Jet Mariano

Tag: DHCP

  • My Essential IT Troubleshooting Guide

    Simple Explanations for Real World Problems

    One of my favorite seasons of my life. Serving the city, keeping critical systems alive, and learning the foundations that shaped who I am as an engineer today. Every console screen taught me something new and every problem strengthened my desire to help others through technology.

    My Essential IT Troubleshooting Guide

    In every company I have worked for, the tools that saved the day were not fancy dashboards but simple commands and fundamentals I could trust.
    This is my personal troubleshooting arsenal, written so even a non technical reader can follow the logic behind what I do.

    Each section answers three things
    • What it is
    • Why it matters
    • How I use it in real life

    Name Resolution Basics

    A record

    What
    • A record is a phone book entry that says “this name belongs to this IP address.”

    Why
    • Users remember names better than numbers. If the A record is wrong or missing, they land in the wrong place or nowhere.

    How I use it
    • When a site is not loading, I ping the name and check if the IP address matches what we expect.
    • If it does not, I fix the A record in DNS and wait for it to replicate.

    CNAME

    What
    • A CNAME is a nickname that points one name to another name.

    Why
    • It lets you move services without breaking users. The public name stays the same while the target changes behind the scenes.

    How I use it
    • For services like autodiscover or app portals, I often see CNAMEs that point to Microsoft or another provider.
    • When something breaks after a cutover, CNAMEs are one of the first things I verify.

    DNS

    What
    • DNS is the global phone book that turns names into IP addresses.

    Why
    • If DNS fails, everything feels broken. Browsers, Outlook, file shares, all of them depend on DNS.

    How I use it
    • I run nslookup name.company.com to see which DNS server is answering and what IP it returns.
    • If users in one site can reach something and other users cannot, I compare DNS answers between locations.

    Hosts file

    What
    • The hosts file is a tiny local phone book on the computer.

    Why
    • It overrides DNS for that machine. One bad line can send traffic to the wrong place.

    How I use it
    • Location on Windows

    C:\Windows\System32\drivers\etc\hosts

    • I open it with Notepad as administrator.
    • If someone hard coded a testing IP and forgot about it, I comment it out or remove it, then flush DNS.

    Flush cache

    ipconfig /flushdns

    Nbtstat and TCP IP

    What
    • Nbtstat is an older tool for NetBIOS name resolution.
    • Hard coded TCP IP means a manual IP instead of DHCP.

    Why
    • Nbtstat helps when legacy name lookups act strange.
    • Hard coded IPs can cause conflicts or make VLAN changes painful.

    How I use it
    • nbtstat -n to see local NetBIOS names.
    • nbtstat -c to see the name cache.
    • When I find static IPs on client machines, I document them and move them to DHCP reservations so the network is easier to manage.

    Network control panel shortcut

    I still use this every week

    From Run

    ncp.cpl

    It opens the Network Connections window so I can quickly check adapters, enable or disable, or look at IPv4 settings.

    DHCP Essentials

    What
    • DHCP hands out IP addresses, gateways and DNS to clients.

    Why
    • If DHCP fails, users cannot get on the network or suddenly have duplicate addresses.

    Best practices
    • Use at least two DHCP servers where possible.
    • Define scopes with correct gateway and DNS.
    • Use reservations for printers and key servers.

    Commands I use on clients

    ipconfig /release
    ipconfig /renew

    If a user can reach the internet but not internal resources, I check that DNS from DHCP is internal and not a public resolver.

    MX, Autodiscover and Mail Flow

    MX record

    What
    • MX tells the world which server receives mail for your domain.

    Why
    • If MX points to the wrong place or has a low priority backup you forgot, email can vanish or queue.

    How I use it
    • I use MXToolbox to check MX records and verify that they point to Exchange Online or the correct email gateway.

    Autodiscover

    What
    • Autodiscover tells Outlook where to find the mailbox and settings.

    Why
    • A broken autodiscover record means constant password prompts or profile creation failures.

    How I use it
    • I verify the Autodiscover CNAME or SRV record.
    • I test with Outlook connectivity tools or Test-OutlookConnectivity when available.

    Hunting spam engines and bad SMTP

    Where malware hides
    • In browser extensions
    • In Outlook add ins
    • In unknown services or scheduled tasks that send mail through SMTP

    How I clean it without reimaging
    • Check Outlook add ins and disable anything suspicious.
    • Run msconfig and Task Manager to review startup items and tasks.
    • Review SMTP logs on the server to see which host is sending unexpected traffic.

    Certificates and SSL in Hybrid Environments

    Internal web apps depend on trusted certificates so browsers know the site is safe. When an SSL expires, internal apps stop working and Chrome or Edge will show warnings.

    Why we create new SSLs
    • Internal web apps must be trusted.
    • Intranet portals and legacy apps often stop working when an internal CA certificate expires.
    • External issued certs from DigiCert or GoDaddy are trusted by browsers.

    PowerShell to generate a CSR example

    $csr = New-ExchangeCertificate -GenerateRequest `
-SubjectName "CN=mail.contoso.com" `
-DomainName "mail.contoso.com","autodiscover.contoso.com"
Set-Content -Path "C:\Certs\mail_csr.req" -Value $csr

    After the CA signs it, import

    Import-ExchangeCertificate -FileData ([Byte[]]$(Get-Content "C:\Certs\mail_cer.cer" -Encoding byte -ReadCount 0)) -PrivateKeyExportable $true

    Enable for necessary services

    Enable-ExchangeCertificate -Thumbprint <Thumbprint> -Services IIS,POP,IMAP

    Where I keep it
    • C:\Certs or another controlled folder
    • Never leave certificates scattered in Downloads

    Core servers
    • I open Task Manager with Ctrl Shift Esc
    • File, Run, then mmc
    • Add the Certificates snap in and import there
    Or I import directly with PowerShell.

    Machine Trust Relationship Problems

    When Windows says “the trust relationship between this workstation and the primary domain failed,” the computer account and the domain no longer agree.

    On a traditional domain
    • Disable LAN and WiFi
    • Log in using cached credentials
    • Reset the local admin password if needed
    • Disjoin from the domain and put it in a workgroup
    • Reboot
    • Join it back to the domain

    For Azure AD joined devices

    Check status

    dsregcmd /status

    If broken

    dsregcmd /leave

    Then re join from Settings under Access work or school.

    RDP Session Cleanup

    Sometimes users cannot remote into their office desktop because a stale session is still connected.

    I run from my admin machine

    query session /server:192.168.10.25
logoff <SessionID> /server:192.168.10.25

    After that, they can reconnect without rebooting the server.

    Active Directory Tools

    ADSIEdit

    What
    • A low level editor for Active Directory objects.

    Why
    • Last resort for fixing broken attributes or lingering records when normal tools cannot reach them.

    How I use it
    • Only with full backups and a clear change plan.
    • I use it to clean up orphaned objects or legacy settings left behind.

    Event Viewer

    What
    • The black box recorder of Windows.

    Why
    • Every blue screen, login failure, replication problem and service crash leaves a trace here.

    How I use it
    • eventvwr.msc
    • I focus on System and Directory Service logs on domain controllers, and Application logs on servers hosting apps.

    FSMO Roles

    What
    • Flexible Single Master Operations are special AD roles for schema, naming, PDC, RID and infrastructure.

    Why
    • These make sure there is one source of truth for sensitive changes.

    Best practice
    • Know exactly which DC holds each role.
    • Protect those DCs like crown jewels.

    If a FSMO owner is gone forever
    • You can seize the role to a healthy DC using ntdsutil.
    • After seizing you never bring the old DC back online.

    This is rare but every senior engineer should know the process in theory.

    AD and Entra ID Health

    On premise AD health

    dcdiag
    repadmin /replsummary
    repadmin /showrepl

    I always confirm
    • DNS is correct
    • SYSVOL is in sync
    • Time is correct and within a few minutes across all DCs

    Entra ID health

    Connect-MgGraph
    Get-MgUser
    Get-MgDirectoryAudit

    I check
    • Sign in logs for failures
    • Conditional Access for blocked locations
    • Device compliance for machines that suddenly appear non compliant

    AD controls computers and users on site.
    Entra controls cloud identity and device trust.
    In a hybrid world, both must be healthy.

    Azure and Terraform

    Azure CLI read only commands

    az login
    az account show
    az group list
    az vm list
    az storage account list

    These tell me what exists without changing anything.

    Terraform for infrastructure as code
    • Initialize the directory
    terraform init
    • Format
    terraform fmt
    • Validate
    terraform validate
    • Plan
    terraform plan

    Nothing changes until terraform apply is run.
    For interviews, being comfortable with init, plan and validate already shows good understanding.

    Microsoft 365 Services

    Group Policy

    Purpose
    • Central control of security and settings for on premise joined machines.

    How I create it
    gpmc.msc
    • New GPO
    • Edit with the settings I want
    • Link to the correct OU

    Universal Print

    What
    • Cloud based printing that removes the need for classic print servers.

    Why
    • Easier management for hybrid and remote users.

    I register printers in Universal Print and assign permissions based on groups, so users can get printers automatically.

    SharePoint Online

    Steps I follow
    • Go to Microsoft 365 admin center
    • Open SharePoint admin
    • Create a new site
    • Assign owners and members
    • Set sharing and retention policies

    This becomes the central place for team documents and intranet content.

    OneDrive and Data Migration

    OneDrive
    • Sync client installed on machines
    • Known Folder Move for Desktop, Documents and Pictures
    • Version history to protect from mistakes and ransomware

    Migrating data
    • I prefer SharePoint Migration Tool or Mover.
    • I clean old data first so I do not carry garbage into the cloud.
    • I communicate to users what will move and what will not.

    Why This Arsenal Matters

    These are the tools I have relied on in city government, banks, energy drinks, and manufacturing.
    They are not fancy, but they work.

    Every time I help a user reconnect, restore a service, or clean up a broken configuration, I am really doing three things

    • Protecting the company and its data
    • Supporting my teammates so they are not alone in the fire
    • Honoring the gift God gave me to understand and fix complex systems

    This arsenal is how I serve.
    Whether I am helping a small office or a multi site enterprise, the pattern is the same ask good questions, run the right checks, fix the root cause, and leave clear notes so the next engineer can see the path.

    © 2012–2025 Jet Mariano. All rights reserved.
    For usage terms, please see the Legal Disclaimer.

  • 🖥️ Path to Become an Infrastructure Engineer (Ivy Falls)

    From Customer Service Rep to PC Specialist, Network Engineer, System Administrator, DevSecOps, and now Infrastructure Engineer — a journey built on faith, discipline, dedication, and gratitude.

    Introduction: The Path Is the Practice

    My story didn’t begin with servers or certifications.
    It began at All Electronics Corporation in Van Nuys, California, where I worked full-time from 6:30 A.M. to 3:00 P.M., taking two Metro buses and walking a block from the station — rain or shine — from December 1990 to late 1995.

    I woke as early as 4 A.M. to catch the first bus at Western and 3rd Street in Los Angeles, sometimes heading straight to my evening shift at the Taco Bell drive-thru in Glendale.
    Those were humble, exhausting days that taught me discipline and grit — lessons that would shape every part of my career.

    At All Electronics, I became fascinated by the IC — Integrated Circuit, the heart of every desktop computer. I wanted to understand it, not just sell it.

    Back in my Koreatown apartment, I turned curiosity into calling.
    No Google. No YouTube. No AI.
    Just library books and endless nights of self-study. I intentionally crashed my computers and rebuilt them until every fix became muscle memory.

    Once confident, I started offering free repairs and computer lessons to friends, relatives, and senior citizens — setting up printers, fixing networks, and teaching email basics. Those acts of service opened the door to my first full-time IT job at the University of Southern California (USC) as a PC Specialist.

    I still remember waiting at the bus stop in the dark, dreaming of the day I wouldn’t have to ride in the rain. Years later, those same dreams became reality — not through luck, but through faith, discipline, dedication, and gratitude.
    The rides changed — from buses to a BMW, an Audi, and now a Tesla — but what never changed was the purpose: to keep moving forward while staying grounded in gratitude.

    Season of Refinement

    While working full-time at USC, I entered what I call my season of refinement.
    By day I supported campus systems and users; by night I was a full-time student at Los Angeles City College (LACC) and a weekend warrior at DeVry University, studying Management in Telecommunications.

    It was during this time that Microsoft introduced the MCSE (Microsoft Certified Systems Engineer) program.
    One of my professors at LACC encouraged me to earn it, saying, “Once you have that license, companies will chase you.”
    He was right — that MCSE became my ticket to GTE (now Verizon), my first step into enterprise-scale IT.

    My tenure at GTE was brief because Aerospace came calling with a six-figure offer just before Y2K — an opportunity too good to refuse.
    After Aerospace, I founded my own consulting firm — Ahead InfoTech (AIT) — and entered what I now call my twelve years of plenty.

    One of my earliest major clients, USC Perinatal Group, asked me to design and implement a secure LAN/WAN connecting satellite offices across major hospitals including California Hospital Medical Center, Saint Joseph of Burbank and Mission Hills, and Hollywood Presbyterian Hospital.
    We used T1 lines with CSU/DSU units and Fortinet firewalls; I supplied every workstation and server under my own AIT brand.

    Through that success I was referred to additional projects for Tarzana and San Gabriel Perinatal Groups, linked by dedicated frame-relay circuits — early-era networking at its finest.
    Momentum led to new partnerships with The Claremont Colleges and the City of West Covina, where I served as Senior Consultant handling forensic analysis and SMTP/email engineering.

    Word spread. One attorney client introduced me to an opportunity in American Samoa to help design and build a regional ISP, and later to a contract with Sanyo Philippines.
    During this period Fortinet was still new, and I became one of its early resellers.
    Refusing to rely on mass-produced systems, I built AIT servers and workstations from the ground up for every environment.
    DSL was just emerging, yet most clients still relied on dedicated T1s — real hands-on networking that demanded precision and patience.

    Those were the twelve years of plenty — projects that stretched from local hospitals to overseas data links, from LAN cables to international circuits.
    By the time AWS arrived in 2006 and Azure followed in 2010, I had already been building and managing distributed networks for years.

    When I returned to Corporate America, my first full-time role was at Payforward, where I led the On-Prem to AWS migration, designing multi-region environments across US-East (1a and 1b) and US-West, complete with VPCs, subnets, IAM policies, and full cloud security.
    That’s when I earned my AWS certifications, completing a journey that had begun with physical servers and matured in the cloud.

    Education, experience, and certification merged into one lesson:
    Discipline comes first. Validation follows.
    Degrees and credentials were never my starting line — they were the icing on the cake of years of practice, service, and faith.

    My Philosophy: One Discipline, Many Forms

    Whether in Martial Arts, IT, or Photography, mastery comes from repetition, humility, and curiosity.
    As Ansel Adams wrote:

    “When words become unclear, I shall focus with photographs. When images become inadequate, I shall be content with silence.”

    Everyone can take a photo; not everyone captures a masterpiece.
    Everyone can study tech; not everyone understands its rhythm.
    Excellence lives in awareness — the moment when curiosity meets purpose.

    The Infrastructure Engineer Path

    1️⃣ Foundations

    Learn the essentials: Windows Server, Active Directory, DNS/DHCP, GPOs, Networking (VLANs, VPNs), Linux basics, and PowerShell.
    Free Resources:

    2️⃣ Cloud Platforms

    Start with AZ-104 Azure Administrator.
    Use free tiers to lab: Azure | AWS | GCP.
    Courses:

    3️⃣ Automation & DevOps

    Learn IaC (Terraform/Bicep), Docker, Kubernetes, and CI/CD.
    Watch TechWorld with Nana.

    4️⃣ Labs & Simulators

    No hardware? Try:

    5️⃣ Portfolio

    Document every lab, build diagrams, post scripts on GitHub, and write short lessons learned.

    Final Reflection

    From bus stops to boardrooms, from fixing desktops to deploying clouds — the principles never changed: serve first, learn always, and build things that last.
    This blog will continue to evolve as technology changes — come back often and grow with it.

    🪶 Closing Note

    I share this story not to boast, but to inspire those still discovering their own path in technology.
    Everything here is told from personal experience and memory; if a date or detail differs from official records, it’s unintentional.
    I’m grateful for mentors like my LACC professor, who once told me to look up a name not yet famous — Bill Gates — and earn my MCSE + I.
    He was right: that single decision opened countless doors.

    I don’t claim to know everything; I simply kept learning, serving, and sharing.
    My living witnesses are my son, my younger brother, and friends who once worked with me and now thrive in IT.
    After all these years, I’m still standing — doing what I love most: helping people through Information Technology.

    ⚖️ Legal Disclaimer

    All events and company names mentioned are described from personal recollection for educational and inspirational purposes only. Any factual inaccuracies are unintentional. Opinions expressed are my own and do not represent any past or current employer.

    © 2012–2025 Jet Mariano. All rights reserved.
    For usage terms, please see the Legal Disclaimer.

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