Networking tools that run on your machine

Subnetting, addressing plans and network design, calculated in your browser. Your addressing plan is not something to hand to a website, so these tools do not ask for it.

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Local toolsEverything on this page is arithmetic performed by your browser. No addressing plan, topology or hostname is uploaded, and there is no server that could receive one.

IP & subnetting

Address arithmetic, done once and shared by every tool here.

192.168.1.130 / 24networkhost192.168.1.0 – .255254 usableSubnet CalculatorNetwork, broadcast, usable range, mask and wildcard, with the network and host bits shown. IPv4 and IPv6.Start here /23/25/27/24free500 100 25 240 hostspacked largest firstVLSM DesignerGive it host counts per segment and it packs the parent network without gaps, sizing for growth and saying what did not fit.Flagship 203.0.113.64/26…113.64…113.12764 addresses62 usable hostsCIDR Range CalculatorA prefix in, its boundaries out — first, last, how many, what it splits into and what it sits inside. .1 → .1009 prefixesexact — nothing outside the rangeIP Range to CIDRTwo addresses in, the smallest exact set of prefixes out. Never covers an address you did not ask for.Exact 10.0.0.0/23only true siblings mergeCIDR AggregatorMerges a list down to the smallest equivalent set, and refuses to merge prefixes that only look adjacent. 2001:0db8:0000:0000:8a2e:0370:7334:00012001:db8::8a2e:370:7334:1longest zero run onlyIPv6 VisualizerExpand, compress and explain — including why a single zero group is never written as a double colon.RFC 5952

VLAN & segmentation

Broadcast domains, the addressing that goes with them, and the misconfigurations that join two networks silently.

10.120.130.1gateway · pool · freeVLAN + Subnet DesignerName your VLANs and say how many devices each holds. It allocates subnets, proposes gateways and DHCP pools, then checks the plan for what actually breaks networks.Flagship 110203010.0.1.0/2410.0.10.0/2410.0.20.0/2410.0.10.128/25!!2 problems foundVLAN PlannerFor a scheme you already run. Write down what is really there and find the overlaps, bad gateways and DHCP pools that cover a router. sw1sw2802.1Qvlan 10untaggeduntaggedtag added here, removed therenative VLAN crosses untaggedVLAN Trunk VisualizerWatch a tag added and removed across a trunk — and what a native VLAN mismatch does to a frame when neither switch logs anything.Teaching 2001:db8:1234::/48:0:1:2:3:4each a /6465,536 availableIPv6 Subnet PlannerDivide a delegated prefix into subnets. Counts subnets rather than hosts, because host counts do not constrain an IPv6 plan.

What is coming

This vertical is being built in stages, and the addressing layer is the foundation the rest depends on. Next are VLAN and subnet design, IPAM, then routing, MPLS and segment routing, fabric design, Wi-Fi planning, and the DNS and mail diagnostics.

On the tools that will need the network. DNS, mail-record and registration lookups genuinely cannot be answered without asking somebody. When those arrive they will carry a different badge saying exactly what is sent and to whom — not a green one pretending the work happened locally. A handful of checks, certificate and HTTP header inspection among them, cannot be done from a browser at all and would need a server; those are being weighed rather than faked.

The rule these tools are built on

An addressing plan describes where things are and how to reach them. It is exactly the document you would not paste into an unfamiliar website, and most free subnet calculators are websites you paste it into.

Everything here is arithmetic, and arithmetic does not need a server. The shared IP engine behind these pages is tested against the cases where calculators usually disagree with real equipment: a /31 has two usable addresses because RFC 3021 says so, a /32 is a single host route, IPv6 has no broadcast address to subtract, and a mask like 255.255.0.255 is refused rather than quietly interpreted.