Second IP needed - ARRIS - SURFboard S33 with Comcast 1200Mbps Service

Hi,

A few days ago, I received notification from Comcast through e-mail stating that my current modem was not able to get advantage of the new 1200Mbps speed increase that has been enabled for customers on my current internet tear. 

So I went ahead and purchased the ARRIS - SURFboard S33 and I also purchased a new Netgear Orbi RBK-852 Router (which as an extra perk has Wi-Fi6 and a 2.5Gb Ethernet Port) problem is with all this setup I have not been able to get the desired and offered 1200Mbps connection when the router is connected to the modem.

If I connect my main desktop directly to the Arris modem through its 2.5GB Ethernet port, then I get all full speed of around 1300Mbps+ in all speed tests with no problem at all. So far so good, right? Well, the problem starts when I then connect the Orbi Router to the second 1GB Ethernet port on the modem, (So the rest of the devices on my home network can get internet) it cannot get a connection at all.

The only way I can get everything connected is by connecting the router to one of the ports on the modem and then connecting EVERYTHING else to the router (Standard setup) but when I do that, then everything is limited to speeds of around 940Mbps (Of course because everything is limited to the weakest link, in this case, the router). Then what is the point of getting a new modem that supports the new speeds if to use it I can only get one device connected?

I understand that all my devices cannot get that speed because they do not have support for those speeds, but my main desktop does (it has a 10GB Network card) I only want to get the 1200Mbps on my main desktop, so that's why I wanted to get the desktop connected directly to the 2.5GB on the modem and the router to the other 1GB Port.

This modem has two Ethernet ports (which means it can provide two different IPs). According to the manufacturer's help page here, they say the following:

 

 >>>>It is possible to connect two devices to the S33.  However, the cable provider must provide an Internet IP Address to each device for Internet access.  If both devices cannot connect to the Internet, contact the cable provider to request an additional Internet IP address.

 

According to my research on the issue, It seems I need an additional IP address from Comcast so my second Ethernet port on this modem actually works. I tried calling Comcast to see if they can provide me with a second IP address and after almost 2 hours nobody seems to know what I'm talking about and then the call got dropped. Really frustrating. :-(   

I purchased this modem and router because Comcast e-mailed me saying I should get a new modem in order to get the new fast speeds of above 1Gb that they are now offering to customers who subscribe to the internet package I have.

 

Anybody from Comcast who can help me here? I would appreciate the help.

Thanks a lot in advance.

-Eli