VLSM Corporate Plan Calculator

About this interactive

On a corporate network the gap between the biggest LAN and the smallest link is huge, which is where VLSM pays. With one mask sized for a 2,000-host LAN, every subnet is a /21 of 2,048 addresses, and every router link burns 2,046 of them. With VLSM, each network gets its own size: the big LAN its /21, a 600-host LAN a /22, and each link a /30 of four addresses. The method is the one used on a /24, with bigger blocks. Size each LAN for the hosts it will have, growth included, sort the networks largest first, and lay the blocks end to end. From 10.60.0.0, a 2,000-host LAN takes 10.60.0.0/21, which runs to 10.60.7.255. A 600-host LAN takes the next /22, 10.60.8.0 to 10.60.11.255, and the first link 10.60.12.0/30. Once the blocks are bigger than 256 addresses the boundary is in the third octet, so a broadcast address ends in .255 and the next network starts at .0 of the next value up. Routers that carry these different masks have to use a classless routing protocol. Type addresses in dotted decimal and counts in digits. Anything you miss shows the answer and how to work it out. Seven of the twenty questions are drawn each run.

What you'll learn

Apply VLSM to a corporate network, sizing each LAN for its planned hosts and each router link as a /30, with the boundary in the third octet
Calculate the addresses a VLSM plan uses and what one mask for every network would have used instead

Aligned to

CompTIA Network+

1.7 Given a scenario, use appropriate IPv4 network addressing.

Cisco CCNA

1.6 Configure and verify IPv4 addressing and subnetting

Cisco CCST Networking

2.2 Identify IPv4 addresses and subnet formats

Key terms

Variable Length Subnet Mask: A subnetting technique that allows a network administrator to divide an address space into subnets of different sizes by using different prefix lengths, allocating address space more efficiently than fixed-length subnetting. VLSM requires a classless routing protocol such as OSPF, EIGRP, or RIPv2 that carries prefix length information in routing updates.
Fixed-Length Subnet Masking: A subnetting method in which all subnets within a network use the same prefix length, resulting in equal-sized address blocks regardless of actual host requirements.
Network Segmentation: The practice of dividing a network into smaller segments to improve performance and limit the spread of security threats.
Network Address: The first address in an IP network range that identifies the network itself and cannot be assigned to a host. It is formed when all host bits are set to zero.
Broadcast Address: The last address in an IP subnet range, formed when all host bits are set to one, used to send a single packet to every device on that network simultaneously.
Scalability: The ability of a system to handle increased load by adding resources without degrading performance.

Topics

Vlsm Subnetting Network Design Network Growth Interactive Calculation

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