Which of the following types of firewalls provide the
GREATEST degree and granularity of control?
A. Screening router
B. Packet filter
C. Application gateway
D. Circuit gateway
Answer Posted / guest
Answer: C
The application gateway is similar to a circuit gateway, but
it has specific proxies for each service. To be able to
handle web services it has an HTTP proxy, which acts as an
intermediary between externals and internals, but
specifically for HTTP. This means that it not only checks
the packet IP addresses (layer 3) and the ports it is
directed to (in this case port 80, layer 4), it also checks
every http command (layer 5 and 7). Therefore, it works in a
more detailed (granularity) way than the others. Screening
router and packet filter (choices A and B) basically work at
the protocol, service and/or port level. This means that
they analyze packets from layers 3 and 4 (not from higher
levels). A circuit-gateway (choice D) is based on a proxy or
program that acts as an intermediary between external and
internal accesses. This means that, during an external
access, instead of opening a single connection to the
internal server, two connections are established-one from
the external to the proxy (which conforms the
circuit-gateway) and one from the proxy to the internal.
Layers 3 and 4 (IP and TCP) and some general features from
higher protocols are used to perform these tasks.
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