Comcast C7100V hanging/crashing

[MMerhar]

Yesterday morning I discovered my C7100V cable modem router was hung: no lights flashing, all connections failing with "no connection possible to that service."   Rebooted and discovered that this situation would reoccur within seconds to minutes.

Assuming a HW failure, I bought a brand-new C7100V replacement (so obviously, factory-default config) and after letting Comcast auto-install it on my CATV service, I found it doing exactly the same thing!

Repeatedly falling back to factory-default config and adding things, this is what I found:

   - changing default admin password OK.

   - changing default name and login string for 2.4G and 5G access point OK.

   - Logging into admin console via a hard-wired Ethernet cable leads to a hang within minutes.  (!)

        Access host is a Macbook Pro using static IP addresses to avoid accessing DHCP and/or DNS.

   - Enabling a differently-named second access point with an AES security password (i.e. a "guest" AP requiring a login) on 2.4G and 5G leads to a hang within minutes.  The "guest" account is named differently than the primary AP, and all 2.4G and 5G APs have different names.

Only external symptom of what's going on during the "hang" is that _sometimes_ the US/DS light pulses bright/dim (NOT off/on).

Other times, Power, US/DS, Online, 2.4 GHz, 5 GHz, Tel1 lights are on solid.  Sometimes one of the 2.4 or 5 lights are off, as if the software stopped during an activity 'blink'.

Software is latest Comcast version, V 2.01.42.   Comcast techs report normal signal levels as seen from their end when it's working, and "no response" when it's not. Also won't respond to a network reset command when it's hung.  Other than that, they can't identify anything awry. No hint from the log file as to anything untoward, and when it starts operating again (minutes to tens of minutes later) the lights do NOT go through a normal startup sequence, they just start blinking again.

[FURRYe38]

Be sure there are no coax cable line splitters in the between the modem and ISP service box. 
Be sure your using good quality RG6 coax cable up to the modem. 
Be sure to power OFF the modem for 1 minute them back ON.
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Mod...

What channels are you using? Auto? Try setting manual channel 1, 6 or 11 on 2.4Ghz and any unused channel on 5Ghz.
Any Wifi Neighbors near by? If so, how many?

[MMerhar]

As this installation contains both a CATV DVR and a Cable Internet Router, there is of necessity exactly one Coax splitter.  All wiring is high quality unspliced RG-6/U, and as I said Comcast reports good signal levels up/down when the unit is working.

Both 2.4 GHz and 5 GHz radios are on fixed channel assignments.  The key elements associated with failure are at least one Guest AP enabled (i.e. on 2.4 GHz) and/or an active login to the "NETGEAR Web-based Gateway Configuration Utility" a.k.a. web admin console, via Ethernet or WiFi.

[MMerhar]

Further details, in case anyone cares:

Comcast has issued MULTIPLE network resets to "clear up the problem."  No impact on the issue.

Comcast has REPEATEDLY updated the network profile/configu to "clear up the problem."  No impact on the issue.

Comcast continues to insist that all signal strengths, channel locks, etc are fine, and there's nothing wrong that they can see.

I have been told repeatedly that they did NOT update the software (again: V 2.01.42 ) at any recent time corresponding to the start of the issue, and that "no one else has reported problems."   Which is not the case, as a search of this forum for "C7100V 2.01.42" shows at least a half dozen similar issues reported, all in the last half year.

Anyhow, enabling ANY guest WiFi service, with or without authentication/security, on any radio channel, with or without AP broadcast, and whether or not any clients attempt to connect to it will cause the C7100V to hang within seconds to minutes, and not recover for minutes to tens of minutes.  Even with just the factory-default WiFi configuration, service is flakey during normal home use, with seconds-long service outages, connection fails, etc.  Ditto for connection via wired Ethernet.

And if anyone tells me that a marginal cable RF level (which Comcast says I do NOT have) can cause the entire unit to hang, my response will be "and why would ANYONE design a router to behave like that?" and immediately ask for a RMA for the (now two) "failing" units I have in hand.

[FURRYe38]

I recommend you contact NG support, seems like having Guest Network enabled is causing problems and needs to be looked at by NG support. 

@vkdelta 

[MMerhar]

Ok, as a way of closing out this thread, here's what Comcast found.

Overseas Comcast technical support reset the unit multiple times, pushed new configs multiple times, "corrected some file organization problems" (never explained), confirmed line levels reported OK, and admitted she had no idea what the problem might be, and ordered a truck roll.

Comcast lineman put a spectrum analyzer on the drop and reported "typical" levels, but as I'd reported trouble he replaced the drop wire and one piece of outdoor wiring, gaining perhaps 1.5 dB from before. Declared the drop to be textbook perfect as measured at the modem interface.  C7100V still continued to hang and recover, hang and recover.  Between failures when I could log into the web UI, I noted that both upstream and downstream channels had good power and S/N ratio, and ZERO errors of any kind.

Comcast lineman pulled out the brand-new C7100V that was hanging and re-installed the old "failing" one.  Long back-and forth with his partner at the NOC to get the telephone service up and running, but it finally came up as well.   I reconfigured the router to NOT provide a guest AP, NOT maintain logs except for security issues, and basically turn off every product feature I could.  It's kept running for 22 hours now.

I did a factory reset on the new one and will take it back to my retail store for a refund.  

[FURRYe38]

Ok, thanks for letting us know. Sounds like a faulty modem. 

Enjoy. 

[MMerhar]

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@FURRYe38 wrote:

Ok, thanks for letting us know. Sounds like a faulty modem. 

Enjoy. 

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"Faulty", as in "acted identically to a new-in-box unit of the same model number, running the same software version."

So, in my humble opinion, if you believe that to be the case then the actual fault stems from a common element, as two possible examples  the software version it's running, or the architectural specs of the product itself that allows the whole thing to go unresponsive if some interface gets into an unexpected state. 

[FURRYe38]

Well something that NG support and pass to engineering to take a look at. 

Something to let them know about.