Methodology

Updated 25 October 2026

Review and corrections

This page describes the models implemented in IT Engineer's Toolbox. Automated checks cover known answers, input errors and browser interactions; they do not establish fitness for every system. Review unexpected output against reproducible examples and authoritative references.

Networking

IPv4 is 32 bits. /p has 2^(32 − p) addresses aligned to that size. Conventional hosts exclude network/broadcast; /31 follows RFC 3021 point-to-point semantics; /32 is a host. VLSM is largest-first. CIDR ranges merge only without adding addresses.

Storage and RAID

Decimal units use 1,000; binary units use 1,024. Time = bytes × 8 / effective bits per second. IOPS × bytes per operation = bytes per second. For n disks of size d: RAID 0 = nd, RAID 1 = d, RAID 3/4/5 = (n-1)d, RAID 6 = (n-2)d, RAID 01/10 = nd/2 for even n >= 4. For g equal groups, RAID 50 = (n-g)d with at least 3 disks per group; RAID 60 = (n-2g)d with at least 4 per group. At least two groups are required and n must divide equally by g. RAID 01 mirrors two stripes; RAID 10 stripes mirror pairs. Their capacity is equal but their failure tolerance differs. RAID 2 Hamming ECC and vendor-specific layouts are not modelled.

Reliability

Downtime = period × (1−availability). Serial availability multiplies components. Independent parallel availability is one minus the product of unavailability. MTBF = operating time/failures; MTTR = repair time/failures.

Automation

Retry delay i = min(cap, base × factor^i), starting at i=0. Expected full jitter halves each capped delay. Numeric five-field cron runs in UTC with lists, ranges and steps. Restricted day fields use OR; starred day fields act as wildcard constraints.

Email authentication

SPF parsing follows RFC 7208 and distinguishes DNS-querying terms from literal IP mechanisms. Flattening is conservative and refuses terms that depend on live DNS or would change ordered evaluation. DKIM record checks follow RFC 6376. DMARC policy, alignment and testing-mode explanations follow RFC 9989; aggregate and failure reports follow RFC 9990 and RFC 9991. DNS tools do not perform live lookups, validate delivery or prove ownership.

AI planning

Cost = input tokens × input price/1,000,000 + output tokens × output price/1,000,000. Prices come from the visitor. RAG stride = chunk−overlap. The final window may be shorter. Token estimates are heuristics; embedding storage excludes index and replication overhead.

Data and cryptography

YAML uses the pinned YAML 1.2 core parser with bounded aliases. XML rejects DOCTYPE. Schema validation is a declared subset and rejects unsupported keywords. UUIDs, passwords and passphrases use cryptographic randomness with unbiased selection. Hashing/HMAC use Web Crypto.

Standards

Concepts follow RFC 4632 (CIDR), RFC 5952 (IPv6 text), RFC 9110 (HTTP), RFC 8259 (JSON), RFC 6901 (JSON Pointer), RFC 7519 (JWT), RFC 2104 (HMAC), and common cron conventions. There are no live standards or pricing feeds.

Read the source material

These references explain the underlying concepts. Check your own platform documentation for implementation-specific behaviour.