Web admin interface does not respond when modem loses downstream link (CM500)

[scootley]

Hi,

I have a CM500 cable modem.  It has an administrative web interface at http://192.168.100.1/

It is connected to a router.

I've noticed that when my ISP has an outage, the administrative web interface fails to load and the modem cannot be pinged (with a command-link ICMP ping tool).  For example recently the modem indicated (via the lights) that it lost the downstream (and upstream) link, and during that time I could not view the web interface.

When it comes back online with the ISP, the web interface works fine and it can be pinged.

Is this normal?  Was it designed this way on purpose?  Why?

In case it is unclear, I am not asking for help with my ISP connection being down.  I am asking only about why I cannot view the modem's admin interface 100% of the time when it is turned on, regardless of whether it has an ISP connection or not.

I guess there is a chance that my router is somehow failing to route packets to the modem during this scenario, but I have not investigated this too much.

I should add that this seems to have been happening since I got the modem several years ago.  It is a consistent issue and not new.

Thanks

[FURRYe38]

Possible that the ISP puts something with in the config file to not allow access. I wouldn't put it past an ISP to do something like that. Depends I guess. 

I presume if you disconnected the ISP coax cable line, can you access the modems web page? Even if you factory reset it? 

Most modem side issues are handle at the ISP level. Not much can be changed or is known for CM series modem since there FW is updated by the ISP and can't be by users. The way it is for C and CM series modems. 

[scootley]

Thanks @FURRYe38 

So netgear allows ISP firmware to somehow configure or control access to the web interface?  That is very strange but I guess if it's known that this is possible then sure.  Is there a known precedent for that where someone else has seen it happen?

We use the term "firmware" with cable modems sometimes as if it is monolithic.  Is it?

Specifically, does the ISP have the ability to send a new or tweaked version of 100% of the firmware that runs on the modem?  Could the ISP create their own custom admin web interface and replace the existing one?  Or is there a component of the firmware that is fixed and not updatable by the ISP?

Or conversely, if it really is monolithic, does the ISP have to distribute the code (binary) for the admin web interface back to the modem every time they do an update involving "normal ISP stuff" (like I dunno the channel bonding configuration) even though they don't want to change the web interface?  Does netgear give these web interface binaries to the ISP so they can be redistributed during an update?

I have not tried doing a factory reset and disconnecting the coax and trying the web interface but if I can find a good time to do that, I will.

What series of modems (since not C and CM) allow better firmware management and/or user updates?

[FURRYe38]

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@scootley wrote:

Thanks @FURRYe38 

So netgear allows ISP firmware to somehow configure or control access to the web interface? Anything is possible with some ISPs.

That is very strange but I guess if it's known that this is possible then sure.  Is there a known precedent for that where someone else has seen it happen? Seen this posted before with some ISPs. Not sure why. Most major ISPs don't do anything with user own modems. Only update FW. For some ISPs, they won't even update FW on user own modems connected to there services. NG develops the FW, then hands it off to the ISP for there testing and certification on there services, once they approve and certify  it, then the ISP can push to modems.

We use the term "firmware" with cable modems sometimes as if it is monolithic.  Is it? It is the operating system that modems run on. Won't with out it. 

Specifically, does the ISP have the ability to send a new or tweaked version of 100% of the firmware that runs on the modem?  Yes. Could the ISP create their own custom admin web interface and replace the existing one?  Possible. Or is there a component of the firmware that is fixed and not updatable by the ISP? No. 

Or conversely, if it really is monolithic, does the ISP have to distribute the code (binary) for the admin web interface back to the modem every time they do an update involving "normal ISP stuff" (like I dunno the channel bonding configuration) even though they don't want to change the web interface?  Does netgear give these web interface binaries to the ISP so they can be redistributed during an update? Possible

I have not tried doing a factory reset and disconnecting the coax and trying the web interface but if I can find a good time to do that, I will.

What series of modems (since not C and CM) allow better firmware management and/or user updates? CAX series which are gateway modem an FW that is user updateable is the router portion of the modem. The modem is still handled by the ISP. 

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[scootley]

Thanks.  Do you recommend paying $50 for a 3-month support contract with netgear to ask them about this?

I would ask them things like:

1) Is it a bug or intentional?  If a bug, which modems are not impacted by it? (so I can buy one) 

2) Can the ISP control this behavior?

3) If so, can your Firmware team talk to the ISP's Firmware team to tell them to stop doing this?

(because I doubt I will have any luck attempting to navigate my ISP's customer support channels to get answers to this type of detailed question)

I kind of doubt that they will answer these questions well even with paid support.

And $50 just to have questions answered but no change in behavior seems too much.  I'd pay $25 for that.

My personal theory is that this is a bug and it's a bug in Netgear's own firmware (distributed by the ISP, but not code written by the ISP), and it just only happens to occur during certain types of "loss of uplink/downlink" scenarios and not in all scenarios (e.g. not in the case where the modem has just been powered up without any coax attached) 

[FURRYe38]

IMO no. 

Possible bug, however nothing would be fixed. FYI, this modem model is several years old and may or may not be supported by all ISPs. Some may and that's on them. No fixe would be forth coming on this model due to it's age. FYI, it very costly for modem mfrs to develop and get there stuff certified with the ISPs so Mfrs tend to keep costs at a minimum and only were needed. Even some newer gen CM series in question. 

Something you could ask the ISP about. However again, some ISPs may not give much information or if it's user owned, will put there hands up in this regard. So, up to you, if the modem is working and there's no issues, use it as you desire. Checking for web UI access after a factory reset with the ISP coax cable should gain access here. Or you might find something newer generation and has full on and better support. Again something to check with the ISP first to see what they officially support on there system. No all modems maybe supported. 

Good Luck. 

[plemans]

Who's your ISP? I've seen a few of them that lock down the GUI. Not all but a couple. 

And I wouldn't invest $50 in contacting anyone with the CM500. Its not a recommended device and isn't rated for much speeds. That $50 would be better saved for investing in a docsis 3.1 device

[scootley]

@plemans 

It's Comcast.  Do you mean "lock down the GUI" on user-owned modems and lock it down entirely?  Or do you just mean this specific exotic scenario of locking it down only when the modem has lost connectivity?  Which ISPs do that (whichever scenario you meant)?

In order to determine whether to invest my $50 toward a new netgear device or not, I would want more information on this issue or knowledge that it does not occur on their newer devices.

Unfortunately, this scenario is so rare and so few people even know that their cable modem has a web GUI, I doubt that it will be reported online.  Best thing I could do is try to reproduce it myself by unplugging the cable and then see if I can also reproduce the same behavior with a newer modem during the return window.

[plemans]

Xfinity doesn't lock them down. 

I know some versions of firmware on device, spectrum locks users out of the GUI. They haven't released an official reason but my bet is it gives users the ability to say "here's whats wrong, fix it" when there is issues. Versus without it they can say, "its not our line" a couple times. I actually ran into this with them with one of my in-laws and had to prove it to them the signal coming in had issues. PITA. there might be a few other ISP's that do the same but there isn't a list of them. 

I'm on xfinity and I've never had an issues accessing the GUI on any of my modems. I've used a cm400, cm1000v1, cm1000v2, cm1100, cm2000, cm3000. Not a single issue. So wondering if maybe you had something go wrong on yours. 

If you're looking at upgrading, I'd look at one of the next gen modems that xfinity has approved for the increased upload speeds. 

Here's the most recent from 4/8/24 list: https://assets.xfinity.com/assets/dotcom/projects/cix-4997_compatible-devices/2024.04.03%20Full%20Li...