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Firewall
The firewall is a kind of software that interrupts the data between the Internet and your computer. It is the
TCP/IP equivalent of a security gate at the entrance to your company. All data must pass through it, and the
firewall (functions as a security guard) will allow only authorized data to be passed into the LAN.
What the firewall can do? It can:
• deny or permit any packet from passing through explicitly
• distinguish between various interfaces and match on the following fields:
• source and destination IP address
• port
To keep track of the performance of IP Filter, a logging device is used. The device supports logging of the TCP/UDP
and IP packet headers and the first 129 bytes of the packet (including headers) whenever a packet is successfully
passed through or blocked, and whenever a packet matches a rule being setup for suspicious packets.
An example for firewall setup:
Internet
Router
with Firewall Protection
PC 1
PC 2
This picture shows the most common and easiest way to employ the firewall. Basically, you can install a
packet-filtering router at the Internet gateway and then configures the filter rule in the router to block or filter
protocols and addresses. The systems behind the router usually have a direct access to the Internet; however
some dangerous services such as NIS and NFS are usually blocked.
For the security of your router, setting the firewall is an important issue.