What?:
A device that isolates the “secure” private network to the “unsecure” public network.
How?
Basically it applies policies (read: rules) that decides whether to allow or deny traffic. May look something like below. Note that the rules go top to bottom. :
Types of Firewalls:
Packet Filters (stateless):
- If a packet matches the packet filter’s set of rules, the filter will drop it.
Stateful:
- Maintains a record of all connections passing through it and can determine if a packet is either the start of a new connection, an existing connection or an invalid packet.
Application Layer:
- Works like a proxy - can “read” through protocols. Would inspect traffic, blocking based on it’s rules (eg blocking websites, viruses etc.).
Takeaway of them?
They’re good. You need one. But they won’t do much.