Decoding SMTP Errors and Mail Failure Messages: A Practitioner’s Diagnostic Guide
Manny Fernandez1. Executive Summary Objective: This guide turns cryptic SMTP reply codes, enhanced status codes, and bounce (NDR/DSN) messages into a...
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A little TCP story…
Manny FernandezToday I was on LinkedIn in the AM to monitor for friends moving companies etc. And I came across a...
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HTTP Error Messages Decoded: A Practitioner’s Field Guide to Status Codes and What They Actually Mean
Manny Fernandez1. Executive Summary Objective. This guide turns the three-digit HTTP status code sitting in your logs, your browser dev tools,...
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Building a Stateful Host Firewall and NAT Gateway with nftables
Manny Fernandez1. Executive Summary Objective: This guide walks you through building a complete, production-grade firewall on modern Linux using nftables: a...
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FortiGate VDOM Deep Dive: Designing, Deploying, and Operating Multi-VDOM on FortiOS
Manny FernandezNote: Version target: FortiOS 7.6.x on an NP6/NP7-class FortiGate. CLI is consistent from 6.2 onward except where flagged. Where a...
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Auditing Web Servers with Nikto 2.6.0: A Practitioner’s Field Guide to Configuration Scanning
Manny Fernandez1. Executive Summary Objective: This guide takes you from a clean host to a repeatable, reportable Nikto workflow you can...
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Beyond the Prompt Series: Large Language Models – The Autoregressive Engine
Manny FernandezHow next-token prediction became the core of applied AI, and the 2026 shifts (MoE, reasoning, long context) that actually matter...
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How CDNs Operate: A Practitioner’s Guide to Edge Caching, Request Routing, and Cache Control
Manny Fernandez1. Executive Summary Objective. This guide explains, at the DNS-record and HTTP-header level, exactly what happens when a Content Delivery...
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Deploying FortiGate cFOS: From a Docker Image to a Kubernetes Firewall Pod
Manny Fernandez1. Executive Summary Objective: This guide takes a Fortinet-supplied Container FortiOS (cFOS) image, validates it standalone in Docker, then promotes...
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FortiGate ADVPN: Classic (1.0) vs. Edge-Discovery (2.0) for Dynamic Spoke-to-Spoke SD-WAN
Manny Fernandez1. Executive Summary Objective. This guide explains what changed between ADVPN 1.0 and ADVPN 2.0 on FortiGate, then walks two...
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Securing the Open SSID on FortiGate: Deploying Enhanced Open (OWE) for Encrypted Guest Wi-Fi
Manny Fernandez1. Executive Summary Objective: This guide replaces the legacy "open" (no-encryption, no-authentication) guest SSID with Enhanced Open, the Wi-Fi Alliance...
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FortiGate Local-Out Routing: Controlling the Traffic the Firewall Sends Itself
Manny FernandezEvery FortiGate is two devices wearing one chassis. One of them is a firewall: it inspects traffic that arrives on...
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The Complete FortiGate execute Command Reference
Manny FernandezEvery FortiGate admin knows execute ping. Most know execute backup config. Almost nobody knows what else is sitting in that...
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Is your FortiGate vulnerable to Management Access when using a FortiToken Push Notification
Manny FernandezEvery few months the same question lands in my inbox. A scanner report flags TCP/4433 open on a customer's WAN...
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Securing the Purdue Model: A FortiGate OT Reference Architecture
Manny Fernandez1. Executive Summary Objective: This guide provides a production-grade reference architecture for retrofitting Fortinet OT security controls onto an existing...
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Deep Dive QUIC Explanation
Manny FernandezExecutive Summary Objective: This guide breaks down QUIC (RFC 9000/9001/9002) at the wire-format level, showing exactly how the transport establishes...
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The Cisco Engineer’s Guide to FortiGate: A Side-by-Side CLI Rosetta Stone for IOS Veterans Landing on FortiOS
Manny FernandezYou have twenty years of muscle memory. You type conf t before your coffee finishes brewing. Then someone hands you...
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Cisco Packet Tracer equivalent in FortiGate Firewall?
Manny FernandezI deployed thousands of ASA firewalls when I was with the different partners. One of my favorite features on the...
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Using host file equivalent on the FortiGate Firewall
Manny FernandezHave you ever wanted to do some testing on a FortiGate using an FQDN verses an IP address? While FortiOS...
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The Different Types of Networks: A Practitioner’s Field Guide
Manny FernandezAsk ten engineers to define "a network" and you will get ten answers that are all correct and none of...
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