- [Instructor] Network firewalls protect entire networks;
therefore, their scope of protection is much broader
than that of host firewalls.
Network firewalls sometimes come in the form of appliances.
These are devices dedicated to controlling
the flow of network traffic
between internal and external networks.
Although the network firewalls themselves are firewalls,
they still need to be protected by host firewalls;
therefore, network firewalls have a dual mission.
The first one is as a host firewall
whose goal is host protection.
The second mission is to protect the network it belongs to,
which has a much wider scope.
One of the core functionalities of a network firewall
is packet forwarding.
In this case, they receive packets
and send them to their destinations
through different network interfaces.
This functionality is very similar to that of routers.
It's challenging to distinguish firewalls from routers
most of the time,
but the difference is that firewalls drop packets.
Making a port forwarding decision
is a pure firewall feature.
In this example, the firewall intercepts a packet
arriving at a host
with its destination port set to 22222,
and then decides to forward or drop the packet,
based on predefined rules.
The network firewall decides to forward
the secure shell packet
to a host whose IP is 10.0.0.2,
behind a network firewall.
Secure Shell allows a remote client to access a host.
Once the packet arrives at the internal host
and the host has an open port, that is 22,
the packet gets to its destination.
A Secure Shell server is running on the internal host.
As you saw here, the packet arrived at port 22222
of the network firewall,
and then the packet got forwarded
to the open port of an internal host, which was 22.
Your home router should have a built-in
network firewall capability.
Often, it comes with the port forwarding feature;
therefore, many of you may already have
set up port forwarding.
Did you know you can set up any computer
as a network firewall?
We'll try this together later in this course.