Implementation of FLSM in Cisco

Pre-Requisite: Fixed Length and Variable Length Subnet Mask Numericals

When a block of addresses is separated into subnets all having an equal number of addresses, this type of subnetting is called Fixed Length Subnetting. The subnet masks used here will be the same for all the subnets as the number of addresses is equal for each subnet.

In this article, we will see the Implementation of FLSM in Cisco.

Steps to Configure and Verify FLSM in Cisco Packet Tracer:

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

S.NO	Device	Model Name	Unit
1.	pc	pc	3
2.	switch	PT-Switch	3
3.	router	PT-Router	3

IP Addressing Table for PCs:

S.NO	Device	IPv4 Address	Subnet Mask(Fixed-Length)	Default Gateway
1.	PC0	192.168.10.2	255.255.255.242	192.168.10.1
2.	PC1	192.168.10.34	255.255.255.242	192.168.10.33
3.	PC2	192.168.10.66	255.255.255.242	192.168.10.65

• 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.
• Add IPv4 address and subnet mask.

Assigning IP address using the ipconfig command.

• 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  255.255.255.224 192.168.10.1

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

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

IP Addressing Table for Routers:

S.NO	Device	Interface	IPv4 Address	Subnet Mask
1.	router0	FastEthernet0/0	192.168.10.1	255.255.255.224
		Serial 2/0	192.168.10.97	255.255.255.224
2.	router1	FastEthernet0/0	192.168.10.33	255.255.255.224
		Serial 2/0	192.168.10.98	255.255.255.224
		Serial 3/0	192.168.10.129	255.255.255.224
3.	router2	FastEthernet0/0	192.168.10.65	255.255.255.224
		Serial 2/0	192.168.10.130	255.255.255.224

• To assign an IP address in router0, click on router0.
• Then, go to config and then Interfaces.
• Then, configure the IP address in FastEthernet and serial ports according to IP addressing Table.
• Add 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 192.168.10.32 255.255.255.224 192.168.10.98
Router(config)#ip route 192.168.10.128 255.255.255.224 192.168.10.98
Router(config)#ip route 192.168.10.64 255.255.255.224 192.168.10.98

Static Routes for Router1 are given below:

Router(config)#ip route 192.168.10.0 255.255.255.224 192.168.10.97
Router(config)#ip route 192.168.10.64 255.255.255.224 192.168.10.130

Static Routes for Router2 are given below:

Router(config)#ip route 192.168.10.32 255.255.255.224 192.168.10.129
Router(config)#ip route 192.168.10.96 255.255.255.224 192.168.10.129
Router(config)#ip route 192.168.10.0 255.255.255.224 192.168.10.129

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

we’ll 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 very fine

Example : ping 192.168.10.34

• A simulation of the experiment is given below we are sending PDU from  PC0 to PC1 and PC1 to PC2: