Expert answer:The CRC is a checksum of the frame contents
Expert answer:Few case study questions : Write paragraph to answer pleaseFew multiple choice questionand in the below, is an example 2) Based on the following article, how would you stop virus in a corporate Network?A computer virus is a computer program that can copy itself and infect a computer. The term “virus” is also commonly but erroneously used to refer to other types of malware, adware, and spyware programs that do not have the reproductive ability. A true virus can only spread from one computer to another (in some form of executable code) when its host is taken to the target computer; for instance because a user sent it over a network or the Internet, or carried it on a removable medium such as a floppy disk, CD, DVD, or USB drive. Viruses can increase their chances of spreading to other computers by infecting files on a network file system or a file system that is accessed by another computer.The term “computer virus” is sometimes used as a catch-all phrase to include all types of malware. Malware includes computer viruses, worms, trojans, most rootkits, spyware, dishonest adware, crimeware, and other malicious and unwanted software, including true viruses. Viruses are sometimes confused with computer worms and Trojan horses, which are technically different. A worm can exploit security vulnerabilities to spread itself to other computers without needing to be transferred as part of a host, and a Trojan horse is a program that appears harmless but has a hidden agenda. Worms and Trojans, like viruses, may cause harm to either a computer system’s hosted data, functional performance, or networking throughput, when they are executed. Some viruses and other malware have symptoms noticeable to the computer user, but many are surreptitious or go unnoticed.Viruses have targeted various types of transmission media or hosts. This list is not exhaustive:Binary executable files (such as COM files and EXE files in MS-DOS, Portable Executable files in Microsoft Windows, and ELF files in Linux)Volume Boot Records of floppy disks and hard disk partitionsThe master boot record (MBR) of a hard diskGeneral-purpose script files (such as batch files in MS-DOS and Microsoft Windows, VBScript files, and shell script files on Unix-like platforms).Application-specific script files (such as Telix-scripts)System specific autorun script files (such as Autorun.inf file needed by Windows to automatically run software stored on USB Memory Storage Devices).Documents that can contain macros (such as Microsoft Word documents, Microsoft Excel spreadsheets, AmiPro documents, and Microsoft Access database files)Cross-site scripting vulnerabilities in web applications (see XSS Worm)Arbitrary computer files. An exploitable buffer overflow, format string, race condition or other exploitable bug in a program which reads the file could be used to trigger the execution of code hidden within it. Most bugs of this type can be made more difficult to exploit in computer architectures with protection features such as an execute disable bit and/or address space layout randomization.PDFs, like HTML, may link to malicious code. PDFs can also be infected with malicious code.In operating systems that use file extensions to determine program associations (such as Microsoft Windows), the extensions may be hidden from the user by default. This makes it possible to create a file that is of a different type than it appears to the user. For example, an executable may be created named “picture.png.exe”, in which the user sees only “picture.png” and therefore assumes that this file is an image and most likely is safe.An additional method is to generate the virus code from parts of existing operating system files by using the CRC16/CRC32 data. The initial code can be quite small (tens of bytes) and unpack a fairly large virus. This is analogous to a biological “prion” in the way it works but is vulnerable to signature based detection.This attack has not yet been seen “in the wild”.
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1)Peter Oberois demonstrates to a group of Network security experts:
The Ethernet Frame structure where the sending adapter encapsulates IP datagram:
Which of the following is the function of the CRC:
A checked at receiver, if error is detected, frame is dropped
B Synchronization of receiver and sender clock rates
C conform to CSMA/CD requirements for Wireless Application Protocol
D Encryption of Data to conform to SSL
requirements
E Provide destination and source address MAC conversion from NIC card
2) Based on the following article, how would you stop virus in a corporate Netwo
rk?
A computer virus is a computer program that can copy itself and infect a computer.
The term “virus” is also commonly but erroneously used to refer to other types of
malware, adware, and spyware programs that do not have the reproductive ability. A
true virus can only spread from one computer to another (in some form of executabl
e code) when its host is taken to the target computer; for instance because a user
sent it over a network or the Internet, or carried it on a removable medium such a
s a floppy disk, CD, DVD, or USB drive. Viruses can increase their chances of spre
ading to other computers by infecting files on a network file system or a file sys
tem that is accessed by another computer.
The term “computer virus” is sometimes used as a catch-all phrase to include all t
ypes of malware. Malware includes computer viruses, worms, trojans, most rootkits,
spyware, dishonest adware, crimeware, and other malicious and unwanted software, i
ncluding true viruses. Viruses are sometimes confused with computer worms and Troj
an horses, which are technically different. A worm can exploit security vulnerabil
ities to spread itself to other computers without needing to be transferred as par
t of a host, and a Trojan horse is a program that appears harmless but has a hidde
n agenda. Worms and Trojans, like viruses, may cause harm to either a computer sys
tem’s hosted data, functional performance, or networking throughput, when they are
executed. Some viruses and other malware have symptoms noticeable to the computer
user, but many are surreptitious or go unnoticed.
Viruses have targeted various types of transmission media or hosts. This list is n
ot exhaustive:
●
●
●
●
●
●
●
●
●
Binary executable files (such as COM files and EXE files in MS-DOS, Portable Execut
able files in Microsoft Windows, and ELF files in Linux)
Volume Boot Records of floppy disks and hard disk partitions
The master boot record (MBR) of a hard disk
General-purpose script files (such as batch files in MS-DOS and Microsoft Windows,
VBScript files, and shell script files on Unix-like platforms).
Application-specific script files (such as Telix-scripts)
System specific autorun script files (such as Autorun.inf file needed by Windows to
automatically run software stored on USB Memory Storage Devices).
Documents that can contain macros (such as Microsoft Word documents, Microsoft Exce
l spreadsheets, AmiPro documents, and Microsoft Access database files)
Cross-site scripting vulnerabilities in web applications (see XSS Worm)
Arbitrary computer files. An exploitable buffer overflow, format string, race condi
tion or other exploitable bug in a program which reads the file could be used to tr
igger the execution of code hidden within it. Most bugs of this type can be made mo
re difficult to exploit in computer architectures with protection features such as
an execute disable bit and/or address space layout randomization.
PDFs, like HTML, may link to malicious code. PDFs can also be infected with malici
ous code.
In operating systems that use file extensions to determine program associations (s
uch as Microsoft Windows), the extensions may be hidden from the user by default.
This makes it possible to create a file that is of a different type than it appear
s to the user. For example, an executable may be created named “picture.png.exe”,
in which the user sees only “picture.png” and therefore assumes that this file is
an image and most likely is safe.
An additional method is to generate the virus code from parts of existing operatin
g system files by using the CRC16/CRC32 data. The initial code can be quite small
(tens of bytes) and unpack a fairly large virus. This is analogous to a biological
“prion” in the way it works but is vulnerable to signature based detection.
This attack has not yet been seen “in the wild”.
17)Case Study 2 :
Based on the following article how would you increase the speed of your corpora
te website?
In computer networking and computer science, digital bandwidth, network bandwidt
h or just bandwidth is a measure of available or consumed data communication res
ources expressed in bit/s or multiples of it (kbit/s, Mbit/s etc).
Bandwidth may refer to bandwidth capacity or available bandwidth in bit/s, which
typically means the net bit rate, channel capacity or the maximum throughput of
a logical or physical communication path in a digital communication system. For
example, bandwidth test implies measuring the maximum throughput of a computer n
etwork. The reason for this usage is that according to Hartley’s law, the maximu
m data rate of a physical communication link is proportional to its bandwidth in
hertz, which is sometimes called frequency bandwidth, radio bandwidth or analog
bandwidth, the last especially in computer networking literature.
Bandwidth may also refer to consumed bandwidth (bandwidth consumption), correspo
nding to achieved throughput or goodput, i.e. average data rate of successful da
ta transfer through a communication path. This meaning is for example used in ex
pressions such as bandwidth shaping, bandwidth management, bandwidth throttling,
bandwidth cap, bandwidth allocation (for example bandwidth allocation protocol a
nd dynamic bandwidth allocation), etc. An explanation to this usage is that digi
tal bandwidth of a bit stream is proportional to the average consumed signal ban
dwidth in Hertz (the average spectral bandwidth of the analog signal representin
g the bit stream) during a studied time interval.
Digital bandwidth may also refer to: average bitrate (ABR) after multimedia data
compression (source coding), defined as the total amount of data divided by the
playback time.
Some authors prefer less ambiguous terms such as gross bit rate, net bit rate, c
hannel capacity and throughput, to avoid confusion between digital bandwidth in
bits per second and analog bandwidth in hertz.
In website hosting, the term “bandwidth” is often incorrectly used to describe t
he amount of data transferred to or from the website or server within a prescrib
ed period of time, for example bandwidth consumption accumulated over a month me
asured in Gigabyte per month. The more accurate phrase used for this meaning of
a maximum amount of data transfer each month or given period is monthly data tra
nsfer.
Consider this example:
● Rented Water Tank = web-server that hosts your website,
● Water company = hosting company where your web-server resides,
● Water = files, data, images, etc. that comprise your website,
● Pipe = the internet,
● Quantity of water delivered = bandwidth consumption,
● You = patron / visitor of your website which is hosted on aforementioned web-serv
er.
There’s a pipe that delivers water from your rented water tank to your home. As
you request water, the water company delivers it to you. All the while, they are
keeping track of how much water was delivered to you, during a billing cycle. Yo
u have a contract with the water company in which they agree to charge you a fix
ed dollar amount per billing cycle, provided you do not request more water than
the allowable quantity, as defined in your contract. If you do request more wate
r, they will not deny you … but you will incur additional charges for the extr
a water requested / delivered.
With that example in mind, web-pages typically equate to a small quantity of wat
er … while images, videos, PDFs and other similar media can potentially equate
to large quantities of water being delivered by your water company. The accumula
ted total can grow rather quickly, especially when your website is popular / vis
ited by many people.
Below is a table showing the maximum bandwidth (the physical layer net bitrate,
often slightly more than the maximum throughput) of common Internet access techn
ologies. For a more detailed list see List of device bandwidths.
18)Case Study 3 :
Based on the following article, what kind of delays do you expect in Packet swi
tching networks?
Packet switching is a digital network communications method that groups all trans
mitted data – irrespective of content, type, or structure – into suitably-sized
blocks, called packets. Packet switching features delivery of variable-bit-rate
data streams (sequences of packets) over a shared network. When traversing netwo
rk adapters, switches, routers and other network nodes, packets are buffered and
queued, resulting in variable delay and throughput depending on the traffic load
in the network.
Packet switching contrasts with another principal networking paradigm, circuit s
witching, a method which sets up a limited number of dedicated connections of co
nstant bit rate and constant delay between nodes for exclusive use during the co
mmunication session. In case of traffic fees, for example in cellular communicat
ion, circuit switching is characterized by a fee per time unit (per minute) of c
onnection time, also when no data is transferred, while packet switching is char
acterized by a fee per unit of information (per Megabyte).
Two major packet switching modes exist; connectionless packet switching (also kn
own as datagram switching) and connection-oriented packet switching (also known
as virtual circuit switching). In the first case each packet includes complete a
dressing or routing information. The packets are routed individually, sometimes
resulting in different paths and out-of-order delivery. In the second case a con
nection is defined and preallocated in each involved node before any packet is t
ransfered. The packets includes a connection identifier rather than address info
rmation, and are delivered in order. See below.
Packet mode communication (or packet-oriented, packet-based) may be utilized with
or without intermediate forwarding nodes (packet switches). In all packet mode c
ommunication, network resources are managed by statistical multiplexing or dynam
ic bandwidth allocation in which a communication channel is effectively divided
into an arbitrary number of logical variable-bit-rate channels or data streams.
Each logical stream consists of a sequence of packets, which normally are forwar
ded by the multiplexors and intermediate network nodes asynchronously using firs
t-in, first-out buffering. Alternatively, the packets may be forwarded according
to some scheduling discipline for fair queuing or for differentiated or guarante
ed quality of service, such as pipeline forwarding or time-driven priority (TDP)
. Any buffering introduces varying latency and throughput in transmission. In ca
se of a shared physical medium, the packets may be delivered according to some p
acket-mode multiple access scheme.
The service actually provided to the user by networks using packet switching nod
es can be either connectionless (based on datagram messages), or virtual circuit
switching (also known as connection oriented). Some connectionless protocols are
Ethernet, IP, and UDP; connection oriented packet-switching protocols include X.
25, Frame relay, Asynchronous Transfer Mode (ATM), Multiprotocol Label Switching
(MPLS), and TCP.
In connection oriented networks, each packet is labeled with a connection ID rat
her than an address. Address information is only transferred to each node during
a connection set-up phase, when an entry is added to each switching table in the
network nodes.
In connectionless networks, each packet is labeled with a destination address, a
nd may also be labeled with the sequence number of the packet. This precludes th
e need for a dedicated path to help the packet find its way to its destination.
Each packet is dispatched and may go via different routes. At the destination, t
he original message/data is reassembled in the correct order, based on the packe
t sequence number. Thus a virtual connection, also known as a virtual circuit or
byte stream is provided to the end-user by a transport layer protocol, although
intermediate network nodes only provides a connectionless network layer service.
Packet switching is used to optimize the use of the channel capacity available i
n digital telecommunication networks such as computer networks, to minimize the
transmission latency (i.e. the time it takes for data to pass across the network
), and to increase robustness of communication.
The most well-known use of packet switching is the Internet and local area netwo
rks. The Internet uses the Internet protocol suite over a variety of Link Layer
protocols. For example, Ethernet and frame relay are very common. Newer mobile p
hone technologies (e.g., GPRS, I-mode) also use packet switching.
X.25 is a notable use of packet switching in that, despite being based on packet
switching methods, it provided virtual circuits to the user. These virtual circu
its carry variable-length packets. In 1978, X.25 was used to provide the first i
nternational and commercial packet switching network, the International Packet S
witched Service (IPSS). Asynchronous Transfer Mode (ATM) also is a virtual circu
it technology, which uses fixed-length cell relay connection oriented packet swi
tching.
Datagram packet switching is also called connectionless networking because no co
nnections are established. Technologies such as Multiprotocol Label Switching (M
PLS) and the Resource Reservation Protocol (RSVP) create virtual circuits on top
of datagram networks. Virtual circuits are especially useful in building robust
failover mechanisms and allocating bandwidth for delay-sensitive applications.
MPLS and its predecessors, as well as ATM, have been called “fast packet” techno
logies. MPLS, indeed, has been called “ATM without cells.” Modern routers, howe
ver, do not require these technologies to be able to forward variable-length pac
kets at multigigabit speeds across the network.
Both X.25 and Frame Relay provide connection-oriented packet switching, also kno
wn as virtual circuit switching. A major difference between X.25 and frame relay
packet switching are that X.25 is a reliable protocol, based on node-to-node aut
omatic repeat request, while Frame Relay is a non-reliable protocol, maximum pac
ket length is 1000 bytes. Any retransmissions must be carried out by higher laye
r protocols. The X.25 protocol is a network layer protocol, and is part of the X
.25 protocol suite, also known as the OSI protocol suite. It was widely used in
relatively slow switching networks during the 1980s, for example as an alternati
ve to circuit mode terminal switching, and for automated teller machines. Frame
relay is a further development of X.25. The simplicity of Frame relay made it co
nsiderably faster and more cost effective than X.25 packet switching. Frame rela
y is a data link layer protocol, and does not provide logical addresses and rout
ing. It is only used for semi-permanent connections, while X.25 connections also
can be established for each communication session. Frame relay was used to inter
connect LANs or LAN segments, mainly in the 1990s by large companies that had a
requirement to handle heavy telecommunications traffic across wide area networks
.[6] (O’Brien & Marakas, 2009, p. 250) Despite the benefits of frame relay pack
et switching, many international companies are staying with the X.25 standard. I
n the United States, X.25 packet switching was used heavily in government and fi
nancial networks that use mainframe applications. Many companies did not intend
to cross over to frame relay packet switching because it is more cost effective
to use X.25 on slower networks. In certain parts of the world, particularly in A
sia-Pacific and South America regions, X.25 was the only technology available.[7
] (Girard, 1997)
ANSWER?:
6)You are assigned with configuring a sensitive data network where here is no scope of tol
erating viruses and worms.
You should keep the emails with attachments in:
A A DMZ
B The proxy server
C Between 2 DMZs of same security sensitiveness
D The gateway router just before the DMZ
E The Intranet
8)Which topology is best suited for factories assembling cars:
A Ring
B A combination of Ring, Bus, and Sta
r
C Star
D Bus
E None of the other choices
…
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