Problem connecting an Arris SB6141 cable modem (Xfinity) to an ASUS RT-BE88U router

[diitto]

I have a recently purchased ASUS RT-BE88U that is doing the routing for my Xfinity Internet setup that currently uses an outdated and soon to be replaced Arris SB6141 cable modem interfaced to the router…. I set up the router a few months ago using the QIS (quick internet setup) feature of the router…. It works until I have a disconnect for whatever reason, say like a brief power outage  Then I’m in trouble and need help…

Though some times the cable modem and ASUS router combined system will reconnect on its own, more often that not, these days, I have to intervene…. Typically, if I just watch, the cable modem will go through it startup process but when it gets to the final “scanning for an internet connetion” it tries for a long time, fails and then starts over with the startup process from the top…. That can go on for hours…. …. However, if I disconnect the router from the cable modem by disconnecting the intervening Ethernet cable and once again power on the cable modem, it steps right on up and shows itself to be fully sync’d and ready to go in less than a minute…

Here is where it gets even more strange…. If I wait for say a few minutes and then reconnect the cable modem to the already powered on RT-BE88U router via the Ethernet cable, the ASUS router NEVER, or at least not for a very long time, will it ever connect and show the correct “white” light showing the system fully connected…. Instead, it continues to show no connection…

But if I next leave the router powered on, disconnect the Ethernet cable, power down the cable modem, then after a few moments again power on the cable modem and watch carefully for the moment when the cable modem sync’s as ready to go and IN THAT MOMENT, quite quickly, if I then plug in the Ethernet connection I will observe the ASUS router coming to a fully connected state within 10 to 20 seconds.  And when I go inside the router page, I now see a valid Xfinity IP address having been assigned to the router….

So won't connect if I just leave both systems connected after a disconnect...  And won't connect if I restart the cable modem with the router disconnected from the modem and then reconnect the router say minutes later via the Ethernet cable..  Instead, only if I quickly reconnect the Ethernet cable to the router shortly after the cable modem has completed its connection process do I have success????

I have a new Arris S34 (Docsis 3.1) cable modem ready to use to replace the old SB6141 (Docsis 3.0) cable modem but I don’t want to make that jump (changing too many things at once) until I figure out how to get a reasonable and stable means of hooking up the SB6141 to the new RT-BE88U router….  

I really need help with this one…. Thoughts???  Tests I could do???  Changes I might need to make to the router setup???  Any help would be much appreciated…. thanks…

[jzchen]

Might be worthwhile to just start connecting the new SB34 modem with RT-BE88U.  If lucky they may work better together right from the start.

I would hate to see you spend a lot of time on the SB6141 RT-BE88U, and then start again with the SB34.  (They may not present the same issue).

[diitto]

I truly understand your point...  And if I knew that it would be easy to move back to the SB6141 after going through the steps to register the new S34, I'd be right there with you...  But I'm a retired EE who spent decades doing diagnostic testing on complex systems (though granted not IT related system) and the idea of changing TWO things at once was always fraught with potential difficulty...  So item 1 would be how the SB6141 plays (not all that well) with my new ASUS router and item two would be moving to the S34 without understanding the                SB6141-->ASUs issues...  But I've certainly considered what you said and one day soon I might do just that... 

Do you believe it would be easy to move BACK to the SB6141, the only working cable modem I currently have, to provision back to that if I moved forward to the S34 provisioning and hit a wall??  Knowing that I could pretty easily move back would likely prompt me to do just what you suggested and move forward...  thoughts???

And just in general, what is the best way to provision a new cable modem, period???  Call Xfinity on the phone???  Use the Xfinity APP which I only recently downloaded and now have coupled to my account???  Other methods???  thoughts???  thanks...

[jzchen]

I'm really not sure it would be easy to transition back.  You could try a coax splitter and see if the new modem works right out of the box, and swap the Ethernet cable over back to the old one if it doesn't...

Xfinity seems to offer their own equipment, and our Frontier service does offer eero routers, but they were free.  Our prior Giggle (not a typo) Fiber service was cable modem but for the longest time did not offer routers, only the modem, which was free.  I am not fond of services that sell what I consider a conflict of interest.  They have no motivation to help you with your own equipment, just motivated to earn by selling/renting theirs.

• Right now in my parents' home we have AT&T fiber and in our home Frontier fiber.

I guess the issue you are having isn't hardware related but firmware related.  There's an issue with the DHCP assigning your BE88U a proper IP address.  Could be the router's fault, could be the modem's fault, could be Xfinity not pushing the latest firmware to the SB modem because they want to encourage you to rent you theirs.  Ethernet has been around a long long time (I experienced Fast Ethernet aka 100 Mbps Full Duplex what feels like ages ago).  You plug it in and it immediately runs.  There's no real excuse for what you are experiencing in my humble opinion...

[diitto]

I think the issue is related to the new ASUS router and how I likely have it set up wrong...  Reason I say that is this SB6141 cable modem ran for 10 years coupled to an Apple AirPort Extreme router...  We have way too many power outages where we live in an outlying town (to the SF Bay Area) and countless times that modem and Apple router reconnected as I sat and watched...  I kept that old Apple router for a long time but recently recycled it...  

We JUST HAD yet another power outage just yesterday for 5 1/2 hours...  When power came back I came and watched...  Cable modem would try to sync up but at the 4th and final step it would sit and flash, and after some timeout, it would start over..  I let it do that a couple times but then intevened...  As the cable modem started its process yet again, I pulled the ethernet cable and waited for the modem to fully sync which it did a minute or so later...  THEN, I immediately plugged in the Ethernet cable connecting the ASUS router to the cable modem and a few seconds later the router connected...  I need to try some more experiments but we count on this network for a lot...  Especially the part about "connecting the ethernet QUICKLY" after the modem syncs which I think sounds crazy but I'm pretty sure that timeliness matters????!!!!!  This ASUS router has one zillion settings...  Way too many...  I think I have one or a few of them set up wrong...  And it sounds like you're not sure about me being able with ease to go back to the SB6141 IF the S34 doesn't work for me...  That would be the worst of all worlds is to lose that network completely...  

Why do you think it might be hard to go back???  It's just offering up the correct MAC address for the new cable modem and wouldn't it be the same to go back to the old one???  Though granted the old one does compromise speed because it is only DOCSIS 3.0 while the 34 is 3.1???  Plus, although the entire world says the S34 is compatible and works with Xfinity, the only one close to this on their approved list is the previous model, the S33...  I chose to take a risk and buy the S34 and just tell them, hey it's the same but newer...  And I've heard that even that is going to be outdated fairly soon as DOCSIS 4.0 is apparently right around the corner...  Any other thoughts???  I do appreciate the help...