XB7 DHCP Pool and Ethernet Connection Issues

@santatollimus​ thanks for the effort, I appreciate it!  I actually tried to do that for my devices but what I found, unfortunately, was that, one, whenever I reset my network connection on my router for any reason at all, I’m unable to get my Roku devices that were able to connect using this method back online without resetting the connection in each device first.  

Secondly, my smart home devices outright refuse to reconnect even if I assign a specific IP address for them, which I think is unfortunate.  I actually don’t really need all 124 addresses that I would have access to with a 25 bit subnet and so I could definitely see myself having the other 124 addresses either as reserved for other devices or for the switch (to which I assigned a 26-bit DHCP pool).

@user_8ceb1e​ I see what you are saying now. You have a smart switch and you have each port set to specific IP address.
despite having correct subnet and gateway you can't reconnect without power cycling all devices as a whole.

that sounds like DHCP device.
You're trusting a rental modem that in my opinion isnt an upgrade from the previous two models
with the job of DHCP. With your current task, go more advanced

look for an xfinity certified docis 3.1 cable modem
I highly recommend Arris Surfboards~
You can probably pick one up from your local electronics store.
Xfinity sometimes charges more for not renting their modem but
sometimes you can't do the job without the correct hardware.

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I'm not official Xfinity support but they can't or won't help me either so
I'm offering support to all other cases hoping someone looks at mine.
https://forums.xfinity.com/conversations/your-home-network/upload-drops-02000-kbps-unstable/6220b1aaaef5c36d133d6334

side note, the devices you have plugged into the smart switch can't be static ip.
I think they have to be able to accept the IP being handed to them by the port on the smart switch.

------------------------------------------------------------------------------
I'm not official Xfinity support but they can't or won't help me either so
I'm offering support to all other cases hoping someone looks at mine.
https://forums.xfinity.com/conversations/your-home-network/upload-drops-02000-kbps-unstable/6220b1aaaef5c36d133d6334

Yes I was wondering if I may need to get a new router or not to make all of this happen.  It’ll be more difficult but, overall, it may be worth it.  So my plan, right now, is actually to get a mesh WiFi system, likely either the X20, X60 or X90 from TP-Link but, although I’ve heard good things about their WiFi capabilities, I do need to support my smart home devices which I hear notoriously may not be supported under those schemes if used as my router, so I wanted to use them as access points (since I need the Ethernet backhaul for my father’s office downstairs without spending a ton on installing an impractical Ethernet cable).  

As for my switching setup, currently I have one completely managed switch (CLI capable) while the other switches connected to it are all only partially managed (as in you can only manage them using their built-in interfaces but not via the command line).  Like I mentioned, when I did have the network setup, I was able to give many of my human interfacing devices (e.g. laptops and TVs) static IP addresses in the switch’s DHCP pool (the switch is the TL-SG2008 from TP-Link if you were wondering), but the smart home devices were attempting to connect using that switch’s pool of addresses, causing them to disconnect.  So I definitely do think that the router may be the issue as well as the switch seems to be doing its job for the most part (only one of my TVs had an issue connecting via Ethernet when I had the DHCP pool for the XB7 connected).

Unfortunately, it looks like the modem is locked as there are literal locks keeping me from being able to take out the rented modem, so if I get any type of external router solution, I will have to use it in bridge mode (which, I read, apparently may not work if you have a gigabit plan from XFinity, which we do).  So I guess that’s where I’m having the confusion.  

But you’re absolutely been of great help so far so thank you!

@user_8ceb1e​ that xFi portal sure is something the way we can no longer get into our gateways is truly helpful.

I am also betting that you can hand IP's to devices with the XB7 disconnected from the network, correct?
That Would Definitely Narrow Down The Possibilities~

Another variable to look out for is 10/100 switches those can seriously screw up your network
if the speed coming in exceeds 100Mbps!

------------------------------------------------------------------------------
I'm not official Xfinity support but they can't or won't help me either so
I'm offering support to all other cases hoping someone looks at mine.
https://forums.xfinity.com/conversations/your-home-network/upload-drops-02000-kbps-unstable/6220b1aaaef5c36d133d6334