The article investigates why a MySQL server shows a large number of TCP connections in TIME_WAIT state, examines OS and MySQL logs, tests sysctl adjustments, captures network packets to reveal short‑lived client connections, and concludes that using persistent connections can eliminate the issue.
This guide shows how to quickly locate and resolve the “Address already in use” error on Linux and macOS by using netstat, ss, and lsof to list listening ports, interpret their output, and filter results for specific services or ports.
This guide details eight common network problems—from switches that won’t communicate after power‑up to IP address conflicts—explaining their symptoms, root causes, and step‑by‑step solutions for reliable LAN performance.
Learn step‑by‑step how to use netstat, ss, and lsof commands to list listening ports, filter results, and pinpoint the exact process occupying a specific port on Linux and macOS systems.
This article explains the fundamentals of the Domain Name System, how DNS queries work, the role of DNS servers, hierarchical name resolution, record types, and useful command‑line tools such as dig, host, and nslookup, providing clear examples and diagrams for each concept.
This comprehensive guide presents a step‑by‑step approach for diagnosing and fixing everyday network problems, covering fault scope identification, link and configuration checks, common diagnostic methods, detailed case studies, and essential command‑line tools for IT professionals.
This guide explains how to use Windows network troubleshooting commands—ping (including -t, -a, -n, -l options and batch ping), arp (display, add, delete), tracert (basic usage and options), and route (view, add, delete)—to diagnose connectivity issues, resolve IP conflicts, and manage routing tables.
Discover eight practical methods to diagnose and resolve common network connectivity problems, from indicator light failures and speed mismatches to firewall settings, configuration errors, and network storms, helping administrators keep networks running smoothly.
This guide walks you through enabling remote connections in Fiddler, configuring Windows firewall, setting up an iPhone/iPad proxy, capturing HTTP traffic, decrypting HTTPS by installing a trusted certificate, and suppressing server‑verification warnings for seamless mobile web debugging.
After users in Singapore reported inability to resolve the internal domain goofy.app, a systematic investigation revealed that DNSSEC misconfiguration—specifically an incorrect DS record—caused DNS resolution failures globally, while Chinese DNS servers succeeded due to disabled DNSSEC validation, and removing the faulty key resolved the issue.
This article introduces MTR, a powerful network diagnostic tool that combines ping and traceroute, explains how to install it on Windows, Linux, macOS, and Android, demonstrates basic usage commands, and details how to interpret its detailed output to troubleshoot connectivity issues.
After deploying a new cluster, a 502 error appeared when logging in because traffic to Redis’s 7000 port was intercepted by Istio’s sidecar, which routed it to a BlackHoleCluster; the article details the root cause, Istio’s listener and cluster configurations, and three practical remediation methods.
This guide explains how to use the mii-tool command on Linux to view, configure, and troubleshoot network interface negotiation settings, covering syntax, option meanings, and practical examples for setting duplex modes and restoring auto‑negotiation.
Learn how to install and use the powerful MTR tool on Windows, Linux, macOS, and Android, understand its key parameters and output columns, and analyze loss and latency to troubleshoot network connectivity issues effectively.
This guide explains nine common Windows network commands—ping, ipconfig, arp, traceroute, route, nslookup, nbtstat, netstat, and net—detailing their purpose, basic syntax, useful options, and step‑by‑step troubleshooting procedures to help diagnose connectivity issues.
This article details a Cisco Nexus network scenario where two switches use VPC and BFD for link fault detection, explains why BFD neighbor establishment fails due to VPC peer‑gateway causing TTL reduction and MAC rewriting, and presents test results and configuration recommendations to resolve the issue.
This article provides a comprehensive overview of wide area network (WAN) dedicated lines, describing the main circuit types such as SDH, MSTP, ATM, and bare‑fiber, their characteristics, common issues, and practical troubleshooting methods for network engineers.
This article explains the common causes of network packet loss on Linux, walks through the packet transmission process, outlines a layer‑by‑layer troubleshooting framework, and provides concrete commands, configuration tweaks, and hardware checks to identify and resolve loss at the NIC, driver, kernel, IP, TCP, UDP, and application layers.
This article explains the purpose, usage, and return codes of the MHA masterha_secondary_check Perl script, demonstrates how to simulate network failures with iptables, and presents a series of tests that verify the script’s ability to detect master reachability and handle various error conditions.
This article explains the ping command’s purpose and inner workings by detailing the ICMP protocol, its message formats, query and error types, the step‑by‑step packet flow between hosts, and how to enable ICMP in cloud security groups for reliable network testing.
This article explains the Ping utility’s operation by detailing how ICMP echo requests travel through the network stack, how ARP resolves MAC addresses, and how routers and switches forward packets, using a concrete PC‑to‑PC example to illustrate each step.
This comprehensive guide walks you through essential network troubleshooting fundamentals—from OSI and TCP/IP basics and common equipment, to systematic checks of physical links, IP/DNS settings, gateway connectivity, external ping tests, and DNS validation—empowering you to quickly isolate and resolve connectivity issues.
These eight network troubleshooting cases cover issues such as a newly powered switch failing to forward traffic, a 5‑port switch using only four ports, persistent COL‑light collisions, gigabit upgrade instability, slow link speeds from broadcast storms, Windows file‑sharing permission problems, hub‑router connectivity failures, and IP address conflicts, each with analysis and practical solutions.
This article walks through eight typical LAN problems—from switches that stay silent after power‑on to IP address conflicts—explaining their symptoms, root causes, and practical solutions such as enabling PortFast, upgrading cabling, or adjusting STP settings.
A Kubernetes cluster experienced a 45‑second delay on one master when running kubectl get nodes due to missing flannel MAC entries, and the issue was resolved by restarting the canal CNI component to refresh ARP/FDB information.
This article explains how to diagnose Linux server network problems using common tools such as ping, a shell script for LAN scanning, traceroute, nslookup, netstat, and telnet, providing command syntax, example outputs, and guidance on interpreting results.
This guide explains how to use tcpdump on Linux to capture packets, filter by ports, hosts, interfaces or protocols, save output for later analysis, and interpret both human‑readable and hexadecimal dumps, with practical examples and tips for integrating Wireshark.
This guide explains how the Linux ss utility provides comprehensive socket statistics—including TCP, UDP, and Unix sockets—offers powerful filtering by state, address, and port, and demonstrates why it outperforms netstat in speed and resource usage through concrete command examples.
A comprehensive guide lists sixteen indispensable network troubleshooting utilities—from classic commands like Ping and Traceroute to advanced platforms such as Nmap, Wireshark, and OpenVAS—explaining their core functions, typical use cases, and how they help engineers quickly pinpoint and resolve connectivity issues.
This article explains how an unstable response time caused by misconfigured public load balancers and the kernel parameters net.ipv4.tcp_tw_recycle and net.ipv4.tcp_tw_reuse led to frequent monitoring alerts, details the diagnostic steps taken, and provides concrete remediation recommendations.
This guide explains what MTR is, how to install it on various platforms, how to run basic and advanced commands, and how to interpret its detailed output to diagnose network connectivity, packet loss, and latency issues.
This tutorial explains why telnet is insecure, shows how to use nmap to discover open ports, demonstrates telnet commands for checking connectivity on specific ports, interprets the results, and provides a simple Bash script to automate multi‑host port testing.
This guide explains how to use Linux's Netem module via the tc command to emulate network conditions such as delay, loss, duplication, corruption, and packet reordering, providing practical examples and command syntax for effective testing and troubleshooting of network performance issues.
This guide details essential Windows network troubleshooting commands—including ping, ipconfig, arp, traceroute, route, nslookup, netstat, and net—explaining their purposes, syntax, common options, and how to interpret results to diagnose connectivity, DNS, routing, and service issues.
This guide explains what MTR is, how to install it on various platforms, the essential command‑line options, how to interpret its detailed output columns, and practical steps for analyzing and troubleshooting network latency and packet loss using real‑world examples.
Learn how to install and use the powerful MTR network diagnostic tool across Windows, Linux, macOS, and Android, explore its key parameters and options, and interpret its detailed reports to identify packet loss and latency issues for effective network troubleshooting.
This article details a production incident where a Go backend service returned "connection reset by peer" due to exhausted process file descriptors caused by a saturated database connection pool, and describes the step‑by‑step troubleshooting, socket internals, and the eventual fix.
This guide explains the core functions of the ping utility, details each common option such as -t, -a, -n, -l, and -r, demonstrates how to interpret bytes, time and TTL values, and shows practical batch‑ping techniques for network troubleshooting.
This comprehensive guide explains the prerequisite knowledge, core principles, and detailed step‑by‑step procedures—including physical link checks, IP/DNS verification, gateway testing, and DNS diagnostics—to help you systematically diagnose and resolve network connectivity issues.
This guide explains the ping utility’s core functions, interprets its output fields such as bytes, time and TTL, and walks through essential options like -t, -a, -n, -l, -r, plus a batch‑ping technique for scanning entire subnets, helping readers troubleshoot and analyze network performance effectively.
This guide explains the fundamentals of the ping utility, interprets its output fields such as bytes, time and TTL, and walks through advanced switches like -t, -a, -n, -l, -r, plus batch‑ping techniques for comprehensive network diagnostics.
This article walks through a step‑by‑step investigation of missing image loads in a Kubernetes ingress‑backed Nginx service, revealing how TCP SYN and accept queues can overflow, how to inspect kernel counters, and multiple ways to raise the somaxconn and Nginx backlog limits for high‑traffic workloads.
BigBrother is a large‑scale internal network connectivity detection system that uses TCP packet coloring to separate probe traffic from user traffic, supports physical and hybrid cloud scenarios, provides a complete detection framework for rapid fault localization, and has been proven in thousands of host migrations with near‑real‑time alerts.
This article walks through the complete ping process, from setting up a Wireshark capture on two PCs to dissecting ICMP and ARP packets, explaining how ping uses ICMP, how ARP resolves MAC addresses, and why ARP caching affects subsequent ping measurements.
This article presents a case study of an overseas user experiencing video upload failures due to international roaming, explains how Qunar's network detection tool (QunarNDT) was used to diagnose the issue, outlines the findings about domestic routing and timeout, and offers recommendations for improving user experience.
This comprehensive guide walks IT engineers through essential network‑troubleshooting fundamentals—covering OSI/TCP‑IP basics, device roles, common commands, and a systematic, data‑flow‑focused workflow—to quickly pinpoint and resolve connectivity issues in small‑to‑medium enterprise environments.
This article details the discovery, analysis, and resolution of a DPDK bug that caused a zero‑byte IP fragment to fill transmission queues, leading to packet loss and tx‑hang in UCloud's high‑availability ULB4 load balancer, and shares the tools and lessons learned for future debugging.
This guide explains how to use tcpdump for network packet capture, covering basic usage, filtering by interface, host, port, protocol, advanced options, saving captures, and a real‑world troubleshooting scenario with Nginx and Node.js.
A colleague noticed a 15‑second pause between the first two ping replies to pop3.sina.net, prompting a deep dive with tcpdump, strace, and DNS tests that revealed the delay was caused by slow local DNS resolution rather than network latency.
This guide outlines seven typical switch networking problems—from delayed port activation and unused ports to broadcast storms and IP conflicts—explaining their symptoms, root causes, and step‑by‑step solutions for reliable network operation.
This article explains how to diagnose ARP IP‑conflict events on a Huawei AR2240 router, identifies the conflicting MAC address from log entries, and provides step‑by‑step ACL configuration commands to block the offending MAC and restore normal network operation.
This article explains the purpose and inner workings of the ping command, detailing how ICMP echo requests and replies are constructed, transmitted across network layers, and how related tools like traceroute leverage ICMP error messages to diagnose connectivity.
This article examines a real‑world case where a client’s multi‑threaded download caused sudden internet‑outbound bandwidth congestion, details the packet‑level investigation that revealed partial HTTP requests, explains the underlying network traffic analysis architecture, and outlines how automated monitoring and alerts improve operations efficiency.
This guide walks you through essential Windows networking commands—ping, ipconfig, arp, traceroute, route, nslookup, netstat, and net—explaining their syntax, options, and practical use cases for diagnosing connectivity, routing, and configuration issues across local and remote networks.
This article walks through a real‑world incident where an e‑commerce site suffered intermittent outages due to TCP SYN and accept queue overflows, explains the underlying handshake mechanics, shows how kernel and Nginx parameters can be tuned, and provides Python scripts for testing and SYN‑flood simulation.
This article walks through diagnosing a packet‑drop issue in OpenStack Neutron security groups, detailing network architecture, packet capture, iptables chain analysis, rule addition, and validation steps to restore communication between Linux Director and virtual machines.
This comprehensive guide explains what Traceroute is, how it works, its limitations, and advanced techniques such as DNS reverse lookup, handling asymmetric paths, MPLS tunneling, and multi‑path routing, helping network engineers diagnose latency and routing issues more accurately.
After a sudden network outage, the author discovers a Linux virtual machine consuming all upstream bandwidth, uncovers a hidden rootkit through process inspection, and documents step‑by‑step methods—including disabling the NIC, using strace, and forcibly removing malicious binaries—to remediate the infection.
This guide explains why Synology DSM DDNS stops working when an IPSec VPN default route is active, and provides step‑by‑step commands to add a pp0.0 nexthop and static routes for DDNS‑related subnets so the service remains reliable under both VPN and non‑VPN conditions.
This article walks readers through practical techniques for identifying and resolving common “unavailable” app problems—such as white screens, slow loading, or error codes—by using the lightweight Ping&DNS Android tool to check domain names, IP connectivity, DNS resolution, and traceroute data, empowering both novice users and professionals.
This article shares real‑world ops stories about a disputed memory upgrade, explains how Linux calculates usable memory, clarifies common subnet‑mask misunderstandings, and demonstrates why Telnet cannot test UDP ports, highlighting practical troubleshooting lessons for system administrators.
When a data center experiences sluggish network speeds despite connectivity, a systematic approach—checking device CPU usage, reviewing logs, using ping, verifying duplex settings, inspecting cables and modules, monitoring port status, conducting comparative tests, and scanning for malware—can pinpoint and resolve the underlying issues.
This article shares practical game‑operation case studies using tcpdump and Wireshark, explains the underlying principles, and provides actionable tips for network troubleshooting, Wireshark configuration, tcpdump parameters, filters, and Android capture methods.
This article recounts two real‑world operations incidents—a network outage caused by an improperly configured portfast on a trunk link and an NFS failure that crippled an API service—then distills practical lessons on pre‑incident procedures, monitoring, fault handling, recovery, and post‑mortem practices.
A step‑by‑step guide shows how to identify abnormal NIC traffic, locate malicious init scripts and hidden processes, use simple shell scripts and netstat to pinpoint the offending connection, and clean a compromised Linux server to restore normal network performance.
This guide introduces the dig command, explains its basic usage, advanced options, query types, TCP mode, domain defaults, trace functionality, and output simplification, providing practical examples for effective DNS troubleshooting and analysis.
This guide outlines how to diagnose and resolve slow internet on AR routers by checking CPU usage, TCP MSS settings, traffic load, uplink bandwidth, link negotiation, NAT resource limits, and potential network virus infections, providing specific commands and configuration steps for each issue.
This guide explains why IP address conflicts happen, how the arp‑scan tool works to discover duplicate IP assignments on a local network, and provides step‑by‑step commands for installing and running arp‑scan on Ubuntu/Debian and Fedora/CentOS/RedHat systems.
