VLSM Variable Length Subnet Mask

In this article I describe the VLSM Variable Length Subnet Mask in computer network for CCNA exam. VLSM Variable Length Subnet Mask in computer network related to IP address system in networking. VLSM Variable Length Subnet Mask in computer network denotes the class of IP address used by the device. It is not possible to categorise the IP address without using the Subnet Mask in computer network in computer networking. So we can say Subnet Mask is a part of IP address system in networking.

Before understand the VLSM Variable Length Subnet Mask in computer network you may read about the IP address system here. Communication between different devices on a network depends on the type of IP address. The VLSM Variable Length Subnet Mask define the type and class of IP address for a device. let’s remember the IP address structure in short before understand the Variable Length Subnet Mask in computer network.

Designing of IP address system

An IP address is combination of 32 bits. Each bit either 0 or 1 but not blank. 32 bits further divided into four Octate. IP can be written in two formats Binary or Decimal. Computer change the decimal into binary during communication. Example of IP in decimal is 10.0.0.0 same in binary 00001010.00000000.00000000.00000000 . User not used the IP in binary system. It is not easy to remember a 32 bit long binary number. During configuration in devices or routing we use the decimal format of IP . Some times IP is also written in Hexadecimal. We discuss about decimal and binary format in this article.

Subnet Mask in computer network

The IP address consist network address and host address. Subnet Mask in computer network denotes the network and host part in a IP address. Subnet Mask in computer network can be used to identify the class of IP address. We can separate the network ID and host ID on the basis of given Subnet Mask. In case of classless inter domain routing CIDR we can define the VLSM Variable Length Subnet Mask according to our requirement. Suppose you have only 25 system in your network then you can use the VLSM Variable Length Subnet Mask which allow 25 computers to communicate in the network. This practice provide the saving of time and reliability in the network.

The Subnet Mask in computer network is a 32 bit and 4 octate number combination similar to IPv4 address system. VLSM Variable Length Subnet Mask also a combination of 1 and 0 like IPv4 address system. The bits which are 1 denotes the network segment and the bits remains 0 denotes the hosts segment. So the whole 32 bit IP address can be divided into network and hosts segment by using the Subnet Mask in computer network.

The large network can be breaks into smaller networks by using the VLSM Variable Length Subnet Mask in computer network. We know the data flow in big network is difficult then in small networks. The point of security is also strong in small network comparison to a large network. We can say the small network are more efficient than the large networks.

VLSM Variable Length Subnet Mask in detail

VLSM Variable Length Subnet Mask in computer network defines the network and host in a network. The VLSM Variable Length Subnet Mask distinguish the network ID and Host ID in a packet. A VLSM Variable Length Subnet Mask is logical segment of IP address in a network. Subnet is a 32 bit binary number combination. To make it user friendly and easy to remember the Subnet Mask in computer network allotted in decimal format. Internally the device convert decimal to binary number. 32 bits are combination of 0 and 1.

Subnet make it easy to identify the class of network. Class A, B and C uses default subnet masks “255.0.0.0”, “255.255.0.0” and “255.255.255.0” respectively. The above values are fix for classfull system. When we working in VLSM( Variable Length Subnet mask) and CIDR (Classless Inter Domain Routing) the subnet has not fix value. We can say there is no class in the network.

Structure of Subnet Mask in computer network.

Subnet is a part of IP address scheme for a device in network. It is a logical part of IP address system. Subnet Mask separates the network ID and host ID in the network. In a network the hosts which lies in the same subnet come in particular subnet. Subnetting in a LAN done by defining the subnet in hosts IP address schema. For example all hosts having subnet 255.172.0.0 communicate with each other. Other hosts which do not have subnet 255.172.0.0 can not communicate with them without a router.

Working of VLSM Variable Length Subnet Mask in computer network

The main purpose of VLSM Variable Length Subnet Mask is to create small networks in a large network. The devices belongs to a particular VLSM Variable Length Subnet Mask can communicate with other devices in the same subnet mask. We can create small networks which can work without interfere each other. Just like VLAN in a layer 3 switch. Router provide the communication between different subnet mask by using the IP routing protocol.

The size of different subnet may be different in a large network. The subnet creates according to requirement of networks and hosts. It is possible that a subnet have 20 hosts and other subnet have 200 hosts is a same network. So before creating subnetting we need the size of subnet and number of hosts.

For example the IP address 192.168.10.3 and subnet mask 255.255.255.0 denotes the network id is 192.168.10.0 and the host id is 0.0.0.3. so in this network we can use 256 IP addresses 0 to 255 for hosts. But as we know we have to leave two addresses for network ID and Broadcast ID so we can use 254 device in this subnet of network. The network ID will be 192.168.10.0 and broadcast ID will be 192.168.10.255. This article is just related to the subnet mask so later in next articles I describe the subnetting basics and method of subnetting for different classes.

Important facts of Subnet Mask in computer network

VLSM Variable Length Subnet Mask breaks the large network into small sub networks. It is helpful to control the network congestion. You can assume the traffic flow in a large network create data loss and other negative factors. These drawbacks overcome by creating subnetting. Subnetting can be done by defining the subnet in hosts.

Without subnet all device monitor the data flow in the network from all devices. Due to this the data traffic become very congested. Data transfer speed also became slow. You can assume the benefits of subnet . When you design a network firstly you keep in mind how many host can be added in the network. Along with numbers of hosts, number of networks also important.

Uses of VLSM Variable Length Subnet Mask in computer network

The IP addresses can be save by using the VLSM Variable Length Subnet Mask. Suppose we have a range of IP address for use of 254 devices but we need only 20 devices to work in the subnet. We can save the IP address which can be used by other networks. This practice is not done in local network. When we need to configure large networks like ISP networks then a single IP address have its own value.

To achieve this CIDR and VLSM used in today scenario of networking. The network congestion may be improved by doing subnetting of the network. Since the number of user and devices reduces in a small network the data flow speed and security improved by using subnetting. Troubleshooting of the network become easy as the size of network reduces by subnetting. It became easy for administrator to manage and maintain the subnetted network.

VLSM Variable Length Subnet Mask in brief

Variable Length Subnet Mask is a kind of subnetting. In previous articles subnetting explained for different class of networks. That subnetting provides the subnet for equal number of host ID in each subnet. In real scenario it is not necessary that each subnet consist same host numbers. IP address are limited so we don’t waste the IP address. VLSM Variable Length Subnet Mask become helpful for full utilisation of IP addresses. When multiple LAN connected with each other via routers VLSM required to save IP address. The VLSM Variable Length Subnet Mask provides creation of subnets with different host counts. VLSM avoid the wastage of IP addresses.

VLSM Variable Length Subnet Mask in brief

Suppose a LAN required only 5 host and another required 62 hosts. We do simple subnetting for both LAN, /26 provides 62 host ID. In first LAN where only 5 host ID are required /26 make 57 IP address waste. To save these 57 address we use Variable Length Subnet Mask and give /29 mask for first LAN. VLSM can be used in a WAN via router. Below table is example to find the mask according to number of hosts in each subnet.

Protocol supports VLSM

Some specific network protocol supports Variable Length Subnet Mask. VLSM work in WAN for various LAN consisting different host count. RIPv2 and OSPF protocols support Variable Length Subnet Mask. Internet is perfect example of VLSM. ISP uses VLSM for different locations according to user.

Creating of VLSM Variable Length Subnet Mask

Suppose we have a network 192.168.1.0/24 . We need to create 6 different subnets. All subnets have different host counts. Suppose 62,25,10,6,5 and 5 are host numbers require in these 6 subnets. How to create such subnets?

First calculation is that how much IP address we have and how many required. Here as per our requirement we need 62+25+10+6+5+5=113 IP address. We have a /24 major network so we have 254 IP address. Now the task is to allot the IP address to required host in different subnets. Look the table above and search IP addresses n in which subnet our requirement full fill.

I observe /26 provides 62 hosts for first subnet. A /27 gives 32 hosts, it can be used for 25 hosts subnet. A /28 mask provides 16 host it can be used for 10 hosts subnet. /29 subnet can be used for 6 and 5 hosts subnet. To connect the routers with each other we use /30 mask. In /30 mask only 2 valid hosts are available remaining 2 ID used for broadcast and subnet ID. So after doing such calculation we can allot IP address to each subnet

Remaining IP address after 192.168.1.135 can be used for connecting router with each other. The above picture explained how the above network designed.

We hope you understood well the Variable Length Subnet Mask by above example. You can create your own network by refer to above example. For any query or suggestion on this article you may contact us or drop a comment below. Your suggestions are always welcome by us.