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# install ufw

  sudo apt-get install ufw
  
# check firewall status

  sudo ufw status

# set up default rules

  sudo ufw default [deny|allow] [incoming|outgoing]

# set up rules for services

  sudo ufw allow ssh
  
# allow incoming tcp and udp packet on port 53

    sudo ufw allow 53

# allow incoming tcp packets on port 53

    sudo ufw allow 53/tcp

# allow incoming udp packets on port 53

    sudo ufw allow 53/udp

# show existing rules

  sudo ufw show added

# delete rule

  sudo ufw delete [existing rule]

# turn firewall on

  sudo ufw enable