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Implementation of VLSM in Cisco

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  • Last Updated : 24 Jun, 2022
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Pre-requisite: Introduction of Variable Length Subnet Mask (VLSM)

VLSM is a Variable Length Subnet Mask in which the subnet design uses more than one mask in the same network which means more than one mask is used for different subnets of a single class A, B, C, or a network. It is used to improve the usability of subnets as they can be of variable size. It is also defined as the process of subnetting a subnet.

Steps:

Step 1: First, open the cisco packet tracer desktop and select the devices given below:

S.NODeviceModel-NameQty.
1.pcpc3
2.switchPT-Switch3
3.routerPT-Router3

IP Addressing Table for PCs

S.NODeviceIPv4 AddressSubnet-MaskDefault-Gateway
1.pc0192.168.10.2255.255.255.192192.168.10.1
2.pc2192.168.10.66255.255.255.224192.168.10.65
3.pc4192.168.10.98255.255.255.252192.168.10.97
  • Then, create a network topology as shown below the image.
  • Use an automatic connecting cable to connect the devices with others.

 

Step 2: Configure the PCs (hosts) with IPv4 address and Subnet Mask according to the IP addressing table given above.

  • To assign an IP address in PC0, click on PC0.
  • Then, go to desktop and then IP configuration and there you will IPv4 configuration.
  • Fill IPv4 address and subnet mask.

 

  • Assigning an IP address using the ipconfig command, or we can also assign an IP address with the help of a command.
  • Go to the command terminal of the PC.
  • Then, type ipconfig <IPv4 address><subnet mask><default gateway>(if needed)
Example: ipconfig 192.168.10.2  255.255.255.192 192.168.10.1

 

  • Repeat the same procedure with other PCs to configure them thoroughly.

Step 3: Configure router with IP address and subnet mask.

S.NODeviceInterfaceIPv4 AddressSubnet mask
1.router0FastEthernet0/0192.168.10.1255.255.255.192
Serial2/0192.168.10.101255.255.255.252
2.router2FastEthernet0/0192.168.10.65255.255.255.224
Serial2/0192.168.10.102255.255.255.252
Serial3/0192.168.10.105255.255.255.252
3.router3FastEthernet0/0192.168.10.97255.255.255.252
Serial2/0192.168.10.106255.255.255.252
  • To assign an IP address in router0, click on router0.
  • Then, go to config and then Interfaces.
  • Now, configure the IP address in FastEthernet and serial ports according to IP addressing Table.
  • Fill IPv4 address and subnet mask.

 

  • Repeat the same procedure with other routers to configure them thoroughly.

Step 4: After configuring all of the devices we need to assign the routes to the routers.

To assign static routes to the particular router:

  • First, click on router0 then Go to CLI.
  • then type the commands and IP information given below.
CLI command : ip route <network id> <subnet mask><next hop>

Static Routes for Router0 are given below:

Router(config)#ip route 192.168.10.64 255.255.255.224 192.168.10.102
Router(config)#ip route 192.168.10.104 255.255.255.252 192.168.10.102
Router(config)#ip route 192.168.10.96 255.255.255.252 192.168.10.102

Static Routes for Router1 are given below:

Router(config)#ip route 192.168.10.0 255.255.255.192 192.168.10.101
Router(config)#ip route 192.168.10.96 255.255.255.252 192.168.10.106

Static Routes for Router2 are given below:

Router(config)#ip route 192.168.10.64 255.255.255.224 192.168.10.105
Router(config)#ip route 192.168.10.100 255.255.255.252 192.168.10.105
Router(config)#ip route 192.168.10.0 255.255.255.192 192.168.10.105

Step 5: Verifying the network by pinging the IP address of any PC.

we will use the ping command to do so.

  • First, click on PC0 then Go to the command prompt.
  • Then type ping <IP address of targeted node>.
  • As we can see in the below image we are getting replies which means the connection is working.
Example : ping 192.168.10.66

 

  • A simulation of the experiment is given below we are sending PDU from  PC0 to PC2 and PC2 to PC4:

 

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