Network connections have gone erratic

[Bret Busby]

On 22/11/23 23:26, Bret Busby wrote:
> Hello.
> 
> 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?
> 
> Thank you in anticipation.
> 
> ....
> Bret Busby
> Armadale
> Western Australia
> (UTC+0800)
> .................
> 
The System Reports -> System information shows

"
Network:
   Device-1: Intel Ethernet I217-LM vendor: Dell driver: e1000e v: 
kernel port: f020
     bus-ID: 00:19.0 chip-ID: 8086:153a
   IF: enp0s25 state: down mac: <filter>
   Device-2: Realtek 802.11ac NIC type: USB driver: rtl8821cu bus-ID: 
3-14:7 chip-ID: 0bda:c811
   IF: wlx90de8039844b state: up mac: <filter>
   IF-ID-1: usb0 state: unknown speed: -1 duplex: half mac: <filter>
"

and

"
USB:
   Hub-1: 1-0:1 info: Full speed or root hub ports: 2 rev: 2.0 speed: 
480 Mb/s chip-ID: 1d6b:0002
   Hub-2: 1-1:2 info: Intel Hub ports: 6 rev: 2.0 speed: 480 Mb/s 
chip-ID: 8087:800a
   Hub-3: 2-0:1 info: Full speed or root hub ports: 2 rev: 2.0 speed: 
480 Mb/s chip-ID: 1d6b:0002
   Hub-4: 2-1:2 info: Intel 8 channel internal hub ports: 8 rev: 2.0 
speed: 480 Mb/s
     chip-ID: 8087:8002
   Hub-5: 3-0:1 info: Hi-speed hub with single TT ports: 15 rev: 2.0 
speed: 480 Mb/s
     chip-ID: 1d6b:0002
   Device-1: 3-1:2 info: Samsung PSSD T7 type: Mass Storage driver: uas 
rev: 2.1 speed: 480 Mb/s
     chip-ID: 04e8:4001
   Device-2: 3-2:3 info: Motorola PCS moto g(50) 5G type: 
Bluetooth,CDC-Data driver: rndis_host
     rev: 2.0 speed: 480 Mb/s chip-ID: 22b8:2e24
   Device-3: 3-6:4 info: Logitech M105 Optical Mouse type: Mouse driver: 
hid-generic,usbhid
     rev: 2.0 speed: 1.5 Mb/s chip-ID: 046d:c077
   Device-4: 3-7:5 info: China Resource Semico Keyboard type: Keyboard,HID
     driver: hid-generic,usbhid rev: 1.1 speed: 1.5 Mb/s chip-ID: 1a2c:2d23
   Device-5: 3-13:6 info: Sunplus Innovation AAPDQT-0622-W type: Video,Audio
     driver: snd-usb-audio,uvcvideo rev: 2.0 speed: 480 Mb/s chip-ID: 
1bcf:2cb4
   Device-6: 3-14:7 info: Realtek 802.11ac NIC type: Network driver: 
rtl8821cu rev: 2.0
     speed: 480 Mb/s chip-ID: 0bda:c811
   Hub-6: 4-0:1 info: Super-speed hub ports: 6 rev: 3.0 speed: 5 Gb/s 
chip-ID: 1d6b:0003
   Device-1: 4-1:2 info: Samsung Portable SSD T5 type: Mass Storage 
driver: uas rev: 3.1
     speed: 5 Gb/s chip-ID: 04e8:61f5
   Device-2: 4-2:3 info: Toshiba America External USB 3.0 type: Mass 
Storage driver: usb-storage
     rev: 3.0 speed: 5 Gb/s chip-ID: 0480:a200
   Hub-7: 5-0:1 info: Hi-speed hub with single TT ports: 2 rev: 2.0 
speed: 480 Mb/s
     chip-ID: 1d6b:0002
   Hub-8: 6-0:1 info: Super-speed hub ports: 4 rev: 3.1 speed: 10 Gb/s 
chip-ID: 1d6b:0003
"

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