CIDR / Subnet Calculator implementation

Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

Record owner

Guth Instruments

Lifecycle

verified-clean

Evidence ID

t3-004

Effect

Computation or source lookup only

Input and validation requirements

The supplied host formula produces an invalid negative host count for /32: 2^(32-32)-2 = -1. The calculator should reject that result or implement an explicit /32 special case. A second convention-sensitive boundary occurs at /31, where the stated traditional formula gives zero usable hosts but RFC3021 point-to-point semantics give two.

Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

{
  "inputs": {
    "ipv4": "192.168.1.10",
    "prefix": 24
  },
  "expected_outputs": {
    "network_address": "192.168.1.0",
    "broadcast_address": "192.168.1.255",
    "first_usable_host": "192.168.1.1",
    "last_usable_host": "192.168.1.254",
    "subnet_mask": "255.255.255.0",
    "wildcard_mask": "0.0.0.255",
    "host_count": 254,
    "binary_breakdown": {
      "ip": "11000000.10101000.00000001.00001010",
      "mask": "11111111.11111111.11111111.00000000",
      "network": "11000000.10101000.00000001.00000000",
      "broadcast": "11000000.10101000.00000001.11111111"
    }
  },
  "working": "prefix=24, so host_bits=32-24=8. host_count=2^8-2=256-2=254. mask=255.255.255.0; wildcard=255.255.255.255-255.255.255.0=0.0.0.255. IP AND mask: 192 AND 255=192, 168 AND 255=168, 1 AND 255=1, 10 AND 0=0, giving network 192.168.1.0. broadcast=network OR wildcard: 192.168.1.0 OR 0.0.0.255=192.168.1.255. first usable=network+1=192.168.1.1; last usable=broadcast-1=192.168.1.254."
}

Other records

Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

• VERIFIED_LEDGER.json
• evidence-tranche3/tranche3-results.json