Carlos Giron
Information Security
Professor Hartunian
June 14, 2012
Chapter 6 Review Questions 2&8 Exercise 2 and
Case exercises 1&2
2. TCP (Transmission Control Protocol) is the most commonly used protocol on the Internet. The reason
for this is because TCP offers error correction. When the TCP protocol is used there is a "guaranteed
delivery." This is due largely in part to a method called "flow control." Flow control determines when
data needs to be re-sent, and stops the flow of data until previous packets are successfully transferred.
This works because if a packet of data is sent, a collision may occur. When this happens, the client rerequests the packet from the server until the whole packet is complete and is identical to its original.
UDP (User Datagram Protocol) is anther commonly used protocol on the Internet. However, UDP is
never used to send important data such as webpages, database information; UDP is commonly used for
streaming audio and video. Streaming media such as Windows Media audio files (.WMA), Real Player
(.RM), and others use UDP because it offers speed! The reason UDP is faster than TCP is because there is
no form of flow control or error correction. The data sent over the Internet is affected by collisions, and
errors will be present. Remember that UDP is only concerned with speed. This is the main reason why
streaming media is not high quality.
8. Firewalls fall into four broad categories: packet filters, circuit level gateways, application level
gateways and stateful multilayer inspection firewalls. Packet filtering firewalls work at the network level
of the OSI model, or the IP layer of TCP/IP. They are usually part of a router. Circuit level gateways work
at the session layer of the OSI model, or the TCP layer of TCP/IP. They monitor TCP handshaking
between packets to determine whether a requested session is legitimate. Information passed to remote
computer through a circuit level gateway appears to have originated from the gateway. Application level
gateways, also called proxies, are similar to circuit-level gateways except that they are application
specific. They can filter packets at the application layer of the OSI model. Incoming or outgoing packets
cannot access services for which there is no proxy. Stateful multilayer inspection firewalls combine the
aspects of the other three types of firewalls. They filter packets at the network layer, determine whether
session packets are legitimate and evaluate contents of packets at the application layer. They allow
direct connection between client and host, alleviating the problem caused by the lack of transparency of
application level gateways.
Exercise 2
2. Timbuktu is a remote control software product developed by WOS Data systems. Remote control
software allows a user to control another computer across the local network or the Internet, viewing its
screen and using its keyboard and mouse as if he or she were sitting in front of it. Timbuktu is
compatible with computers running both Mac OS X and Windows.
Case Exercises
1. What is more efficient for the company? What is a better set up, subnet with bastion hosts?
Or a screened subnet with proxy servers? How will that decision affect the way they
implement application and web servers? What type of security protection program does the
company need?
2. Cost versus maintaining high security for SLS; I think that in the long run maintaining high
security is more important than the cost. Not having high security can result in spending
more money therefore cost versus maintaining high security I would choose a high security
because that is most important at this moment.