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Linux Mastering Development Ubuntu

Network Problems after creating network bridge

i wanted to install some virtual machines on my server using KVM so for this purpose i created a network bridge. so far so good…

My OS is Ubuntu 20.04.

I change the 01-netcfg.yaml file in /etc/netplan:

before:

network:
  version: 2
  renderer: networkd
  ethernets:
   enp5s0:
    dhcp4: no
    addresses: [192.168.192.222/24]
    gateway4: 192.168.192.1
    nameservers:
     addresses: [8.8.8.8]
     search: [example.net]

to after:

network:
  version: 2
  renderer: networkd

  ethernets:
   enp5s0:
    dhcp4: false
    dhcp6: false
#    addresses: [192.168.192.222/24]
#    gateway4: 192.168.192.1
#    nameservers:
#     addresses: [8.8.8.8]
#     search: [example.net]
  bridges:
    br0:
      interfaces: [enp5s0]
      dhcp4: no
      dhcp6: no
      addresses: [192.168.192.222/24]
      gateway4: 192.168.192.1
      mtu: 1500
      nameservers:
        addresses: [8.8.8.8]
      parameters:
        stp: true
        forward-delay: 4

i registered the bridge and i got no error whatsoever.

in /etc/netplan i got one host-bridge.xml file:

<network>
  <name>host-bridge</name>
  <forward mode="bridge"/>
  <bridge name="br0"/>
</network>

BUT… after some hours my ssh connection to the server vanished.
i went to the physical machine and made ping attempts:

ping google.de -> sucesss

ping router -> error

ping other machine in LAN -> error

Afterwards i played back my initial .yaml config file, applied netplan, rebooted…

Everything works again like a charm.

I reproduced this error after setting up the bridge again -> after some hours the same stuff happened.
Playing back the original .yaml files helped.

So it seems to me that the bridge is the cause of error.
Do you have any hint for me what could be the solution here?

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