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EDIT:

Before running Docker containers:

$ ip route get 1.1.1.1
1.1.1.1 via 192.168.1.254 dev wlp2s0 src 192.168.1.54 uid 1000 
    cache 

After running the Docker container:

$ ip route get 1.1.1.1
1.1.1.1 dev vethf6c1790 src 169.254.198.92 uid 1000 
    cache
$ ping 1.1.1.1
PING 1.1.1.1 (1.1.1.1) 56(84) bytes of data.
From 169.254.198.92 icmp_seq=1 Destination Host Unreachable
^C 

That vethf6c1790 always appears as a new network interface when I run a new Docker container.

This issue happens to me with a variety of Linux Ubuntu/Debian versions and Docker versions, anyway my current setup is:

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 20.04.2 LTS
Release:        20.04
Codename:       focal
$ docker --version
Docker version 20.10.6, build 370c289

• What's wrong with the docker configuration?
• What do I have to do to make the 2 network interfaces to work together simultaneously?

However this might be related to a bug or mis-configuration with Network Manager because when I check the logs of the service with service network-manager status then I see this:

May 05 08:49:05 my-host NetworkManager[1269565]: <info>  [1620200945.9900] dhcp6 (wlp2s0): option dhcp6_name_servers   => '2001:b07:6477:ebfa:aa2b>
May 05 08:49:05 my-host NetworkManager[1269565]: <info>  [1620200945.9900] dhcp6 (wlp2s0): state changed unknown -> bound
May 05 08:49:06 my-host NetworkManager[1269565]: <info>  [1620200946.2184] manager: startup complete
May 05 08:53:43 my-host NetworkManager[1269565]: <info>  [1620201223.6347] manager: (veth90dd212): new Veth device (/org/freedesktop/NetworkManage>
May 05 08:53:43 my-host NetworkManager[1269565]: <info>  [1620201223.6358] manager: (veth9cfce50): new Veth device (/org/freedesktop/NetworkManage>
May 05 08:53:43 my-host NetworkManager[1269565]: <info>  [1620201223.6374] device (veth90dd212): carrier: link connected
May 05 08:53:43 my-host NetworkManager[1269565]: <info>  [1620201223.6389] device (veth9cfce50): carrier: link connected
May 05 08:53:43 my-host NetworkManager[1269565]: <info>  [1620201223.6394] device (docker0): carrier: link connected
May 05 08:55:29 my-host NetworkManager[1269565]: <info>  [1620201329.0433] manager: (veth90dd212): new Veth device (/org/freedesktop/NetworkManage>
May 05 08:55:29 my-host NetworkManager[1269565]: <info>  [1620201329.0777] device (veth9cfce50): released from master device docker0

1. until 08:53 all good: the WiFi works and no Docker containers run
2. at 08:53:43 I start a Docker container and Network Manager links to both docker0 and some other transient network interfaces that appear because I run a new Docker container. The internet is not on reach.
3. at 08:55:29 I stop the Docker container, then Network Manager releases resources from docker0. The internet is back to normal: I can see web pages again.

This issue happens to me with a variety of Linux Ubuntu/Debian versions and Docker versions, anyway my current setup is:

Ubuntu:

$ lsb_release -a
No LSB modules are available.
Distributor ID: Ubuntu
Description:    Ubuntu 20.04.2 LTS
Release:        20.04
Codename:       focal

Docker:

$ docker --version
Docker version 20.10.6, build 370c289

Network Manager:

$ /usr/sbin/NetworkManager --version
1.22.10
$ nmcli --version
nmcli tool, version 1.22.10

• What's wrong with the docker configuration?
• Is there any mis-configuration with Network Manager?
• What do I have to do to make the 2 network interfaces to work together simultaneously?

This issue happens to me with a variety of Linux Ubuntu/Debian versions and Docker versions, anyway my current setup is:

I've also tried to change the NetworkManager configuration (see here) at /etc/NetworkManager/NetworkManager.conf by adding:

[keyfile]
unmanaged-devices=interface-name:docker0

Then restarting the service with sudo systemctl restart network-manager.service. But the effect is the same: after a few seconds from when the Docker container starts, then the internet is not on reach via WiFi.

This issue happens to me with a variety of Linux Ubuntu/Debian versions and Docker versions, anyway my current setup is: