Chapter 5 Flash Cards - IP Addressing

Question 1

What are the two rules that summarize the facts about which IP addresses need to be in the same grouping?

Answer 1

1. All IP addresses in the same group must not be separated by a router.
2. IP addresses separated by a router must be in different groups

Question 2

Explain the following about a Class A Network:

• Number of Network Bytes (Bits)
• Number of Host Bytes (Bits)
• Number of Addresses per Network

Answer 2

Network Bytes (Bits): 1 (8)
Host Bytes (Bits): 3 (24)
Number of Addresses: 2^24 - 2 (Reserved)

Question 3

Explain the following about a Class B Network:

• Number of Network Bytes (Bits)
• Number of Host Bytes (Bits)
• Number of Addresses per Network

Answer 3

Network Bytes (Bits): 2 (16)
Host Bytes (Bits): 2 (16)
Number of Addresses: 2^16 - 2 (Reserved)

Question 4

Explain the following about a Class C Network:

• Number of Network Bytes (Bits)
• Number of Host Bytes (Bits)
• Number of Addresses per Network

Answer 4

Network Bytes (Bits): 3 (24)
Host Bytes (Bits): 1 (8)
Number of Addresses: 2^8 - 2 (Reserved)

Question 5

Describe the two reserved addresses in each network.

Answer 5

Network number represented by all binary 0s in the host section of the IP Address.

Broadcast address represented by all binary 1s in the host section of the IP Address.

Question 6

Provide the following information for a Class A Network:

• First Octet Range
• Valid Network Numbers
• Total Number for This Class of Network
• Number of Hosts Per Network

Answer 6

• First Octet Range - 1 to 126
• Valid Network Numbers - 1.0.0.0 to 126.0.0.0
• Total Number for This Class of Network - 2^7 -2 (126)
• Number of Hosts Per Network - 2^24 -2 (16,777,214)

Question 7

Provide the following information for a Class B Network:

• First Octet Range
• Valid Network Numbers
• Total Number for This Class of Network
• Number of Hosts Per Network

Answer 7

• First Octet Range - 128 to 191
• Valid Network Numbers - 128.0.0.0 to 191.255.0.0
• Total Number for This Class of Network - 2^14 (16,384)
• Number of Hosts Per Network - 2^16 -2 (65,534)

Question 8

Provide the following information for a Class C Network:

• First Octet Range
• Valid Network Numbers
• Total Number for This Class of Network
• Number of Hosts Per Network

Answer 8

• First Octet Range - 192 to 223
• Valid Network Numbers - 192.0.0.0 to 223.255.255.0
• Total Number for This Class of Network - 2^21 (2,097,152)
• Number of Hosts Per Network - 2^8 -2 (254)

Question 9

Describe Address Formats when Subnetting (Classful)

Answer 9

N + S + H = 32 (bits)
Class A : N (8) + S + H
Class B : N (16) + S + H
Class C : N (24) + S + H

Question 10

Describe Address Formats when Subnetting (Classless)

Answer 10

Subnet or Prefix (32) - X (host)

Question 11

Explain the two step simple routing logic used by hosts.

Answer 11

1. If the destination IP address is in the same subnet as I am, send the packet directly to that destination host.
2. If the destination IP address is not in the same subnet as I am, send the packet to my default gateway (a router’s Ethernet interface on the subnet).

Question 12

Explain the four step logic used by a router when receiving a data-link frame.

Answer 12

1. Use the data-link FCS field to ensure that the frame had no errors; if errors occured, discard the frame.
2. Assuming the frame was not discarded at step 1, discard the old data-link header and trailer, leaving the IP packet.
3. Compare the IP packet’s destination IP address to the routing table, and find the route that matches the destination address. This route identifies the outgoing interface of the router, and possibly the next-hop router.
4. Encapsulate the IP packet inside a new data-link header and trailer, appropriate for the outgoing interface, and forward the frame.

Question 13

Describe the goals for any IP routing protocol.

Answer 13

1. To dynamically learn and fill the routing table with a route to all sub nets in the network.
2. If more than one route to a sub net is available, to place the best route in the routing table.
3. To notice when routes in the table are no longer valid, and to remove them from the routing table.
4. If a route is removed from the routing table and another route through another neighboring router is available, to add the route to the routing table. (Many people view this goal and the preceding goal as a single goal.)
5. To add new routes, or to replace lost routes, with the best currently available route as quickly as possible. The time between losing a route and finding a working replacement route is called convergence time.
6. To prevent routing loops.

Question 14

Explain the steps a router uses to advertise routes on a network.

Answer 14

1. Each router adds a route to its routing table for each sub net directly connected to the router.
2. Each router’s routing protocol tells its neighbors about all the routes in its routing table, including the directly connected routes and routes learned from other routers.
3. After learning a new route from a neighbor, the router’s routing protocol adds a route to its routing table, with the next-hop router typically being the neighbor from which the route was learned.

Question 15

List four tools used almost every day to help the network layer with its task of routing packets from end to end through an internetwork.

Answer 15

1. Address Resolution Protocol (ARP)
2. Domain Name System (DNS)
3. Dynamic Host Configuration Protocol (DHCP)
4. Ping

Question 16

Describe the DNS Request and Reply Process.

Answer 16

Computer 1 sends a DNS request to the DNS server, the DNS server replies with the address.

Question 17

Describe the ARP process.

Answer 17

ARP is used to find the MAC Address of the other computer. ARP is broadcast so that everyone on the LAN can see it. The machine whose IP address is being used to make the request responds when it receives the ARP with it’s MAC Address.

Question 18

In most networks today, DHCP supplies what facts to a typical end-user host?

Answer 18

1. IP addresses
2. Subnet masks
3. Default Gateway
4. IP address of any DNS servers

Question 19

Define ARP

Answer 19

Address Resolution Protocol. An Internet Protocol used to map an IP address to a MAC address. Defined in RFC 826

Question 20

Define Default Gateway/Default Router

Answer 20

On an IP host, the IP address of some router to which the host sends packets when the packet’s destination address is on a subnet other than the local subnet.

Question 21

Define DHCP

Answer 21

Dynamic Host Configuration Protocol. A protocol used by hosts to dynamically discover and lease an IP address, and learn the correct subnet mask, default gateway, and DNS server IP addresses.

Question 22

Define DNS

Answer 22

Domain Name System. An application layer protocol used througout the Internet for translating hostnames into their associated IP Addresses.

Question 23

Define Host Part

Answer 23

A term used to describe a part of an IPv4 address that is used to uniquely identify a host inside a subnet. The host part is identified by the bits of value 0 in the subnet mask.

Question 24

Define IP Address

Answer 24

In IP Version 4 (IPv4), a 32-bit address assigned to hosts using TCP/IP. Each address consists of a network number, an optional subnetwork number, and a host number. The network and subnetwork numbers together are used for routing, and the host number is used to address an individual host with the network or subnetwork.

Question 25

Define Logical Address

Answer 25

A generic reference to addresses as defined by Layer 3 protocols, which do not have to be concerned with the physical details of the underlying physical media. used mainly to contrast these addresses with data-link addresses, which are generically considered to be physical addressed because they differ based on the type of physical medium.

Question 26

Define Network Broadcast Address

Answer 26

In IPv4, a special address in each classful network that can be used to broadcast a packet to all hosts in that same classful network. Numerically, the address has the same value as the network number in the network part of the address, and all 255s in the host octets–for example, 10.255.255.255 is the network broadcast address for classful network 10.0.0.0.

Question 27

Define Network Number/Network Address

Answer 27

A number that uses dotted decimal notation like IP addresses, but the number itself represents all hosts in a single Class A, B, or C IP network.

Question 28

Define Network Part

Answer 28

The portion of an IPv4 address that is either 1,2, or 3 octets/bytes long, based on whether the address is in a class A, B, or C network.

Question 29

Define Routing Table

Answer 29

A list of routes in a router, with each route listing the destination subnet and mask, the router interface out which to forward packets destined to that subnet, and, as needed, the next-hop router’s IP address.

Question 30

Define Subnet Broadcast Address

Answer 30

A special address in each subnet, specifically the largest numeric address in the subnet, designed so that packets sent to this address should be delivered to all hosts in that subnet.

Question 31

Define Subnet Number/Subnet Address

Answer 31

In IPv4, a dotted decimal number that represents all addresses in a single subnet. Numerically, the smallest value in the range of numbers in a subnet reserved so that it cannot be used as a uni-cast IP address by a host.

Question 32

Define Subnet Part

Answer 32

In a subnetted IPv4 address, interpreted with classful addressing rules, one of three parts of the structure of an IP address, with the subnet part uniquely identifying different subnets of a classful IP network.