Week_6_NEF

NETWORK ENGINEERING FUNDAMENTALS

VLSM Simulator

Variable Length Subnet Masking — step-by-step subnet allocation practice

Theory recap: How VLSM works

1. Arrange host requirements in descending order — always allocate the largest subnet first.
2. Add +2 to every host requirement — one address is reserved for the network address and one for the broadcast address, so neither can be assigned to a host.
3. Find the number of host bits needed — the smallest number of bits n such that 2ⁿ ≥ (hosts required + 2). This determines the block size (2ⁿ) and the new subnet mask.
4. Build the new subnet mask — take the existing mask, turn the remaining host-portion 0's (up to the number of bits still needed) into 1's, starting from the left of the host portion.
5. Calculate the subnet range — Network address = start IP; Broadcast address = network address + block size − 1; Usable range = network+1 to broadcast−1.
6. Move to the next subnet — the next subnet's start IP is the current broadcast address + 1.

Host bits	Block size (2^n)	Hosts fit (block−2)	CIDR (from /24)	Last octet mask
2	4	2	/30	252
3	8	6	/29	248
4	16	14	/28	240
5	32	30	/27	224
6	64	62	/26	192
7	128	126	/25	128
8	256	254	/24	0 (next octet)

Loading question...

Host bits needed

CIDR prefix (just the number)

Subnet mask (decimal)

Network address

Broadcast address

First usable host

Last usable host

Powers of 2 reference

n	2	3	4	5	6	7	8
2^n	4	8	16	32	64	128	256

Binary ↔ Decimal octet converter

Calculator

0