Networking

Networking

The assessment questions.

In your own words, please answer the questions below:

1)   Explain how routers forward packets in a datagram network and in a virtual circuit network.
2)   Routing on the Internet would not work if IP addresses were assigned at random to hosts. Explain the problem that would arise in that case. Then explain how IP addresses are allocated and why that strategy avoids the above problem.
[6 marks]
3)   Suppose an IP packet of 5000 bytes travels on network A with MTU of 1500 and then on network B with an MTU of 512 bytes. Show the content of the fields of the first 8 bytes of each IP packet received at the destination (for example the original IP packet can be described as ver = 4, hlen= 20, type=T, length= 5000, id=X, fflag=0, foffset=0)
4)
a.   Consider a network with link costs c(a,b)= 4, c(b,c) = 20, c(b,e) = 7, c(c,d) = 3, c(d,e)=1. Simulate the execution of the distance vector protocol presented in Appendix, filling in Table 2.
b.   The simplified algorithm presented in the Appendix does not work if link costs increase during the execution. Starting from the final situation of the execution in the previous point show why an increase in cost would not be correctly reflected in the distance vectors (assume nodes connected by the link whose cost changes update their distance vector accordingly and start updating their neighbours). In the algorithm presented during the lectures, nodes keep a copy of past distance vectors received from all nodes. Explain why this would solve the above problem.
[7 marks]

5) A typical attack on non-switched Ethernet is packet sniffing, i.e. disabling the hardware filtering of frames performed by the network card, so that also packets addressed to other nodes are passed to upper layers.
This attack is not effective on a switched network. Explain why, with an example on a network composed by hosts A,B,C (the attacker) connected to a switch, where node A sends 3 packets to node B which replies to each packet. Suppose switch tables starts empty.
6) Now reconsider the above case focusing on IP packets sent from A to B supposing that at the start A does not yet know B’s MAC address. Explain the process for A to send 10 IP packets to B, including every operation performed by hosts, and every message sent. Is there anything C can do to receive packets destined to B in this case? If no explain why the process is secure, if yes explain the attack and think about possible ways to detect or prevent it.

7) Suppose host A need to send the following 3 bytes of data to B (in hexadecimal): E2,34,9F. Compute the parity bits according to the following schemes: a) single bit odd parity, b) column (odd) parity scheme with 2, 4 and 6 columns c) two dimensional parity schemes with 6 columns. Then say how many errors can be detected or corrected with each scheme, and compute the overhead of the scheme i.e., the ratio between the number of bits used for error correction and the number of data bits.
8) Suppose the only factor to define the maximum length of Ethernet cables is allowing the transmitting node to detect collisions with other nodes. Find out the minimum length of an Ethernet frame L and compute the maximum length of a cable for R=10Mbps, 100Mbps and 1Gbps Ethernets (assume the speed of signal propagation is 200.000Km/sec). Then compute the CSMA/CD efficiency for such long cables using the formula in the slides (note that efficiency is computed from the maximum length frame size).

DV updates table
•   The table shows the sequence of messages exchanged by nodes, and the corresponding updates to the recipient distance vector. Initially the table only has the distance vector for the immediate neighbors of a given node, and “-“ (inifinity) for the others.
•   At each step y receives the distance vector of x Dx and potentially updates its own distance vector Dy. Y updates the distance for each destination n Dy(n), if the distance advertised by x (i.e., Dx(n)) plus the cost of the link c(x,y) is less than the y’s current distance for n. In mathematical terms at each step Dy(n) ? min{Dy(n), c(x,y) + Dx(n)}
Columns description
•   “Message x->y”: write the sending node and the receiving node followed by an arrow
•   “c(x,y)”: report here the cost of the link connecting the sending and receiving node
•   “DV of”: report the node y receiving the message, whose DV is potentially updated by the receipt of the message, this will make it easier to spot the “last” version of the DV vector for each node
•   “A,B,…”: report here the updated Dy(A), Dy(B), … i.e. the components of the updated distance vector of the receiving node y. If a component is changed from the most recent version of y, underline the new value.
•   “DV updated”: y if any component of the distance vector was updated in this step, – otherwise
•   “Node completed”: x if this is the last message x is sending at this iteration, “-“ otherwise
•   “Nodes to execute”: the set of nodes that still needs to be executed, computed from the value of the previous row, adding “DV updated” (if necessary) and removing “Node completed”
Notes to complete the table
1)   Simulate the execution of nodes in lexicographical order, i.e. first send messages from A, then from B, etc. When the last node executes, restart from A, if needed (see below). Also send messages to nodes in order, i.e. if B is connected to both E and G, fist send B’s distance vector to E (B->E) and then to G (B->G). To keep track of the nodes that still needs to execute due to their distance vector being updated use the columns “DV updated”,”Node completed” and “Nodes to execute” as explained before. If it is node X turn and X does not need to be executed, skip its execution. The algorithm terminates when “Nodes to execute” is empty.
2)   Be sure when comparing x and y distance vector to consider the last DV in the table, i.e. the most recent one.

Example on a network with link costs: c(A,B) = 5, c(B,C)=3, c(B,E)=10, c(C,D)=10, c(D,E)=1

Message x->y   c(x,y)   DV of   A   B   C   D   E   DV updated   Node completed   Nodes to execute
A   0   5   –   –   –
B   5   0   3   –   10
C   –   3   0   10   –
D   –   –   10   0   1
E   –   10   –   1   0           {A,B,C,D,E}
A->B   5   B   5   0   3   –   10   –   A   {B,C,D,E}
B->A   5   A   0   5   8   –   15   A   –   {A,B,C,D,E}
B->C   3   C   8   3   0   10   13   C   –   {A,B,C,D,E}
B->E   10   E   15   10   13   1   0   E   B   {A,C,D,E}
C->B   3   B   5   0   3   13   10   B   –   {A,B,C,D,E}
C->D   10   D   18   13   10   0   1   D   C   {A,B,D,E}
D->C   10   C   8   3   0   10   11   C   –   {A,B,C,D,E}
D->E   1   E   15   10   11   1   0   E   D   {A,B,C,E}
E->B   10   B   5   0   3   11   10   B   –   {A,B,C,E}
E->D   1   D   16   11   10   0   1   D   E   {A,B,C,D}
A->B   5   B   5   0   3   11   10   –   A   {B,C,D}
B->A   5   A   0   5   8   16   15   A   –   {A,B,C,D}
B->C   3   C   8   3   0   10   11   –   –   {A,B,C,D}
B->E   10   E   15   10   11   1   0   –   B   {A,C,D}
C->B   3   B   5   0   3   11   10   –   –   {A,C,D}
C->D   10   D   16   11   10   0   1   –   C   {A,D}
D->C   10   C   8   3   0   10   11   –   –   {A,D}
D->E   1   E   15   10   11   1   0   –   D   {A}
A->B   5   B   5   0   3   11   10   –   A   {}

Table 1

Message x->y   c(x,y)   DV of   A   B   C   D   E   DV updated   Node completed   Nodes to execute
A   0   4   –   –   –
B   4   0   20   –   7
C   –   20   0   3   –
D   –   –   3   0   1
E   –   7   –   1   0           {A,B,C,D,E}

Table 2

Compelling correspondence is essential to the achievement all things considered but since of the changing idea of the present working environments, successful correspondence turns out to be more troublesome, and because of the numerous impediments that will permit beneficiaries to acknowledge the plan of the sender It is restricted. Misguided judgments.In spite of the fact that correspondence inside the association is rarely completely open, numerous straightforward arrangements can be executed to advance the effect of these hindrances.

Concerning specific contextual analysis, two significant correspondence standards, correspondence channel determination and commotion are self-evident. This course presents the standards of correspondence, the act of general correspondence, and different speculations to all the more likely comprehend the correspondence exchanges experienced in regular daily existence. The standards and practices that you learn in this course give the premise to additionally learning and correspondence.

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This course starts with an outline of the correspondence cycle, the method of reasoning and hypothesis. In resulting modules of the course, we will look at explicit use of relational connections in close to home and expert life. These incorporate relational correspondence, bunch correspondence and dynamic, authoritative correspondence in the work environment or relational correspondence. Rule of Business Communication In request to make correspondence viable, it is important to follow a few rules and standards. Seven of them are fundamental and applicable, and these are clear, finished, brief, obliging, right, thought to be, concrete. These standards are frequently called 7C for business correspondence. The subtleties of these correspondence standards are examined underneath: Politeness Principle: When conveying, we should build up a cordial relationship with every individual who sends data to us.

To be inviting and polite is indistinguishable, and politeness requires an insightful and amicable activity against others. Axioms are notable that gracious “pay of graciousness is the main thing to win everything”. Correspondence staff ought to consistently remember this. The accompanying standards may assist with improving courtesy:Preliminary considering correspondence with family All glad families have the mystery of progress. This achievement originates from a strong establishment of closeness and closeness. Indeed, through private correspondence these cozy family connections become all the more intently. Correspondence is the foundation of different affiliations, building solid partners of obedient devotion, improving family way of life, and assisting with accomplishing satisfaction (Gosche, p. 1). In any case, so as to keep up an amicable relationship, a few families experienced tumultuous encounters. Correspondence in the family is an intricate and alluring marvel. Correspondence between families isn’t restricted to single messages between families or verbal correspondence.

It is a unique cycle that oversees force, closeness and limits, cohesiveness and flexibility of route frameworks, and makes pictures, topics, stories, ceremonies, rules, jobs, making implications, making a feeling of family life An intelligent cycle that makes a model. This model has passed ages. Notwithstanding the view as a family and family automatic framework, one of the greatest exploration establishments in between family correspondence centers around a family correspondence model. Family correspondence model (FCP) hypothesis clarifies why families impart in their own specific manner dependent on one another ‘s psychological direction. Early FCP research established in media research is keen on how families handle broad communications data. Family correspondence was perceived as an exceptional scholastic exploration field by the National Communications Association in 1989. Family correspondence researchers were at first impacted by family research, social brain science, and relational hypothesis, before long built up the hypothesis and began research in a family framework zeroed in on a significant job. Until 2001, the primary issue of the Family Communication Research Journal, Family Communication Magazine, was given. Family correspondence is more than the field of correspondence analysts in the family. Examination on family correspondence is normally done by individuals in brain science, humanism, and family research, to give some examples models. However, as the popular family correspondence researcher Leslie Baxter stated, it is the focal point of this intelligent semantic creation measure making the grant of family correspondence special. In the field of in-home correspondence, correspondence is normally not founded on autonomous messages from one sender to one beneficiary, yet dependent on the dynamic interdependency of data shared among families It is conceptualized. The focal point of this methodology is on the shared trait of semantic development inside family frameworks. As such, producing doesn’t happen in vacuum, however it happens in a wide scope of ages and social exchange.

Standards are rules end up being followed when performing work to agree to a given objective. Hierarchical achievement relies significantly upon compelling correspondence. So as to successfully impart, it is important to follow a few standards and rules. Coming up next are rules to guarantee powerful correspondence: clearness: lucidity of data is a significant guideline of correspondence. For beneficiaries to know the message plainly, the messages ought to be sorted out in a basic language. To guarantee that beneficiaries can without much of a stretch comprehend the importance of the message, the sender needs to impart unmistakably and unhesitatingly so the beneficiary can plainly and unquestionably comprehend the data.>

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