How Linux Resolves Names: resolv.conf, systemd-resolved, nsswitch
dig tests a nameserver. getent tests name resolution. The full path from nsswitch.conf to the wire, with the resolver deliberately broken and fixed.
Troubleshooting
Broken networks, reproduced on purpose. Articles tagged Troubleshooting walk a fault from symptom to root cause using show commands, captures and a repeatable method.
Latest posts — page 2
host: The Fastest DNS Lookup Tool
One name in, one line out, and the only exit status of the three you can trust. Plus the timing test that complicates the fastest claim.
nslookup: Quick DNS Queries That Still Matter
Declared deprecated for twenty years and still on every machine. What it does well, where it will mislead you, and the debug flag nobody uses.
dig: The Complete DNS Query Guide
Read the status line first. Flags, sections, TTLs, delegation traces and DNSSEC, all against a real authoritative server in the lab.
netstat vs ss: Why It Was Replaced and How to Switch
The full command map, wall clock timings on a host holding ten thousand sockets, and the surprise result when you add process lookup.
ss: The Modern Socket Statistics Tool
Queue columns that tell you which end stopped working, filters that run in the kernel, and the TCP internals nothing else on the box will give you.
tracepath and Path MTU Discovery on Linux
Small things work and big things hang. One unprivileged command finds the narrow link, and one iptables rule shows what a black hole looks like.
mtr: Continuous Path Monitoring on Linux
Loss and latency per hop against a link with 12 percent loss injected on purpose, and the one rule that separates real loss from cosmetic loss.
traceroute: UDP, ICMP, and TCP Modes Explained
Three probe types down one four hop path, the packets on the wire for each, and the ICMP rate limit that makes a perfect path look broken.
ethtool: Link Speed, Duplex, Offloads, NIC Stats
The driver layer below the kernel: link settings, offloads that make packet captures disagree with the wire, rings, and where host-side drops show up.
Native VLAN Mismatch: Read the CDP Log, Fix the Trunk
%CDP-4-NATIVE_VLAN_MISMATCH hands you both interfaces and both native VLANs in one line. The real damage is underneath it: untagged frames get re-homed at the trunk boundary and two VLANs quietly become one. Captured live on IOS XE 17.18.2 in CML.
Errdisable Recovery on Cisco: Every Cause and How to Bring the Port Back
An err-disabled port stays down forever by default, because nothing auto-recovers until you arm it. The full cause list from IOS XE 17.18.2, how to identify which one fired in ten seconds, and the captured proof that auto-recovery is a retry loop rather than a fix.