On Fri, 23 Feb 2024 10:13:44 -0500, "jason_warren@ieee.org"
<jason_warren@ieee.org> wrote:

>> You may find the status is no longer available. This might be because
>> the ISP sees that your modem is out of date and sends the new firmware
>> immediately. You might see it reboot a couple of times.
>
>The modem (Motorola DOCSIS 3.1)

Note that DOCSIS 3.1 refers only to the DOCSIS version, not the cable modem
model. An example of a Motorola cable modem that supports DOCSIS 3.1 is the
MB8600, chosen randomly here to serve as an example.

https://www.amazon.com/MOTOROLA-Approved-Comcast-Gigablast-MB8600/dp/B0723599RQ

>and the router (Linksys mesh). The modem
>is half a year old and the router s/w is up to date.

If the router currently works for Internet access, it's not likely to be the
culprit. Traffic sent to the cable modem's management GUI is just Internet
traffic, as far as the router is concerned.

>Today's experiment is to connect my laptop directly to
>the modem. That's worked before.

I haven't read ahead, but if the ISP has disabled GUI access, that's not going
to work. After connecting directly, be sure to reboot the cable modem, then the
PC, in that order, assuming your PC is configured to use DHCP to get an address.

Rebooting the cable modem clears the single entry from its 'locally connected'
device table, which is required before another device can be recognized. In this
case, you're trying to switch from a router to a PC and the modem's device table
has no room for a second entry. Rebooting the PC, after the modem has finished
booting, allows the PC to acquire an Internet-routable IP address from your ISP.

On Mon, 26 Feb 2024 17:58:12 +0000, Graham J <nobody@nowhere.co.uk> wrote:

>jason_warren@ieee.org wrote:
>
>[snip]
>
>>
>> The modem (Motorola DOCSIS 3.1) and the router (Linksys mesh). The modem
>> is half a year old and the router s/w is up to date.
>>
>> Today's experiment is to connect my laptop directly to
>> the modem. That's worked before.
>
>Ah, some useful information at last.
>
>So how is your laptop configured? First try "Auto" so it looks for a
>DHCP server.
>
>Disconnect your Motorola DOCSIS 3.1 from its fibre input.

Cable modems use coax, not fiber/fibre.

>Connect your laptop to the Motorola DOCSIS 3.1 and power up.

DOCSIS 3.1 refers to the cable standard supported by the modem, and not its
model number.

>Does the laptop get an IP address?
>Does the laptop get a default gateway address? (Possibly 192.168.100.1)
>Can you ping the default gateway address?
>Can you open a web browser at the default gateway address?
>
>Disconnect the laptop
>Now connect the fibre and wait until the relevant lights show that the
>service is connected.
>Re-connect the laptop.
>
>Repeat the 4 tests above.
>
>It is likely that when not connected to fibre, the modem issues an IP
>address on its LAN, and you might be able to see its status page.
>
>However, when connected to fibre, the DHCP server will stop, and the
>laptop's DHCP requests will be sent to the ISP, so the laptop sees the
>public IP address issued by the ISP. It will also get a different
>default gateway. The laptop should be able to browse the web. Since
>there is no firewall involved it will be susceptible to all the malware
>out there. It won't be able to see the modem's status page because it
>is now not on the same network.

No, the modem's management GUI is not much different from any other Internet
address. The only difference is that it's not routable, but it doesn't need to
be because it's literally 'right there'. It's in the device that's in the path.

<snip>

>If you interpose a network switch between the router and the modem, you
>should be able to have a laptop connected to the modem as the same time
>as the router.

Most cable modems, probably well over 99%, will only respond to the first device
that they see (on the LAN side) after they've been rebooted, so inserting a
switch and connecting a second device isn't likely to work. You have to pay
extra to get more than one routable IP address, and very few people do that.
With a router, there's rarely any need to have a second routable address.

"jason_warren@ieee.org" <jason_warren@ieee.org> wrote in
news:MPG.404280366e1114d29896a0@reader80.eternal-september.org:

> In article <ur89sv$2dgp$1@dont-email.me>, nobody@nowhere.co.uk says...
>>
>> GlowingBlueMist wrote:
>> > On 2/21/2024 2:54 PM, Jason wrote:
>> >> I've always been able to log in to my cable modem,
>> >> a Motorola. Just now, I no longer can. Nothing's changed
>> >> that I know of (famous last words...). I log in to look
>> >> at the error rates to assure myself that the connection
>> >> is not deteriorating. I also changed the default password.
>> >>
>> >> The modem's IP address is 192.168.100.1. Linking to that
>> >> address times out. The net mask in the router is ff ff ff 00.
>> >>
>> >> Any ideas?
>> >>
>> > Try plugging a PC directly into the cable modem, verify you have
>> > internet access, then try to log into the cable modem.� If it works
>> > then I strongly suspect something in your router is blocking access
>> > to the cable modem.
>> >
>> > If a direct Ethernet cable does not let you log into the modem then
>> > try temporarily disabling all Firewalls and anti-virus software on
>> > the PC and see if that works.� If it does then you are on your way
>> > to identifying the culprit.
>>
>> Is this a combined router and cable modem? Or are there two separate
>> devices?
>>
>> Disconnect modem from cable supplier.
>>
>> Apply factory reset. This should revert it to its original stage
>> when you first got it.
>>
>> Connect your PC using the Ethernet cable; you should get access.
>> Continue to monitor the connection status so you can see if anything
>> changes
>>
>> Then connect the modem to the cable supplier. After a minute or two
>> you should get internet access - check using a different browser
>> window. You might have to apply a username and password for the WAN
>> connection - what did you do when this was first set up?
>>
>> You may find the status is no longer available. This might be
>> because the ISP sees that your modem is out of date and sends the new
>> firmware immediately. You might see it reboot a couple of times.
>
> The modem (Motorola DOCSIS 3.1) and the router (Linksys mesh). The
> modem is half a year old and the router s/w is up to date.
>
> Today's experiment is to connect my laptop directly to
> the modem. That's worked before.

I have a Surboard model SB6141. The modem IP is 192.168.100.1.

"DHCP Server Enabled (No option to turn this off)
The SURFboard cable modem can be used as a gateway to the Internet by a
maximum of 32 users on a Local Area Network (LAN). When the Cable Modem is
disconnected from the Internet, users on the LAN can be dynamically
assigned IP Addresses by the Cable Modem DHCP Server. These addresses are
assigned from an address pool which begins with 192.168.100.11 and ends
with 192.168.100.42. Statically assigned IP addresses for other devices on
the LAN should be chosen from outside of this range"

While you're testing, disconnect the modem from your provider and leave it
that way until you complete your tasks.

run these commands and save the output.

Ping 192.168.100.1 > modem_check.txt
arp -a >> modem_check.txt

Try connecting to it with a broweser.
After pass or fail on the latter, go ahead and reconnect to yor provider.
It will be interesting to see what you found. Share what you captured.