标签：#Networking

Most VPN troubleshooting goes wrong in the same predictable way: three things get changed at once, and whatever happens next, nothing has been learned. The alternative is boring and effective — check one layer at a time, in an order that rules things out, and write down what each layer shows. One boundary before starting: troubleshooting means finding where a problem lives, not working against anyone's rules. On a network you don't control, or a device your organization manages, the policies in place stay in place. If a managed device is part of the picture, your organization's IT function is part of the troubleshooting — and switching off device security tooling is never a troubleshooting step. 1. Device basics first Start embarrassingly simple, because this layer resolves more than anyone likes to admit. Restart the VPN client. If that changes nothing, restart the device. Confirm that the operating system and the client are updated. An update that has been pending for weeks is a suspect, not background noise. Note whether anything changed around the time the problem started: an update, a new app, different settings, a different location. 2. Does the internet work without the VPN? Disconnect the VPN entirely and test ordinary browsing. If the connection is broken without the VPN, this isn't a VPN problem yet. Solve the underlying connection first, because nothing downstream is testable until this layer works. If the internet is fine without the VPN and wrong with it, you have genuinely narrowed something down. Write that down. 3. Client state: connected to what, exactly? Open the client and look, rather than assume. Is it actually connected, or still trying? Is the right profile selected — the current one, not an older entry left over from a previous setup? Disconnect and reconnect once, deliberately, and watch what the client reports. If multiple profiles have accumulated in the client, that is a finding in itself. Stale entries are a classic source of "it connect

When you open a website, send a message, or watch a YouTube video, many technologies work together in the background. As a beginner in DevOps, understanding these basic networking concepts will help you understand how applications communicate over the internet. **What Is a Protocol? A protocol is a set of rules that devices follow when communicating with each other. Think about two people having a conversation. For communication to be successful, both people must speak the same language and follow simple rules, like taking turns to talk and listening before responding. Computers work the same way. They use protocols to know how to send, receive, and understand information. Without protocols, computers would not be able to communicate with one another. **2. What Is Packet Switching? **Imagine you want to send a large book to a friend. Instead of sending the entire book in one huge package, you divide it into many smaller packages. Each package travels separately and, when they all arrive, your friend puts them back together in the correct order. This is exactly how the internet works. When you visit a website, your data is broken into small pieces called packets. Each packet travels across the internet and is reassembled when it reaches its destination. This process is called packet switching, and it makes internet communication faster and more reliable. **3. What Is an IP Address? **Every house has a unique address that helps delivery drivers know where to deliver packages. Similarly, every device connected to the internet has a unique Internet Protocol (IP) address. An IP address helps the internet know exactly where information should be sent. Without an IP address, websites, computers, and phones would not know where to send or receive data. **4. What Is TCP/IP? **Breaking data into packets is not enough. The packets must also arrive correctly. This is where TCP/IP (Transmission Control Protocol/Internet Protocol) comes in. IP finds the correct destination for ea

Hello, I'm Maneshwar. I'm building git-lrc, a Micro AI code reviewer that runs on every commit. It is...

Every five minutes or so, my entire Windows machine would drop off the network for a few seconds — not just WSL, the whole host. Browser tabs would stall, calls would drop, and it only happened while WSL2 was running. This is the story of finding that, plus the WSL memory-tuning landmines I hit right alongside it. The flapping The symptom was a host-wide network blip on a short, regular interval, correlated tightly with WSL2 being up. The cause: WSL2's default networking mode creates a virtual NAT switch on the Windows side, and on this machine that virtual switch was intermittently conflicting with the real network adapter — enough to cause the whole host to briefly renegotiate its connection. The fix was switching WSL2's networking mode entirely, via .wslconfig (on Windows, not inside the Linux filesystem): [wsl2] networkingMode = mirrored dnsTunneling = true autoProxy = true Mirrored networking makes the WSL2 interface share the host's actual network identity instead of sitting behind a separate virtual NAT switch. You can confirm it actually took effect (rather than just trusting the config file) by checking, from inside WSL after a full restart, that its network interface holds the same IP as the Windows host, that the default route points at the real LAN gateway rather than a private NAT range, and that loopback carries mirrored mode's marker address rather than a 172.x NAT address. If any of those don't match, the setting isn't actually active yet. Worth noting: this requires a reasonably recent WSL version and Windows build. If you're on an older one, mirrored mode may not be available at all. The memory landmines, found the hard way Separately — and this had actually caused full VM crashes, not just hangs, at one point — I'd been carrying a few .wslconfig settings that looked reasonable and were each, individually, a documented source of instability: An explicit kernelCommandLine override. Resizing swap past a few GB, which forces WSL to rebuild its virtual

Hello, I'm Maneshwar. I'm building git-lrc, a Micro AI code reviewer that runs on every commit. It is...

Ethereal Bytecode for the Network: Unlocking XDP's Magic! Hey there, fellow tech enthusiasts! Ever felt like the traditional networking stack in your Linux kernel was a bit… sluggish? Like it was taking the scenic route when you needed it to be a supersonic jet? Well, let me introduce you to a superhero that swoops in and turbocharges your network packet processing: eBPF, specifically in the context of XDP (eXpress Data Path). Forget the days of wrestling with complex kernel modules or praying for better hardware offload. eBPF and XDP offer a revolutionary, in-kernel, safe, and incredibly efficient way to program packet processing at the very edge of your network interface. Think of it as giving your network card a tiny, super-smart brain, capable of making lightning-fast decisions before the packet even bothers the main kernel stack. Pretty cool, right? So, buckle up as we dive deep into the wonderful world of XDP and eBPF, demystifying its power and showing you why it's becoming the darling of modern networking. 1. The "What's the Big Deal?" Section: Introduction to XDP & eBPF Imagine a bustling highway (your network). Traditional networking is like having every car stop at a toll booth, get inspected, and then directed by a central traffic controller. This works, but it can get congested. XDP, on the other hand, is like having intelligent on-ramps where some cars can be instantly identified, rerouted, or even rejected before they even hit the main highway. eBPF (extended Berkeley Packet Filter) is the technology that makes this possible. It's a powerful, sandboxed virtual machine that runs within the Linux kernel. Unlike traditional kernel modules, which can potentially crash your entire system if written incorrectly, eBPF programs are rigorously verified by the kernel for safety and correctness before they are allowed to execute. This means you get the power of kernel-level access without the existential dread of a kernel panic. XDP (eXpress Data Path) leverages

What We Learned Building a Location-Aware Contact Management App Most contact apps are built like digital phonebooks. They store a name, phone number, email, maybe a company name, and then leave the user to remember everything else. That works when someone has 50 people saved. It starts breaking when someone has hundreds or thousands of professional connections from events, client meetings, referrals, business cards, conferences, online communities, and local networking groups. The hard part is not storing people. The hard part is helping users find the right person at the right time. While building a location-aware contact management app, we learned that contact data becomes far more useful when it is connected to context: where someone is, how the user met them, what they discussed, what industry they belong to, and why the relationship matters. Here are some product, UX, and privacy lessons we learned along the way. 1. A contact list is not the same as a usable network A normal contact list answers one basic question: “Do I have this person’s number?” But professionals usually need better questions answered: Who do I know in this city? Who did I meet at that event? Which industry contacts are nearby? Who should I follow up with before visiting this area? Who was that consultant I met last month? Which contacts are important but easy to forget? This is where the product problem becomes interesting. A user may technically have the contact, but still fail to use the relationship because the contact is buried inside a long list. So the first learning was simple: Saving contact details is not enough. The app needs to help users retrieve useful relationships when the context matters. That changed how we thought about the product. We were not just designing a place to store people. We were designing a system to make saved professional relationships easier to act on. 2. Location context changes the experience Most contact managers are list-first. You search by name, comp

I'm the developer of DeviceShelf, a local-first network scanner for desktop, mobile and a headless server edition. Until this week the iOS app only existed on TestFlight. Apple has now approved version 1.3.0, so for the first time you can get it straight from the App Store: DeviceShelf on the App Store . What the app does on a phone The iOS app is not a companion viewer. It runs the same scanning engine as the desktop version: it scans the network you're on, identifies devices (vendor, type, OS fingerprint), shows open ports per device, builds a security report, and raises presence alerts when devices appear or drop off. You can export and share results from the phone. The multicast entitlement iOS restricts multicast traffic for ordinary apps, and SSDP/UPnP discovery depends on it. Apple grants the multicast entitlement on request, and DeviceShelf's App Store build has it. In practice, UPnP/SSDP devices show up in scans on the phone the same way they do on desktop. Licensing The download is free and comes with a trial. Full features unlock in one of two ways: activate a DeviceShelf license, which covers desktop, mobile and the server edition with a single purchase, or use the in-app purchase upgrade on iOS. Pricing is on the website if you want the details. Local-first, on mobile too Scans stay on the device. There is no cloud account, and the AI-assisted device identification is bring-your-own-key; no key is bundled or required. The app is still young, and a phone is an unforgiving place for a network scanner. If it mislabels a device on your network or misses one entirely, I'd genuinely like to hear about it. Website: deviceshelf.app

local + echo = locho Sometimes you don't need access to a machine. You don't need a shell. You...

Introduction Linux is the backbone of modern infrastructure. From cloud servers and firewalls to SIEM platforms and security tools, Linux runs silently behind most enterprise environments. For a Security Operations Center (SOC) analyst, understanding Linux is not optional — it is a core skill. One of the most critical security mechanisms in Linux is its file permission and ownership model. Attackers abuse permissions to execute malware, hide persistence, escalate privileges, and erase evidence. SOC analysts rely on permission analysis to detect anomalies, investigate incidents, and build accurate timelines. Become a Medium member This article covers Linux File Permissions and Ownership in deep detail from a SOC analyst’s perspective. It is designed to take you from absolute beginner to security-aware professional, with real-world examples, attack scenarios, and investigation insights. Why Linux File Permissions Matter in SOC In SOC operations, analysts constantly deal with: Authentication logs System logs Application logs Scripts and binaries Configuration files Evidence files during incident response Every one of these objects is protected by Linux permissions. From a SOC perspective: Incorrect permissions = security risk Permission changes = potential indicator of compromise Executable permissions = possible malware Ownership changes = possible log tampering Understanding permissions allows SOC analysts to: Detect unauthorized access Identify privilege escalation Spot malware execution Preserve forensic evidence Reconstruct attacker activity Understanding Linux File Permission Basics Linux follows a Discretionary Access Control (DAC) model. This means: The owner of a file controls who can access it Permissions define what actions are allowed Every file and directory in Linux has: A type Permissions An owner (user) A group These attributes decide: Who can read the file Who can modify it Who can execute it Viewing Permissions Using ls -l The most common command to i

Week 0 of my DevOps Micro Internship was about the foundations—the parts of the internet you use every day without thinking about them. The exercise that made it click was a simple scenario: a friend launches an online bookstore called EpicReads, hosted on a server in Finland, and asks how people anywhere in the world can open it. The answer is a short chain of technologies working together. The Chain of Technologies Packet Switching: When someone opens the site, their request does not travel as one big lump. Packet switching breaks the data into small packets that each take the best available path across the network and get reassembled at the other end. This is what keeps the internet fast and resilient even across continents. IP Addresses & TCP/IP: Every device on the way has a unique IP address, like a postal address, so the user's computer and the Finland server can actually find each other. The TCP/IP suite runs the conversation: IP handles addressing and routing, while TCP makes sure the packets arrive complete and in the right order, asking again for anything that went missing. HTTP & HTTPS: On top of that sits HTTP and HTTPS, which define how the browser and server actually exchange the web pages. HTTPS adds encryption, so a customer's details and payment stay private. DNS: The last piece is DNS. Nobody wants to type an IP address, so DNS acts as the internet's phonebook, translating epicreads.com into the server's IP. To point a domain at an IPv4 address, you use an A record . The Biggest Takeaway The biggest lesson for me was not any single term. It was seeing how these layers hand off to each other so cleanly that the whole thing feels instant to a user. Understanding that chain is the groundwork for everything else in DevOps, because once you know how a request really travels, troubleshooting stops being guesswork. P.S. This post is part of the DevOps Micro Internship with Agentic AI Cohort 3 by Pravin Mishra. You can begin your DevOps journey by joining

Today I'm excited to launch RegionCheck , a tool for testing, monitoring, and debugging endpoints from cloud regions around the world. The idea is simple - test an endpoint's DNS and HTTP connectivity and response from a defined set of cloud regions. Whether you're troubleshooting an API, validating a deployment, checking DNS propagation, or investigating latency, seeing the results from multiple cloud regions can quickly reveal issues that aren't obvious from your own machine. What is RegionCheck? RegionCheck lets you run endpoint checks from AWS, Azure, and Google Cloud regions without provisioning infrastructure or maintaining test instances. Current capabilities include: HTTP endpoint testing DNS lookups TLS certificate validation Continuous monitoring with alerts Side-by-side comparison across cloud providers and regions Shareable result pages for collaboration API/MCP access for automation and agents Why I built it When debugging production issues, I often wanted to answer questions like: Is DNS returning the same result everywhere? Or is geo-DNS returning the results intended? Is TLS certificate propagation for my CDN working as intended? Is one region significantly slower than another? Is my CDN caching working as expected? Are my geo-HTTP redirects working as intended? (For some interesting examples try www.yahoo.com and www.cnn.com in non-US regions) There are many tools that exist that provide these answers, but nothing that answers all of these questions in one place. That's what RegionCheck aims to provide. Who it's for RegionCheck is designed for engineers who work with cloud infrastructure, including: DevOps engineers Site Reliability Engineers (SREs) Platform engineers Backend developers Anyone who likes to take a peek at backend infrastructure Try it out RegionCheck is available at https://regioncheck.io You can run free checks directly from the website; or create an account to access monitoring, alerting, the API, and additional features. I'd love

I have been working on building a private, secure network accessible from anywhere. The goal was to connect my mobile phone and my local development laptop using a WireGuard VPN , hosting the central gateway on a free-tier Google Cloud Platform (GCP) e2-micro instance. I wanted to access my self-hosted services, specifically my Docker-hosted Open WebUI , running on my local home Wi-Fi connected laptop, directly from my phone using mobile data. It sounded straightforward. But if you read my other from scratch journeys, you might have already guessed, it was not. The Setup My architectural plan was a simple hub-and-spoke topology: The Hub: GCP VM ( 10.66.66.1 ) with IPv4 forwarding enabled. Spoke 1 (My Phone): 10.66.66.2 Spoke 2 (My Laptop): 10.66.66.3 I wrote my server configurations, enabled IP forwarding ( net.ipv4.ip_forward=1 ), wrote the iptables rules to allow forwarding between peers, and started the interfaces. Then came the moment of truth. I tried to bring up the tunnel. Absolute silence. No packet moving from anywhere. Hurdle 1: The Classic Cloud NAT Trap (Internal vs. Public IP) Before I could even worry about routing packets between my phone and laptop, I couldn't even get them to handshake with the GCP server. Like many of us do when working inside a VM, I had run ip addr on the GCP instance to grab its IP address for my client configurations. I set up the WireGuard peers to point to this IP. Nothing connected. The Culprit: GCP (and AWS) operates on a 1:1 NAT mapping. The virtual network interface inside your VM only sees and binds to a private, internal cloud IP (e.g., 10.128.0.x ). The public IP assigned to your instance lives outside the VM at the VPC gateway level. By putting the internal IP into my client configs, my phone and laptop were trying to connect to a private address that didn't exist on their local networks. The Fix: I had to swap the internal IP in the client configurations with the GCP Ephemeral/Static External IP . Once the handshake

You've probably registered a domain with Route53 or another popular registrar. You pick something...

What Is My IP Address? IPv4 vs IPv6 Explained for Developers If you've ever debugged a CORS error, set up an IP allowlist, or wondered why req.ip returned something weird in your Express logs, you've run into the same question from a different angle: what actually is an IP address, and which one is "mine"? fastestchecker.com This post breaks down IPv4 vs IPv6, public vs private IPs, and how to reliably detect a user's IP address in your own code — plus a fast way to check yours right now. fastestchecker.com TL;DR IPv4 addresses look like 192.168.1.1 — four numbers, 0-255, separated by dots. There are about 4.3 billion of them, and we've run out. IPv6 addresses look like 2001:0db8:85a3::8a2e:0370:7334 — a much larger address space designed to replace IPv4. Your device usually has a private IP (local network) and shares a public IP (internet-facing) with everyone else on your router. You can check your current public IP instantly with a tool like FastestChecker's IP Checker — useful for confirming what your server or API actually sees. > IPv4 vs IPv6 : What's the Actual Difference IPv4 IPv4 has been the backbone of the internet since the 1980s. It's a 32-bit address, which caps the total number of unique addresses at roughly 4.3 billion. Given how many devices are online today, that pool has been effectively exhausted for years — which is why NAT (Network Address Translation) exists: it lets an entire household or office share one public IPv4 address. Example IPv4: 203.0.113.42 IPv6 IPv6 uses 128-bit addresses, which gives it an address space so large it's effectively unlimited for practical purposes (2^128 addresses). It was designed specifically to solve IPv4 exhaustion, and adoption has been climbing steadily — most major cloud providers and mobile carriers support it by default now. ** Example IPv6:** 2001:0db8:85a3:0000:0000:8a2e:0370:7334 Quick Comparison IPv4IPv6Address length32-bit128-bitFormatDotted decimal (192.168.1.1)Hexadecimal, colon-separatedTotal addre

Native XDP and generic SKB-mode XDP are not the same thing in practice. The same BPF program can pass the verifier and still behave differently depending on which mode the kernel uses, this could be a different verdict, different frame bytes, or different metadata. This post ships three things: an open differential test harness, a fixed eleven-packet corpus, and a simple way to classify the differences it finds. A tagged release lets anyone reproduce the virtio/veth baseline on Linux 6.8. The operational risk is straightforward. A firewall or rate-limiter validated only under native XDP can fall back to generic mode on an unsupported driver, a veth port, or after a reload. You keep the same bytecode, but behaviour can change, often without a clear error line. What this release includes: A harness loop: corpus → inject on the RX path → native vs generic sweep → xdpdump capture → compare.py manifest, comparing both the captured frame bytes and the XDP verdict ( PASS / DROP / TX / REDIRECT ). A deterministic corpus with eleven embedded test IDs ( 0xA001 – 0xA005 , 0xA007 – 0xA00C ; 0xA006 is intentionally omitted as a reserved gap in the generator). An operational divergence taxonomy (Class A / B / C). A virtio/veth smoke gate on Linux 6.8; now gating on frame bytes and verdict agreement that shows the full path is reproducible end to end. Scope for this post: native vs generic XDP on the virtio_vm profile only (five BPF programs, pinned manifests). This is part 1 of 2; it establishes the harness and an instrument-validity baseline; a follow-up post covers bare-metal divergence results. Physical NIC results are not part of this baseline. Ordinary conformance checks stop at “did the program load?” Differential testing asks a sharper question: given identical input packets, do the backends produce the same observable outcome at the hook? Background: native vs generic XDP Both modes load the same BPF object. They diverge at the hook point and in how the packet is represen

I released php-quic 1.0.0, a PHP extension that gives you raw QUIC transport with first-class access to streams. It links against the same OpenSSL that PHP already links against, and that is the whole trick. Why This Was Awkward Before QUIC is not a protocol you bolt on in userland. It is TLS 1.3, congestion control, loss recovery, and stream multiplexing, all riding on UDP, and all of it has to be right before you can send a single useful byte. You could get there from PHP if you were willing to bind to a foreign QUIC library like ngtcp2 or quiche through FFI. That works, but now your PHP app carries a second TLS stack, a second set of CVEs to track, a build story that involves Rust, and a version matrix that has nothing to do with the one your distro maintains. For a language whose entire deployment story is "the package manager handles it," that is a lot of rope. What Changed OpenSSL 3.5 shipped a native QUIC stack. Client and server, in the library PHP is already built against. That reframes the problem. The extension is no longer "embed a QUIC implementation into PHP." It is "expose the QUIC that is already sitting there." No new TLS stack, no FFI layer, no Rust toolchain in your build. If your OpenSSL is patched, your QUIC is patched. The requirements fall out of that directly: PHP 8.4 or newer (8.5 on Windows), NTS or ZTS OpenSSL 3.5.0 or newer, built with QUIC support Transport, Not HTTP/3 The thing I most wanted to avoid was shipping an HTTP/3 client and calling it a QUIC library. QUIC is a transport. HTTP/3 is one protocol that runs on it, and it is not the interesting one for everybody. DNS-over-QUIC runs on it. So does anything you want to invent that needs multiplexed, ordered, loss-recovered streams without head-of-line blocking across them. So php-quic hands you connections and streams, and stays out of the framing business. If you want HTTP/3, you build HEADERS frames and QPACK on top of it, and the README has a worked example. If you want something

Chipset makers and router manufacturers are talking about Wi-Fi 8, but what is the new standard, and when will it arrive?

This is Part 1 of a 5-part series on Cisco EEM. We start here with the fundamentals and a few working applets, then build toward self-healing networks, automated diagnostics, compliance guardrails, and a complete real-world deployment. Ask ten network engineers what they use EEM for, and nine will say the same thing: "Oh, I have an applet that auto-recovers err-disabled ports." Then they never touch it again. That's a shame, because Embedded Event Manager is one of the most capable tools already sitting inside every Cisco IOS device you own — and almost nobody uses more than 1% of it. It's a full automation engine that lives on the box . No external server. No API gateway. No orchestration platform. Just the router or switch, watching itself, ready to react the instant something happens — even if the WAN is cut, the NMS is down, and it's three in the morning. This series is about using that other 99%. By the end you'll have a toolkit of applets you can deploy and, more importantly, a way of thinking about on-box automation. But we start at the foundation: what EEM actually is, how it's put together, and why "on the box" is a bigger deal than it sounds. What EEM actually is Embedded Event Manager is an event-driven automation framework built into Cisco IOS, IOS-XE, and NX-OS. Strip away the jargon and it's a very simple idea: When something happens, do something about it — automatically, on the device itself. That "something happens" is an event . That "do something" is one or more actions . Bundle an event with its actions and you have an applet — the basic unit of EEM. That's the whole model. The power comes from how many different things can be an event , and how much an action can do. Events EEM can watch for include: A syslog message matching a pattern (an interface flapping, an HSRP state change, a config being saved). An SNMP OID crossing a threshold (CPU over 85%, a power supply going absent, temperature rising). A CLI command being entered (someone typing wr

Modern applications, especially AI agents and distributed systems, need more than logs to understand what is happening. That's why I explored SigNoz, an open-source observability platform built on OpenTelemetry. Setting up SigNoz with Docker was simple. After connecting a sample application, I could view logs, metrics, and traces from a single dashboard within minutes. My favorite feature is distributed tracing. Instead of guessing where requests slow down or fail, SigNoz clearly shows the complete request journey across services, making debugging much easier. The built-in dashboards provide valuable insights into CPU usage, memory, request latency, throughput, and error rates. Having centralized logs alongside metrics and traces saves time by eliminating the need to switch between multiple tools. I also liked the alerting feature, which helps detect issues before they affect users. For AI applications, observability is essential. AI agents make multiple API calls, use tools, and perform complex workflows. SigNoz makes it easier to understand each step, identify failures, measure latency, and optimize performance. Overall, my experience with SigNoz was excellent. It combines logs, metrics, traces, dashboards, and alerts into one intuitive platform. Among all its features, distributed tracing impressed me the most because it provides deep visibility into application behavior and simplifies troubleshooting. I'm excited to use SigNoz in future AI and cloud-native projects.