Trying to cascade ARRIS BGW210 to another router, need help with the Network Address.

After enabling IP Passthrough, renew your WAN address in DD-WRT and you should now have a public address. Nothing else needed.

It kind of sounds like there's a setting I'm forgetting to set up over on dd-wrt as my WAN always looked like this and renewing and releasing doesn't do anything.

Am I suppose to input my BGW router's Gateway and local DNS into the secondary router? Its just 0.0.0.0 for both fields.  I wish I could ask over on dd-wrt's site but that place is too slow for a response.

Let's start with the basics. I'm not trying to be demeaning, but sometimes I screw up the little things.

1) Is the DHCP server still on in the BGW?

2) Have you tried the renew IP button for the WAN interface. I'm assuming yes on this one.

3) Is the WAN port of the DDWRT router connected to a LAN port on the BGW?

4) If all else fails, try a factory reset on the BGW and see if the Linksys gets a 192.186.1.x IP on the WAN interface. Then setup IP passthrough. Then renew the WAN IP.

The BGW will provide DNS servers through DHCP, but you don't have to use them.  Once you get an address to the Linksys, you should be good to go.

Its no problems, I've been slowly trying to learn networking these past few months and just when I think I understand it, I get thrown a curve ball.

1) Yes

2) Yes, on the the secondary dd-wrt router

3) Both routers are connected to each other using just the LAN ports. To go into more details, I was following this guide because that's exactly how I wanted my network set up in the diagram, where the BGW is the main router and the Linkys dd-wrt router is the secondary.

https://youtube.com/watch?v=J5QJb3O19zI

4) For the BGW router, I just hold the reset button for 30 seconds?

As for the not needing to use my IPS's DNS, is that for both routers as well, as in both routers can have different DNS? I know I turned off the DHCP Server on the secondary dd-wrt router following the guide and wondering if it should be on. There's also an option for DHCP Type in the dd-wrt page for either "DHCP Sever" which its set to by default or "DHCP Forwarder".

I haven't watched the YouTube video yet, but you have nothing on your DDWRT WAN port, so no IP would be correct. That said, all devices on one subnet should have the same IPv4 prefix (192.168.1.x/24). One of the DHCP servers needs to be disabled, the WAN on DDWRT will not be used, so no IP address. The DHCP range should be outside any statics (i.e. DDWRT could be 192.168.1.10, BGW 192.168.1.254, DHCP range 192.168.1.100-200. 

Oh is that what they meant by outside? I thought the secondary router had to be on the inside with like a section of its own like this pic

That's how I wanted my set up but with similar IP's. My BGW router is that 192.168.1.1/60 range while the dd-wrt is 192.168.1.50/60

I thought that's what they meant by "outside".