Network Level Firewalls and Application Level

Network Level Firewalls and Application Level
Firewalls
Firewalls contain packet filters and /or proxies as their main
components. Depending on which one of the two mechanisms
provides the most vital services, the firewall will be operating
predominantly on one network layer:
• Application layer - This will be used if proxies are dominant.
• Network layer - This will be used if packet filters are dominant.
Both types will inherit properties associated with the layer they operate
on, regardless of the specific architecture that is being used.
Generally, firewalls are subdivided into three categories:
• Network Level Firewalls.
• Application Level Firewalls.
• Circuit Level Firewalls.
Network Level Firewalls
Network level firewalls generally make their decisions based on three
aspects of an IP packet:
• The source address.
• The destination address.
• The ports.

They have become increasingly sophisticated, and now maintain
internal information about the state of connections passing through
them and the content of some data streams, thus leading to a new type
of firewall commonly referred to as a dynamic packet filtering firewall.
An important thing to realize is that they usually route traffic directly
through themselves, in which case one needs a validly assigned IP
address block for the internal network. They tend to be very fast and
totally transparent to users; it is quite obvious that network level
firewalls inherit most of the properties discussed in packet filtering.