Subnetting Suite — IP Network Calculators

A support tool for IP addressing and subnetting topics. Each tab shows the solution step by step so you understand the reasoning, not just the result.

The five tools

DDN Mask ↔ /slash

Converts a subnet mask between the two equivalent notations:

The panel shows the bit-by-bit binary representation (network bits in orange, host bits in grey), the wildcard mask (inverse) and the number of usable hosts.

Procedure: each DDN octet is converted to 8 bits; the consecutive “1” bits from the most significant bit define the network portion. Their count gives the /n prefix.

Network Analysis

Given an IP address and a mask (slash or DDN), calculates:

• Network address → IP AND Mask
• Broadcast address → Network OR NOT(Mask)
• First and last host → network+1 and broadcast−1
• Usable hosts → 2^h − 2 (where h = host bits)
• IP class and classful default mask
• Number of subnets created relative to the default class

FLSM — Fixed Length Subnet Mask

Classic subnetting: all subnets have the same size.

The requirement can be specified two ways:

• Number of subnets required (e.g. 6 departments → at least 6 subnets)
• Minimum number of hosts per subnet (e.g. at least 30 hosts → /27 subnet)

Procedure:

1. Determine how many bits to borrow: find the minimum n such that 2^n ≥ required_subnets
2. Calculate the new prefix: original_prefix + n
3. Calculate the block size: 2^(32 − new_prefix)
4. List all subnets by incrementing the network address by blockSize

The table lists all generated subnets (up to 128) with network, mask, broadcast, first host, last host and usable hosts.

VLSM — Variable Length Subnet Mask

Optimised subnetting: each subnet receives exactly the space it needs, reducing address waste. Each network may have a different prefix.

Procedure:

1. List the requirements (name + number of hosts)
2. Sort requirements from largest to smallest
3. For each, find the minimum number of host bits h such that 2^h − 2 ≥ required_hosts
4. Assign the first available block, advance the pointer
5. Repeat for all requirements

Sorting from largest to smallest is essential: it ensures each subsequent block is naturally aligned to its size with no wasted space.

The table shows the complete allocation with remaining free resources.

Supernetting (Route Aggregation)

The inverse operation: aggregate multiple contiguous networks into a single summary route, reducing routing table entries.

Procedure:

1. Sort the networks by address
2. Compare the bits of the network addresses from left to right
3. Count the common bits: the supernet prefix equals that count
4. The supernet address is the AND of the first address and the new mask

The tool indicates whether the networks are contiguous and have the same prefix (perfect aggregation) or whether the route also covers space not belonging to the original networks.

Supernetting is the foundation of CIDR (Classless Inter-Domain Routing) used by BGP routers to reduce the size of global routing tables.