Chapter 4: The Network Layer: Data Plane

Question 1

What does the sender in the network layer do?

Answer 1

Encapsulates segments into datagrams and then passes them to the link layer

Question 2

What does the receiver in the network layer do?

Answer 2

Delivers segments to the transport layer protocol

Question 3

What do routers do?

Answer 3

Mode datagrams from input ports to output ports to transfer them along the end-end path based on the header fields of the IP datagram

Question 4

Describe forwarding

Answer 4

Moving packets from a router’s input link to the appropriate router output link

Question 5

Describe routing

Answer 5

Determining the route taken by packets from source to destination

Question 6

Describe the data plane

Answer 6

A local, per-router function that determines how arriving datagrams on the router input port are forwarded to the router output port

Question 7

Which plane is a network-wide logic that determines how datagrams are routed among routers along the end-end path from source host to destination host?

Answer 7

Control plane

Question 8

Which approach in the control plane has individual routing algorithm components in each and every router that interact in the control plane?

Answer 8

Per-router control plane

Question 9

Which control plane has a remote controller that computes and installs forwarding tables in routers, to be used by the routers?

Answer 9

Software-Defined Networking (SDN)

Question 10

What does the physical layer of the input port of a router do?

Answer 10

Terminates incoming physical links at routers

Question 11

What do the link-layer functions of the input port of a router do?

Answer 11

Interoperate with the link layer at the other side of an incoming link

Question 12

What does the routing processor of a router do?

Answer 12

Performs control-plane functions

Question 13

What function is described below?
The forwarding table is consulted to determine the router output port to which an arriving packet will be forwarded via the switching fabric. Control packets are then forwarded from an input port to the routing processor

Answer 13

Lookup function

Question 14

What sort of queueing occurs when datagrams arrive faster than the forwarding rate into the switch fabric?

Answer 14

Input port queueing

Question 15

What sort of forwarding is based only on the destination IP address?

Answer 15

Destination-based forwarding

Question 16

What sort of forwarding is based on any set of header field values?

Answer 16

Generalized forwarding

Question 17

Give the definition:
When looking for forwarding table entries for given destination addresses, use the longest address prefix that matches the destination address

Answer 17

Longest prefix match

Question 18

What do switching fabrics do?

Answer 18

Transfer packets from the input link to the appropriate output link

Question 19

What is the switching rate?

Answer 19

The rate at which packets can be transferred from the input link to the output link

Question 20

How is the switching rate often measured?

Answer 20

As a multiple of input/output link rate

Question 21

What are the three major types of switching fabrics?

Answer 21

Memory
Bus
Interconnection network

Question 22

What sort of switching is done in the following way: packet copied to system’s memory

Answer 22

Switching via memory

Question 23

What sort of switching is done in the following way: datagram from input port memory to output port memory via a shared bus

Answer 23

Switching via a bus

Question 24

Give the definition:
When switching speed is limited by bus bandwidth

Answer 24

Bus contention

Question 25

What sort of switching is done in the following way: scaling using multiple switching planes in parallel to get speedup and scaleup via parallelism

Answer 25

Switching via interconnection networks

Question 26

What sort of queueing occurs at the input queues when the switch fabric is slower than the input ports combined?

Answer 26

Input port queueing

Question 27

Give the definition: Queued datagram at the front of a queue that prevents others in the queue from moving forward

Answer 27

Head-Of-Line blocking (HOL)

Question 28

Which ports store packets received from the switching fabric and transmit these packets on the outgoing link by performing the necessary link-layer and physical-layer functions?

Answer 28

Output ports

Question 29

What is required when datagrams arrive from the switching fabric faster than the link transmission rate?

Answer 29

Buffering

Question 30

To determine which datagrams to drop if there are no free buffers we need a...

Answer 30

drop policy

Question 31

What discipline chooses among queued datagrams for transmission?

Answer 31

Scheduling discipline

Question 32

What sort of queueing occurs when there is buffering when the arrival rate via the switch fabric exceeds the output line speed?

Answer 32

Outport port queueing

Question 33

What happens if there is too much buffering?

Answer 33

Delays increase

Question 34

Give the definition: Which packet tot drop when buffers are full

Answer 34

Drop

Question 35

What sort of drop drops arriving packets when buffers are full?

Answer 35

Tail drop

Question 36

What sort of drop drops/removes packets on a priority basis when the buffers are full?

Answer 36

Priority drop

Question 37

What do we call the process of choosing which packets to mark to signal congestion?

Answer 37

Marking

Question 38

What do we call the deciding of which packet to send next on a link?

Answer 38

Packet scheduling

Question 39

What do we call the packet scheduling method where packets are transmitted in order of arrival to output port?

Answer 39

First Come, First Serve (FCFS)

Question 40

What do we call the packet scheduling method when the arriving traffic is classified, then queued by class, and then the packet from the highest priority queue that has buffered packets is sent?

Answer 40

Priority queueing

Question 41

What do we call the packet scheduling method where the arriving traffic is classified, then queued by class, and the the server cyclically and repeatedly scans class queues, to then send one complete packet from each class in turn?

Answer 41

Round Robin (RR) scheduling

Question 42

What do we call the packet scheduling method where each class has a weight and gets a weighted amount of service in each cycle?

Answer 42

Weighted Fair Queueing (WFQ)

Question 43

What do we call the 32-bit identifier associated with each host / router interface?

Answer 43

IP address

Question 44

What two parts does the IP address consist of?

Answer 44

Subnet and host part

Question 45

What do we call the connection between host/router and the physical link?

Answer 45

Interface

Question 46

What are the device interfaces that can physically reach each other without passing through an intervening router?

Answer 46

Subnets

Question 47

How do we define subnets?

Answer 47

By detaching each interface from its host/router and creating islands of isolated networks, where each isolated network is a subnet

Question 48

What do we call the routing that enables the subnet portion of an address to be of arbitrary length?

Answer 48

Classless InterDomain Routing (CIDR)

Question 49

What protocols makes it possible for a host to get an IP address?

Answer 49

Dynamic Host Configuration Protocol (DHCP)

Question 50

How does an ISP get blocks of addresses?

Answer 50

Through the Internet Corporation for Assigned Names and Numbers (ICANN)

Question 51

How does the network get the subnet part of an IP address?

Answer 51

Gets allocated a portion of its provider ISPs address space

Question 52

What sort of protocol is DHCP?

Answer 52

Client-server

Question 53

What protocol has the following goal: Host dynamically obtains IP address from network server when it joins the network

Answer 53

DHCP

Question 54

What DHCP protocol message is on the following format: host broadcasts [optional]

Answer 54

DHCP discover

Question 55

What DHCP protocol message is on the following format: DCHP server response [optional]

Answer 55

DHCP offer

Question 56

What DHCP protocol message is on the following format: host requests IP address

Answer 56

DHCP request

Question 57

What DHCP protocol message is on the following format: DHCP server sends address

Answer 57

DHCP ack

Question 58

Is DHCP a client-server protocol?

Answer 58

Yes

Question 59

What sort of addressing allows efficient advertisement of routing information?

Answer 59

Hierarchical addressing

Question 60

Give the definition: All devices in a local network have 32-bit addresses in a "private" IP address space that can only be used in the local network

Answer 60

Network Address Translation (NAT)

Question 61

What is the main advantage of NAT?

Answer 61

Only 1 IP address is needed from a provider ISP for all devices

Question 62

What parts of outgoing datagrams does a NAT router replace, and what are the parts replaced with?

Answer 62

source IP address replaced with NAT IP address old port number replaced with new port number

Question 63

What parts of incoming datagrams does a NAT router replace, and what are the parts replaced with?

Answer 63

NAT IP address replaced with corresponding source IP address new port number replaced with port number stored in NAt table

Question 64

What was the main motivation with IPv6?

Answer 64

The 32-bit address space of IPv4 could be completely allocated

Question 65

What parts of a IPv6 datagram have been removed in comparison to a IPv4 datagram?

Answer 65

Header checksum Fragmentation/reassembly Options

Question 66

What is the main method used to handle the fact that not all routers have been upgraded to IPv6, and therefore still used IPv4?

Answer 66

Tunneling

Question 67

Give the definition: IPv6 datagram carried as payload in IPv4 datagram IPv4 routers - packet within a packet

Answer 67

Tunneling

Question 68

What are the three cornerstone beliefs of the internet?

Answer 68

Simple connectivity IP protocols Intelligence & complexity at network edge

Question 69

What is the following argument called: Some network functionality can be implemented in networks or at the network edge

Answer 69

The end-end argument