Subnet Mask Binary Converter

About this interactive

Subnetting is the one networking skill that has to be fast and automatic, because everything downstream of it — addressing plans, ACLs, routing, troubleshooting a host that cannot reach its gateway — assumes you can already see where a subnet starts and stops. This drill works the chain a prefix length implies: the mask in dotted decimal, the same mask in binary, the number of subnets it carves out of a Class C, the usable hosts each one holds, and the network and broadcast addresses bounding the subnet a given host lives in. You type every answer rather than choosing one, and a miss shows the working, not just the number.

What you'll learn

Convert a CIDR prefix length into the dotted-decimal and binary form of its subnet mask
Calculate how many subnets a prefix length carves out of a Class C network and how many usable hosts each subnet holds
Determine the network and broadcast addresses of the subnet a given host address falls inside

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

Subnet Mask: A 32-bit number that divides an IP address into network and host portions.
Prefix Length: The number of consecutive 1-bits in a subnet mask, written after a slash (e.g., /24), that defines how many bits of an IP address represent the network portion versus the host portion. A /24 prefix means the first 24 bits identify the network, leaving 8 bits for host addresses.
Host Bits: The portion of an IPv4 address that identifies individual devices within a network segment, as determined by the subnet mask.
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.
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.
Octet: One of the four 8-bit sections of an IPv4 address, each separated by a dot in dotted decimal notation and representing a decimal value from 0 to 255. For example, in 192.168.1.1, the four octets are 192, 168, 1, and 1.
Classless Inter-Domain Routing: A method for allocating IP addresses and expressing routing prefixes that replaces the older classful addressing scheme by using variable-length prefix notation (e.g., /24). CIDR enables more efficient use of IPv4 address space and reduces the size of internet routing tables through route aggregation.

Topics

Interactive Drill

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