chapter 4 - network layer: data plane

Question 1

What is the role of the network layer?

Answer 1

Transfer segments from sender to receiver across networks

Question 2

What is forwarding?

Answer 2

Moving a packet from router input to output link

Question 3

What is routing?

Answer 3

Determining the path from sender to receiver

Question 4

What’s the difference between forwarding and routing?

Answer 4

• Forwarding = local(inside router) - actual movement
• Routing = global - planning the path

Question 5

What is the data (forwarding) plane?

Answer 5

handles the actual movement of packets

responsible for forwarding packets

Question 6

What is the control plane?

Answer 6

figures out where packets should go

builds the forwarding table the data plane use

Question 7

What are the two control-plane approaches?

Answer 7

Per-router control and Software-Defined Networking (SDN)

Question 8

What service model does the Internet use?

Answer 8

best-effort delivery

Question 9

what are key parts of a router

Answer 9

• input port
• switching fabric
• output port
• routing processor

Question 10

what is longest prefix matching

Answer 10

Match destination IP to the longest matching entry in forwarding table

Question 11

what is switching fabric

Answer 11

connects all input ports to output ports
–
internal network inside a route

Question 12

What are 3 types of switching fabrics?

Answer 12

• Memory
• Bus
• Interconnection network

Question 13

what is head of line blocking (HOL)

Answer 13

front packet blocks others behind it in the input queue

Question 14

why does output port buffering happen

Answer 14

packets arrive faster than they can be sent out

Question 15

what is tail drop

Answer 15

drop new packet when buffer is full

Question 16

what is RED (random early detection)

Answer 16

randomly drop packets before buffer is full

Question 17

What is FCFS?

Answer 17

sends packets in arrival order

Question 18

what is round-robin

Answer 18

Each queue gets one packet sent in a cycle

Question 19

What is weighted fair queuing?

Answer 19

flows with higher weight get more bandwidth

Question 20

What is an IP address?

Answer 20

A 32-bit identifier for a host/router interface

Question 21

what is an interface - can you have multiple interfaces

Answer 21

connection between host/router and a physical link

yes, routers -> several, hosts -> 1/2

Question 22

what is a subnet

Answer 22

group of interfaces that can reach each other without going trough a router

Question 23

What is CIDR? - What do the “/x” bits in CIDR mean?

Answer 23

Classless Inter-Domain Routing ( 192.168.1.0/x)

Number of bits in the subnet prefix

Question 24

what is Dynamic Host Configuration Protocol(DHCP) used for

Answer 24

automatically assigns IP addresses to devices when they join a network

Question 25

4 steps of DHCP

Answer 25

discover -> offer -> request -> ack

Question 26

how does a network gets it IP address

Answer 26

From its ISP, which gets blocks from regional registries via ICANN

Question 27

What is route aggregation?

Answer 27

summarizing multiple IP prefixes into one

Question 28

what is netowk adress translation (NAT)

Answer 28

routers translate private (local) IP addresses into a public IP address allows multiple devices to share one public IP

Question 29

main benefit of NAT

Answer 29

saves IP addresses and improves security

Question 30

how does NAT work (outgoing)

Answer 30

replaces source IP/port with NAT IP/port, stores mapping

Question 31

how does NAT work (incoming)

Answer 31

NAT replaces the destination IP/ port in incoming with the original source IP/ port from its NAT table

Question 32

What is the length of an IPv6 address?

Answer 32

128 bits 8 groups of 4 hexadecimal digits

Question 33

IPv6 key differences from IPv4?

Answer 33

No checksum, no fragmentation, simplified header

Question 34

What is tunneling (IPv6)?

Answer 34

sending IPv6 packets inside IPv4 packets to carry them across an IPv4-only network | wraps the ipv6 pavkets in ipv4 datagram - removes wrapping after end

Question 35

What is the end-to-end argument?

Answer 35

Functions like reliability should be handled at the endpoints, not the network

Question 35

What is the "thin waist" of the Internet?

Answer 35

IP – the single universal network layer protocol

Question 36

How does per-router control plane work?

Answer 36

Each router runs its own routing algorithm and makes routing decisions independently

Question 37

How does SDN control plane work?

Answer 37

A remote controller computes and installs flow tables in routers -> uses this table to forward packets | It separates the control plane from the data plane