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Understanding DNS is fundamental to understanding how the internet works, whether you're a developer, system administrator, or simply curious about the technology that powers your daily web browsing.</p> <p>In this comprehensive guide, we'll demystify DNS, explore how it works, and equip you with practical knowledge to troubleshoot common issues. By the end, you'll understand why DNS is often called the internet's most critical infrastructure.</p> <h2 id="what-is-dns">What Is DNS?</h2> <p>DNS (Domain Name System) is like the internet's phone book. It translates human-readable domain names (like <code>google.com</code>) into IP addresses (like <code>142.250.80.46</code>) that computers use to communicate with each other. Without DNS, you'd have to memorize numerical IP addresses for every website you want to visit.</p> <p>Imagine trying to remember that Facebook is <code>157.240.241.35</code> or that Amazon is <code>205.251.242.103</code>. It would be nearly impossible to navigate the modern internet. DNS solves this problem by creating a distributed database that maps memorable names to machine-readable addresses.</p> <p>The DNS system was invented in 1983 by Paul Mockapetris and has become one of the most critical components of internet infrastructure. It handles billions of queries every day, operating as a distributed, hierarchical system that's both resilient and scalable.</p> <div style="background:var(--bg-secondary);border:1px solid var(--border);border-radius:8px;padding:1.25rem;margin:1.5rem 0"> <p style="margin:0"><strong>Quick tip:</strong> DNS doesn't just translate domain names to IP addresses. It also handles email routing, service discovery, and various other internet protocols. It's far more versatile than most people realize.</p> </div> <h2 id="how-dns-works">How DNS Works: Step by Step</h2> <p>When you type a URL into your browser, a sophisticated chain of events unfolds in milliseconds. Here's the complete DNS resolution process:</p> <ol> <li><strong>Browser cache check:</strong> Your browser first checks its own DNS cache to see if it recently looked up this domain. Modern browsers cache DNS records for performance.</li> <li><strong>Operating system cache:</strong> If the browser cache misses, your operating system checks its DNS cache. Both Windows and macOS maintain their own DNS caches.</li> <li><strong>Router cache:</strong> Your home or office router may also cache DNS queries to reduce network traffic and improve response times.</li> <li><strong>Recursive resolver query:</strong> If none of the caches have the answer, your computer contacts a DNS recursive resolver (usually provided by your ISP or a public DNS service like Google or Cloudflare).</li> <li><strong>Root nameserver query:</strong> The recursive resolver asks one of the 13 root nameserver clusters (labeled A through M) where to find information about the top-level domain (TLD) like <code>.com</code>, <code>.org</code>, or <code>.net</code>.</li> <li><strong>TLD nameserver query:</strong> The root server responds with the address of the TLD nameserver. The resolver then queries the TLD nameserver for the authoritative nameserver of the specific domain.</li> <li><strong>Authoritative nameserver query:</strong> The TLD server directs the resolver to the domain's authoritative nameserver, which holds the actual DNS records for that domain.</li> <li><strong>Final response:</strong> The authoritative nameserver returns the IP address. The resolver caches this information and sends it back to your computer.</li> <li><strong>Connection established:</strong> Your browser now has the IP address and can establish a connection to the web server.</li> </ol> <p>This entire process typically takes between 20-100 milliseconds, though it can be much faster with caching. The distributed nature of DNS means that even if one server fails, the system continues to function.</p> <div style="background:var(--bg-secondary);border:1px solid var(--border);border-radius:8px;padding:1.25rem;margin:1.5rem 0"> <p style="margin:0"><strong>Pro tip:</strong> You can see this process in action using the <code>dig</code> command on Linux/Mac or <code>nslookup</code> on Windows. Try running <code>dig +trace google.com</code> to watch the full DNS resolution path.</p> </div> <h2 id="dns-hierarchy">Understanding the DNS Hierarchy</h2> <p>DNS operates as a hierarchical, tree-like structure. Understanding this hierarchy is crucial to grasping how DNS scales to handle billions of domains.</p> <h3>The Root Level</h3> <p>At the top of the DNS hierarchy are the root servers. There are 13 root server identifiers (A-Root through M-Root), though each identifier represents a cluster of servers distributed globally using anycast routing. These root servers are operated by different organizations including Verisign, NASA, the University of Maryland, and ICANN.</p> <p>The root servers don't know the IP address of every domain. Instead, they know where to find the authoritative servers for each top-level domain.</p> <h3>Top-Level Domains (TLDs)</h3> <p>TLDs are the extensions you see at the end of domain names. They fall into several categories:</p> <ul> <li><strong>Generic TLDs (gTLDs):</strong> <code>.com</code>, <code>.org</code>, <code>.net</code>, <code>.info</code>, <code>.biz</code></li> <li><strong>Country Code TLDs (ccTLDs):</strong> <code>.uk</code>, <code>.de</code>, <code>.jp</code>, <code>.ca</code>, <code>.au</code></li> <li><strong>Sponsored TLDs:</strong> <code>.edu</code>, <code>.gov</code>, <code>.mil</code> (restricted use)</li> <li><strong>New gTLDs:</strong> <code>.app</code>, <code>.dev</code>, <code>.blog</code>, <code>.tech</code> (introduced after 2013)</li> </ul> <p>Each TLD has its own set of nameservers managed by a registry organization. For example, Verisign manages <code>.com</code> and <code>.net</code>, while Public Interest Registry manages <code>.org</code>.</p> <h3>Second-Level Domains and Subdomains</h3> <p>The second-level domain is what most people think of as their "domain name" — the part you register with a domain registrar. For <code>example.com</code>, "example" is the second-level domain.</p> <p>Subdomains are additional levels beneath the second-level domain, like <code>blog.example.com</code> or <code>mail.example.com</code>. You can create unlimited subdomains once you own a second-level domain.</p> <h2 id="dns-record-types">DNS Record Types Explained</h2> <p>DNS records are instructions stored in authoritative DNS servers. Each record type serves a specific purpose. Here are the most important ones you'll encounter:</p> <table style="width:100%;border-collapse:collapse;margin:1.5rem 0"> <thead> <tr style="background:var(--bg-secondary);border-bottom:2px solid var(--border)"> <th style="padding:0.75rem;text-align:left;border:1px solid var(--border)">Record Type</th> <th style="padding:0.75rem;text-align:left;border:1px solid var(--border)">Purpose</th> <th style="padding:0.75rem;text-align:left;border:1px solid var(--border)">Example</th> </tr> </thead> <tbody> <tr> <td style="padding:0.75rem;border:1px solid var(--border)"><strong>A</strong></td> <td style="padding:0.75rem;border:1px solid var(--border)">Maps domain to IPv4 address</td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>example.com → 192.0.2.1</code></td> </tr> <tr style="background:var(--bg-secondary)"> <td style="padding:0.75rem;border:1px solid var(--border)"><strong>AAAA</strong></td> <td style="padding:0.75rem;border:1px solid var(--border)">Maps domain to IPv6 address</td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>example.com → 2001:0db8::1</code></td> </tr> <tr> <td style="padding:0.75rem;border:1px solid var(--border)"><strong>CNAME</strong></td> <td style="padding:0.75rem;border:1px solid var(--border)">Creates an alias to another domain</td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>www.example.com → example.com</code></td> </tr> <tr style="background:var(--bg-secondary)"> <td style="padding:0.75rem;border:1px solid var(--border)"><strong>MX</strong></td> <td style="padding:0.75rem;border:1px solid var(--border)">Specifies mail servers</td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>10 mail.example.com</code></td> </tr> <tr> <td style="padding:0.75rem;border:1px solid var(--border)"><strong>TXT</strong></td> <td style="padding:0.75rem;border:1px solid var(--border)">Holds arbitrary text data</td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>v=spf1 include:_spf.google.com ~all</code></td> </tr> <tr style="background:var(--bg-secondary)"> <td style="padding:0.75rem;border:1px solid var(--border)"><strong>NS</strong></td> <td style="padding:0.75rem;border:1px solid var(--border)">Specifies authoritative nameservers</td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>ns1.example.com</code></td> </tr> <tr> <td style="padding:0.75rem;border:1px solid var(--border)"><strong>SOA</strong></td> <td style="padding:0.75rem;border:1px solid var(--border)">Start of Authority (zone information)</td> <td style="padding:0.75rem;border:1px solid var(--border)">Contains admin email, serial number, timers</td> </tr> <tr style="background:var(--bg-secondary)"> <td style="padding:0.75rem;border:1px solid var(--border)"><strong>PTR</strong></td> <td style="padding:0.75rem;border:1px solid var(--border)">Reverse DNS lookup (IP to domain)</td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>192.0.2.1 → example.com</code></td> </tr> <tr> <td style="padding:0.75rem;border:1px solid var(--border)"><strong>SRV</strong></td> <td style="padding:0.75rem;border:1px solid var(--border)">Service location record</td> <td style="padding:0.75rem;border:1px solid var(--border)">Used for SIP, XMPP, and other protocols</td> </tr> </tbody> </table> <h3>A and AAAA Records</h3> <p>These are the most fundamental DNS records. An A record maps a domain name to an IPv4 address (the traditional 32-bit format like <code>192.0.2.1</code>). An AAAA record (pronounced "quad-A") maps to an IPv6 address (the newer 128-bit format like <code>2001:0db8::1</code>).</p> <p>Most domains have both A and AAAA records to support both IPv4 and IPv6 connectivity. When you visit a website, your browser will typically prefer IPv6 if available.</p> <h3>CNAME Records</h3> <p>CNAME (Canonical Name) records create aliases. They're commonly used to point <code>www.example.com</code> to <code>example.com</code>, or to point multiple subdomains to the same destination. However, CNAME records have an important limitation: you cannot use a CNAME at the root level of your domain (the apex).</p> <p>For example, this is valid: <code>www.example.com CNAME example.com</code>, but you cannot make <code>example.com</code> itself a CNAME.</p> <h3>MX Records</h3> <p>MX (Mail Exchange) records tell email servers where to deliver mail for your domain. They include a priority number — lower numbers have higher priority. This allows you to set up backup mail servers:</p> <pre><code>example.com. MX 10 mail1.example.com. example.com. MX 20 mail2.example.com.</code></pre> <p>If <code>mail1.example.com</code> is unavailable, email will be delivered to <code>mail2.example.com</code> instead.</p> <h3>TXT Records</h3> <p>TXT records hold arbitrary text and are incredibly versatile. Common uses include:</p> <ul> <li><strong>SPF records:</strong> Specify which mail servers can send email on behalf of your domain</li> <li><strong>DKIM records:</strong> Provide cryptographic signatures for email authentication</li> <li><strong>DMARC records:</strong> Define email authentication policies</li> <li><strong>Domain verification:</strong> Prove domain ownership to services like Google Workspace or Microsoft 365</li> <li><strong>Site verification:</strong> Verify ownership for search engines and other platforms</li> </ul> <h2 id="dns-caching">DNS Caching and TTL</h2> <p>DNS caching is crucial for performance and reducing load on DNS servers. Every DNS record has a TTL (Time To Live) value, measured in seconds, that tells resolvers how long they can cache the record before checking for updates.</p> <p>For example, a TTL of 3600 means the record can be cached for one hour. After that time expires, the resolver must query the authoritative nameserver again for fresh data.</p> <h3>Caching Layers</h3> <p>DNS responses are cached at multiple levels:</p> <ul> <li><strong>Browser cache:</strong> Typically 60 seconds to a few minutes</li> <li><strong>Operating system cache:</strong> Varies by OS, often several minutes to hours</li> <li><strong>Router cache:</strong> Depends on router configuration</li> <li><strong>ISP resolver cache:</strong> Respects the TTL value from authoritative servers</li> </ul> <p>This multi-layer caching dramatically improves performance. Popular websites like Google or Facebook are cached everywhere, so most DNS queries for them never reach the authoritative nameservers.</p> <div style="background:var(--bg-secondary);border:1px solid var(--border);border-radius:8px;padding:1.25rem;margin:1.5rem 0"> <p style="margin:0"><strong>Pro tip:</strong> When planning DNS changes, lower your TTL values 24-48 hours in advance. Set them to 300 (5 minutes) so that when you make the actual change, it propagates quickly. After the change is complete and stable, raise the TTL back to 3600 or higher.</p> </div> <h3>Negative Caching</h3> <p>DNS also caches negative responses (when a domain doesn't exist). This prevents repeated queries for non-existent domains. The negative cache TTL is specified in the SOA record and is typically shorter than positive cache times.</p> <h2 id="public-dns-servers">Public DNS Servers</h2> <p>While your ISP provides DNS servers by default, many users switch to public DNS servers for better performance, privacy, or additional features. Here are the most popular options:</p> <table style="width:100%;border-collapse:collapse;margin:1.5rem 0"> <thead> <tr style="background:var(--bg-secondary);border-bottom:2px solid var(--border)"> <th style="padding:0.75rem;text-align:left;border:1px solid var(--border)">Provider</th> <th style="padding:0.75rem;text-align:left;border:1px solid var(--border)">Primary IPv4</th> <th style="padding:0.75rem;text-align:left;border:1px solid var(--border)">Secondary IPv4</th> <th style="padding:0.75rem;text-align:left;border:1px solid var(--border)">Key Features</th> </tr> </thead> <tbody> <tr> <td style="padding:0.75rem;border:1px solid var(--border)"><strong>Google Public DNS</strong></td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>8.8.8.8</code></td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>8.8.4.4</code></td> <td style="padding:0.75rem;border:1px solid var(--border)">Fast, reliable, global infrastructure</td> </tr> <tr style="background:var(--bg-secondary)"> <td style="padding:0.75rem;border:1px solid var(--border)"><strong>Cloudflare</strong></td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>1.1.1.1</code></td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>1.0.0.1</code></td> <td style="padding:0.75rem;border:1px solid var(--border)">Privacy-focused, fastest average response</td> </tr> <tr> <td style="padding:0.75rem;border:1px solid var(--border)"><strong>Quad9</strong></td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>9.9.9.9</code></td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>149.112.112.112</code></td> <td style="padding:0.75rem;border:1px solid var(--border)">Security-focused, blocks malicious domains</td> </tr> <tr style="background:var(--bg-secondary)"> <td style="padding:0.75rem;border:1px solid var(--border)"><strong>OpenDNS</strong></td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>208.67.222.222</code></td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>208.67.220.220</code></td> <td style="padding:0.75rem;border:1px solid var(--border)">Content filtering, parental controls</td> </tr> <tr> <td style="padding:0.75rem;border:1px solid var(--border)"><strong>AdGuard DNS</strong></td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>94.140.14.14</code></td> <td style="padding:0.75rem;border:1px solid var(--border)"><code>94.140.15.15</code></td> <td style="padding:0.75rem;border:1px solid var(--border)">Ad blocking, tracker blocking</td> </tr> </tbody> </table> <h3>Why Switch DNS Servers?</h3> <p>There are several compelling reasons to use public DNS servers instead of your ISP's defaults:</p> <ul> <li><strong>Performance:</strong> Public DNS providers often have better infrastructure and more global points of presence than smaller ISPs</li> <li><strong>Reliability:</strong> Major providers have redundant systems and better uptime</li> <li><strong>Privacy:</strong> Some ISPs log DNS queries or inject ads; privacy-focused providers don't</li> <li><strong>Security:</strong> Services like Quad9 block known malicious domains</li> <li><strong>Content filtering:</strong> OpenDNS offers parental controls and customizable filtering</li> <li><strong>Bypassing restrictions:</strong> Some ISPs use DNS to block certain websites</li> </ul> <h3>DNS over HTTPS (DoH) and DNS over TLS (DoT)</h3> <p>Traditional DNS queries are sent in plain text, which means your ISP or anyone monitoring your network can see which websites you're visiting. DNS over HTTPS (DoH) and DNS over TLS (DoT) encrypt DNS queries, providing privacy and preventing tampering.</p> <p>Most modern browsers support DoH, and you can enable it in settings. Cloudflare's <code>1.1.1.1</code> and Google's <code>8.8.8.8</code> both support encrypted DNS protocols.</p> <h2 id="dns-security">DNS Security Concerns</h2> <p>DNS was designed in a more trusting era of the internet, and security wasn't a primary concern. This has led to several vulnerabilities that attackers exploit.</p> <h3>DNS Spoofing and Cache Poisoning</h3> <p>DNS cache poisoning occurs when an attacker injects false DNS data into a resolver's cache. When users query for a legitimate domain, they receive the attacker's malicious IP address instead. This can redirect users to phishing sites or intercept sensitive data.</p> <p>DNSSEC (DNS Security Extensions) helps prevent this by adding cryptographic signatures to DNS records, allowing resolvers to verify that responses haven't been tampered with.</p> <h3>DDoS Attacks</h3> <p>DNS servers are frequent targets of Distributed Denial of Service (DDoS) attacks. In 2016, the Dyn DNS attack took down major websites including Twitter, Netflix, and Reddit by overwhelming Dyn's DNS infrastructure with traffic.</p> <p>DNS amplification attacks are particularly dangerous. Attackers send small queries with a spoofed source address, causing DNS servers to send large responses to the victim, amplifying the attack traffic by 50x or more.</p> <h3>DNS Hijacking</h3> <p>DNS hijacking occurs when attackers gain control of a domain's DNS settings, either by compromising the domain registrar account or exploiting vulnerabilities in DNS infrastructure. This allows them to redirect all traffic to malicious servers.</p> <p>To protect against DNS hijacking:</p> <ul> <li>Enable two-factor authentication on your domain registrar account</li> <li>Use registry lock services for critical domains</li> <li>Monitor your DNS records for unauthorized changes</li> <li>Use a reputable DNS hosting provider with strong security</li> </ul> <h3>DNS Tunneling</h3> <p>DNS tunneling is a technique where attackers encode data within DNS queries and responses to exfiltrate information or establish command-and-control channels. Because DNS traffic is rarely blocked, it's an attractive vector for bypassing security controls.</p> <h2 id="common-dns-issues">Common DNS Issues</h2> <p>DNS problems are among the most frequent causes of website and email outages. Understanding common issues helps you diagnose and resolve them quickly.</p> <h3>DNS Propagation Delays</h3> <p>When you change DNS records, the changes don't take effect instantly worldwide. DNS propagation refers to the time it takes for DNS changes to spread across the internet. This typically takes 24-48 hours, though it's often much faster.</p> <p>Propagation delays occur because:</p> <ul> <li>Resolvers cache old records until the TTL expires</li> <li>Some resolvers ignore TTL values and cache longer</li> <li>Changes must propagate through multiple layers of caching</li> </ul> <p>You can check propagation status using tools like <a href="/tools/dns-lookup/">DNS Lookup</a> or <a href="/tools/dns-propagation-checker/">DNS Propagation Checker</a> to query DNS servers worldwide.</p> <h3>Incorrect DNS Records</h3> <p>Typos or configuration errors in DNS records are surprisingly common. A single character mistake can break your website or email. Common errors include:</p> <ul> <li>Missing trailing dots in CNAME or MX records</li> <li>Incorrect IP addresses in A records</li> <li>Wrong priority values in MX records</li> <li>Conflicting CNAME and A records for the same name</li> </ul> <div style="background:var(--bg-secondary);border:1px solid var(--border);border-radius:8px;padding:1.25rem;margin:1.5rem 0"> <p style="margin:0"><strong>Quick tip:</strong> Always use a DNS validation tool before making changes to production DNS records. Many DNS hosting providers include built-in validation that catches common errors.</p> </div> <h3>Nameserver Configuration Issues</h3> <p>Your domain must point to the correct nameservers at your registrar. If the nameserver records are wrong or missing, DNS resolution fails completely. This often happens when:</p> <ul> <li>Migrating between DNS providers and forgetting to update nameservers</li> <li>Nameserver records are accidentally deleted</li> <li>Nameservers are changed but the old provider's records aren't updated</li> </ul> <h3>DNSSEC Validation Failures</h3> <p>If you enable DNSSEC but configure it incorrectly, resolvers that validate DNSSEC will refuse to resolve your domain. This can make your site inaccessible to a portion of users while working fine for others.</p> <p>DNSSEC requires careful configuration and maintenance. If you're not prepared to manage it properly, it's better to leave it disabled than to risk breaking DNS resolution.</p> <h3>Expired Domains</h3> <p>If you forget to renew your domain registration, it expires and DNS stops working. Most registrars provide a grace period (typically 30 days) where you can renew without penalty, followed by a redemption period where renewal is possible but expensive.</p> <h2 id="troubleshooting-dns">Troubleshooting DNS Problems</h2> <p>When DNS issues arise, systematic troubleshooting helps identify the root cause quickly. Here's a step-by-step approach:</p> <h3>Step 1: Verify the Problem</h3> <p>First, confirm that DNS is actually the issue. Try accessing the site by IP address directly. If that works, DNS is the problem. If it doesn't, the issue lies elsewhere (web server, network, etc.).</p> <h3>Step 2: Clear DNS Caches</h3> <p>Stale cached records often cause problems. Clear caches at multiple levels:</p> <p><strong>Windows:</strong></p> <pre><code>ipconfig /flushdns</code></pre> <p><strong>macOS:</strong></p> <pre><code>sudo dscacheutil -flushcache sudo killall -HUP mDNSResponder</code></pre> <p><strong>Linux:</strong></p> <pre><code>sudo systemd-resolve --flush-caches</code></pre> <p><strong>Browser:</strong> Clear browsing data and specifically select "Cached images and files" and "Cookies and site data".</p> <h3>Step 3: Test with Different DNS Servers</h3> <p>Try using a different DNS server to isolate whether the problem is with your resolver. Temporarily switch to Google DNS (<code>8.8.8.8</code>) or Cloudflare (<code>1.1.1.1</code>) and test again.</p> <h3>Step 4: Use DNS Diagnostic Tools</h3> <p>Command-line tools provide detailed DNS information:</p> <p><strong>nslookup</strong> (Windows, macOS, Linux):</p> <pre><code>nslookup example.com nslookup example.com 8.8.8.8</code></pre> <p><strong>dig</strong> (macOS, Linux):</p> <pre><code>dig example.com dig example.com @8.8.8.8 dig example.com ANY</code></pre> <p><strong>host</strong> (macOS, Linux):</p> <pre><code>host example.com host -a example.com</code></pre> <p>These tools show you exactly what DNS records exist and what responses you're getting from different servers.</p> <h3>Step 5: Check Authoritative Nameservers</h3> <p>Query the authoritative nameservers directly to see if the records are correct at the source:</p> <pre><code>dig example.com NS dig @ns1.example.com example.com</code></pre> <p>If the authoritative servers have correct records but resolvers don't, it's a propagation or caching issue. If the authoritative servers have wrong records, you need to fix them at your DNS provider.</p> <h3>Step 6: Verify Nameserver Configuration</h3> <p>Check that your domain's nameservers are correctly set at your registrar. Use a WHOIS lookup tool or your registrar's control panel to verify the NS records match your DNS provider's nameservers.</p> <h3>Step 7: Check DNS Propagation</h3> <p>Use online tools to check DNS propagation across different geographic locations and DNS servers. This helps identify whether changes have propagated globally or if some regions still have old records.</p> <div style="background:var(--bg-secondary);border:1px solid var(--border);border-radius:8px;padding:1.25rem;margin:1.5rem 0"> <p style="margin:0"><strong>Pro tip:</strong> When troubleshooting </article> </main> <footer class="site-footer"> <div class="container"> <div class="footer-grid"> <div class="footer-col"><h4>DNS</h4><a href="/tools/dns-lookup/">Dns Lookup</a><a href="/tools/whois-lookup/">Whois Lookup</a></div> <div class="footer-col"><h4>IP</h4><a href="/tools/ip-lookup/">Ip Lookup</a><a href="/tools/ip-geolocation/">Ip Geolocation</a><a href="/tools/subnet-calculator/">Subnet Calculator</a><a href="/tools/cidr-calculator/">Cidr Calculator</a></div> <div class="footer-col"><h4>Security</h4><a href="/tools/ssl-checker/">Ssl Checker</a><a href="/tools/header-checker/">Header Checker</a><a href="/tools/port-scanner/">Port Scanner</a><a href="/tools/password-generator/">Password Generator</a></div> <div class="footer-col"><h4>Tools</h4><a href="/tools/traceroute/">Traceroute</a><a href="/tools/speed-test/">Speed Test</a><a href="/tools/mac-lookup/">Mac Lookup</a></div> <div class="footer-col"><h4>Company</h4><a href="/about.html">About</a><a href="/blog/">Blog</a><a href="/contact.html">Contact</a><a href="/sitemap.xml">Sitemap</a></div> </div> <div class="footer-bottom"> <span>© 2026 NetTool. 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