Knowledge Checks

The network layer - where is it?

Check all of the statements below about where (in the network) the network layer is implemented that are true.

The network layer is implemented in routers in the network core.

The network layer is implemented in Ethernet switches in a local area network.

The network layer is implemented in wired Internet-connected devices but not wireless Internet-connected devices.

The network layer is implemented in hosts at the network's edge.

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1/5

Forwarding versus routing.

Consider the travel analogy discussed in the textbook - some actions we take on a trip correspond to forwarding and other actions we take on a trip correspond to routing. Which of the following travel actions below correspond to forwarding? The other travel actions that you don't select below then correspond to routing.

A traveler decides to fly to Sydney through Singapore rather that Dubai.

A car waits at light and then turns left at the intersection.

A climber decides to take the South Col Route to the top of Mt Everest rather than the Northeast Ridge route.

A car stops at an intersection to “gas-up” and take a “bathroom break”

A car takes highway 80 between New York and Chicago, rather than highway 87 to Albany and from there take Interstate 90 to Chicago.

A car takes the 3rd exit from a roundabout.

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2/5

The control plane versus the data plane.

For each of the actions below, select those actions below that are primarily in the network-layer data plane. The other actions that you don't select below then correspond to control-plane actions.

Computing the contents of the forwarding table.

Moving an arriving datagram from a router’s input port to output port

Looking up address bits in an arriving datagram header in the forwarding table.

Dropping a datagram due to a congested (full) output buffer.

Monitoring and managing the configuration and performance of an network device.

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3/5

What type of control plane?

We've seen that there are two approaches towards implementing the network control plane - a per-router control-plane approach and a software-defined networking (SDN) control-plane approach. Which of the following actions occur in a per-router control-plane approach? The other actions that you don't select below then correspond to actions in an SDN control plane.

A router exchanges messages with another router, indicating the cost for it (the sending router) to reach a destination host.

A control agent in router receives a complete forwarding table, which it installs and
uses to locally control datagram forwarding.

All routers in the network send information about their incoming and outgoing links to a logically centralized controller.

Routers send information about their incoming and outgoing links to other routers in the network.

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4/5

Best effort service.

Which of the following quality-of-service guarantees are part of the Internet’s best-effort service model? Check all that apply.

In-order datagram payload delivery to the transport layer of those datagrams arriving to the receiving host.

A guaranteed minimum bandwidth is provided to a source-to-destination flow of packets

Guaranteed delivery from sending host to receiving host.

None of the other services listed here are part of the best-effort service model. Evidently, best-effort service really means no guarantees at all!

Guaranteed delivery time from sending host to receiving host.

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5/5

Knowledge checks

The network layer - where is it?

Forwarding versus routing.

The control plane versus the data plane.

What type of control plane?

Best effort service.