<p>How can I enable DNS pre-resolution and TCP pre-connection in a Chrome browser (Mac OS X), when the <code>chrome://dns</code> page tells that "DNS pre-resolution and TCP pre-connection is disabled"?</p> <p><img src="https://i.stack.imgur.com/qYMVX.png" alt="enter image description here"></p>

<p>It's in the advanced settings and called "Predict network actions to improve page load performance" </p> <p><img src="https://i.stack.imgur.com/lqiLF.png" alt="Screenshot"></p>

<p>FWIW I had the behavior as in Q&A above in Chrome on Windows:</p> <ul> <li> <code>chrome://dns</code> says "DNS pre-resolution and TCP pre-connection is disabled.", </li> </ul> <p>whereas</p> <ul> <li> <code>chrome://settings</code> shows "Use a prediction service to load pages more quickly" as ticked</li> </ul> <p><strong>I was wondering how this relates to <code><link rel="dns-prefetch" href="//some.domain"></code> and <code><link rel="preconnect" href="https://some.domain"></code>.</strong></p> <h3>Browsers:</h3> <ul> <li>Chrome 67 stable with uBlock</li> <li>Chrome 68 beta (no extensions)</li> </ul> <h3>Before the tests</h3> <ul> <li>have <code>chrome://dns</code> tell you that the services are disabled (perhaps by installing uBlock) </li> <li> <p>serve the following HTMLs on localhost</p> <pre class="prettyprint"><code><!doctype html><html><head> <link rel="dns-prefetch" href="//ajax.googleapis.com"> </head><body></html> <!doctype html><html><head> <link rel="preconnect" href="https://ajax.googleapis.com"> </head><body></html> </code></pre> </li> </ul> <h3>Test 1: with Fiddler</h3> <ul> <li>go to <code>chrome://net-internals/#dns</code> and clear host cache</li> <li>enable Fiddler and make it listen to the traffic</li> <li>open new tab in Chrome on <code>http://localhost</code> </li> <li>observe Fiddler to have a <em>"Tunnel to ajax.googleapis.com:443"</em> session</li> </ul> <h3>Test 2: without Fiddler</h3> <ul> <li>go to <code>chrome://net-internals/#dns</code> and clear host cache</li> <li>open new tab in Chrome on <code>http://localhost</code> </li> <li>refresh <code>chrome://net-internals/#dns</code> and observe DNS entries</li> </ul> <h3>Results and conclusions:</h3> <ul> <li>Chrome 67 stable with uBlock: <code>preload</code> always works; <code>dns-prefetch</code> is blocked by uBlock if uBlock setting <code>Disable pre-fetching (to prevent any connection for blocked network requests)</code> is enabled</li> <li>Chrome 68 beta (no extensions): both <code>dns-prefetch</code> and <code>preload</code> work</li> <li>At this point it's hard to say which of those behaviors are features or bugs and in which part of the stack.</li> </ul>

enable DNS pre-resolution and TCP pre-connection

How can I enable DNS pre-resolution and TCP pre-connection in a Chrome browser (Mac OS X), when the chrome://dns page tells that "DNS pre-resolution and TCP pre-connection is disabled"?

enter image description here

What is DNS-prefetch and Preconnect?

dns-prefetch : indicates to the browser that it should perform the resolution of a given domain name (determining the IP to contact) before that domain is used to download resources. preconnect : indicates to the browser that it should connect a given origin, before that domain is used to download resources.

What is DNS pre?

Prefetching, also known as DNS prefetching, is the act of resolving a website's IP address before a user clicks on its link.

What is the use of DNS-prefetch?

DNS-prefetch is an attempt to resolve domain names before resources get requested. This could be a file loaded later or link target a user tries to follow.

What is Preconnect?

What is a preconnect? A preconnect is a resource hint that tells the browser to make a proactive HTTP connection to a domain the browser has not yet determined needs to be made. Creating an HTTP connection takes many steps, including: Making a DNS lookup. Connecting a TCP.

It's in the advanced settings and called "Predict network actions to improve page load performance"

Screenshot

FWIW I had the behavior as in Q&A above in Chrome on Windows:

chrome://dns says "DNS pre-resolution and TCP pre-connection is disabled.",

whereas

chrome://settings shows "Use a prediction service to load pages more quickly" as ticked

I was wondering how this relates to <link rel="dns-prefetch" href="//some.domain"> and <link rel="preconnect" href="https://some.domain">.

Browsers:

Chrome 67 stable with uBlock
Chrome 68 beta (no extensions)

Before the tests

have chrome://dns tell you that the services are disabled (perhaps by installing uBlock)

serve the following HTMLs on localhost

<!doctype html><html><head>
    <link rel="dns-prefetch" href="//ajax.googleapis.com">
</head><body></html>

<!doctype html><html><head>
    <link rel="preconnect" href="https://ajax.googleapis.com">
</head><body></html>

Test 1: with Fiddler

go to chrome://net-internals/#dns and clear host cache
enable Fiddler and make it listen to the traffic
open new tab in Chrome on http://localhost
observe Fiddler to have a "Tunnel to ajax.googleapis.com:443" session

Test 2: without Fiddler

go to chrome://net-internals/#dns and clear host cache
open new tab in Chrome on http://localhost
refresh chrome://net-internals/#dns and observe DNS entries

Results and conclusions:

Chrome 67 stable with uBlock: preload always works; dns-prefetch is blocked by uBlock if uBlock setting Disable pre-fetching (to prevent any connection for blocked network requests) is enabled
Chrome 68 beta (no extensions): both dns-prefetch and preload work
At this point it's hard to say which of those behaviors are features or bugs and in which part of the stack.

enable DNS pre-resolution and TCP pre-connection

Tags:

google-chrome

wintermeyer

People also ask

2 Answers

wintermeyer

Browsers:

Before the tests

Test 1: with Fiddler

Test 2: without Fiddler

Results and conclusions:

jakub.g

Recent Activity

Donate For Us

enable DNS pre-resolution and TCP pre-connection

Tags:

google-chrome

wintermeyer

People also ask

2 Answers

wintermeyer

Browsers:

Before the tests

Test 1: with Fiddler

Test 2: without Fiddler

Results and conclusions:

jakub.g

Related questions

Recent Activity

Donate For Us