4 ms·

Why did it do ANY?

• msbarnett 8y ago
  > This is really just an old workaround that's no-longer needed. Let me explain... > Once upon a time, back in 1996, there was a really unfortunate bug in the most popular DNS server software (BIND 4.9.3): it did not respond correctly to "CNAME" requests (that is to say, requests for any CNAME data about a particular domain name). This is critical information that an email server needs to know to do its job. Thankfully, there was a way to work around the problem: "ANY" requests. These requests ask the DNS server, essentially, for any and ALL information it has about the domain name in question, including CNAME information. > These ANY queries have two big problems: > As you might imagine, for big domains with lots of mirrors (e.g. gmail.com), that's a lot of information, and so the response can be quite big. Big responses pose two problems: first, it's a waste of bandwidth, and second, it can expose a bug in qmail's handling of large DNS responses (see the next patch). > ANY queries are often not cached by relaying DNS proxies (for whatever reason), and so ANY queries cause more traffic EVEN behind a caching DNS proxy server.