Step1: Download driver source code--------------------------------------------------------------------------------------------------

https://www.realtek.com/en/component/zoo/category/network-interface-controllers-10-100-1000m-gigabit-ethernet-pci-express-software

FE Ethernet LINUX driver r8101 for kernel up to 5.6

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Step2: Download gcc, make *.deb--------------------------------------------------------------------------------------------------

PACKAGES="gcc" apt-get download $(apt-cache depends --recurse --no-recommends --no-suggests \ --no-conflicts --no-breaks --no-replaces --no-enhances \ --no-pre-depends ${PACKAGES} | grep "^\w")

PACKAGES="make" apt-get download $(apt-cache depends --recurse --no-recommends --no-suggests \ --no-conflicts --no-breaks --no-replaces --no-enhances \ --no-pre-depends ${PACKAGES} | grep "^\w")

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Step2: copy to USB & mount--------------------------------------------------------------------------------------------------

mount /dev/sda1 /mnt

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Step3: install--------------------------------------------------------------------------------------------------

 cd /mnt/deb_cache

dpkg -i *.deb

cd /mnt/driver_src

./autorun

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 Step4: netplan--------------------------------------------------------------------------------------------------

cd /etc/netplan

nano 00-installer-config.yaml

network:
  version: 2
  renderer: networkd
  ethernets:
    enp1s0:
      addresses: [192.168.31.5/24]
      dhcp4: no
      optional: true
      gateway4: 192.168.31.1
      nameservers:
        addresses: [192.168.31.1, 114.114.114.114, 8.8.8.8]

netplan apply

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