Network connections have gone erratic

[Bret Busby]

On 22/11/23 23:36, Jeffrey Walton wrote:
> On Wed, Nov 22, 2023 at 10:28 AM Bret Busby <bret at busby.net> wrote:
>>
>> On one of my computers running Linux Mint Mate 21.2, I, yesterday or the
>> day before, did a system update that included an update of avahi, which
>> is apparently, a networking utility.
>>
>> Afterward, the computer, which I have had connected by wifi to a wifi
>> modem, and, by USB tethering, to my cellphone for Internet access, both
>> devices using 4G cellphone networks with different carriers, to access
>> the Internet, with the USB tethering involving "hot plugging" (?), can
>> no longer use the USB tethering, which, whilst I set the USB tethering
>> to "On", on the cellphone, is automatically severed, with no data shown
>> as being transferred, and, the NetworkManager Applet shows the wifi
>> connection to the wifi modem, to be in an endless loop of dropping out
>> and reconnecting.
>>
>> I can send and receive data, but, it is erratic.
>>
>> I do not know whether the networking connections failing, is due to the
>> avahi upgrade, or just coincides with the timing, but, it is worrying.
>>
>> Prior to the avahi update, I had not encountered this problem, and, the
>> networking connections had been stable.
>>
>> I had performed an orderly shutdown and reboot, to find whether that
>> might fix this, but, it did not fix the problem.
>>
>> How do I find what is causing this, and, how do I fix it?
> 
> I _think_ I encountered a similar issue about a year or so ago. When
> my Pixel was tethered to my Desktop, the desktop would try to use the
> network connection from the phone rather than wired ethernet. The
> pixel used wifi, and wifi was outside my internal wired network. So my
> desktop (using the Pixel) could no longer talk to other hosts on my
> internal (wired ethernet) network.
> 
> I filed a bug report about it. I don't think it was fixed. I
> eventually installed a new distro for this machine. The problem went
> away. I _think_ changing network costs or priorities could have fixed
> the issue.
> 
> I don't think Avahi has anything to do with it. Avahi is just mDNS.
> 
> Jeff
> 

Prior to the update, the computer would use the wifi connection to the 
modem, if the cellphone was not connected, and, when the cellphone was 
connected and USB tethering switched on, the computer would switch to 
using that, which was shown as a wired (like Ethernet) connection.

The Mate Netspeed applet, whilst, when the cellphone is not connected, 
shows zero data transmission speeds (but, shows as being connected to 
the wifi modem), before this problem incident, would show the data 
transmission rates for the USB tethered cellphone, showing that as a 
wired connection.

The wifi adaptor on the computer, is a USB wifi dongle, which, I 
believe, is why (a shortcoming, I believe, in the software involved in 
the applet) the MATE Netspeed applet does not show data transmission 
speeds as non-zero, for the wifi adaptor. On my other computers, running 
the identical operating system, the MATE Netspeed applet correctly shows 
  the data transmission speeds; the difference being that, on the other 
computers, the wifi devices are integral parts of the respective 
computers, causing me to believe that the failure to show the data 
transmission speeds for the USB wifi dongle, is a shortcoming of the 
applet, in that it does not properly deal with the USB wifi dongle.

But, the MATE Netspeed applet correctly displays the data transmission 
speeds for the USB tethered cellphone connection, which is also, a USB 
connected device...

....
Bret Busby
Armadale
Western Australia
(UTC+0800)
.................