What is a firewall?
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What is a firewall?
A firewall is an appliance or piece of software running on a computer that inspects all network traffic running through it. It’s often the door to the internet, placed between the inter- and intranet. Each firewall has a set of rules defined by its administrator about which traffic is allowed to go where. Some firewalls can even inspect packages on a deep level.
For example when a company wants its employees only to receive e-mail at work they can place a firewall that blocks all traffic in coming and going to the internet except for port 21. The most secure practice is to block everything at first and only open the ports that you really need to use.