Date 04.03.2021

Time: 70 min
60 Points
It was an online-exam on Isis. The tasks were chosen randomly from a set of tasks. So everbody had other tasks.
Allowed to use was all material of the course, but the time was relatively short for looking at the slides.
The time was a bit too short to answer all questions.

The following questions are not all questions I had on this exam, but those I can remember.

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Given was an image with a Host H, Local DNS server L, Authoritative DNS Server N1 (tu-berlin.de), N2 (.de), N5 (.), N8 (inet.tu-berlin.de), and the corresponding arrows.
Above there were the numbers 1 to 10.
Task: Assign the numbers 1 to 10 to the arrows in the correct DNS request order.

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Given was an image with ASs with several numbers, numbered clients and servers in the AS. Arrows between the ASs indicated Customer-provider and peer-to-peer relationships.

Task: Specific clients access specific websites (about 6 different cases). Write down all possible AS Paths for each case.

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Apply Dijkstra on a graph.

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Shorten a given IPv6 address as far as possible.

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TCP fits the data rate sent to the actual network capacity.
TCP is _________ . (Adjective was asked)

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Network with two NATs. IPv4 addresses were assigned.

One client in one NAT accesses the webserver into the other NAT.
We look now at the answer packet from the webserver to the client.
Write down source and target IP address on specific LAN segment.

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TCP graph like the following

Client            Server
|                   |
|------------------>|
|<------------------|
|<------------------|
|                   |
|       .           |
|       .           |
|       .           |
|                   |

Initial window size was given.
On specific time a packet loss occurs.
Question: What is wrong in shown the TCP flow?

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How many user can use a 30 Mbit/s bandwidth link, if circuit switching is used and every user needs 1.5 Mbit/s to send and uses the link only in 10 % of the time.

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A link has a bandwidth of 200 Mbps.
A file has a length of 300 bytes.
How long is the transmission delay?

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A diagram with packets sent between client and server, plotted over the time.

Tasks:
1. Write down the measured RTTs

(3 ms, 4 ms, 7 ms)

2. Calculate the estimated RTT after the third round, at least three digits after the comma.

3. Why are RTTs of retransmitted segments not counted for the measure?

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Routing table given.

On which interface will the packet with destination IP 134.17.21.65 be forwarded?