subnetCalc

subnetCalc

Description

This is a Go CLI utility (built with Cobra) to calculate network information from a CIDR.

It can also split a “supernet” into smaller subnets and render the result either as a styled table or JSON. There is also an optional interactive TUI for splitting/joining subnets.

IPv4 is the primary target. IPv6 works for basic calculations/output, but deeper functionality (especially around very large splits) is intentionally limited.

Usage

subnetCalc <ip address>/<subnet mask>

Flags

• --subnet_size, -s — split the input network into subnets of this prefix length
• --json, -j — output JSON
• --interactive, -i — launch the interactive TUI (mutually exclusive with --json)
• --verbose, -v — increase verbosity (repeat for more)

Examples

List /12 Subnets Contained in a /8 Network Using the Interactive TUI

Get Network Information for a /19 Network

subnetCalc 10.12.34.56/19

               Network: 10.12.32.0/19
    Host Address Range: 10.12.32.1 - 10.12.63.254
     Broadcast Address: 10.12.63.255
           Subnet Mask: 255.255.224.0
         Maximum Hosts: 8,190

List /27 Subnets Contained in a /25 Network

subnetCalc 192.168.10.0/25 --subnet_size 27

               Network: 192.168.10.0/25
    Host Address Range: 192.168.10.1 - 192.168.10.126
     Broadcast Address: 192.168.10.127
           Subnet Mask: 255.255.255.128
         Maximum Hosts: 126

  192.168.10.0/25 contains 4 /27 subnets:
╭──────────────────────────────────────────────────────────────────────────────────────────────────╮
│ #   Subnet              Subnet Mask     Assignable Range              Broadcast       Hosts      │
│1   192.168.10.0/27     255.255.255.224 192.168.10.1 - 192.168.10.30  192.168.10.31   30          │
│2   192.168.10.32/27    255.255.255.224 192.168.10.33 - 192.168.10.62 192.168.10.63   30          │
│3   192.168.10.64/27    255.255.255.224 192.168.10.65 - 192.168.10.94 192.168.10.95   30          │
│4   192.168.10.96/27    255.255.255.224 192.168.10.97 - 192.168.10.126192.168.10.127  30          │
╰──────────────────────────────────────────────────────────────────────────────────────────────────╯

List /20 Subnets Contained in a /19 Network in JSON Format

subnetCalc 10.12.34.56/19 --subnet_size 20 --json

{
  "cidr": "10.12.32.0/19",
  "firstIP": "10.12.32.1",
  "lastIP": "10.12.63.254",
  "networkAddr": "10.12.32.0",
  "broadcastAddr": "10.12.63.255",
  "subnetMask": "255.255.224.0",
  "maskBits": 19,
  "maxHosts": "8,190",
  "subnets": [
    {
      "cidr": "10.12.32.0/20",
      "firstIP": "10.12.32.1",
      "lastIP": "10.12.47.254",
      "networkAddr": "10.12.32.0",
      "broadcastAddr": "10.12.47.255",
      "subnetMask": "255.255.240.0",
      "maskBits": 20,
      "maxHosts": "4,094"
    },
    {
      "cidr": "10.12.48.0/20",
      "firstIP": "10.12.48.1",
      "lastIP": "10.12.63.254",
      "networkAddr": "10.12.48.0",
      "broadcastAddr": "10.12.63.255",
      "subnetMask": "255.255.240.0",
      "maskBits": 20,
      "maxHosts": "4,094"
    }
  ]
}

Notes / Limitations

• --subnet_size will refuse to generate an extremely large number of subnets (currently capped at 1,000,000) to avoid accidental OOM/hangs.
• IPv6 output is supported, but some concepts (like “broadcast”) are displayed as the last address in the range.

Feedback

Bug reports, feature requests, and pull requests are welcome but may not be responded to in an even remotely timely manner.