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: All contents are Copyright © 1992–2007 Cisco Systems, Inc. All rights reserved. This document is Cisco Public Information. Page 1 of 7 • • • • • 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: • • • • • • • • 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
