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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"?
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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.
Prefetching, also known as DNS prefetching, is the act of resolving a website's IP address before a user clicks on its link.
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 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"
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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 tickedI was wondering how this relates to <link rel="dns-prefetch" href="//some.domain"> and <link rel="preconnect" href="https://some.domain">.
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>
chrome://net-internals/#dns and clear host cachehttp://localhost
chrome://net-internals/#dns and clear host cachehttp://localhost
chrome://net-internals/#dns and observe DNS entriespreload always works; dns-prefetch is blocked by uBlock if uBlock setting Disable pre-fetching (to prevent any connection for blocked network requests) is enableddns-prefetch and preload work
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