{"id":78499,"date":"2025-09-14T04:07:31","date_gmt":"2025-09-14T04:07:31","guid":{"rendered":"http:\/\/bangla.sitestree.com\/?p=78499"},"modified":"2025-09-14T04:07:31","modified_gmt":"2025-09-14T04:07:31","slug":"subdomains-and-dns-servers-iterative-vs-recursive","status":"publish","type":"post","link":"http:\/\/bangla.sitestree.com\/?p=78499","title":{"rendered":"Subdomains and DNS Servers \u2014 Iterative vs Recursive"},"content":{"rendered":"\n<p><\/p>\n\n\n\n<p>REF: AI Tools\/OpenAI\/ChatGPT<\/p>\n\n\n\n<p>You\u2019re thinking very carefully about how <strong>authority and recursion interact in DNS<\/strong>, and you\u2019re spot on to distinguish between <strong>root\/TLDs<\/strong> and <strong>other domain servers<\/strong>. Let me unpack this clearly:<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h1 class=\"wp-block-heading\">Subdomains and DNS Servers \u2014 Iterative vs Recursive<\/h1>\n\n\n\n<h2 class=\"wp-block-heading\">1. Authoritative Servers (for domains &amp; subdomains)<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Every domain can delegate parts of its namespace to <strong>child servers<\/strong>.<\/li>\n\n\n\n<li>Example:\n<ul class=\"wp-block-list\">\n<li><code>example.com<\/code> has an authoritative server.<\/li>\n\n\n\n<li><code>shop.example.com<\/code> could have its own DNS server.<\/li>\n\n\n\n<li><code>us.shop.example.com<\/code> could delegate further.<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<p>Each of these servers is <strong>authoritative for its zone<\/strong>.<br>\ud83d\udc49 Their primary job: return <strong>authoritative records<\/strong> (A, MX, CNAME, etc.) for their zone, or <strong>referrals<\/strong> if they delegate to a subdomain.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">2. Do Authoritative Servers Perform Recursion?<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>By design (in the DNS model):<\/strong> Authoritative servers are <em>not required<\/em> to do recursion.<\/li>\n\n\n\n<li>Most authoritative servers are configured <strong>not<\/strong> to provide recursive lookups, because:\n<ul class=\"wp-block-list\">\n<li>They\u2019re optimized for answering only about their zone.<\/li>\n\n\n\n<li>Recursion adds workload and caching responsibilities.<\/li>\n\n\n\n<li>Mixing roles (authoritative + recursive) can create <strong>security risks<\/strong> (e.g., cache poisoning).<\/li>\n<\/ul>\n<\/li>\n\n\n\n<li><strong>But technically:<\/strong> Nothing prevents a DNS server from being configured as both authoritative <em>and<\/em> recursive. Some smaller organizations or ISPs do this, though best practice is to separate the roles.<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">3. Why Root &amp; TLDs Must Be Iterative Only<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li>As you said:\n<ul class=\"wp-block-list\">\n<li><strong>Root<\/strong> and <strong>TLDs<\/strong> cannot be recursive \u2014 it would be unsustainable at global scale.<\/li>\n\n\n\n<li>They just give referrals back (iteration).<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">4. Subdomains Can Delegate Too<\/h2>\n\n\n\n<p>Let\u2019s take your example further:<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>A query for <code>us.shop.example.com<\/code>:\n<ol class=\"wp-block-list\">\n<li>Resolver asks root \u2192 referral to <code>.com<\/code>.<\/li>\n\n\n\n<li>Resolver asks <code>.com<\/code> \u2192 referral to <code>example.com<\/code>.<\/li>\n\n\n\n<li>Resolver asks <code>example.com<\/code> \u2192 referral to <code>shop.example.com<\/code>.<\/li>\n\n\n\n<li>Resolver asks <code>shop.example.com<\/code> \u2192 referral to <code>us.shop.example.com<\/code>.<\/li>\n\n\n\n<li>Finally, <code>us.shop.example.com<\/code> authoritative server returns the IP.<\/li>\n<\/ol>\n<\/li>\n<\/ul>\n\n\n\n<p>At each step, the servers gave <strong>iterative referrals<\/strong>, not recursive answers.<br>\ud83d\udc49 The recursive behavior happened only at the <strong>resolver<\/strong> (ISP\/public DNS).<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<h2 class=\"wp-block-heading\">5. Can Subdomain Servers Be Recursive?<\/h2>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>They can, but usually aren\u2019t.<\/strong><\/li>\n\n\n\n<li>Example: <code>dns.shop.example.com<\/code> could be configured as both authoritative (for <code>shop.example.com<\/code>) and recursive (to fetch answers for clients).<\/li>\n\n\n\n<li>But best practice is:\n<ul class=\"wp-block-list\">\n<li>Keep <strong>authoritative servers iterative-only<\/strong>.<\/li>\n\n\n\n<li>Use <strong>dedicated recursive resolvers<\/strong> (like ISP or Google DNS).<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n\n\n\n<p>This separation keeps the DNS system <strong>clean, scalable, and secure<\/strong>.<\/p>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p>\u2705 <strong>So the rule of thumb for your blog post:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>Root and TLDs<\/strong> \u2192 Always iterative-only.<\/li>\n\n\n\n<li><strong>Authoritative servers (for domains\/subdomains)<\/strong> \u2192 Typically iterative-only, but can technically be recursive if configured (not recommended).<\/li>\n\n\n\n<li><strong>Resolvers (ISP\/public)<\/strong> \u2192 Perform recursion on behalf of clients.<\/li>\n<\/ul>\n\n\n\n<hr class=\"wp-block-separator has-alpha-channel-opacity\"\/>\n\n\n\n<p>Would you like me to write this up as a <strong>section titled \u201cCan Authoritative DNS Servers Be Recursive?\u201d<\/strong> so your blog readers understand why it\u2019s possible but rare?<\/p>\n","protected":false},"excerpt":{"rendered":"<p>REF: AI Tools\/OpenAI\/ChatGPT You\u2019re thinking very carefully about how authority and recursion interact in DNS, and you\u2019re spot on to distinguish between root\/TLDs and other domain servers. Let me unpack this clearly: Subdomains and DNS Servers \u2014 Iterative vs Recursive 1. Authoritative Servers (for domains &amp; subdomains) Each of these servers is authoritative for its &hellip; <\/p>\n<p><a class=\"more-link btn\" href=\"http:\/\/bangla.sitestree.com\/?p=78499\">Continue reading<\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[1978],"tags":[],"class_list":["post-78499","post","type-post","status-publish","format-standard","hentry","category-computer-networks","item-wrap"],"jetpack_featured_media_url":"","jetpack_sharing_enabled":true,"jetpack-related-posts":[{"id":78512,"url":"http:\/\/bangla.sitestree.com\/?p=78512","url_meta":{"origin":78499,"position":0},"title":"Zone vs. Domain vs. Subdomain in DNS","author":"Author-Check- Article-or-Video","date":"September 22, 2025","format":false,"excerpt":"Ref: AI Tools\/OpenAI\/ChatGPT Here\u2019s a blog-ready, copyright-free article explaining Zone vs. Domain vs. Subdomain in DNS. Zone vs. Domain vs. Subdomain in DNS When learning DNS, people often get confused between the terms zone, domain, and subdomain. They sound similar, but each has a specific meaning in the Domain Name\u2026","rel":"","context":"In &quot;Computer Networks&quot;","block_context":{"text":"Computer Networks","link":"http:\/\/bangla.sitestree.com\/?cat=1978"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":78468,"url":"http:\/\/bangla.sitestree.com\/?p=78468","url_meta":{"origin":78499,"position":1},"title":"How DNS Names Work: Example with chat.811tech.ca","author":"Sayed","date":"September 12, 2025","format":false,"excerpt":"Ref: AI Tools\/Open AI\/ChatGPT \" \"Here\u2019s a single, blog-ready explanation that ties all your points together: How DNS Names Work: Example with chat.811tech.ca When you type a web address like chat.811tech.ca into your browser, you\u2019re using the Domain Name System (DNS) to find the right server. Let\u2019s break down what\u2026","rel":"","context":"In &quot;Computer Networks&quot;","block_context":{"text":"Computer Networks","link":"http:\/\/bangla.sitestree.com\/?cat=1978"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":78493,"url":"http:\/\/bangla.sitestree.com\/?p=78493","url_meta":{"origin":78499,"position":2},"title":"Iterative vs. Recursive DNS Resolution","author":"Sayed","date":"September 14, 2025","format":false,"excerpt":"REF: AI Tools\/Open AI\/ChatGPT (posted as is) \"Perfect follow-up \ud83d\udc4d \u2014 here\u2019s a blog-ready, copyright-free comparison of Iterative vs. Recursive Resolution in DNS: Iterative vs. Recursive DNS Resolution When you enter a domain name like www.example.com, your computer needs its IP address to connect. There are two main ways DNS\u2026","rel":"","context":"In &quot;Computer Networks&quot;","block_context":{"text":"Computer Networks","link":"http:\/\/bangla.sitestree.com\/?cat=1978"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":78491,"url":"http:\/\/bangla.sitestree.com\/?p=78491","url_meta":{"origin":78499,"position":3},"title":"Iterative DNS Resolution Explained","author":"Sayed","date":"September 14, 2025","format":false,"excerpt":"Got it \ud83d\udc4d \u2014 here\u2019s a blog-ready, copyright-free explanation of Iterative Resolution in DNS that you can publish directly. Iterative DNS Resolution Explained When you type a domain name like www.example.com into your browser, the system needs to translate it into an IP address. One way this happens is through\u2026","rel":"","context":"In &quot;Computer Networks&quot;","block_context":{"text":"Computer Networks","link":"http:\/\/bangla.sitestree.com\/?cat=1978"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":78495,"url":"http:\/\/bangla.sitestree.com\/?p=78495","url_meta":{"origin":78499,"position":4},"title":"Who Resolves DNS Queries: ISP, Resolver, or Your PC?","author":"Sayed","date":"September 14, 2025","format":false,"excerpt":"Great question \ud83d\udc4c \u2014 this gets into the roles of DNS components in the real world. Let\u2019s break it down clearly, blog-ready and copyright-free: Who Resolves DNS Queries: ISP, Resolver, or Your PC? When you sit at home and connect to the internet through your ISP, different systems can play\u2026","rel":"","context":"In &quot;Computer Networks&quot;","block_context":{"text":"Computer Networks","link":"http:\/\/bangla.sitestree.com\/?cat=1978"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]},{"id":78501,"url":"http:\/\/bangla.sitestree.com\/?p=78501","url_meta":{"origin":78499,"position":5},"title":"What is a Flat Name Space in DNS?","author":"Sayed","date":"September 14, 2025","format":false,"excerpt":"REF: AI Tools\/ChatGPT\/OpenAI\/Internet What is a Flat Name Space? Sure! Let\u2019s break down DNS flat name space clearly. 1. What is a Flat Name Space? A flat name space is a naming system where all names exist at the same level, without any hierarchy. In other words: Every name is\u2026","rel":"","context":"In &quot;Computer Networks&quot;","block_context":{"text":"Computer Networks","link":"http:\/\/bangla.sitestree.com\/?cat=1978"},"img":{"alt_text":"","src":"","width":0,"height":0},"classes":[]}],"_links":{"self":[{"href":"http:\/\/bangla.sitestree.com\/index.php?rest_route=\/wp\/v2\/posts\/78499","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/bangla.sitestree.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/bangla.sitestree.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/bangla.sitestree.com\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"http:\/\/bangla.sitestree.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=78499"}],"version-history":[{"count":1,"href":"http:\/\/bangla.sitestree.com\/index.php?rest_route=\/wp\/v2\/posts\/78499\/revisions"}],"predecessor-version":[{"id":78500,"href":"http:\/\/bangla.sitestree.com\/index.php?rest_route=\/wp\/v2\/posts\/78499\/revisions\/78500"}],"wp:attachment":[{"href":"http:\/\/bangla.sitestree.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=78499"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/bangla.sitestree.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=78499"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/bangla.sitestree.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=78499"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}