Page 165 - DCAP516_COMPUTER_SECURITY

Unit 13: Firewalls

However, both encryption and encapsulation are generic terms that describe a function that can Notes
be performed by a myriad of specific technologies. To add to the confusion, these two sets of
technologies can be combined in different implementation topologies. Thus, VPNs can vary
widely from vendor to vendor.

Figure 13.3: Diagram of VPN

13.3 Types of Firewalls

There are mainly three types of firewalls and these are:

13.3.1 Network Layer

Network layer generally make their decisions based on the source, destination addresses and
ports in individual IP packets. A simple router is the “traditional’’ network layer firewall, since
it is not able to make particularly sophisticated decisions about what a packet is actually talking
to or where it actually came from. Modern network layer firewalls have become increasingly
sophisticated, and now maintain internal information about the state of connections passing
through them, the contents of some of the data streams, and so on. One thing that’s an important
distinction about many network layer firewalls is that they route traffic directly though them,
so to use one you either need to have a validly assigned IP address block or to use a “private
internet’’ address block. Network layer firewalls tend to be very fast and tend to be very
transparent to users.

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