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Networking Toolbox
Subnet math, DNS lookups, DHCP options, and certificate checks share one browser tab in Networking Toolbox, a free toolkit for sysadmins and network engineers. Need to carve a /24 into departments? The VLSM planner fits named subnet requirements into a parent block, reports each subnet's efficiency and the leftover space, and exports the plan as CSV or JSON. Merging address lists? CIDR utilities summarize, split, compare, and deaggregate prefixes, with set operations for difference, overlap, and containment. Writing configs? Generators build DHCPv4 and DHCPv6 options, PXE profiles, Kea or ISC snippets, and SPF, DKIM, DMARC, CAA, TLSA, and SRV records, and DNSSEC helpers calculate key tags and DS records. Something broken? Diagnostics query DNS through Cloudflare, Google, Quad9, OpenDNS, or a resolver of your choice, read TLS certificate chains, grade HTTP security headers, trace redirects, check TCP ports, look up BGP routes and RDAP records, and test mail servers. Need a refresher? Reference guides explain private ranges, CGNAT, IPv6 address types, and common ports. A keyboard search palette puts any tool a few keystrokes away, and bookmarked tools stay available offline. Eighteen themes, four languages, custom branding, and accessibility switches make it feel like your own, and a keyless JSON API serves the subnet, CIDR, IP, and DNS utilities to scripts. Running on a dedicated VPS on RepoCloud with guaranteed CPU, RAM, and SSD, full root SSH access, and a browser serial console. MIT licensed.
Benefits
- Plan address space without spreadsheets
- The VLSM planner allocates subnet requirements from a parent network using Fit Best or Preserve Order, shows per-subnet efficiency and leftover space, and exports the plan as CSV or JSON.
- Debug DNS, TLS, and headers
- Run live lookups through Cloudflare, Google, Quad9, OpenDNS, or a custom resolver, then inspect certificate chains and expiry dates and grade HTTP security headers without opening a terminal.
- Paste-ready configs and records
- Builders produce DHCP Option 43 and Option 82 values, Kea or ISC snippets, and SPF, DKIM, DMARC, CAA, and TLSA records, so routine changes start from ready-made output.
- Bookmark tools for offline use
- Right-click any tool to bookmark it, pin it to the top of the homepage, and keep it available offline, while Ctrl+/ lists every keyboard shortcut for mouse-free navigation.
Features
- CIDR Set Operations
- Summarize, split, compare, and deaggregate prefixes, compute difference, overlap, and containment between two sets, and find free space or the next available subnet in a pool.
- DHCP Option Builders
- Generate DHCPv4 options 43, 82, 119, and 121/249, DHCPv6 prefix delegation and client FQDN values, DUIDs, PXE boot profiles, and Kea or ISC configuration snippets.
- DNS Record Builders
- Build SPF, DKIM, DMARC, CAA, TLSA, SSHFP, SRV, and SVCB/HTTPS records, lint and diff zone files, and compute DNSSEC key tags, DS records, and NSEC3 hashes.
- Live Diagnostics Suite
- Check DNS propagation and DNSSEC validation chains, TLS certificates and protocol versions, HTTP headers and CORS policy, TCP ports, BGP routes, RDAP records, and MX health.
- Themes and Accessibility
- Choose from 18 color themes and four languages, set custom site branding and CSS, and enable reduced motion, high contrast, large text, or a dyslexia-friendly font.
- Keyless JSON API
- A public REST API with 60+ documented endpoints returns JSON for subnet, CIDR, IP, and DNS calculations, is described by an OpenAPI spec, and needs no API key.