Hello Paul,

On Sun, Apr 18, 2021 at 12:20 PM sciguy via talk <talk@gtalug.org> wrote:
I have a desktop computer that dual boots into Ubuntu Studio and Windows
10. It is connected to the internet using a cat-5 cable to my router.

After the last update and rebooting, it turns out that I no longer have
ethernet on Linux. This is not true on Windows, as I am writing you this
email from the same computer.

I strongly suspect that there is an update issue that is disabling
ethernet on Linux. Right now, my computer is in splendid isolation from
the rest of the world. I can't even see computer resources from other
computers in my apartment. I also can't see the router itself through my
browser.

Any ideas as to what to do next to diagnose the problem?

Paul

What does it show when you type /sbin/ifconfig -a in a terminal ?

aruna@debian:~$ /sbin/ifconfig -a
eth0      Link encap:Ethernet  HWaddr d8:50:e6:53:0d:90  
          inet addr:192.168.2.124  Bcast:192.168.2.255  Mask:255.255.255.0
          inet6 addr: xxxx::xxxx:xxxx:xxxx:d90/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2871734 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1934374 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:3777418026 (3.5 GiB)  TX bytes:187326708 (178.6 MiB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:2593 errors:0 dropped:0 overruns:0 frame:0
          TX packets:2593 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:170133 (166.1 KiB)  TX bytes:170133 (166.1 KiB)

And what does ip link show ?

aruna@debian:~$ ip link
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP mode DEFAULT group default qlen 1000
    link/ether xx:xx:xx:xx:xx:xx brd ff:ff:ff:ff:ff:ff

If you see LOWER_UP your interface is up.

you can try :
aruna@debian:~$ sudo /sbin/ifconfig eth0 up

and change the interface to match your own.

If you are using iptables sometimes that can mess up the internet connection, very rare but has happened to me
when I was initially learning and experimenting with iptables :-)

Hope this helps - Aruna