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Amazon is a good place to start.
https://www.xfinity.com/support/articles/voice-internet-manufacturer-promotions - a couple of deals listed
It all kind of depends on your speed plan and future proofing. I would start with at least 8x4 channel modems and preferably 16x4 to guard against being stuck under any new speed floor that comes along say 100M is the bare minimum in 6-12 months with the system upgrades being done continuously.
If you want to buy a modem and not have to worry about technology for several years you could go to D3.1 and invest a little more cash for a longer horizon. If you want to combine the modem/wifi into a single box the promo page listing the SBG7580 would be the best option in mu opinion. I was thinking about going that direction before changing directions and going D3.1 with the MB8600 + another / existing router. Turned out my existing router was a bottleneck on the network capping things off at 250M throughput.
For DOCSIS 3.0, the theoretical maximum throughput for the number of bonded channels are listed in the table below.
|Channel configuration||Downstream throughput||Upstream throughput|
|Number of downstream channels||Number of upstream channels||DOCSIS|
|4||4||171.52 (152) Mbit/s||122.88 (108) Mbit/s|
|8||4||343.04 (304) Mbit/s||122.88 (108) Mbit/s|
|16||4||686.08 (608) Mbit/s||122.88 (108) Mbit/s|
|24||8||1029.12 (912) Mbit/s||245.76 (216) Mbit/s|
|32||8||1372.16 (1216) Mbit/s||245.76 (216) Mbit/s|
OP. FWIW, my advice is to stay far far away from those combo gateway devices !! Just look around the forums and you'll see that there are boatloads of issues with them.
There is always an inherent disadvantage with these. Combo gateway devices are always a compromise in both quality and performance compared to separate units. Also, only the ISP can update the firmware so you are always a prisoner of that fact / of them. And the firmware is typically crippled by the ISP's customizing of it and they typically eliminate valuable features.
One of the biggest issues with them is that it is far more difficult to diagnose connectivity issues when it comes to troubleshooting. You can't narrow things down by using the process of elimination by removing just the router from the path. And if either segment fails / malfunctions, you have a total failure.
Get separate units and keep the control of your home network in your hands instead of theirs, you'll be much happier !
I agree with EG that it is better to have a separate Modem and router. In the long run it is less expensive than renting. Last year my modem was marked as "end of life" by Comcast and it was somewhat lacking in performance. I never got the rated speeds. I went with one of the higher end ones that has DOCSIS 3.1 and had as lot of channels. I did this for two reasons. First, to get the performance and second to get a longer life out of the product. Go to the Comcast web site and look for the accepted/approved models. I got the Motorola MB8600. (Note the MB8600 has multiple Gigabit ports on the back but only one can be used for almost all setups Some, assume it can act as a router also which it cannot). It did cost more than the others that would have worked but in the long run I think it will be a better deal for me. I recommend what ever you get, get it from a place that has a return policy in case it does not work for you. For the router be sure to get one that is rated high (gigabit ports) and can support faster speeds. I had a TP-Link Archer C8 before I got the modem and now there are newer more capable ones out. I have one issue with my router which is I cannot sign on to the modem from my computer but can if I bypass the router. In my area, I have Comcast Blast with 75 Mbps. They just upped it to 100 Mbps and after power restarting my modem I am getting over 115Mbps on the download. Hope this helps.
I have the MB8600 as well and once the modem is synced and online you can plug in a direct connection and set your IP to 192.168.100.x with the modem gateway IP of 192.168.100.1 through ethernet and be able to connect to the diag screen. If your modem reboots with more than one port in use you won't have connectivity but, if you disable the 2nd port to your PC device and reboot it will start working again and then reenable the PC port. It's a strange security feature compared to older models that allow login through a router form the LAN side w/o needing to be directly connected to the modem. It might be something to due with the firmware that's pushed out to the modem from Comcast.
I went with the MB8600 for the 4 x gig ports for future expansion when Comcast turns up some additional 3.1 features allowing the bundling of the ports for higher speeds beyond 1 gig. It sounds as if the capability will be coming in 2018 depending on the demand for the option. In a couple of years when FDX is proven and released there's potential for symmetrical speeds similar to what you can get with gig pro w/o the need for the fiber to the router. With the FDX feature the option to push 10G x 10G symmetrical over coax will become an option. Lab testing has shown 7.5Gbps throughput so far.