Can comeone please explain to me what the exact definition of a firewall is? I have a vague idea of what it is, but something a little more precise would help. Specifically, in an office network, is it something that sits outside the router to the office network, on the router, between the router and the other computers, or is there one firewall on each computer in the network? How can I check to see if we have one running on our computers or network?
A firewall is a system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented in both hardware (i.e. into the router) and software (a standalone computer), or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the Intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.
If you're part of a big company or institution you probably have a firewall. If you don't then your IT guy should be fired. It's hard to say how you can specifically check to see if you have a firewall. Some firewall rules are less restrictive than others. Many block ICMP so you can try pinging your gateway from outside the network to see if it's blocked. If you can't do FTP or POP from your computer outside your Intranet then you probably have a firewall.
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