Network engineers & ISPs
Plan subnets and identify unknown devices before a client or colleague asks
AdminKit's free subnet calculator and MAC vendor lookup let network engineers and ISPs plan IPv4/IPv6 address ranges and identify an unfamiliar device by its MAC's registered manufacturer, today, calculated live rather than from a static table, since reusing an overlapping subnet or guessing at an unlabeled device on a client's network are exactly the kind of mistakes that surface later as an outage or a support ticket, with a scriptable Check API for wiring these into other tooling planned for later.
Updated October 30, 2026
At a glance
The problem
Carving one address block into several right-sized subnets, for separate VLANs, client allocations, or point-to-point links, is arithmetic that’s easy to get wrong under time pressure: oversize a range and the parent block runs out of room before every planned subnet is deployed; undersize one and it runs out of host addresses sooner than expected. Two overlapping ranges cause a different kind of problem — a router can’t reliably tell which interface should handle traffic for an address two connected subnets both claim, which shows up as an intermittent, address-dependent fault rather than a clean error, and is expensive to trace back to its cause after the fact.
A related, recurring task is identifying an unfamiliar device from nothing more than a MAC address in an ARP table, a switch’s CAM table, or a DHCP lease log, especially during an inventory pass or while chasing down a device nobody can immediately place. The address itself gives no hint beyond its first three bytes, the OUI block IEEE assigned to whichever manufacturer registered it.
Neither task needs a paid platform to answer — they need arithmetic done correctly and a registry looked up accurately, ideally without installing anything or creating an account first.
Talk to an expert
Huy Nguyen (David), Founder & CEO, Netbase JSC
Ask how AdminKit fits network engineers & isps — setup, timeline, or pricing.
What you can do for free today
- Calculate IPv4/IPv6 subnet ranges, masks and host counts from CIDR notation — enter an address with a prefix or a dotted mask and the network address, broadcast address, usable host range and host count update as you type, entirely in your browser.
- Look up the manufacturer behind a MAC address’s OUI prefix — checked live against AdminKit’s copy of the IEEE OUI registry, useful for identifying an unlabeled device in an ARP table or switch log, though it won’t identify a phone or laptop using a randomized address.
- Check your own public IP and whether it sits behind CGNAT — useful context before investigating exposure or explaining to a client why their address looks “shared.”
For planning several VLANs out of one block without ranges overlapping, see using a subnet calculator to plan VLANs, and subnet and CIDR basics for a walkthrough of the calculator’s output fields. If you’re also standing up DNS for a block you’re allocating, glue records and lame delegation explained covers a specific failure mode worth checking before it causes a hard-to-diagnose resolution problem, and IPv6 SLAAC and EUI-64 addressing explained covers how IPv6 host addresses get assigned differently from IPv4’s host-count-driven sizing. See also how AdminKit’s subnet calculator compares to other free options.
What AdminKit will add
AdminKit’s Check API is in early access and development. Its documented plan is to expose the same DNS, mail, TLS, port, MQTT and Modbus checks behind the free tool pages as structured, machine-readable results — useful for wiring checks into other tooling instead of running them one at a time through a website. MAC vendor lookups and subnet arithmetic aren’t part of that documented scope, so there’s no indication scripting the two tools on this page will come from that API specifically, even once it ships.
There’s no device inventory, network topology map, or monitoring dashboard built for network engineers today. The honest status is that the tools above are exactly what they look like: free, point-in-time lookups you run yourself, with the guides above as reference for the arithmetic and delegation concepts behind them.
This page is general guidance, not a security audit of your specific network — see our disclaimer for what AdminKit's guidance does and does not commit to.
Frequently asked questions
Does the subnet calculator check whether two planned ranges overlap with each other?
No — it calculates one CIDR block's network address, broadcast address, usable range and host count at a time, entirely as arithmetic in your browser. It has no memory of other ranges you've already planned, so checking that a new VLAN or client allocation doesn't overlap an existing one is a manual comparison you do yourself, typically by listing each range in a table as you plan them.
Can the MAC vendor lookup identify any device I see in an ARP table or switch log?
Only if the device's address is a factory-assigned OUI an IEEE-registered manufacturer actually owns. Android 10+ and recent iOS/desktop systems randomize the MAC address used per network by default, specifically to prevent this kind of lookup, so expect it to work well on fixed infrastructure like routers, access points and IoT devices, and not at all on personal phones or laptops.
Is there a bulk or scriptable way to run these checks across many ranges or devices?
Not today. Each tool runs one lookup at a time through the website. AdminKit's Check API is in early access and development, and its documented scope so far covers DNS, mail, TLS, port, MQTT and Modbus checks — subnet math and MAC vendor lookups aren't part of that list, so scripting the two tools on this page specifically isn't something that API is currently planned to cover either.
Does AdminKit offer an inventory or topology tool built for network engineers?
No. These are standalone, free, point-in-time tools — there's no device inventory, network map, or monitoring dashboard built for this segment today, and this page won't claim otherwise.
Can I plan IPv6 subnets the same way as IPv4 with this tool?
The tool calculates both, but the practice differs: IPv6 subnets are conventionally sized at /64 regardless of host count, since that's what Stateless Address Autoconfiguration (SLAAC) assumes, rather than sized to fit a specific host count the way an IPv4 VLSM range is. See subnet and CIDR basics for how to read each type of result.
Related
- Subnet calculator
- MAC vendor lookup
- What is my IP
- Check API & MCP server
- /guides/using-a-subnet-calculator-to-plan-a-vlan-or-multi-subnet-network/
- /guides/subnet-and-cidr-basics-reading-a-subnet-calculator-result/
- /guides/glue-records-and-lame-delegation/
- /guides/ipv6-slaac-and-eui-64-addressing-explained/
- /compare/best-free-subnet-calculators/
Want AdminKit set up for you?
Tell us about your setup — we will follow up about early access and, if you need it, expert help.
How AdminKit works with you
- Delivered remotely — Netbase JSC, the company behind AdminKit, has worked with clients in 80 countries.
- Contracts and invoices are issued by Netbase JSC; payment goes to the company by bank transfer to Netbase JSC's company account or PayPal Business.
- Talk to the CEO, Huy Nguyen (David), directly on WhatsApp or by email at [email protected].