You can access some websites from a public library network but not others. What is the likely reason?

Accessing some websites from a public library network while being unable to reach others is most likely due to a proxy server filtering access. In many public networks, such as those in libraries, proxy servers are implemented to manage internet traffic and enforce specific access policies. These servers can restrict access to certain sites deemed inappropriate or non-educational based on established guidelines.

Typically, libraries use this approach to ensure that their resources are used for educational and informational purposes, thereby fostering a safe and productive environment for all users. By filtering content, they can block harmful or non-compliant websites, while still allowing access to those that fit within their accepted use policies.

This filtering mechanism is an important aspect of cybersecurity in public networks, helping to protect users from accessing potentially harmful content while guiding them toward useful resources. The other reasons do not specifically relate to controlled access policies in the same way that a proxy server does, which makes this answer the most relevant in the context of the question.