Routing – How to Connect 192.168.1.x Network to 192.168.100.x Gateway

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Hello fellow networkers.
I am very new to this world and don't know a great deal about IP addresses and subnetting.

I however stumbled upon quite a big problem (for me at least – haha)

My entire network and infrastructure I have built is all in the 192.168.1.x / 255.255.255.0 range.

Up until now I have had a router/modem that I have always used in modem mode with an IP I could change; said IP would be 192.168.1.254 and would be the gateway which the DHCP (windows server) would use.

Everything worked fine until I had to change the router/modem.
This one comes with a fixed IP in router mode: 192.168.100.1
Which makes it unusable for me.

Is there a way to still use it or re-map it somehow in DHCP (windows server)?

I am thinking maybe translating the address, but I don't know how to do it. Ideally I wouldn't change the current configuration, it's a lot of machines and mappings, etc… it would take me a long time!

Thanks a lot for any help!

Best Answer

Any serious hardware should be able to have the IP address changed. I'd dump that router.

However, if that isn't an option there are three basic solutions.

  1. renumber - Renumber your network to make it use 192.168.100.0/24 subnet addresses. If most devices are configured using DHCP this is not much more than changing your (few) static devices, updating your DHCP server, DNS server and documentation. If you're mostly using static addresses, now's a good time to reconsider.
  2. route - On the new router, add a static route to 192.168.1.0/24 (or set up a routing protocol) via another router attached to that subnet.
  3. NAT - If everything else fails you can attach a (source) NAT router to the 192.168.100.0/24 network and "hide" 192.168.1.0/24 behind it. Note that this is the ugliest solution - port forwarding/destination NAT would require both routers to separately forward external requests.

So would that act as the gateway ( 192.168.1.1 ) that then would send the request to 192.168.100.1?

Source NAT on an intermediate router replaces any 192.168.1.0/24 address with e.g. 192.168.100.2 on outgoing traffic. The uplink router can't see that there's a whole network behind that address.

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