Insert DNS prefetch links
PageSpeed Optimization Filters
Reduce DNS lookup time by pre-resolving at the browser.
DNS resolution time varies from <1ms for locally cached results, to hundreds of milliseconds due to the cascading nature of DNS. This can contribute significantly towards total page load time. This filter reduces DNS lookup time by providing hints to the browser at the beginning of the HTML, which allows the browser to pre-resolve DNS for resources on the page.
pagespeed EnableFilters insert_dns_prefetch
pagespeed DisableFilters insert_dns_prefetch