Do I have a Firewall - How many Firewalls do I Need
Finding answer to the question - Do I have a Firewall - is not hard. If you are using Windows XP SP2 or later versions, you have a firewall. Microsoft introduced a built-in firewall from Windows XP SP2 onwards. You can check this from Control Panel -> Security Center. Another method to know if you have a firewall is to check if you have an Internet Security Suite on your computer. An Internet Security Suite such as Norton, McAfee, Comodo, or similar software essentially contains a firewall. Normally, these appear in the taskbar of your computer. You may open them to see if they mention firewalls. If you are still stuck with the question - Do I have a Firewall - I recommend you run a test from online sites to see if you are covered. Though the link is to check if your firewall is strong enough, it also serves the purpose of finding if you have a firewall.
Coming to "How many firewalls do I need," an average user who uses Internet just to check email does not essentially need a firewall. If you use an "Always ON" Internet connection or stay hours on stretch using a broadband modem, you need a good firewall. For a single, standalone computer, one of the best software firewalls should be sufficient. If you are using a firewall enabled router or modem, you may skip software firewall. However, the firmware firewall should offer good protection.
In case you are on a network, you can use a hardware firewall against the main computer or server to protect the entire network. Each computer on the network can have a low-level firewall for protection against malicious users in the network. The outer, hardware based firewall should be as strong as the size of network. For a smaller network of three to five computers, Linksys routers are good enough. For enterprise level networks, you need firewalls that are more powerful. Examples of such firewalls can be the ones from Cisco. The number of firewalls and their configuration is dependent on network designers in case of enterprise level networks.
To sum up, the answer to "how many firewalls do I need" depends on the usage of Internet or any network. The more you use it, the stronger protection you need. Still, it should NEVER be more than one software firewall on same computer.