Quiz #2

Question 1

Why is a true crossbar architecture not used in Cloud computing?

Answer 1

Too expensive

Question 2

Why do data centers need layer 2 semantics?

Answer 2

To have increased app performance

Question 3

What is NOT an advantage of Clos networks?

1. Usage of commodity switches.
2. Constant latency between two hosts
3. Redundancy (multi-paths)
4. Minimum hardware cost for a direct host-host connected network

Answer 3

4.

Question 4

In a three-tiered network topology, what is the functionality of the Edge tier?

Answer 4

Edge: layer 2 switches connecting the aggregation layer to the servers.

Question 5

In a three-tiered network topology, what is the functionality of the Aggregation tier?

Answer 5

Transforming to/from layer 2 traffic from/to the edge to layer 3 traffic for the core.

Question 6

In a three-tiered network topology, what is the functionality of the Core tier?

Answer 6

Layer 3 switches connecting aggregation layer to Internet

Question 7

What are characteristics of a Fat Tree topology?

Answer 7

1. Same aggregate bandwidth at each layer.
2. Identical bisection bandwidth.
3. Constant latency between any two hosts.

Question 8

What is the problem with a true tree formation of a three-tiered network topology?

Answer 8

Bandwidth shrinks as we go towards the root of the tree

Question 9

What are the main reasons to use SDN?

Answer 9

1. Intelligent routing
2. Separating the decision making (control plane) from the transport of the payload (data plane)
3. Infer traffic patterns and centralize the control

Question 10

What are packet level issues to be addressed in the networking fabric?

Answer 10

1. Packet loss
2. Out of order delivery
3. Packet corruption (very rare… less than 0.1%)

Question 11

What is the main reason for packet loss in the internet?

Answer 11

mostly due to dropped packets due to congestion, that happens when offered load to the network exceeds network capacity.

Question 12

With reference to congestion avoidance, what is “conservation at equilibrium”?

Answer 12

Injecting a new packet into the network when a packet leaves the network.

*The equilibrium state refers to stable set of data packets in transit.

Question 13

What are the challenges with traffic engineering?

Answer 13

VM migration

Node and connection
failures

Application
characteristics

Scale of data centers
and geo-distribution