write answers for the questions 21

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12.1 List three design goals for a firewall.
12.2 List four techniques used by firewalls to control access and enforce a security policy.
12.3 What information is used by a typical packet filtering firewall?
12.4 What are some weaknesses of a packet filtering firewall?
12.5 What is the difference between a packet filtering firewall and a stateful inspection firewall?
12.6 What is an application-level gateway?
12.7 What is a circuit-level gateway?
12.9 What are the common characteristics of a bastion host?
12.10 Why is it useful to have host-based firewalls?
12.11 What is a DMZ network and what types of systems would you expect to find on such networks?
12.12 What is the difference between an internal and an external firewall?