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The typical cable modem is capable of serving multiple IP addresses. I'm having issues with my cox security system 'seeing' the cameras. If I move the CHS Router as the first device off the cable modem, it works great. But that means the CHS router grabs the 'real-world' IP and I can't get to any of my servers inside my network. The CHS router is also a 10/100 device and I have a GIG network ready to go to GIGABLAST fiber, so that won't work....
Anyway, I added a DMZ to my router/firewall and bridged that to my WAN port hoping to get a 2nd IP for the CHS router and not impact my home network. But, I don't get an IP on that port.... I'm thinking that Cox limits the number of IPs to a single address on resi cable Modems. How do I get another IP so that my CHS router works correctly and does not impact my existing network?
Having 2 routers on the same network won't work unless you have 2 subnets and use one of the routers to route between subnets. At the very best it's tricky. What is the make/model of your main router? I don't know how Cox sets up their home security but I have my own security cameras installed and can access them from the outside with simple port forwarding. I only have one router and it routes the unique camera ports directly to the IP address of the associated camera. A little more detail on your hardware and what you are trying to do will help making suggestions.