Blogs on Mai Tan Duc

Optus 2025 Outage: Firewall Misconfiguration, Failed Redundancy, and Emergency Services Impact

Fri, 19 Sep 2025 00:00:00 +0000

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On September 18, 2025, Optus suffered a major network outage that disrupted Triple Zero (000) emergency services across several Australian states. The outage lasted over 13 hours and resulted in four confirmed deaths and hundreds of failed emergency calls — making it not just an infrastructure failure, but a public safety crisis with real human consequences.

The Camera That Moved at Midnight: Why Default Passwords Are Not a Minor Risk

Sun, 03 Aug 2025 00:00:00 +0000

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What the Night Guard Saw Link to heading

At some point past midnight, the security guard on night duty noticed one of the office PTZ cameras rotating on its own — panning slowly across the room as if someone were operating it remotely. No one was at the control workstation. No one was supposed to be accessing the system.

The Routing Protocol Triangle: EIGRP, OSPF, and BGP Explained Through Real-World Analogies

Sat, 02 Aug 2025 00:00:00 +0000

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The Problem That Sends Engineers to the Wrong Place Link to heading

Every network engineer has sat in front of a black CLI screen asking the same question: “The cable is in. The IP is correct. So why won’t these two routers talk to each other?”

Cameras Dropping Every Day at 2 PM: When the Root Cause Is Not the Camera

Wed, 30 Jul 2025 00:00:00 +0000

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The Initial Picture: Symptoms That Do Not Point to Root Cause Link to heading

The security team described the symptoms accurately: cameras lose signal for a few minutes, consistently around 2 PM, then recover on their own. Not every day — only on hot, sunny ones.

Static LAG with VMware ESXi – Why LACP Is Not Always the Right Answer

Wed, 16 Jul 2025 00:00:00 +0000

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Static LAG or LACP – The Wrong Question from the Start Link to heading

In working with virtualisation network infrastructure, I’ve noticed a consistent pattern: when a network engineer looks at the uplink configuration between a switch and an ESXi host, the first question is almost always “why aren’t you using LACP?” — and that’s the wrong question to start with.

How Meta and Yandex Exploited Android's Localhost Channel to Bypass Privacy Controls

Fri, 13 Jun 2025 00:00:00 +0000

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Background: A Support Case That Exposed a Tracking Vector Link to heading

It started with a support ticket in June 2025. A user noticed that content he’d browsed in a standard Chrome session was surfacing as targeted recommendations inside a completely separate native app — one he hadn’t opened during that browsing session. The correlation was too precise to be coincidence, and too consistent to be a caching artefact.

AWX for Scheduled and Event-Driven Network Automation

Sat, 15 Mar 2025 00:00:00 +0000

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Scheduled Playbook Execution with AWX Link to heading

Once AWX is deployed and integrated with your Git repository, the typical onboarding sequence is straightforward: define an inventory, link your playbook source, then wire it to a schedule. The real value of AWX over raw Ansible CLI is the audit trail and scheduling engine — every job run is logged with its output, timing, and exit status, giving you the operational visibility that cron-based automation lacks.

Ansible Playbooks for Network Automation: From Basics to Production

Fri, 14 Mar 2025 00:00:00 +0000

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Foundational Playbooks Link to heading

Gathering Device Facts Link to heading

Gathering device facts is often the first playbook written in a new automation environment — and one of the most immediately useful. Running ios_facts across your inventory gives you a structured snapshot of platform, version, interface state, and IP configuration without logging into a single device manually. The output can feed dashboards, validation checks, or change pre-conditions.

Network Automation with Ansible and AWX: Setup, Playbooks, and Best Practices

Thu, 13 Mar 2025 00:00:00 +0000

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Network configuration is inherently repetitive: new devices get the same baseline hardening, VLANs get pushed to every switch in a fabric, ACLs get updated across all firewalls simultaneously. Manual execution of these tasks doesn’t scale, introduces inconsistency, and leaves no auditable record of what changed and when. Ansible addresses this by externalising configuration intent into playbooks that are version-controlled, idempotent, and executable across an entire inventory in a single run.

Network Incident Case Studies: DNS, DHCP, Bandwidth, and Firewall Failures

Mon, 11 Nov 2024 00:00:00 +0000

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The most instructive network incidents are rarely the ones caused by hardware failure or DDoS attacks — the root cause is usually obvious. The difficult ones are caused by misconfigurations, overlooked dependencies, or single points of failure that nobody thought to protect. The cases below are representative of that category: failures that looked complex on the surface but resolved to a single traceable root cause.

Password Management with pass, GPG, and Git

Wed, 07 Aug 2024 00:00:00 +0000

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password-store (commonly invoked as pass) is the Unix-philosophy answer to credential management: passwords are stored as GPG-encrypted files, organised in a directory tree, with Git providing synchronisation and version history. There are no proprietary formats, no cloud lock-in, and no dependencies beyond tools that are standard in any Linux environment. The entire store is auditable, portable, and backed by well-understood cryptographic primitives.

IT Outage Case Studies: CrowdStrike, AWS, Facebook, and AT&T

Tue, 25 Jun 2024 00:00:00 +0000

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The most instructive outages are rarely caused by exotic failure modes. The cases below are representative of the incidents that define real-world IT risk: software updates that bypassed staging validation, human errors in high-stakes operational tooling, and configuration changes that hadn’t been tested against the failure scenarios they were meant to prevent. Each one is instructive not because it was unusual, but because the conditions that caused it are common.

GPG Encryption and Key Management in Practice

Sat, 20 Apr 2024 00:00:00 +0000

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GPG and the OpenPGP Standard Link to heading

GNU Privacy Guard (GPG) is the de facto open-source implementation of the OpenPGP standard, widely used to secure emails, files, and digital communications. Built on asymmetric cryptography, it provides confidentiality, authenticity, and integrity — the three pillars of secure data exchange.

Windows Printer Sharing via SMB: Operational Risks and the Case for Network Printers

Thu, 14 Mar 2024 00:00:00 +0000

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Shared printing via Windows Share is the kind of solution that looks reasonable in a pinch and becomes a recurring nightmare in practice. IT teams inherit these setups constantly — they work just well enough to avoid being prioritised for replacement, yet generate a disproportionate share of helpdesk tickets, usually at the worst possible times.

IPv4 Addressing Design: Subnetting, VLSM, and Operational Standards

Sun, 14 Jan 2024 00:00:00 +0000

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Design Inputs: What to Establish Before Allocating Subnets Link to heading

A well-structured IP addressing plan is one of the most durable investments in any network design. Getting it right early avoids the painful process of re-addressing production networks — a task that, in large environments, can take months and carry significant risk.

Cisco IOS Router Initial Configuration Reference

Tue, 02 Jan 2024 00:00:00 +0000

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This guide covers first-time router configuration on Cisco IOS from console access through to production-ready hardening. Each section includes the relevant CLI commands and a verification step — in production, the verify commands matter as much as the configuration commands. An unverified config is an assumption.

Cisco IOS Switch Initial Configuration Reference

Mon, 01 Jan 2024 00:00:00 +0000

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This guide covers Cisco IOS switch configuration from initial console access through to a production-hardened state. Each section pairs the configuration commands with a verification step — in operational environments, the verify commands are as important as the config commands. An unchecked config is an assumption.

The Operational Cost of Legacy Systems: Security Debt, Maintenance Burden, and Scalability Limits

Wed, 29 Nov 2023 00:00:00 +0000

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The argument for keeping legacy systems is almost always framed as cost avoidance: migration is expensive, risky, and disruptive. What rarely appears in that calculation is the ongoing cost of staying — the accumulated inefficiencies, security debt, and operational friction that compound quietly over time until they become impossible to ignore.

Optus 2023 Outage: BGP Routing Failure and Network Resilience Lessons

Tue, 14 Nov 2023 00:00:00 +0000

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What Happened Link to heading

Info

The Optus 2023 outage was a major network failure affecting approximately 10 million customers on November 8, 2023, disrupting mobile voice, internet access, and emergency services for the better part of a day.

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Note

According to Optus’s post-incident disclosure, at approximately 4:05 AM, a routine software upgrade triggered a change in routing information received from an international peering network. These BGP updates propagated through multiple layers of the Optus IP core, exceeding preset safety thresholds on key routers. Unable to process the load, those routers withdrew from the IP core to protect themselves — a self-preservation mechanism that cascaded into a nationwide outage.

The underlying failure mode is a well-known class of BGP incident: a peer advertises an excessive number of prefixes or malformed route attributes, and the receiving network lacks adequate filtering or dampening to absorb the impact. In this case, the routing update volume wasn’t anomalous on its own — what failed was the chain of safeguards that should have caught it before it reached production infrastructure.

Blogs on Mai Tan Duc

Optus 2025 Outage: Firewall Misconfiguration, Failed Redundancy, and Emergency Services Impact

Table of Contents Link to heading

The Camera That Moved at Midnight: Why Default Passwords Are Not a Minor Risk

Table of Contents Link to heading

What the Night Guard Saw Link to heading

The Routing Protocol Triangle: EIGRP, OSPF, and BGP Explained Through Real-World Analogies

Table of Contents Link to heading

The Problem That Sends Engineers to the Wrong Place Link to heading

Cameras Dropping Every Day at 2 PM: When the Root Cause Is Not the Camera

Table of Contents Link to heading

The Initial Picture: Symptoms That Do Not Point to Root Cause Link to heading

Static LAG with VMware ESXi – Why LACP Is Not Always the Right Answer

Table of Contents Link to heading

Static LAG or LACP – The Wrong Question from the Start Link to heading

How Meta and Yandex Exploited Android's Localhost Channel to Bypass Privacy Controls

Table of Contents Link to heading

Background: A Support Case That Exposed a Tracking Vector Link to heading

AWX for Scheduled and Event-Driven Network Automation

Table of Contents Link to heading

Scheduled Playbook Execution with AWX Link to heading

Ansible Playbooks for Network Automation: From Basics to Production

Table of Contents Link to heading

Foundational Playbooks Link to heading

Gathering Device Facts Link to heading

Network Automation with Ansible and AWX: Setup, Playbooks, and Best Practices

Table of Contents Link to heading

Network Incident Case Studies: DNS, DHCP, Bandwidth, and Firewall Failures

Table of Contents Link to heading

Password Management with pass, GPG, and Git

Table of Contents Link to heading

IT Outage Case Studies: CrowdStrike, AWS, Facebook, and AT&T

Table of Contents Link to heading

GPG Encryption and Key Management in Practice

Table of Contents Link to heading

GPG and the OpenPGP Standard Link to heading

Windows Printer Sharing via SMB: Operational Risks and the Case for Network Printers

Table of Contents Link to heading

Why Printer Sharing Looks Simple and Isn’t Link to heading

IPv4 Addressing Design: Subnetting, VLSM, and Operational Standards

Table of Contents Link to heading

Design Inputs: What to Establish Before Allocating Subnets Link to heading

Cisco IOS Router Initial Configuration Reference

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Cisco IOS Switch Initial Configuration Reference

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The Operational Cost of Legacy Systems: Security Debt, Maintenance Burden, and Scalability Limits

Table of Contents Link to heading

Optus 2023 Outage: BGP Routing Failure and Network Resilience Lessons

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What Happened Link to heading

Root Cause Link to heading