Computer Networking Chapter 4 Exam Questions and Answers 100% Pass
What are the two most important network-layer functions in a datagram network? What are the three
most important network-layer functions in a virtual-circuit network? - Answers Datagram-based network
layer: forwarding; routing. VC-based network layer: forwarding, routing, call setup.
What is the difference between routing and forwarding? - Answers Forwarding is about moving a packet
from a router's input link to the appropriate output link. Routing is about determining the end-to-end
routes between sources and destinations.
*Why each input port in a high-speed router stores a shadow copy of the forwarding table? - Answers
With the shadow copy, the forwarding decision is made locally, at each input port, without invoking the
centralized routing processor. Such decentralized forwarding avoids creating a forwarding processing
bottleneck at a single point within the router.
What are the three types of switching fabrics? - Answers Switching via memory; switching via a bus;
switching via an interconnection network.
*Why packet loss can occur at input ports and output ports? - Answers Packet loss occurs if queue size
at the input port grows large because of slow switching fabric speed and thus exhausting router's buffer
space. It can be eliminated if the switching fabric speed is at least n times as fast as the input line speed,
where n is the number of input ports.
Packet loss can occur if the queue size at the output port grows large because of slow outgoing line-
speed.
What is HOL(Head Of Line) blocking? Does it occur in input ports or output ports? - Answers HOL
blocking - a queued packet in an input queue must wait for transfer through the fabric because it is
blocked by another packet at the head of the line. It occurs at the input port.
Suppose there are three routers between a source host and a destination host. Ignoring fragmentation,
an IP datagram sent from the source host to the destination host will travel over how many interfaces?
How many forwarding tables will be indexed to move the datagram from the source to the destination?
- Answers An IP datagram sent from a source host to a destination host will travel through 8 interfaces. 3
forwarding tables will be indexed to move the datagram from source to destination.
What is NAT? Describe a scenario where you would use NAT. - Answers NAT stands for Network Address
Translation, a technique to hide the private address spaces utilized by a private network. It is
implemented at the edge router to map a globally unique IP address with a primate address inside the
private network.
List three techniques that might contribute to slow down the adoption of IPv6. - Answers NAT, CIDR, and
DHCP
What are the two most important network-layer functions in a datagram network? What are the three
most important network-layer functions in a virtual-circuit network? - Answers Datagram-based network
layer: forwarding; routing. VC-based network layer: forwarding, routing, call setup.
What is the difference between routing and forwarding? - Answers Forwarding is about moving a packet
from a router's input link to the appropriate output link. Routing is about determining the end-to-end
routes between sources and destinations.
*Why each input port in a high-speed router stores a shadow copy of the forwarding table? - Answers
With the shadow copy, the forwarding decision is made locally, at each input port, without invoking the
centralized routing processor. Such decentralized forwarding avoids creating a forwarding processing
bottleneck at a single point within the router.
What are the three types of switching fabrics? - Answers Switching via memory; switching via a bus;
switching via an interconnection network.
*Why packet loss can occur at input ports and output ports? - Answers Packet loss occurs if queue size
at the input port grows large because of slow switching fabric speed and thus exhausting router's buffer
space. It can be eliminated if the switching fabric speed is at least n times as fast as the input line speed,
where n is the number of input ports.
Packet loss can occur if the queue size at the output port grows large because of slow outgoing line-
speed.
What is HOL(Head Of Line) blocking? Does it occur in input ports or output ports? - Answers HOL
blocking - a queued packet in an input queue must wait for transfer through the fabric because it is
blocked by another packet at the head of the line. It occurs at the input port.
Suppose there are three routers between a source host and a destination host. Ignoring fragmentation,
an IP datagram sent from the source host to the destination host will travel over how many interfaces?
How many forwarding tables will be indexed to move the datagram from the source to the destination?
- Answers An IP datagram sent from a source host to a destination host will travel through 8 interfaces. 3
forwarding tables will be indexed to move the datagram from source to destination.
What is NAT? Describe a scenario where you would use NAT. - Answers NAT stands for Network Address
Translation, a technique to hide the private address spaces utilized by a private network. It is
implemented at the edge router to map a globally unique IP address with a primate address inside the
private network.
List three techniques that might contribute to slow down the adoption of IPv6. - Answers NAT, CIDR, and
DHCP
