposed to be – the computer doesn't recognize it as "local" and sends the packet to the gateway, and the gateway sends it to the ISP, and the ISP just drops it.

But if you temporarily set up a static IP address from the old subnet (e.g. 192.168.1.7) on your computer, it would be able to access the old router again.

(While it is possible to add custom "local subnet" routes on Windows, this wouldn't be enough, as the old router itself would still have the same problem in reverse – it wouldn't know where to send responses back to your computer's 10.0.0.x address, either.)

Ipconfig shows that my main computer, which is connected via LAN to the old router, has a default gateway of 10.0.0.1, and not my old router (which I thought it would show).

No, because you were not using it as a router in the first place.

To start, if it's not serving DHCP, then it cannot advertise itself as a router – your devices use DHCP to learn the gateway address (not just to obtain their own address), and a DHCP lease issued by the new router will of course say "gateway = 10.0.0.1" in it.

That means your devices are communicating only through the old router's built-in Ethernet switch, without involving its CPU (the "router proper") at all. Packets that are routed through 10.0.0.1 are addressed to the new router's MAC address, so the switch sends them straight out through the appropriate port.

(In other words, devices with addresses in the same subnet don't use a gateway. This is the same reason why changing your computer's address 192.168.1.7 will work without any need to reconfigure the new router.)

In this situation the old router's IP address doesn't even matter – you can change it to 10.0.0.x, or you can leave it as it is. (As long as it doesn't serve things like DHCP or UPnP.)

u1686_grawity
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  • Well... Thank you so much for this explanation and, solution because after manually assigning an ip address to my computer I was, like you said, able to connect to my old router and change it's ip address so its on the same range as everything else. Again, thank you. Saturday morning headache averted! ;) – Eric Jun 19 '21 at 14:36
  • Another question... If I assign a fixed IP to that router via it's web interface, is it going to get in conflict with the main router's DHCP function? Or can I reserve this address on my main router for the second one? Thanks, – Eric Jun 19 '21 at 14:42
  • It _could_ conflict – check what DHCP pool range is set up on your main router. Most likely, it will be preconfigured to reserve some addresses for non-DHCP usage (for example, my ISP-provided router was set to use 192.168.0.64–.255 for DHCP, leaving .2–.63 for static assignments). – u1686_grawity Jun 19 '21 at 16:04
  • Of course... Why didn't I remember that! Thanks again for the help. – Eric Jun 22 '21 at 11:44