What roles do firewalls and proxy servers play in network

Question

1. What roles do firewalls and proxy servers play in network security?
2. What is the importance of maintaining security on a LAN? Provide examples to support your answer.
3. What are the key security requirements of confidentiality, integrity and availability?
4. What are some vulnerabilities in today's networks? How do these relate to current threats and exploits?
5. What are some ways a network administrator can counter threats, vulnerabilities and exploits?
6. What are some current computer threats?Describe the nature of three threats.
7. What are the potential repercussions these threats could have for a network?