Chapter 4: Routing Packets Across a Network

Question 1

What is the Network Layer (Layer 3) of the protocol stack responsible for doing?

Answer 1

Responsible for finding a route over the network that will allow the packet to teach its ultimate destination

Question 2

Each ___ has a ___ that contains the ___ of the ___ ___

Answer 2

Packet, header, address, final, destination

Question 3

At the highest level, the internet can be _____

Answer 3

considered a connection of large sub-networks called autonomous systems (AS)

Question 4

Each AS is identified by what?

Answer 4

Autonomous System Number (ASN), which are autonomous

Question 5

The Internet Assigned Number Authority (IANA) assigns what?

Answer 5

Autonomous System Numbers (ASNs) and IP addresses

Question 6

Interior Gateway Protocols (IGPs) are what?

Answer 6

They are routing protocols that direct packets between nodes within an Autonomous System

Question 7

Exterior Gateway Protocols (EGPs) are what?

Answer 7

They are routing protocols that direct packets between AS networks. The Border Gateway Protocol is the most reelvant

Question 8

What is a switch?

Answer 8

Switches are connection oriented and are aware of the source and final destination of the packet

Question 9

What is a router?

Answer 9

Routers are connectionless and forwards the packet along a next hop without any knowledge of what the rest of the path is going to look like

Question 10

Why must every AS peer with at least one other AS?

Answer 10

The internet is based on global/end-to-end reachability

Question 11

Define a Circuit Switched scenario

Answer 11

The switches simply serve to connect a direct wire between the source and destination

Question 12

Define a Whole File Transfer scenario

Answer 12

The entire file is sent in one-piece with N_o overhead bits

Question 13

Define a Packet Transfer scenario

Answer 13

The file is divided into K packets before transmission. Each packet is transmitted using N_o overhead bits

Question 14

What is the purpose of maintaining a routing table?

Answer 14

Allows routers to not have to know the entire route a packet will take. It only needs to forward it to the next hop along the journey. We utilize hierarchical routing

Question 15

What is the purpose for hierarchical routing?

Answer 15

Makes it so that routers do not need to keep every possible destination stored on a routing table

Question 16

What is the NetID in an IP address?

Answer 16

Describes the network that the user is on

Question 17

What is the HostID in an IP address?

Answer 17

Describes the host that is on a specific network (described by the NetID)

Question 18

In the simplest case, what is a NetID? And why is it “simple”/convenient?

Answer 18

Each NetID is a single router that is connected via a LAN to all the hosts within that network. Routers outside of each network now only need to store the NetIDs in their routing table, similar to a postal office organizing based on country

Question 19

What is the purpose of subnetting?

Answer 19

Allows us to overcome the inflexibility of having a limited number of NetIDs and HostIDs for a number of networks.

Question 20

How does subnetting work?

Answer 20

Done by defining a subnet mask that is then ANDed with an IP address to determine its subnet address

Question 21

Define Classless Interdomain Routing (CIDR)

Answer 21

The removal of class distinctions within addresses and was replaced with a variable length subnet mask that indicates the NetID portion of the address

Question 22

What is the purpose of Classless Interdomain Routing (CIDR)

Answer 22

Allows multiple levels of hierarchical addressing to be used in the internet than just one. The length of the netmask increases as the packet gets closer to its destination

Question 23

Why are MAC addresses used by ethernet connections?

Answer 23

Once a packet reaches its final subnet, it is necessary to map its IP address to a MAC address so it may reach its destination

Question 24

What is the Address Resolution Protocol (ARP)? And how does it work?

Answer 24

ARP is used to map an IP address to a MAC address via Ethernet. Asks the computer with a specific IP address to reply