Chapter 5:Connection Mode
Firewall
The firewall is a 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 which supports logging of the
TCP/UDP and IP packet headers and the first 129 bytes of the packet (including headers) when a
packet is successfully
passed
through, a packet is
blocked
from passing through and it matches a
rule setup to look for suspicious packets
Filtering by IP address
An example for firewall setup:
This picture is 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, set the firewall is an important issue.
Choose
Disabled
to disable the firewall
function. Click
Enabled
to invoke the
settings that you set in this web page.
To open the IP Filtering, please click the
Enabled
radio button. The web page will be
shown as the right picture.
Select the direction to filter packets:
The way of the data transmission. In Bound
means the data is transferred from outside
onto your computer. Out Bound means the
data is transferred from your computer onto
outside through Internet. Please choose
Outbound traffic
or
Inbound traffic
as the
direction for filtering packets.
