Installation guide

8
STEP 1: Understanding firewalls in principle
• A firewall is a means of shielding your private computer system from an untrusted network,
like the Internet.
• Any outside connection puts your network at some risk, and should be regarded as gateways
to an untrusted network, whether or not it is in use. Some standard computer services
increase this risk by running less than secure IP protocols such as FTP (File Transfer
Protocol) and UDP (User Datagram Protocol).
• Firewalls mediate network traffic to allow authorised traffic and bar unauthorised or risky
traffic.
• However, your firewall cannot completely shield you from the outside, as you may want to
browse the Internet, send and receive emails etc. For that purpose, your firewall needs to
open some doors for traffic between the networks. Step 7, the section on
understanding ports and configuration explains which doors are safe to open and how to
safely open and close such doors.
• There is no point in establishing a connection to another network if you do not use it.
• If your private network is not connected to any other network, you do not need a firewall.
Understanding that firewalls have limits
• Firewalls are not the panacea of computer security.
• Firewalls are one important tool to secure your network, but are not going to solve all your
security problems. They are an essential ingredient in your total IT security strategy, but
cannot be the only one.
• In particular, firewalls offer only limited protection from attacks originating from within your
private network. They will not prevent you from opening dangerous attachments to emails,
or downloading unsafe applications.