I thought even if you put it into bridge mode the XB6 still leaves it’s wifi on; or at least some “secret” wifi signals still on which can conflict with your primary wifi router??
Yes, Wi-Fi is still enabled and some hidden networks are still active on the XB6, even when it is in Bridge Mode. However, interference is not a huge problem. There should not be any traffic on those hidden networks, just beacon frames. However, if channel selection is set to "Auto", the XB6 will pick the best channels that it can find and this will cause neighbouring Wi-Fi routers and APs to avoid auto-selecting that channel. Good, usable Wi-Fi spectrum is scarce and this kinda takes away that prime spectrum.
I find that one of these two channel selection strategies usually work well:
Option 1: I use a Wi-Fi scanner to find a 2.4 GHz channel that is neither the strongest (i.e. being used by my neighbour) nor the weakest (i.e. a prime candidate for auto-selection) and manually set that on the XB6. I also set a 5 GHz DFS channel that would also not be a "first choice" for auto-selection by a neighbouring AP. I then manually set the best available Wi-Fi channels in my APs.
Option 2: Pick the best (least used) Wi-Fi channels in the 2.4 and 5GHz bands and set them manually in both the XB6 and my Wi-Fi gear. There's hardly any traffic coming from the XB6 so it does not cause any interference. With multiple APs using a channel, it minimizes the chance that any neighbour will manually set or auto-select it in their Wi-Fi gear.
Thank you to the contributors for helping me reason my way through this. I took the plunge.
My new Ignite gateway and set top boxes arrived today, and so after viewing the last unwatched documentaries on my old NextBox PVR, I disconnected the legacy equipment and hooked everything up according to my Option 2 diagram a few posts back. The Ignite box is a Technicolor XB7 DOCSIS 3.1 Gateway Gen 2 (it's white, 4 ethernet RJ45s, 2 phone RJ11s).
I went with the easiest solution first, and left the private and guest network topography alone on my own old (Linksys) router, and just swapped out the legacy "Hitron" box for the new Gen2 gateway box, and let it set up a new "Rogers' network out of the new box.
The hardest part was tracing and pulling (out) old coax and splitters that won't be needed anymore. Everything new went together easily, and seems to work fine. Rogers network works, my own home network works, and the private guest network works. (there seemed to be room in the neighbourhood spectrum analysis). Initial connectivity tests show the XBox works for live Rocket League (I don't do live chat on it), SSLs work, and a third-party VPN still works. Energizing the phone lines around the house was a simple connection and a no-brainer, but it took the phone about an hour to get itself sorted out on the network while I did the TVs. I got a little ahead of myself and plugged in my own router before getting the TV wifi boxes set up, and that caused some momentary confusion as I think they picked up my private network first. Unplugged my own router, and they set themselves up and work fine now on the 2.4Ghz band of the Rogers box.
So it all seems to work fine, and 10.0.0.1 gets you inside to see the admin bits. No surprises, and I did not notice any hidden "guest network" switches to toggle, which is fine since I have my own still running.
The most profound change I notice so far is that for the first time in 40 years, I don't have a tiny digital clock display below the TV screen that I can glance at really quickly.
Otherwise, on Day 1, it seems to be working fine with that Option 32 diagram (Ignite - no bridging).
Funny, it's now 2021 and still no guest functionality on your gateway model CGM4140COM..... get with the times and build a firmware update that will allow a guest or additional SSID's. Absolutely no excuse not to have such!!! Very disappointed
@jhandley67 this looks like a Comcast decision to use the extra SSID capability to support their wifi hotspots instead of guest networks. Looks like Comcast expects their customers and all of the customer's guests to be Comcast customers so that any guests would automatically be able to use the wifi hotspots. I guess the thinking must be "Why would anyone invite non-Comcast users to their home?"
So, since Comcast doesn't support guest networks, looks like their licencee's can't have that capability as well.
Technicolor XB7 DOCSIS 3.1 Gateway Gen 2 does not, so it's unlikely that any of the other boxes built for Comcast have one either.
I'll describe how it works for me. It's close to Eddiepet's diagram option 2, but the smart home devices are fully on the legacy WiFi. The Rogers Gateway is of course at the top, and it did not need any configuration. The second router has the guest WiFi capability. Log into the 2nd router and make sure the Wifi SSID is different from the Rogers gateway one, and that it's LAN address range is also different from the Rogers LAN range. This is normally already the case, as most personal routers are 192.168x.x and Rogers uses 10.0.0.x for its Local IP network. When you plug the 2nd router's WAN port into the Rogers Gateway LAN side, the 2nd router gets an address and gateway automatically, and in turn deals out WiFi addresses to your users in the 192.168 range and routes traffic to the Rogers Gateway. This is double NATing but should not require special configuration.