Ch4-Fundamentals of IPv4 Addressing & Routing

Question 1

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.

Answer 1

Default gateway/default router

Question 2

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

Answer 2

routing table

Question 3

Subdivisions of a Class A, B, or C network, as configured by a network administrator.

Answer 3

IP subnet

Question 4

A set of messages and processes with which routers can exchange information about routes to reach subnets in a particular network

Answer 4

routing protocol

Question 5

An IP address that represents a single interface.

Answer 5

unicast IP address

Question 6

The process of subdividing a Class A, B, or C network into smaller groups

Answer 6

subnetting

Question 7

An internet protocol used to map an IP address to a MAC address. Defined in RFC 826

Answer 7

ARP (Address Resolution Protocol)

Question 8

How does IPv4 expect addresses to be grouped into subnets or networks?

Answer 8

1. IP addresses in the same group MUST NOT be separated by router.
2. IP addresses in different groups MUST be separated by a router.
3. 5 IP addresses separated by a router MUST be in different groups.

Question 9

Break down the IPv4 Class A address space in terms of first octet range, portion of total address space, and intended purpose (unicast, multicast, etc) of addressing.

Answer 9

1. First octet 1-126
2. 1/2 total IPv4 address space
3. Unicast addressing

Question 10

Break down the IPv4 Class B address space in terms of first octet range, portion of total address space, and intended purpose (unicast, multicast, etc) of addressing.

Answer 10

1. First octet 128-191
2. 1/4 total IPv4 address space
3. Unicast addressing

Question 11

Break down the IPv4 Class C address space in terms of first octet range, portion of total address space, and intended purpose (unicast, multicast, etc) of addressing.

Answer 11

1. First octet 192-223
2. 1/8 total IPv4 address space
3. Unicast addressing

Question 12

Break down the IPv4 Class D address space in terms of first octet range, portion of total address space, and intended purpose (unicast, multicast, etc) of addressing.

Answer 12

1. First octet 224-239
2. 1/16 total IPv4 address space
3. Multicast addressing

Question 13

Break down the IPv4 Class E address space in terms of first octet range, portion of total address space, and intended purpose (unicast, multicast, etc) of addressing.

Answer 13

1. First octet 240-255
2. 1/16 total IPv4 address space
3. Reserved/experimental addressing

Question 14

Describe the size of the Class A network space in terms of number of networks available and number of hosts per network.

Answer 14

126 networks, approx 16 million hosts per network

Question 15

Describe the size of the Class B network space in terms of number of networks available and number of hosts per network.

Answer 15

approx 16 thousand networks, approx 65 thousand hosts per network

Question 16

Describe the size of the Class C network space in terms of number of networks available and number of hosts per network.

Answer 16

approx 2 million networks, 254 hosts per network

Question 17

List all possible network addresses in the Class A address space

Answer 17

First octet defines the group

1.0.0.0-126.0.0.0

Question 18

List all possible network addresses in the Class B address space

Answer 18

First 2 octets define the group

128.0.0.0 - 191.255.0.0

Question 19

List all possible network addresses in the Class C address space

Answer 19

First 3 octets define the group

192.0.0.0 - 223.255.255.0

Question 20

A host needs to send a packet to another host. Explain the 2-step process of host routing.

Answer 20

1. Is the destination IP address in my subnet? If so, forward directly to that destination host.
2. Is the destination IP address in a different subnet? If so, forward to my default gateway for delivery.

Question 21

A router is forwarding packets between two hosts. Describe the 4-step process of the router’s forwarding logic.

Answer 21

1. Does the incoming frame have errors in the FCS? If so, drop the frame.
2. De-encapsulate the packet.
3. Compare the packet destination IP address with the routing table. Find the route that best matches the destination IP address. This will determine the exit interface and next hop’s IP address.
4. Re-encapsulate the packet in a new frame appropriate for the exit interface and forward the frame.

Question 22

Describe the goals of a routing protocol

Answer 22

1. Dynamically learn and fill the routing table with a route for each subnet.
2. Place the best route in the routing table.
3. Notice when routes become invalid and remove them from the routing table.
4. Work quickly when learning new routes or replacing lost ones (convergence)
5. Prevent routing loops

Question 23

Describe the ARP process

Answer 23

1. For every outgoing frame, check the ARP cache for the correct destination IP & MAC.
2. If not found, broadcast an ARP request containing the sender MAC, sender IP, and target IP (“Who has 192.168.1.4?”)
3. Target receives broadcast and responds with a unicast ARP reply containing the target IP, target MAC, and sender IP and MAC)
4. On receiving the ARP reply, original sender adds target MAC and IP to arp cache.