Ch. ELEven
Subnetting
Summary
■ The subnet mask uses a series of ones to identify the network portion of an
IP address and a series of zeros to identify the host portion.
■ To create a subnet, bits are borrowed from the host portion of an IP address
to expand the network portion of the IP address.
■ An IP address with all zeros in the host portion cannot be assigned to any
network device.
■ An IP address with all ones in the host portion cannot be assigned to any
network device.
■ A Fixed Length Subnet Mask (FLSM) has two or more equal-sized subnets.
■ A Variable Length Subnet Mask (VLSM) occurs when you create additional
subnets from a subnet.
■ Subnetting provides security because subnetworks cannot be seen from
outside the subnetwork.
■ Subnetting reduces network traffic by isolating broadcasts to each subnet.
■ Bridges and switches are layer 2 devices that filter frames based on physical
(MAC) addresses.
■ Routers are layer 3 devices and filter frames based on logical addresses (IP
addresses).
■ A router is used to connect switches that are located in a separate network.
■ Routers make decisions based on source and destination IP addresses.
■ Routers do not forward broadcasts and, therefore, reduce collision domains.
■ A router metric is the mechanism used to determine or measure the best
route.
■ A metric calculation may be based on but not limited to throughput,
reliability, packet loss, latency, and number of hops.
■ A hop is a device such as a router located in the network path between the
destination and the source.
■ Two basic routing protocol classifications are Interior Gateway Protocol (IGP)
and Exterior Gateway Protocol (EGP).
■ An autonomous network is a network under one authority.
■ RIP is one of the oldest router protocols and determines the best path based
on number of hops.
■ EIGRP is a sophisticated routing protocol that guarantees loop-free operation.
■ An Application Specific Integrated Circuit (ASIC) is incorporated into a
switch to expand its function.
■ A multilayer switch is a dedicated switch that uses IP information and packet
contents to route frames or packets.
■ A Virtual LAN (VLAN) is a communication path between workstations on
separate or the same network segment.
■ Switches can be used to create VLANs.
■ Switch loops are generally caused by misconfigured routers and switches or
corrupt data.
■ Spanning Tree Protocol detects and corrects switch loops.
■ Link aggregation is when two or more network cables are paralleled to
increase bandwidth and provide redundancy.
Review Questions
Answer the following questions on a separate sheet of paper. Please do not write in this book.
1. Convert the following binary bit patterns to decimal number values. Do not
use a calculator for this activity. You may use the following tables for support.
1 1 1 1 1 1 1 1
128 64 32 16 8 4 2 1
1 0 0 1 0 1 0 1
128 0 0 16 0 4 0 1
A.
0 0 0 0 1 1 0 0
B.
0 0 0 0 1 1 1 1
C.
1 1 0 0 0 0 0 0
D.
0 0 0 1 0 1 0 1
E.
1 1 0 1 1 1 1 1
2. A subnet mask can be divided into two descriptive sections. What are the
two sections called?
3. Why would a network administrator create subnets?
4. What do the binary ones in a subnet mask indicate?
5. What do the binary zeros in a subnet mask indicate?
6. Using the information provided, identify which part of the IP address
190.134.124.112 with a subnet mask of 255.255.255.0 is the network address
and which part is the host address?
7. How many bits are borrowed from a Class B host address to create 30 new
subnets?
8. How many bits are borrowed from a Class C host address to create 6 new
subnets?
9. How many subnets can be formed using a subnet mask of 255.255.255.224
for a Class C network and using hardware that allows the use of all zeros
and all ones in the network portion of the subnet mask?
10. How many hosts are created from the following Class C subnet mask:
255.255.255.240?
11. A network administrator decides to partition an existing Class C network
into six equal parts. Each part of the network must hold at least 22
computers. What subnet mask must be used to satisfy the requirement?
12. How many subnets can be created from the following Class C subnet mask:
255.255.255.224?
13. How many subnets can be created from the following Class C subnet mask:
255.255.255.248?
14. What is the difference between a router and a layer 3 switch?
15. What is an autonomous network?
16. A bridge filters frames based on which type of address?
17. A switch filters frames based on which type of address?
18. What IEEE term is used to represent individual ports on a switch?
19. A router filters frames based on which type of address?
20. What is a VLAN?
21. How many VLANs are created by default on a network switch?
22. At which layer of the OSI model do bridges and switches operate?
23. At which layer of the OSI model do routers operate?
24. What is a broadcast domain?
25. Name three devices that will forward a broadcast?
26. Name one device that will not forward a broadcast?
27. Which IGP router protocol uses only hop count to determine the best path?
28. What is the difference between an Interior Gateway Protocol and an Exterior
Gateway Protocol?
29. Name four IGP protocols.
30. What network class is represented by the following CIDR:
XXX.XXX.XXX.XXX/16?
31. What is the network portion of 179.124.244.2/16?
32. What is the host portion of 179.124.244.2/16?
■ The subnet mask uses a series of ones to identify the network portion of an
IP address and a series of zeros to identify the host portion.
■ To create a subnet, bits are borrowed from the host portion of an IP address
to expand the network portion of the IP address.
■ An IP address with all zeros in the host portion cannot be assigned to any
network device.
■ An IP address with all ones in the host portion cannot be assigned to any
network device.
■ A Fixed Length Subnet Mask (FLSM) has two or more equal-sized subnets.
■ A Variable Length Subnet Mask (VLSM) occurs when you create additional
subnets from a subnet.
■ Subnetting provides security because subnetworks cannot be seen from
outside the subnetwork.
■ Subnetting reduces network traffic by isolating broadcasts to each subnet.
■ Bridges and switches are layer 2 devices that filter frames based on physical
(MAC) addresses.
■ Routers are layer 3 devices and filter frames based on logical addresses (IP
addresses).
■ A router is used to connect switches that are located in a separate network.
■ Routers make decisions based on source and destination IP addresses.
■ Routers do not forward broadcasts and, therefore, reduce collision domains.
■ A router metric is the mechanism used to determine or measure the best
route.
■ A metric calculation may be based on but not limited to throughput,
reliability, packet loss, latency, and number of hops.
■ A hop is a device such as a router located in the network path between the
destination and the source.
■ Two basic routing protocol classifications are Interior Gateway Protocol (IGP)
and Exterior Gateway Protocol (EGP).
■ An autonomous network is a network under one authority.
■ RIP is one of the oldest router protocols and determines the best path based
on number of hops.
■ EIGRP is a sophisticated routing protocol that guarantees loop-free operation.
■ An Application Specific Integrated Circuit (ASIC) is incorporated into a
switch to expand its function.
■ A multilayer switch is a dedicated switch that uses IP information and packet
contents to route frames or packets.
■ A Virtual LAN (VLAN) is a communication path between workstations on
separate or the same network segment.
■ Switches can be used to create VLANs.
■ Switch loops are generally caused by misconfigured routers and switches or
corrupt data.
■ Spanning Tree Protocol detects and corrects switch loops.
■ Link aggregation is when two or more network cables are paralleled to
increase bandwidth and provide redundancy.
Review Questions
Answer the following questions on a separate sheet of paper. Please do not write in this book.
1. Convert the following binary bit patterns to decimal number values. Do not
use a calculator for this activity. You may use the following tables for support.
1 1 1 1 1 1 1 1
128 64 32 16 8 4 2 1
1 0 0 1 0 1 0 1
128 0 0 16 0 4 0 1
A.
0 0 0 0 1 1 0 0
B.
0 0 0 0 1 1 1 1
C.
1 1 0 0 0 0 0 0
D.
0 0 0 1 0 1 0 1
E.
1 1 0 1 1 1 1 1
2. A subnet mask can be divided into two descriptive sections. What are the
two sections called?
3. Why would a network administrator create subnets?
4. What do the binary ones in a subnet mask indicate?
5. What do the binary zeros in a subnet mask indicate?
6. Using the information provided, identify which part of the IP address
190.134.124.112 with a subnet mask of 255.255.255.0 is the network address
and which part is the host address?
7. How many bits are borrowed from a Class B host address to create 30 new
subnets?
8. How many bits are borrowed from a Class C host address to create 6 new
subnets?
9. How many subnets can be formed using a subnet mask of 255.255.255.224
for a Class C network and using hardware that allows the use of all zeros
and all ones in the network portion of the subnet mask?
10. How many hosts are created from the following Class C subnet mask:
255.255.255.240?
11. A network administrator decides to partition an existing Class C network
into six equal parts. Each part of the network must hold at least 22
computers. What subnet mask must be used to satisfy the requirement?
12. How many subnets can be created from the following Class C subnet mask:
255.255.255.224?
13. How many subnets can be created from the following Class C subnet mask:
255.255.255.248?
14. What is the difference between a router and a layer 3 switch?
15. What is an autonomous network?
16. A bridge filters frames based on which type of address?
17. A switch filters frames based on which type of address?
18. What IEEE term is used to represent individual ports on a switch?
19. A router filters frames based on which type of address?
20. What is a VLAN?
21. How many VLANs are created by default on a network switch?
22. At which layer of the OSI model do bridges and switches operate?
23. At which layer of the OSI model do routers operate?
24. What is a broadcast domain?
25. Name three devices that will forward a broadcast?
26. Name one device that will not forward a broadcast?
27. Which IGP router protocol uses only hop count to determine the best path?
28. What is the difference between an Interior Gateway Protocol and an Exterior
Gateway Protocol?
29. Name four IGP protocols.
30. What network class is represented by the following CIDR:
XXX.XXX.XXX.XXX/16?
31. What is the network portion of 179.124.244.2/16?
32. What is the host portion of 179.124.244.2/16?