A vulnerability scanner is a tool that scans a network or a system for known vulnerabilities, such as misconfigurations, outdated software, or weak passwords. A vulnerability scanner can provide valuable information for improving the security posture of a system, but it can also cause serious disruption of a control network if used on a live system. This is because a vulnerability scanner may generate a large amount of network traffic, consume system resources, trigger alarms, or even crash devices by exploiting vulnerabilities.
Therefore, a vulnerability scanner should not be used on a live system without proper authorization and precautions. A vulnerability scanner should only be used on a test or isolated network, or during a scheduled maintenance window with minimal impact on the system operation. References: ISA/IEC 62443 Standards to Secure Your Industrial Control System, Module 5: Assessing the Current Security Level, Slide 25.

ISA-TR62443-2-3 is the technical report that describes the requirements for asset owners and industrial automation and control system (IACS) product suppliers that have established and are now maintaining an IACS patch management program. Patch management is the process of applying software updates to fix vulnerabilities, bugs, or performance issues in the IACS components. Patch management is an essential part of maintaining the security and reliability of the IACS environment. The technical report provides guidance on how to establish a patch management policy, how to assess the impact and risk of patches, how to test and deploy patches, and how to monitor and audit the patch management process. References: 1, 2, 3

According to the OSI model, the physical address is assigned in the layer 2, also known as the data link layer.
The physical address is a unique identifier for each device on a network, such as a MAC address or a serial number. The data link layer is responsible for transferring data between adjacent nodes on a network, using the physical address to identify the source and destination of each frame. The data link layer also provides error detection and correction, flow control, and media access control. References: ISA/IEC 62443 Cybersecurity Fundamentals Specialist Exam Prep, section 2.2; ISA/IEC 62443 Standards to Secure Your Industrial Control System, section 3.1.2.

One of the primary goals of providing a framework that addresses secure product development lifecycle requirements is to ensure that security policies and procedures are well-documented. This objective is crucial because it establishes a structured and standardized approach to security that is integrated throughout the development process of software or systems. This framework helps in aligning the development process with security best practices, thereby mitigating risks associated with security vulnerabilities. Documentation of security policies and procedures ensures that security considerations are consistently applied and that compliance with relevant standards, such as ISA/IEC 62443, is maintained. This foundational approach supports the overall security posture by embedding security considerations directly into the lifecycle of product development, rather than addressing security as an afterthought.

A router and a VPN can be employed as barrier devices in a segmented network. A barrier device is a device that controls the flow of traffic between different network segments, based on predefined rules and policies1. A router is a device that forwards packets between different networks, based on their IP addresses2. A router can act as a barrier device by applying access control lists (ACLs) or firewall rules to filter or block unwanted or malicious traffic2. A VPN is a technology that creates a secure and encrypted tunnel between different networks, such as a remote site and a corporate network3. A VPN can act as a barrier device by encrypting the traffic and authenticating the users or devices that access the network3. A VPN can also prevent unauthorized access or eavesdropping by outsiders3.
References: LAYERING NETWORK SECURITY - CISA, Router (computing) - Wikipedia, What Is Network Segmentation? - Cisco.