Local DNS Failure Can Look Like a Dead Server
Test the known address before rebooting a host just because its name stopped resolving.
TOPIC
Networking
Lessons, explainers, experiments, and implementation notes.
What a Switch Actually Learns from a MAC Address
A switch learns from source MAC addresses, not destination addresses. Watching the table populate makes unknown unicast, flooding and forwarding much easier to reason about.
Why Subnetting Felt Hard Until I Stopped Memorizing Tables
Subnetting became much easier once I treated it as address boundaries and binary arithmetic instead of a collection of shortcut tables.
The Default Route Is a Fact, Not a UI Guess
A topology view should consume routing state rather than infer a gateway from labels or layout.
My First Packet Tracer Lab: Two PCs, One Switch, No Magic
A two-PC switch lab is simple enough to expose the actual sequence behind a successful ping: addressing, ARP, MAC learning and frame forwarding.
Exit Node or Subnet Router? I Choose Based on Which Traffic Must Move
Both features route packets through another tailnet device, but they solve different problems.
Spanning Tree Stopped Looking Weird Once I Built a Loop on Purpose
STP made more sense after I created the failure it is designed to prevent: a Layer 2 loop with no TTL to save the network.
Tailscale Connectivity and Tailscale SSH Are Different Permissions
A peer can be reachable over the tailnet while an SSH login is correctly denied by another policy layer.
A Network Map Should Show Boundaries Before Services
Topology is most useful when it explains packet movement across gateways, hosts, overlays and ingress first.
Network Reliability Starts by Naming the Failure Domain
Resolve the symptom into DNS, routing, transport, policy, ingress or application before changing configuration.
DNS SRV Made SIP Service Discovery Feel Less Hard-Coded
Using DNS SRV records showed me how SIP clients can discover service hosts and ports without baking one server address into every configuration.
NAT Overload Made More Sense When I Looked at the Translation Table
PAT stopped feeling like a magic Internet-sharing feature once I watched inside local addresses, public translations and transport ports change in the NAT table.
My First Useful Wireshark Capture: ARP Before ICMP
Capturing a simple ping showed that the interesting packet often arrives before ICMP: ARP has to resolve the Layer 2 destination first.
My First OSPF Lab: Watching Routes Appear Instead of Typing Them
OSPF became useful when I compared it directly with the static routes I had been maintaining by hand and watched neighbors and learned routes change with the topology.
VLANs Made Sense When I Stopped Thinking of Them as Extra Networks
A VLAN is first a Layer 2 boundary. IP subnets often map to VLANs, but keeping those two concepts separate makes switching and routing much easier to reason about.
Ping Works but the Browser Does Not: Separating IP, DNS and Applications
Connectivity tests become useful only when each test is tied to a layer: local addressing, routing, DNS resolution, TCP reachability and the application itself.
When SSH Fails, Separate the Failure Layers
"SSH is not working" can mean several different things: the address is wrong, there is no route, nothing is listening on the port, or authentication failed. Restarting the server is not the universal answer.
How I Read Tailscale Status: Direct Paths, Relays and What They Actually Tell Me
A peer marked online is only the start. I also care whether the path is direct, relayed and stable enough for the workload.
My Tailscale Failure Drill for a Home Server: Name, Peer, Policy, Port, Service
I troubleshoot from the network boundary inward so I do not restart a healthy server because one naming or authorization layer failed.
The ACL That Worked Perfectly and Locked Me Out
My first memorable ACL mistake was technically correct: it blocked exactly what I told it to block, including the management traffic I still needed.
How I Use a Tailscale Subnet Router to Reach Devices That Cannot Run Tailscale
The tailnet can reach printers, embedded devices and LAN-only services without installing a Tailscale client on every endpoint.
When One VLAN Would Not Cross the Trunk
A trunk can be up while one VLAN is still broken. That lab pushed me to verify allowed VLANs and operational state instead of assuming the link was simply good or bad.
Static Routing in a Three-Router Lab
A three-router topology is enough to show the most important routing lesson: reachability is directional, and the return path matters just as much as the forward path.
Router-on-a-Stick Was My First Clean Inter-VLAN Routing Lab
One router interface, an 802.1Q trunk and a few subinterfaces were enough to connect separate VLANs without hiding what was happening at Layer 2 and Layer 3.
DHCP Is More Than Automatic IP
DHCP is easier to troubleshoot when treated as a timed client-server exchange that delivers an address plus the parameters a host needs to participate in the network.
When You Widen a Channel, Who Are You Sharing the Spectrum With?
Wider channels suggest higher speed, but nearby networks still occupy the same radio environment. Increasing your own peak capacity and getting stable performance in that environment are not the same design decision.
Working DNS Does Not Mean the Application Is Healthy
Resolving a domain to an address is an important first step, but DNS cannot tell you whether the service is reachable, the certificate matches, or the application itself is working. Successful name resolution is not system health.
Trunk Ports: The Part of VLANs I Initially Misunderstood
A trunk does not merge VLANs. It preserves multiple Layer 2 domains across one physical link by carrying VLAN identity with the frame.