Comcast cable internet, looking to escape

I did some searching and was surprised this wasn't asked yet, AFAICT.
I'm a residential Comcast Xfinity cable customer. I only use Comcast for Internet, not VOIP or cable or anything. Xfinity 100 Mbps. The current leased hardware is a TC8305C which I would love to give back to them.

I searched the compatibility chart and it's not clear which are cable modems, if any. I'd really like a single piece of hardware that is both cable modem and wifi compatible with my service.

I found a wifi router in the Table of Hardware that would suit my needs, except it's not a cable modem. So immediate term, I plan to disable wifi on the Comcast box, plug in the wifi router, and run OpenWRT on the presumably-compatible router.

But, is there a single cable modem/wifi unit that is compatible both with Comcast Xfinity (again, I'm using internet only) and OpenWRT?

If not, I don't mind installing OpenWRT on two separate devices. What cable modem should I buy, and is there a FAQ/doc for this kind of basic home networking setup?

Thanks in advance!

I'm not sure about modems but they are really not doing much by themselves. if you have to go with a separate box, ideally you want a modem in bridge mode, and then a router sitting behind it. the router runs Openwrt, the modem just sits there providing a port to send and get packets from

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The solution which gives you the most freedom of choice in regards to the real router part is to get a separate modem and a separate router.

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As far as I know there are zero DOCSIS modems available that allow to run a non-vendor firmware at all. I believe (but have no data to hack this up) that this is a consequence of the tight grip Cablelabs and the DOCSIS ISPs maintain over their infrastructure (a misbehaving modem can take out a considerable part/all of a cable segment with potentially hundreds of customers). As far as I can tell the best you can do is to configure a DOCSIS modem in bridge mode, where it will not try to do router duty.

Please be aware that if you connect a new router behind a bridged DOCSIS modem you will most likely need to reboot the modem, since in DOCSIS a modem will only allow/pass dhcp address to devices in the internal network for a short period of time....

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A "modem" device has only one Ethernet port and defaults to working as a bridge. A "gateway" has more than one Ethernet port and also has WiFi hardware and defaults to working as a modem and router in one box. So buy a "modem" not a "gateway". They are also less expensive.

Yes the cable company controls the firmware in all modems by pushing it down the cable, and modem manufacturers typically don't even offer a way for the consumer to download and install updated firmware themselves. When your modem model is approved by the company, the cable company maintains a version of firmware which is known to work on their network. It will be pushed to your modem the first time you connect it to the cable and may get occasionally upgraded.

So be sure that the modem you're about to buy is approved by the company you have. Most models on the market are approved by most of the major cable companies but always check before buying.

To obtain service, the modem's MAC address must be registered to your account. I think that Comcast has an automated way to do that. Only one modem can be active at a time.

DOCSIS 3.0 modem hardware can have differing amounts of potential downlink and uplink bandwidth, referred to as "channels" such as "16 x 8". If you don't buy one with enough channels for your subscribed speed, it cannot deliver full speed. I think all 3.1 models have the same very large bandwidth, and can fall back to 3.0 with lots of channels, so you don't have to consider this.

As far as recommending a certain model, for 150 Mb 3.0 service I've had good results with a TP-Link TC-7610. Avoid models that have the Intel Puma chipset.

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Yea, I agree. My last Comcast/OpenWrt setup was a self-purchased DOCSIS 3.0 modem in bridge mode connected to the router. BTW, PM me if you need to purchase one. I have one available.

Thanks everyone, this link cleared up the needed hardware configuration for me, so posting it here:
https://openwrt.org/docs/guide-user/network/switch_router_gateway_and_nat#device_as_a_gateway_with_a_true_modem_between_it_and_the_internet

So. No problem, I will keep my Comcast-provided DOCSIS Xfinity modem, and put it in bridge mode.

This was really easy; the modem IP addr is 10.0.0.1 ; admin user is "admin", default password (which of course I had already previously changed) is "password"

The default "At a glance" modem webpage has a giant button front and center labeled "Enable Bridge Mode". Clicked it, modem resets. In bridge mode now. Easy! (Pic is from before it was activated)

As it turns out, I still don't have the networking correct; devices on the LAN aren't able to get to the WAN. I'm digesting this page now:
https://openwrt.org/docs/guide-user/network/wan/access.modem.through.nat#docsis

I will post again, either with another cry for help, or with an exact step-by-step guide for any Comcast cable customers with similar hardware.