Subnet Requirements Planner

About this interactive

Subnetting starts with two numbers: how many networks you need and how many hosts each must hold. Both come from the design. Every LAN is a network, and so is every link between two routers, because each end of the link needs an address on a network of its own. A ring of five routers has five links; five routers each linked to every other have ten. With one mask for the whole network every subnet is the same size, so each one must fit the largest LAN, and it must fit it as it will be, not as it is: plan around three years of growth. The hosts set the host bits, the smallest h where 2^h - 2 is enough, and the networks set the borrowed bits, the smallest b where 2^b is enough. If the class default plus the borrowed bits plus the host bits comes to exactly 32, only one mask fits; if it comes to less, you have a choice, and if more, the network you were given is too small. A router-to-router link here gets a full-sized subnet, which wastes most of its addresses. Variable-length subnet masking fixes that by giving each link a /30, or a /31 on point-to-point links under RFC 3021. Type counts in digits; commas are fine. 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

Determine the number of networks a design needs, counting each LAN and each router-to-router link
Determine the hosts every subnet must hold, from the largest LAN and its expected growth, and turn both needs into host bits, borrowed bits and a mask

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

Network Segmentation: The practice of dividing a network into smaller segments to improve performance and limit the spread of security threats.
Scalability: The ability of a system to handle increased load by adding resources without degrading performance.
Usable Hosts: The number of valid host addresses within a subnet, calculated by subtracting two from the total host count to exclude the network and broadcast addresses.
Borrowed Bits: Host bits reallocated to the network portion of a subnet mask to create additional subnets, reducing the number of available hosts per subnet.
Host Bits: The portion of an IPv4 address that identifies individual devices within a network segment, as determined by the subnet mask.
Router: A network device that forwards data packets between networks based on IP addresses.

Topics

Subnetting Network Design Subnet Requirements Network Growth Interactive Calculation

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