MTU / Packet Fragmentation 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

t5-037

Effect

Computation or source lookup only

Input and validation requirements

The formula permits MTU equal to header overhead, producing a zero payload capacity and an undefined fragment-count division. The calculator must reject MTU <= header_size. The specification also leaves KB-versus-KiB interpretation ambiguous.

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": {
    "payload": 4000,
    "MTU": 1500,
    "protocol": "IPv4",
    "header_size": 20
  },
  "expected_outputs": {
    "will_fragment": true,
    "payload_per_fragment": 1480,
    "fragment_count": 3,
    "fragment_payload_sizes": [
      1480,
      1480,
      1040
    ],
    "fragment_sizes": [
      1500,
      1500,
      1060
    ],
    "total_overhead_bytes": 60
  },
  "working": "payload_per_fragment = 1500 - 20 = 1480 bytes. fragment_count = ceil(4000 / 1480) = ceil(2.702702...) = 3. First two fragment payloads are 1480 bytes: 1480 + 1480 = 2960. Last payload = 4000 - 2960 = 1040 bytes. Total fragment sizes = 1480 + 20 = 1500, 1480 + 20 = 1500, and 1040 + 20 = 1060 bytes. Total overhead = 3 x 20 = 60 bytes."
}

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-tranche5/tranche5-results.json