Practitioner-built, privacy-first
The network and security toolbox that keeps your data on your machine.
Subnet math, DNS and email diagnostics, certificate inspection, and more, computed locally in your browser. No upload, no logging, no account required.
Around the tools: sourced articles on how the technology works, a record of the companies that built this industry, the practice of doing the work, and the roles that do it.
Currently serving
Built by someone who has done the work since 1996.
Thirty years in enterprise networking and security.
The chapters lived from inside
In every one of these, employer or vendor, the work was the same shape: facing the end customer, in pre-sales and in post-sales technical support, and very often acting as the technical proxy and enablement facilitator for the partners who had to carry the product themselves. The job was to leave the customer with something that worked better than it did before — an innovation, a solution, an improvement they could keep running after I left. The full telling lives at the career record.
- Cabletron and Enterasys1996 – 2007
- Riverstone Networks2000 – 2002
- Cisco Systems2003 – 2008
- IronPort Systems2004 – 2005
- NetScreen and Juniper2009 – 2014
- Extreme Networks2013 – 2014
- FireEye, McAfee and Ixia2015 – 2019
- Pulse Secure2018 – 2019
- Palo Alto Networks2013 – 2015
- F52015 – present
- Fortinet2022 – present
- Netskope2024 – present
- Ping Identity and ForgeRock2025 – present
- Zscaler2026 – present
- Check Point2026 – present
The roles I have held
Eight positions across the path a product takes, each linking to what that job answers for, who it serves and how it is measured. The years are the ones on each entry, including the spans that are not continuous.
- Field network engineer1996-2000, 2005-2007
- Product support engineer2000-2002
- Knowledge base manager2000-2002
- High-touch operations manager2003-2004
- Systems engineer2004-2005, 2009-2010
- Network consulting engineer2008, 2010-2011, 2012, 2013-2014, 2020
- Channel systems engineer2015-2019
- Technical instructor2020-present
Platforms I currently teach.
What is here
Vendor hubs →
One door per platform: the tools, articles and certification material for that vendor, gathered in one place.
8 vendor hubs
Certification guides →
What each exam tests and what to study for it. Free, and useful whether or not you ever book a course.
105 guides
Study guides →
Curated reading paths through the Learn library: an ordered route through a subject, built for understanding it rather than for passing an exam.
105 guides
Glossary →
Every term and acronym used across this site, defined once and cross-referenced. The thing to open mid-article.
1242 entries
The Practice →
How the work is actually done rather than how the technology works. Triage, escalation, evidence, handover.
64 published
The Roles →
The positions this industry is made of, grouped by the path a product takes from the company that builds it to the person who depends on it.
39 positions
Tools →
Deterministic calculators and explainers for networks, security and identity. They compute in your browser and send nothing anywhere.
152 live
Learn →
Technical articles on the protocols and products behind the tools, written to be read rather than skimmed.
553 articles
Industry →
Company histories from the beginning of networking to now, including the ones that failed and the ones nobody remembers.
289 companies4 of them turn 50 this year
About →
Who is writing all of this, what I have done, and why any of it should be trusted.
The career record →
Fifteen chapters from 1996 onward, each told from inside the company it happened in.
15 chapters
Advisory →
Independent judgement on decisions that have not been made yet. Scoped work, written answer, no on-call.
By engagement
Training I teach →
Authorized instructor-led courses across four platforms, delivered through Red Education.
28 courses across 4 vendors
Red Education →
The global authorized training centre my courses are delivered through, and the story of how it got there.
Why local-first matters for security work.
When you paste a configuration, a packet capture, or a certificate into a tool, that data often contains secrets. Here, the everyday tools run entirely in your browser. The input never leaves your device, so there is nothing to log, leak, or subpoena.
Try a tool right now.
The CIDR calculator below runs locally. Type a network and prefix to see the address range, host count, and mask. Nothing is sent anywhere.
CIDR Calculator
Analyze a single IPv4 CIDR block: network, broadcast, mask, and host range.
Runs locally. Nothing is sent to any server.
All results are computed locally from the address and prefix you enter, using standard IPv4 addressing arithmetic. Nothing is looked up remotely and nothing is sent anywhere.
- RFC 4632 (CIDR)Classless Inter-Domain Routing address aggregation
- RFC 1918Private address ranges
- RFC 791 (IPv4)The Internet Protocol