Issue: I’ve observed that each time I ran a WebPageTest, the first test would indicate a longer DNS lookup time than all the subsequent tests.
How I helped it: I changed the TTL of all the records at my DNS from 30 minutes to 14 days. (14 days is probably unusually long, but I don’t plan on switching my current host, and if I ever do, I will lower the TTL at least a couple of weeks in advance.)
Is there anything more I can do? Tests show that the issue has been resolved for the base page, which is served from my origin server, but the issue has not been helped for files served by my CDN, even though I changed the DNS TTL of cdn.mydomain.com, too. I suspect the CDN provider would have to change their TTL settings, too, for this to improve. Am I correct in my assumption? Is there a chance a CDN provider will do it if I request it?