User guide

Old Firewall Technologies
Chapter 2: The ZoneAlarm Firewall 13
Table 4: Packet Filter Advantages and Disadvantages
Advantages Disadvantages
Application independence Low security
High performance No screening above the network layer
Scalability
Application-Layer Gateways
Application-layer gateways improve security by examining all application layers, bringing
context information into the decision-making process. However, the method they use to do
this disrupts the client/server model, reducing scalability. Ordinarily, a client sends
requests for information or action according to a specific protocol, and the server responds,
all in one connection. With application-layer gateways, each client/server communications
requires two connections: one from a client to a proxy, and one from a proxy to a server. In
addition, each proxy requires a different process (or daemon), making support for new
applications a problem.
Application-layer gateways have the following advantages and disadvantages:
Table 5: Application-Layer Gateway Advantages and Disadvantages
Advantages Disadvantages
Good security Poor performance
Full application-layer awareness Limited application support
Poor scalability (breaks the client/server model)