Lesson no.11 Configure the network using VLSM.

Configure the network using VLSM.

Definition - What does Variable Length Subnet Mask (VLSM) mean?

A Variable Length Subnet Mask (VLSM) is a numerical masking sequence, or IP address subset, based on overall network requirements. A VLSM allows a network administrator to use long masks for networks with few hosts and short masks for networks with multiple hosts. A VLSM is used with a VLSM router and must have routing protocol support.

A VLSM is also known as a classless Internet Protocol (IP) address.

Techopedia explains Variable Length Subnet Mask (VLSM)

Key VLSM features include:

• Simple network configuration
• Network IP addressing through empty subnet filling
• Greater efficiency than fixed-length subnet masks (FLSM)
• Streamlined routing, where a router functions only with a VLSM sequence, versus a full IP address

VLSMs are used by a variety of network systems and services, including:

• Intermediate System to Intermediate System Protocol (IS-IS)
• Border Gateway Protocol (BGP)
• Enhanced Interior Gateway Routing Protocol (EIGRP)
• Cisco's Open Shortest Path First (OSPF)

Description: There are 2 switches (Switch 0 and Switch 1) joined together, also attached with 3 end devices. Switch0 has 2 PC’s having network 1 and 1 PC having network 2. Switch1 has 1 PC having network 1 and 2 PC’s having network 2. As it is VLSM, PC can only communicate with other PC that is attached to another switch provided they should have the same network. PC with one network cannot communicate with PC having different network also if they are attached to the same switch.

Solution: The given topology is:

     

Steps:

 Following are the PC’s attached to switch0:

Configuring steps for PC0:

Network 1

Ip address: 192.16.10.1

Subnet mask: 255.255.255.248

Configuring steps for PC1:

Network 1

Ip address: 192.16.10.2

Subnet mask: 255.255.255.248

Configuring steps for PC2:

Network 2

Ip address: 192.16.10.9

Subnet mask: 255.255.255.248

Following are the PC’s attached to switch1:

Configuring steps for PC3:

Network 2

Ip address: 192.16.10.10

Subnet mask: 255.255.255.248

Configuring steps for PC4:

Network 2

Ip address: 192.16.10.11

Subnet mask: 255.255.255.248

Configuring steps for PC5:

Network 1

Ip address: 192.16.10.3

Subnet mask: 255.255.255.248

Output:

Ping command from PC4 to PC0 and PC2