Browser-based utilities

Network Toolkit

IPv4 and IPv6 subnet calculations, a secure ULA generator, CIDR overlap and summarization tools, and a practical VLSM/VLAN planner. No login, backend, tracking, or alphabet-soup subscription required.

IPv4 subnet calculator

Calculate the network, broadcast, usable range, subnet mask, wildcard mask, address class, and smaller child subnets.

32-bit

Network —

Usable range —

Usable hosts —

Address type —

Subnet details

Address details

Binary view

Network bits are cyan; host bits are violet.

Split this IPv4 network

New prefix

Calculate a network first.

#	Subnet	First usable	Last usable	Broadcast	Usable hosts

IPv6 calculator and decoder

Expand, compress, classify, and subnet IPv6 addresses while explaining whether an address is global, unique-local, link-local, multicast, or reserved for documentation.

128-bit

fd00::/8 Unique Local Address

The practical private-style IPv6 space. Routable inside your network, not on the public Internet.

fe80::/10 Link-local

Only works on the local layer-2 link. It is not your routed private address space.

2000::/3 Global unicast

The broad globally routable IPv6 allocation range, subject to provider and registry assignments.

ff00::/8 Multicast

IPv6 has no broadcast addresses; multicast performs those one-to-many jobs.

2001:db8::/32 Documentation

Safe for examples and diagrams. It should never appear as real production addressing.

/64 Normal LAN size

A standard IPv6 LAN normally receives a /64, even though the address count looks gloriously absurd.

Network prefix —

Address type —

Addresses in prefix —

Host/interface bits —

Address forms

Prefix details

Common containing networks

Useful when identifying the site, delegated block, or individual LAN containing this address.

Split this IPv6 prefix

IPv6 has no broadcast address, and normal unicast subnets do not reserve the first and last address like IPv4.

New prefix

Calculate a prefix first.

#	Child prefix	First address	Last address	Addresses

IPv6 ULA generator

Generate a locally assigned Unique Local Address /48 using cryptographically secure browser randomness, then build /64 prefixes mapped to your VLAN IDs.

RFC 4193

Generated site prefix

The fd byte marks a locally assigned ULA. The remaining 40-bit Global ID is randomized to reduce collision risk if separately designed networks are ever joined.

Generating…

ULA is the closest IPv6 equivalent to private addressing, but it is not a security boundary and does not replace firewall rules. Also, fe80::/10 is link-local—not your routed private network.

Build /64 prefixes from VLAN IDs

VLAN numbers are converted from decimal to hexadecimal exactly. For example, VLAN 10 becomes subnet ID 000a, not 0010.

VLANs, one per line

Suggested gateway host ID

VLAN	Name	Subnet ID	IPv6 /64	Suggested gateway

CIDR and mask tools

Find overlapping routes, collapse adjacent networks, convert an arbitrary address range into CIDRs, and translate IPv4 subnet masks and wildcard masks.

IPv4 + IPv6

Overlap checker

Paste IPv4 and/or IPv6 CIDRs. Comparisons are only made within the same address family.

Networks

Results

CIDR summarizer

Normalize, remove contained routes, and merge adjacent sibling networks when possible.

Networks

Collapsed networks

Address range to CIDR

Supports either IPv4 or IPv6, provided both addresses use the same family.

First address

Last address

Smallest exact CIDR set

Subnet mask / wildcard converter

Translate Cisco-style wildcard masks and standard IPv4 subnet masks.

IPv4 mask

Input is a

Conversion

VLSM and VLAN planner

Enter the usable host requirement for each network. The planner assigns the largest subnets first, shows utilization, and can map each VLAN to an IPv6 /64 from a site prefix.

Plan + export

Parent IPv4 network

Optional IPv6 site prefix, /64 or larger block

Name, usable hosts, VLAN ID (optional)

Allow /31 point-to-point networks for entries requiring exactly two addresses

Name	VLAN	Needed	IPv4 subnet	Mask	Gateway	Usable range	Broadcast	Capacity	IPv6 /64