Activity 6.4.1: Basic VLSM Calculation and Addressing Design
Topology Diagram
192.168.1.64/26
192.168.1.0/26
192.168.1.160/27
192.168.1.208/28
192.168.1.224/30
192.168.1.128/27
192.168.1.228/30
192.168.1.232/30
192.168.1.192/28
Addressing Table
Device
HQ
Branch1
Branch2
Interface
IP Address
Subnet Mask
Default Gateway
Fa0/0
192.168.1.1
255.255.255.192
N/A
Fa0/1
192.168.1.65
255.255.255.192
N/A
S0/0/0
192.168.1.225
255.255.255.252
N/A
S0/0/1
192.168.1.229
255.255.255.252
N/A
Fa0/0
192.168.1.129
255.255.255.224
N/A
Fa0/1
192.168.1.161
255.255.255.224
N/A
S0/0/0
192.168.1.226
255.255.255.252
N/A
S0/0/1
192.168.1.233
255.255.255.252
N/A
Fa0/0
192.168.1.193
255.255.255.240
N/A
Fa0/1
192.168.1.209
255.255.255.240
N/A
S0/0/0
192.168.1.234
255.255.255.252
N/A
S0/0/1
192.168.1.230
255.255.255.252
N/A
Learning Objectives
Upon completion of this activity, you will be able to:
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Determine the number of subnets needed.
Determine the number of hosts needed for each subnet
Design an appropriate addressing scheme using VLSM.
Assign addresses and subnet mask pairs to device interfaces.
Examine the use of the available network address space.
Scenario
In this activity, you have been given the network address 192.168.1.0/24 to subnet and provide the IP
addressing for the network shown in the Topology Diagram. VLSM will be used so that the addressing
requirements can be met using the 192.168.1.0/24 network. The network has the following addressing
requirements:
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The HQ LAN1 will require 50 host IP addresses.
The HQ LAN2 will require 50 host IP addresses.
The Branch1 LAN1 will require 20 host IP addresses. •
The Branch1 LAN2 will require 20
host IP addresses
The Branch2 LAN1 will require 12 host IP addresses.
The Branch2 LAN2 will require 12 host IP addresses.
The link from HQ to Branch1 will require an IP address for each end of the link.
The link from HQ to Branch2 will require an IP address for each end of the link.
The link Branch1 to Branch2 will require an IP address for each end of the link.
Summary:
In this exercise, the focus is solely on VLSM (Variable Length Subnet Mask) calculation, without requiring
topology and its configuration. The primary task involves verifying network requirements in the initial
exercise and addressing the following questions. It's crucial to remember that each LAN interface requires
an IP address. Therefore, assigning IP addresses to interfaces is necessary to configure networks. In the
second exercise, we needed to develop an IP addressing scheme for our network design. Effectively
segmenting a network entails calculating the number of hosts required for each subnet interface and then
selecting the appropriate CIDR notation. VLSM techniques will be employed to create subnets and
allocate suitable IP addresses to each network device. Finally, in the third and last task, we assigned
appropriate IP addresses to each device in the network. Initially, we must identify network interfaces and
subnets and choose suitable addresses based on the IP addressing scheme created in the previous
exercise. These addresses must then be assigned to the corresponding devices and their network
interfaces.
Task 1: Examine the Network Requirements.
Examine the network requirements and answer the questions below. Keep in mind that IP addresses will
be needed for each of the LAN interfaces.
1. How many subnets are needed?
9
2. What is the maximum number of IP addresses that are needed for a single subnet? 50
3. How many IP addresses are needed for each of the BranchBranch1 LANs? 20
4. How many IP addresses are needed for each of the BranchBranch2 LANs?
12
5. How many IP addresses are needed for each of the WAN links between routers? 2
6. What is the total number of IP addresses that are needed? 170
7. What is the total number of IP addresses that are available in the 192.168.1.0/24 network? 254
8. Can the network addressing requirements be met using the 192.168.1.0/24 network? Yes
Task 2: Design an IP Addressing Scheme
Step 1: Determine the subnet information for the largest network segment or segments.
In this case, the two HQ LANs are the largest subnets.
1. How many IP addresses are needed for each LAN? 50
2. What is the smallest size subnet that can be used to meet this requirement? /26
3. What is the maximum number of IP addresses that can be assigned in this size subnet? 62
Step 2: Assign subnets to HQ LANs.
Start at the beginning of the 192.168.1.0/24 network.
1. Assign the first available subnet to HQ LAN1.
2. Fill in the chart below with the appropriate information.
HQ LAN1 Subnet
Network
Address
Decimal
Subnet Mask
CIDR Subnet
Mask
First Usable IP
Address
Last Usable IP
Address
Broadcast
Address
192.168.1.0
255.255.255.192
/26
192.168.1.1
192.168.1.62
192.168.1.63
In this scenario, we require 50 host IP addresses, necessitating a
minimum of 64 IP addresses. With a subnet mask of /24, 8 bits are
allocated for the network prefix and 24 bits for the host IP address. By
borrowing 6 bits from the host IP address, we can accommodate 64
IP addresses within this subnet. Consequently, a new subnet mask of
/26 is needed, utilizing 26 bits for the network prefix and 6 bits for the
host IP address. To derive the new network address, maintain the
original network prefix and reset the first 6 bits of the host IP address.
Thus, the new HQ-LAN1 network address becomes 192.168.1.0/26.
This subnet yields a total of 64 IP addresses, with 62 available for
hosts, as 2 addresses are reserved for network and broadcast
addresses.
3. Assign the next available subnet to HQ LAN2.
4. Fill in the chart below with the appropriate information.
HQ LAN2 Subnet
Network
Address
192.168.1.64
Decimal
Subnet Mask
CIDR Subnet
Mask
First Usable IP
Address
Last Usable IP
Address
Broadcast
Address
/26
192.168.1.65
192.168.1.126
192.168.1.127
255.255.255.192
In this scenario, the requirement is for 50 host IP addresses, implying a need for at least 64 IP addresses.
Given a subnet mask of /24, 8 bits are allocated for the network prefix and 24 bits for the host IP address.
To accommodate the necessary 64 IP addresses, borrowing 6 bits from the host IP address is considered.
Consequently, a new subnet mask of /26 is warranted, utilizing 26 bits for the network prefix and 6 bits for
the host IP address. Calculating a new network address involves preserving the original network prefix
and resetting the first 6 bits of the host IP address. Therefore, the new HQ-LAN2 network address would
be 192.168.1.64/26. This subnet provides a total of 64 IP addresses, with 62 available for hosts, as 2
addresses are reserved for network and broadcast purposes.
Step 3: Determine the subnet information for the next largest network segment or segments.
In this case, the two Branch1 LANs are the next largest subnets.
1. How many IP addresses are needed for each LAN? 20
2. What is the smallest size subnet that can be used to meet this requirement? /27
3. What is the maximum number of IP addresses that can be assigned in this size subnet? 30
Step 4: Assign subnet to BRANCH1 LANs.
Start with the IP address following the HQ LAN subnets.
1.
Assign the next subnet to Branch1 LAN1.
2.
Fill in the chart below with the appropriate information.
Branch1 LAN1 Subnet
Network
Address
Decimal
Subnet Mask
CIDR Subnet
Mask
First Usable IP
Address
Last Usable IP
Address
Broadcast
Address
192.168.1.128
255.255.255.224
/27
192.168.1.129
192.168.1.158
192.168.1.159
For Branch1 LAN1, 20 host IP addresses are needed, requiring a minimum of 32 IP addresses. With a
subnet mask of /24, this means an 8-bit network prefix and 24-bit host IP address. To accommodate the
32 IP addresses, borrowing 5 bits from the host IP address is necessary, resulting in a new subnet mask
of /27. The new network address for Branch1 LAN1 is 192.168.1.128/27, providing 32 IP addresses, with
30 available for hosts. Since Branch1 LAN2 also requires 20 host IP addresses, a new network address
must be chosen as 192.168.1.128/27 is already allocated for Branch1 LAN1.
3.
Assign the next available subnet to Branch1 LAN2.
4.
Fill in the chart below with the appropriate information.
Branch1 LAN2 Subnet
Network
Address
Decimal
Subnet Mask
CIDR Subnet
Mask
First Usable IP
Address
Last Usable IP
Address
Broadcast
Address
192.168.1.160
255.255.255.224
/27
192.168.1.161
192.168.1.190
192.168.1.191
For Branch1 LAN2, we require 20 host IP addresses, meaning at least 32 IP addresses are necessary.
With a subnet mask of /24, this implies using an 8-bit network prefix and a 24-bit host IP address. To
accommodate the 32 IP addresses needed, borrowing 5 bits from the host IP address is essential,
resulting in a new subnet mask of /27. By retaining the original network prefix and setting the first 5 bits of
the host IP address to zero, the new network address for Branch1 LAN2 becomes 192.168.1.160/27. This
subnet provides a total of 32 IP addresses, with 30 available for hosts, as 2 addresses are reserved for
network and broadcast purposes.
Step 5: Determine the subnet information for the next largest network segment or segments.
In this case, the two Branch2 LANs are the next largest subnets.
1. How many IP addresses are needed for each LAN? 12
2. What is the smallest size subnet that can be used to meet this requirement? /28
3. What is the maximum number of IP addresses that can be assigned in this size subnet? 14
Step 6: Assign subnets to BRANCH2 LANs.
Start with the IP address following the Branch1 LAN subnets.
1. Assign the next subnet to the Branch2 LAN1. Fill in the chart below with the appropriate information.
Branch2 LAN1 Subnet
Network
Address
Decimal
Subnet Mask
CIDR Subnet
Mask
First Usable IP
Address
Last Usable IP
Address
Broadcast
Address
192.168.1.192
255.255.255.240
/28
192.168.1.193
192.168.1.206
192.168.1.207
For Branch2 LAN1, 12 host addresses are required, indicating a need
for at least 16 IP addresses. With a subnet mask of /24, this entails
using 8 bits for the network portion and 24 bits for the host portion of
the IP address. To provide the required 16 IP addresses, borrowing 4
bits from the host IP address is necessary, resulting in a new subnet
mask of /28, utilizing 28 bits for the network prefix and 4 bits for the
host IP address. Calculating a new network address involves
retaining the original network prefix and resetting the first 4 bits of the
host IP address. Thus, the new LAN1 network address for Branch2
becomes 192.168.1.192/28. This subnet offers a total of 16 IP
addresses, with 14 available for hosts, as 2 addresses are reserved
for network and broadcast purposes.
2. Assign the next available subnet to Branch2 LAN2.
3. Fill in the chart below with the appropriate information.
Branch2 LAN2 Subnet
Network
Address
Decimal
Subnet Mask
CIDR Subnet
Mask
First Usable IP
Address
Last Usable IP
Address
Broadcast
Address
192.168.1.208
255.255.255.240
/28
192.168.1.209
192.168.1.222
192.168.1.223
For Branch2 LAN2, 12 host IP addresses are needed, requiring a minimum of 16 IP addresses. With a
subnet mask of /24, 8 bits are allocated for the network prefix and 24 bits for the host IP address. To
provide the necessary 16 IP addresses, utilizing the 4 bits from the host IP address is feasible. This
necessitates a new subnet mask of /28, utilizing 28 bits for the network prefix and 4 bits for the host IP
address. Calculating the new network address involves maintaining the original network prefix and setting
the first 4 bits of the host IP address to zero. Therefore, the new LAN2 network address for Branch2 is
192.168.1.208/28. This subnet offers a total of 16 IP addresses, with 14 available for hosts, as 2
addresses are reserved for network and broadcast purposes.
Step 7: Determine the subnet information for the links between the routers.
1. How many IP addresses are needed for each link? 2
2. What is the smallest size subnet that can be used to meet this requirement? /30
3. What is the maximum number of IP addresses that can be assigned in this size subnet? 2
Step 8: Assign subnets to links.
Start with the IP address following the Branch2 LAN subnets.
1.
Assign the next available subnet to the link between the HQ and Branch1 routers.
2.
Fill in the chart below with the appropriate information.
Link between HQ and Branch1 Subnet
Network
Address
Decimal
Subnet Mask
CIDR Subnet
Mask
First Usable IP
Address
Last Usable IP
Address
Broadcast
Address
192.168.1.224
255.255.255.252
/30
192.168.1.225
192.168.1.226
192.168.1.227
To assign subnets to links, we must first calculate the IP addresses required for the connections between
routers and subnets. Starting with the IP address following Branch2 LAN's subnet, we proceed to other
subnets. The subsequent available subnet is 192.168.1.224/27. This IP is designated for the connection
between HQ and Branch1 routers, such as 192.168.1.225/27. The remaining subnets are then assigned,
typically using the first or last IP addresses in each subnet for router-subnet connections to facilitate
device addressing and ensure clear separation between subnets and router links.
3.
Assign the next available subnet to the link between the HQ and Branch2 routers.
4.
Fill in the chart below with the appropriate information.
Link between HQ and Branch2 Subnet
Network
Address
Decimal
Subnet Mask
CIDR Subnet
Mask
First Usable IP
Address
Last Usable IP
Address
Broadcast
Address
192.168.1.228
255.255.255.252
/30
192.168.1.229
192.168.1.230
192.168.1.231
After defining the subnet for the connection between the HQ router and the Branch1 router, the next
available subnet needs to be assigned for the connection between HQ and the Branch2 router. The IP
address following the LAN2 subnet of Branch1 is 192.168.1.192/28. Thus, the next available subnet is
192.168.1.208/28. This IP address can now be assigned to the connection between HQ and the Branch2
router. For this connection, the IP address 192.168.1.209/28 can be used, with the subnet mask also
being /28.
5.
Assign the next available subnet to the link between the Branch1 and Branch2 routers.
6.
Fill in the chart below with the appropriate information.
Link between Branch1 and Branch2 Subnet
Network
Address
Decimal
Subnet Mask
CIDR Subnet
Mask
First Usable IP
Address
Last Usable IP
Address
Broadcast
Address
192.168.1.232
255.255.255.252
/30
192.168.1.233
192.168.1.234
192.168.1.235
Now that subnets have been allocated for the connection between the HQ router and the two branch
routers, the next step is to configure the connection between the branch routers. The IP address following
the LAN2 subnet of Branch2 is 192.168.1.208/28. The next available subnet is 192.168.1.224/27. This IP
address can now be assigned to the connection between the Branch1 and Branch2 routers. For this
connection, the IP address 192.168.1.225/27 can be used, with the subnet mask also being /27.
Task 3: Assign IP Addresses to the Network Devices
Assign the appropriate addresses to the device interfaces. Document the addresses to be used in the
Addressing Table provided under the Topology Diagram.
Step 1: Assign addresses to the HQ router.
1. Assign the first valid host address in the HQ LAN 1 subnet to the Fa0/0 LAN interface.
192.168.1.1/27
2. Assign the first valid host address in the HQ LAN 2 subnet to the Fao/1 LAN interface.
192.168.1.32/27
3. Assign the first valid host address in the link between HQ and Branch1 subnet to the S0/0/0
interface.
192.168.1.65/30
4. Assign the first valid host address in the link between HQ and Branch2 subnet to the S0/0/1
interface.
192.168.1.69/30
Step 2: Assign addresses to the Branch1 router.
1. Assign the first valid host address in the Branch1 LAN1 subnet to the Fa0/0 LAN interface.
192.168.1.66/27
2. Assign the first valid host address in the Branch1 LAN2 subnet to the Fa0/1 LAN interface.
192.168.1.96/27
3. Assign the last valid host address on the link between Branch1 and HQ subnet to the S0/0/0
interface
192.168.1.65/30
4. Assign the first valid host address on the link between Branch1 and Branch2 subnet to the S0/0/1
interface.
192.168.1.100/30
Step 3: Assign addresses to the Branch2 router.
1. Assign the first valid host address in the Branch2 LAN1 subnet to the Fa0/0 LAN interface.
192.168.1.130/27
2. Assign the first valid host address in the Branch 2 LAN 2 subnet to the Fa0/1 LAN interface.
192.168.1.160/27
3. Assign the last valid host address on the link between HQ and Branch2 subnet to the S0/0/1
interface
192.168.1.69/30
4. Assign the last valid host address on the link between Branch1 and Branch2 subnet to the S0/0/0
interface.
192.168.1.100/30