learnyounode

<!DOCTYPE html><html lang="en"><head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width"> <title>DNS | Node.js v12.10.0 Documentation</title> <link rel="stylesheet" href="data:text/css;base64,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"> <link rel="stylesheet" href="data:text/css;base64,/*--------------------- Layout and Typography ----------------------------*/
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em code {
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#gtoc {
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li.version-picker {
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li.version-picker:hover > a {
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tt, code {
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a code {
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#column2 > ul:nth-child(2) {
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#intro a:hover, #intro a:focus,
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th > *:last-child, td > *:last-child {
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.changelog > summary {
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/* simpler clearfix */
.clearfix:after {
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.github_icon {
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@media only screen and (max-width: 1024px) {
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@media print {
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"> <link rel="stylesheet" href="data:text/css;base64,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"> <link rel="canonical" href="https://nodejs.org/api/dns.html"> </head> <body class="alt apidoc" id="api-section-dns"> <div id="content" class="clearfix"> <div id="column2" class="interior"> <div id="intro" class="interior"> <a href="https://nodejs.org/" title="Go back to the home page"> Node.js </a> </div> <ul> <li><a href="https://nodejs.org/api/documentation.html" class="nav-documentation">About these Docs</a></li> <li><a href="https://nodejs.org/api/synopsis.html" class="nav-synopsis">Usage & Example</a></li> </ul> <div class="line"></div> <ul> <li><a href="https://nodejs.org/api/assert.html" class="nav-assert">Assertion Testing</a></li> <li><a href="https://nodejs.org/api/async_hooks.html" class="nav-async_hooks">Async Hooks</a></li> <li><a href="https://nodejs.org/api/buffer.html" class="nav-buffer">Buffer</a></li> <li><a href="https://nodejs.org/api/addons.html" class="nav-addons">C++ Addons</a></li> <li><a href="https://nodejs.org/api/n-api.html" class="nav-n-api">C/C++ Addons - N-API</a></li> <li><a href="https://nodejs.org/api/child_process.html" class="nav-child_process">Child Processes</a></li> <li><a href="https://nodejs.org/api/cluster.html" class="nav-cluster">Cluster</a></li> <li><a href="https://nodejs.org/api/cli.html" class="nav-cli">Command Line Options</a></li> <li><a href="https://nodejs.org/api/console.html" class="nav-console">Console</a></li> <li><a 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class="version-picker"> <a href="#">View another version <span>▼</span></a> <ol class="version-picker"><li><a href="https://nodejs.org/docs/latest-v12.x/api/dns.html">12.x</a></li> <li><a href="https://nodejs.org/docs/latest-v11.x/api/dns.html">11.x</a></li> <li><a href="https://nodejs.org/docs/latest-v10.x/api/dns.html">10.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v9.x/api/dns.html">9.x</a></li> <li><a href="https://nodejs.org/docs/latest-v8.x/api/dns.html">8.x <b>LTS</b></a></li> <li><a href="https://nodejs.org/docs/latest-v7.x/api/dns.html">7.x</a></li> <li><a href="https://nodejs.org/docs/latest-v6.x/api/dns.html">6.x</a></li> <li><a href="https://nodejs.org/docs/latest-v5.x/api/dns.html">5.x</a></li> <li><a href="https://nodejs.org/docs/latest-v4.x/api/dns.html">4.x</a></li> <li><a href="https://nodejs.org/docs/latest-v0.12.x/api/dns.html">0.12.x</a></li> <li><a href="https://nodejs.org/docs/latest-v0.10.x/api/dns.html">0.10.x</a></li></ol> </li> <li class="edit_on_github"><a href="https://github.com/nodejs/node/edit/master/doc/api/dns.md"><span class="github_icon"><svg height="16" width="16" viewBox="0 0 16.1 16.1" fill="currentColor"><path d="M8 0a8 8 0 0 0-2.5 15.6c.4 0 .5-.2.5-.4v-1.5c-2 .4-2.5-.5-2.7-1 0-.1-.5-.9-.8-1-.3-.2-.7-.6 0-.6.6 0 1 .6 1.2.8.7 1.2 1.9 1 2.4.7 0-.5.2-.9.5-1-1.8-.3-3.7-1-3.7-4 0-.9.3-1.6.8-2.2 0-.2-.3-1 .1-2 0 0 .7-.3 2.2.7a7.4 7.4 0 0 1 4 0c1.5-1 2.2-.8 2.2-.8.5 1.1.2 2 .1 2.1.5.6.8 1.3.8 2.2 0 3-1.9 3.7-3.6 4 .3.2.5.7.5 1.4v2.2c0 .2.1.5.5.4A8 8 0 0 0 16 8a8 8 0 0 0-8-8z"></path></svg></span>Edit on GitHub</a></li> </ul> </div> <hr> </header> <div id="toc"> <h2>Table of Contents</h2> <ul> <li> <p><span class="stability_2"><a href="#dns_dns">DNS</a></span></p> <ul> <li> <p><a href="#dns_class_dns_resolver">Class: dns.Resolver</a></p> <ul> <li><a href="#dns_resolver_cancel">resolver.cancel()</a></li> </ul> </li> <li><a href="#dns_dns_getservers">dns.getServers()</a></li> <li> <p><a href="#dns_dns_lookup_hostname_options_callback">dns.lookup(hostname[, options], callback)</a></p> <ul> <li><a href="#dns_supported_getaddrinfo_flags">Supported getaddrinfo flags</a></li> </ul> </li> <li><a href="#dns_dns_lookupservice_address_port_callback">dns.lookupService(address, port, callback)</a></li> <li><a href="#dns_dns_resolve_hostname_rrtype_callback">dns.resolve(hostname[, rrtype], callback)</a></li> <li><a href="#dns_dns_resolve4_hostname_options_callback">dns.resolve4(hostname[, options], callback)</a></li> <li><a href="#dns_dns_resolve6_hostname_options_callback">dns.resolve6(hostname[, options], callback)</a></li> <li><a href="#dns_dns_resolveany_hostname_callback">dns.resolveAny(hostname, callback)</a></li> <li><a href="#dns_dns_resolvecname_hostname_callback">dns.resolveCname(hostname, callback)</a></li> <li><a href="#dns_dns_resolvemx_hostname_callback">dns.resolveMx(hostname, callback)</a></li> <li><a href="#dns_dns_resolvenaptr_hostname_callback">dns.resolveNaptr(hostname, callback)</a></li> <li><a href="#dns_dns_resolvens_hostname_callback">dns.resolveNs(hostname, callback)</a></li> <li><a href="#dns_dns_resolveptr_hostname_callback">dns.resolvePtr(hostname, callback)</a></li> <li><a href="#dns_dns_resolvesoa_hostname_callback">dns.resolveSoa(hostname, callback)</a></li> <li><a href="#dns_dns_resolvesrv_hostname_callback">dns.resolveSrv(hostname, callback)</a></li> <li><a href="#dns_dns_resolvetxt_hostname_callback">dns.resolveTxt(hostname, callback)</a></li> <li><a href="#dns_dns_reverse_ip_callback">dns.reverse(ip, callback)</a></li> <li><a href="#dns_dns_setservers_servers">dns.setServers(servers)</a></li> <li> <p><a href="#dns_dns_promises_api">DNS Promises API</a></p> <ul> <li><a href="#dns_class_dnspromises_resolver">Class: dnsPromises.Resolver</a></li> <li><a href="#dns_dnspromises_getservers">dnsPromises.getServers()</a></li> <li><a href="#dns_dnspromises_lookup_hostname_options">dnsPromises.lookup(hostname[, options])</a></li> <li><a href="#dns_dnspromises_lookupservice_address_port">dnsPromises.lookupService(address, port)</a></li> <li><a href="#dns_dnspromises_resolve_hostname_rrtype">dnsPromises.resolve(hostname[, rrtype])</a></li> <li><a href="#dns_dnspromises_resolve4_hostname_options">dnsPromises.resolve4(hostname[, options])</a></li> <li><a href="#dns_dnspromises_resolve6_hostname_options">dnsPromises.resolve6(hostname[, options])</a></li> <li><a href="#dns_dnspromises_resolveany_hostname">dnsPromises.resolveAny(hostname)</a></li> <li><a href="#dns_dnspromises_resolvecname_hostname">dnsPromises.resolveCname(hostname)</a></li> <li><a href="#dns_dnspromises_resolvemx_hostname">dnsPromises.resolveMx(hostname)</a></li> <li><a href="#dns_dnspromises_resolvenaptr_hostname">dnsPromises.resolveNaptr(hostname)</a></li> <li><a href="#dns_dnspromises_resolvens_hostname">dnsPromises.resolveNs(hostname)</a></li> <li><a href="#dns_dnspromises_resolveptr_hostname">dnsPromises.resolvePtr(hostname)</a></li> <li><a href="#dns_dnspromises_resolvesoa_hostname">dnsPromises.resolveSoa(hostname)</a></li> <li><a href="#dns_dnspromises_resolvesrv_hostname">dnsPromises.resolveSrv(hostname)</a></li> <li><a href="#dns_dnspromises_resolvetxt_hostname">dnsPromises.resolveTxt(hostname)</a></li> <li><a href="#dns_dnspromises_reverse_ip">dnsPromises.reverse(ip)</a></li> <li><a href="#dns_dnspromises_setservers_servers">dnsPromises.setServers(servers)</a></li> </ul> </li> <li><a href="#dns_error_codes">Error codes</a></li> <li> <p><a href="#dns_implementation_considerations">Implementation considerations</a></p> <ul> <li><a href="#dns_dns_lookup"><code>dns.lookup()</code></a></li> <li><a href="#dns_dns_resolve_dns_resolve_and_dns_reverse"><code>dns.resolve()</code>, <code>dns.resolve*()</code> and <code>dns.reverse()</code></a></li> </ul> </li> </ul> </li> </ul> </div> <div id="apicontent"> <h1>DNS<span><a class="mark" href="#dns_dns" id="dns_dns">#</a></span></h1> <p></p><div class="api_stability api_stability_2"><a href="https://nodejs.org/api/documentation.html#documentation_stability_index">Stability: 2</a> - Stable</div><p></p> <p>The <code>dns</code> module contains functions belonging to two different categories:</p> <p>1) Functions that use the underlying operating system facilities to perform name resolution, and that do not necessarily perform any network communication. This category contains only one function: <a href="#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a>. <strong>Developers looking to perform name resolution in the same way that other applications on the same operating system behave should use <a href="#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a>.</strong></p> <p>For example, looking up <code>iana.org</code>.</p> <pre><code class="language-js">const dns = require('dns'); dns.lookup('iana.org', (err, address, family) => { console.log('address: %j family: IPv%s', address, family); }); // address: "192.0.43.8" family: IPv4 </code></pre> <p>2) Functions that connect to an actual DNS server to perform name resolution, and that <em>always</em> use the network to perform DNS queries. This category contains all functions in the <code>dns</code> module <em>except</em> <a href="#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a>. These functions do not use the same set of configuration files used by <a href="#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a> (e.g. <code>/etc/hosts</code>). These functions should be used by developers who do not want to use the underlying operating system's facilities for name resolution, and instead want to <em>always</em> perform DNS queries.</p> <p>Below is an example that resolves <code>'archive.org'</code> then reverse resolves the IP addresses that are returned.</p> <pre><code class="language-js">const dns = require('dns'); dns.resolve4('archive.org', (err, addresses) => { if (err) throw err; console.log(`addresses: ${JSON.stringify(addresses)}`); addresses.forEach((a) => { dns.reverse(a, (err, hostnames) => { if (err) { throw err; } console.log(`reverse for ${a}: ${JSON.stringify(hostnames)}`); }); }); }); </code></pre> <p>There are subtle consequences in choosing one over the other, please consult the <a href="#dns_implementation_considerations">Implementation considerations section</a> for more information.</p> <h2>Class: dns.Resolver<span><a class="mark" href="#dns_class_dns_resolver" id="dns_class_dns_resolver">#</a></span></h2> <div class="api_metadata"> <span>Added in: v8.3.0</span> </div> <p>An independent resolver for DNS requests.</p> <p>Creating a new resolver uses the default server settings. Setting the servers used for a resolver using <a href="#dns_dns_setservers_servers"><code>resolver.setServers()</code></a> does not affect other resolvers:</p> <pre><code class="language-js">const { Resolver } = require('dns'); const resolver = new Resolver(); resolver.setServers(['4.4.4.4']); // This request will use the server at 4.4.4.4, independent of global settings. resolver.resolve4('example.org', (err, addresses) => { // ... }); </code></pre> <p>The following methods from the <code>dns</code> module are available:</p> <ul> <li><a href="#dns_dns_getservers"><code>resolver.getServers()</code></a></li> <li><a href="#dns_dns_resolve_hostname_rrtype_callback"><code>resolver.resolve()</code></a></li> <li><a href="#dns_dns_resolve4_hostname_options_callback"><code>resolver.resolve4()</code></a></li> <li><a href="#dns_dns_resolve6_hostname_options_callback"><code>resolver.resolve6()</code></a></li> <li><a href="#dns_dns_resolveany_hostname_callback"><code>resolver.resolveAny()</code></a></li> <li><a href="#dns_dns_resolvecname_hostname_callback"><code>resolver.resolveCname()</code></a></li> <li><a href="#dns_dns_resolvemx_hostname_callback"><code>resolver.resolveMx()</code></a></li> <li><a href="#dns_dns_resolvenaptr_hostname_callback"><code>resolver.resolveNaptr()</code></a></li> <li><a href="#dns_dns_resolvens_hostname_callback"><code>resolver.resolveNs()</code></a></li> <li><a href="#dns_dns_resolveptr_hostname_callback"><code>resolver.resolvePtr()</code></a></li> <li><a href="#dns_dns_resolvesoa_hostname_callback"><code>resolver.resolveSoa()</code></a></li> <li><a href="#dns_dns_resolvesrv_hostname_callback"><code>resolver.resolveSrv()</code></a></li> <li><a href="#dns_dns_resolvetxt_hostname_callback"><code>resolver.resolveTxt()</code></a></li> <li><a href="#dns_dns_reverse_ip_callback"><code>resolver.reverse()</code></a></li> <li><a href="#dns_dns_setservers_servers"><code>resolver.setServers()</code></a></li> </ul> <h3>resolver.cancel()<span><a class="mark" href="#dns_resolver_cancel" id="dns_resolver_cancel">#</a></span></h3> <div class="api_metadata"> <span>Added in: v8.3.0</span> </div> <p>Cancel all outstanding DNS queries made by this resolver. The corresponding callbacks will be called with an error with code <code>ECANCELLED</code>.</p> <h2>dns.getServers()<span><a class="mark" href="#dns_dns_getservers" id="dns_dns_getservers">#</a></span></h2> <div class="api_metadata"> <span>Added in: v0.11.3</span> </div> <ul> <li>Returns: <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a></li> </ul> <p>Returns an array of IP address strings, formatted according to <a href="https://tools.ietf.org/html/rfc5952#section-6">RFC 5952</a>, that are currently configured for DNS resolution. A string will include a port section if a custom port is used.</p>  <pre><code class="language-js">[ '4.4.4.4', '2001:4860:4860::8888', '4.4.4.4:1053', '[2001:4860:4860::8888]:1053' ] </code></pre> <h2>dns.lookup(hostname[, options], callback)<a class="srclink" href="https://github.com/nodejs/node/blob/3a2e75d9a5c31d20e429d505b82dd182e33f459a/lib/dns.js#L90">[src]</a><span><a class="mark" href="#dns_dns_lookup_hostname_options_callback" id="dns_dns_lookup_hostname_options_callback">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v8.5.0</td> <td><p>The <code>verbatim</code> option is supported now.</p></td></tr> <tr><td>v1.2.0</td> <td><p>The <code>all</code> option is supported now.</p></td></tr> <tr><td>v0.1.90</td> <td><p><span>Added in: v0.1.90</span></p></td></tr> </tbody></table> </details> </div> <ul> <li><code>hostname</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> <li> <p><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></p> <ul> <li><code>family</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> The record family. Must be <code>4</code>, <code>6</code>, or <code>0</code>. The value <code>0</code> indicates that IPv4 and IPv6 addresses are both returned. <strong>Default:</strong> <code>0</code>.</li> <li><code>hints</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a> One or more <a href="#dns_supported_getaddrinfo_flags">supported <code>getaddrinfo</code> flags</a>. Multiple flags may be passed by bitwise <code>OR</code>ing their values.</li> <li><code>all</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> When <code>true</code>, the callback returns all resolved addresses in an array. Otherwise, returns a single address. <strong>Default:</strong> <code>false</code>.</li> <li><code>verbatim</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> When <code>true</code>, the callback receives IPv4 and IPv6 addresses in the order the DNS resolver returned them. When <code>false</code>, IPv4 addresses are placed before IPv6 addresses. <strong>Default:</strong> currently <code>false</code> (addresses are reordered) but this is expected to change in the not too distant future. New code should use <code>{ verbatim: true }</code>.</li> </ul> </li> <li> <p><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></p> <ul> <li><code>err</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> <li><code>address</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> A string representation of an IPv4 or IPv6 address.</li> <li><code>family</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><integer></a> <code>4</code> or <code>6</code>, denoting the family of <code>address</code>, or <code>0</code> if the address is not an IPv4 or IPv6 address. <code>0</code> is a likely indicator of a bug in the name resolution service used by the operating system.</li> </ul> </li> </ul> <p>Resolves a hostname (e.g. <code>'nodejs.org'</code>) into the first found A (IPv4) or AAAA (IPv6) record. All <code>option</code> properties are optional. If <code>options</code> is an integer, then it must be <code>4</code> or <code>6</code> – if <code>options</code> is not provided, then IPv4 and IPv6 addresses are both returned if found.</p> <p>With the <code>all</code> option set to <code>true</code>, the arguments for <code>callback</code> change to <code>(err, addresses)</code>, with <code>addresses</code> being an array of objects with the properties <code>address</code> and <code>family</code>.</p> <p>On error, <code>err</code> is an <a href="https://nodejs.org/api/errors.html#errors_class_error"><code>Error</code></a> object, where <code>err.code</code> is the error code. Keep in mind that <code>err.code</code> will be set to <code>'ENOTFOUND'</code> not only when the hostname does not exist but also when the lookup fails in other ways such as no available file descriptors.</p> <p><code>dns.lookup()</code> does not necessarily have anything to do with the DNS protocol. The implementation uses an operating system facility that can associate names with addresses, and vice versa. This implementation can have subtle but important consequences on the behavior of any Node.js program. Please take some time to consult the <a href="#dns_implementation_considerations">Implementation considerations section</a> before using <code>dns.lookup()</code>.</p> <p>Example usage:</p> <pre><code class="language-js">const dns = require('dns'); const options = { family: 6, hints: dns.ADDRCONFIG | dns.V4MAPPED, }; dns.lookup('example.com', options, (err, address, family) => console.log('address: %j family: IPv%s', address, family)); // address: "2606:2800:220:1:248:1893:25c8:1946" family: IPv6 // When options.all is true, the result will be an Array. options.all = true; dns.lookup('example.com', options, (err, addresses) => console.log('addresses: %j', addresses)); // addresses: [{"address":"2606:2800:220:1:248:1893:25c8:1946","family":6}] </code></pre> <p>If this method is invoked as its <a href="https://nodejs.org/api/util.html#util_util_promisify_original"><code>util.promisify()</code></a>ed version, and <code>all</code> is not set to <code>true</code>, it returns a <code>Promise</code> for an <code>Object</code> with <code>address</code> and <code>family</code> properties.</p> <h3>Supported getaddrinfo flags<span><a class="mark" href="#dns_supported_getaddrinfo_flags" id="dns_supported_getaddrinfo_flags">#</a></span></h3> <p>The following flags can be passed as hints to <a href="#dns_dns_lookup_hostname_options_callback"><code>dns.lookup()</code></a>.</p> <ul> <li><code>dns.ADDRCONFIG</code>: Returned address types are determined by the types of addresses supported by the current system. For example, IPv4 addresses are only returned if the current system has at least one IPv4 address configured. Loopback addresses are not considered.</li> <li><code>dns.V4MAPPED</code>: If the IPv6 family was specified, but no IPv6 addresses were found, then return IPv4 mapped IPv6 addresses. It is not supported on some operating systems (e.g FreeBSD 10.1).</li> </ul> <h2>dns.lookupService(address, port, callback)<a class="srclink" href="https://github.com/nodejs/node/blob/3a2e75d9a5c31d20e429d505b82dd182e33f459a/lib/dns.js#L167">[src]</a><span><a class="mark" href="#dns_dns_lookupservice_address_port_callback" id="dns_dns_lookupservice_address_port_callback">#</a></span></h2> <div class="api_metadata"> <span>Added in: v0.11.14</span> </div> <ul> <li><code>address</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></li> <li><code>port</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Number_type" class="type"><number></a></li> <li> <p><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></p> <ul> <li><code>err</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> <li><code>hostname</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> e.g. <code>example.com</code></li> <li><code>service</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> e.g. <code>http</code></li> </ul> </li> </ul> <p>Resolves the given <code>address</code> and <code>port</code> into a hostname and service using the operating system's underlying <code>getnameinfo</code> implementation.</p> <p>If <code>address</code> is not a valid IP address, a <code>TypeError</code> will be thrown. The <code>port</code> will be coerced to a number. If it is not a legal port, a <code>TypeError</code> will be thrown.</p> <p>On an error, <code>err</code> is an <a href="https://nodejs.org/api/errors.html#errors_class_error"><code>Error</code></a> object, where <code>err.code</code> is the error code.</p> <pre><code class="language-js">const dns = require('dns'); dns.lookupService('127.0.0.1', 22, (err, hostname, service) => { console.log(hostname, service); // Prints: localhost ssh }); </code></pre> <p>If this method is invoked as its <a href="https://nodejs.org/api/util.html#util_util_promisify_original"><code>util.promisify()</code></a>ed version, it returns a <code>Promise</code> for an <code>Object</code> with <code>hostname</code> and <code>service</code> properties.</p> <h2>dns.resolve(hostname[, rrtype], callback)<span><a class="mark" href="#dns_dns_resolve_hostname_rrtype_callback" id="dns_dns_resolve_hostname_rrtype_callback">#</a></span></h2> <div class="api_metadata"> <span>Added in: v0.1.27</span> </div> <ul> <li><code>hostname</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Hostname to resolve.</li> <li><code>rrtype</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Resource record type. <strong>Default:</strong> <code>'A'</code>.</li> <li> <p><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></p> <ul> <li><code>err</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> <li><code>records</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object[]></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></li> </ul> </li> </ul> <p>Uses the DNS protocol to resolve a hostname (e.g. <code>'nodejs.org'</code>) into an array of the resource records. The <code>callback</code> function has arguments <code>(err, records)</code>. When successful, <code>records</code> will be an array of resource records. The type and structure of individual results varies based on <code>rrtype</code>:</p> <table><thead><tr><th><code>rrtype</code></th><th><code>records</code> contains</th><th>Result type</th><th>Shorthand method</th></tr></thead><tbody><tr><td><code>'A'</code></td><td>IPv4 addresses (default)</td><td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></td><td><a href="#dns_dns_resolve4_hostname_options_callback"><code>dns.resolve4()</code></a></td></tr><tr><td><code>'AAAA'</code></td><td>IPv6 addresses</td><td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></td><td><a href="#dns_dns_resolve6_hostname_options_callback"><code>dns.resolve6()</code></a></td></tr><tr><td><code>'ANY'</code></td><td>any records</td><td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></td><td><a href="#dns_dns_resolveany_hostname_callback"><code>dns.resolveAny()</code></a></td></tr><tr><td><code>'CNAME'</code></td><td>canonical name records</td><td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></td><td><a href="#dns_dns_resolvecname_hostname_callback"><code>dns.resolveCname()</code></a></td></tr><tr><td><code>'MX'</code></td><td>mail exchange records</td><td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></td><td><a href="#dns_dns_resolvemx_hostname_callback"><code>dns.resolveMx()</code></a></td></tr><tr><td><code>'NAPTR'</code></td><td>name authority pointer records</td><td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></td><td><a href="#dns_dns_resolvenaptr_hostname_callback"><code>dns.resolveNaptr()</code></a></td></tr><tr><td><code>'NS'</code></td><td>name server records</td><td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></td><td><a href="#dns_dns_resolvens_hostname_callback"><code>dns.resolveNs()</code></a></td></tr><tr><td><code>'PTR'</code></td><td>pointer records</td><td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a></td><td><a href="#dns_dns_resolveptr_hostname_callback"><code>dns.resolvePtr()</code></a></td></tr><tr><td><code>'SOA'</code></td><td>start of authority records</td><td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></td><td><a href="#dns_dns_resolvesoa_hostname_callback"><code>dns.resolveSoa()</code></a></td></tr><tr><td><code>'SRV'</code></td><td>service records</td><td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></td><td><a href="#dns_dns_resolvesrv_hostname_callback"><code>dns.resolveSrv()</code></a></td></tr><tr><td><code>'TXT'</code></td><td>text records</td><td><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a></td><td><a href="#dns_dns_resolvetxt_hostname_callback"><code>dns.resolveTxt()</code></a></td></tr></tbody></table> <p>On error, <code>err</code> is an <a href="https://nodejs.org/api/errors.html#errors_class_error"><code>Error</code></a> object, where <code>err.code</code> is one of the <a href="#dns_error_codes">DNS error codes</a>.</p> <h2>dns.resolve4(hostname[, options], callback)<span><a class="mark" href="#dns_dns_resolve4_hostname_options_callback" id="dns_dns_resolve4_hostname_options_callback">#</a></span></h2> <div class="api_metadata"> <details class="changelog"><summary>History</summary> <table> <tbody><tr><th>Version</th><th>Changes</th></tr> <tr><td>v7.2.0</td> <td><p>This method now supports passing <code>options</code>, specifically <code>options.ttl</code>.</p></td></tr> <tr><td>v0.1.16</td> <td><p><span>Added in: v0.1.16</span></p></td></tr> </tbody></table> </details> </div> <ul> <li><code>hostname</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string></a> Hostname to resolve.</li> <li> <p><code>options</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object></a></p> <ul> <li><code>ttl</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#Boolean_type" class="type"><boolean></a> Retrieve the Time-To-Live value (TTL) of each record. When <code>true</code>, the callback receives an array of <code>{ address: '1.2.3.4', ttl: 60 }</code> objects rather than an array of strings, with the TTL expressed in seconds.</li> </ul> </li> <li> <p><code>callback</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function" class="type"><Function></a></p> <ul> <li><code>err</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error" class="type"><Error></a></li> <li><code>addresses</code> <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Data_structures#String_type" class="type"><string[]></a> | <a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object" class="type"><Object[]></a></li> </ul> </li> </ul> <p>Uses the DNS protocol to resolve a IPv4 addresses (<code>A</code> records) for the <code>hostname</code>. The <code>addresses</code> argument passed to the <code>callback</code> function will contain an array of IPv4 addresses (e.g. <code>['74.125.79.104', '74.125.79.105', '74.125.79.106']</code>).</p> <h2>dns.resolve6(hostname[, options], callback)<span><a class="mark" href="#dns_dns_resolve6_hostname_options_callback" id="dns_dns_resolve6_hostname_options_callback">#</a></span></h2> <div class="api_met