Bridge networking for Ubuntu 20.04 Desktop system

cg flag

I want to run a a computer emulator like SimH that offers ethernet device emulation via a tap interface. It should be possible to access the host system and the internet from the emulator, and it should be possible to reach the emulator from the host system.

On older Ubuntu systems it was easy to set this up with a few commands.

With NetworkManager I haven't been able to create a working bridge configuration. The recipe for Ub 18.04 from 1257262 doesn't work under Ub 20.04. After

sudo nmcli con add ifname br0 type bridge con-name br0
sudo nmcli con add type bridge-slave ifname eno1 master br0
sudo nmcli con modify br0 bridge.stp no
sudo nmcli con up br0

I get for the last command the output

  Connection successfully activated (master waiting for slaves)

and nmcli c gives

  NAME                    UUID                                  TYPE      DEVIC
  br0                     32fbc4bc-0ed7-49d3-aa32-2c9ed25c666f  bridge    br0  
  Wired connection 1      40a4b49b-c44f-3937-a19e-1951efc650a3  ethernet  eno1
  bridge-slave-eno1       c39ebf5d-6b0a-46d9-bd41-10e2f71e86d1  ethernet  --

and brctl show gives

  bridge name     bridge id               STP enabled     interfaces
  br0             8000.000000000000       no

So the interface eno1 is not a slave of br0 and br0 is not receiving an IP address from DNS.

Any help or hint on what is wrong here is very welcome.

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