3 ms·

Doesn't this ignore the fact that a lot of DNS resolvers don't respect the TTL and cache for way longer than they should?

zhfliz 4y ago
isn't it usually the opposite, except for client applications that ignore the ttl they got from their recursive resolver as they don't want to bother with keeping track of ttls?
- icedchai 4y ago
  When I ran a small web hosting provider, we had some clients (mostly bots, I think) hitting old IPs for months. We had kept the TTL below 5 minutes for a very long time before migration. Also, older Java apps would cache DNS lookups forever, until you restarted the JVM. I remember arguing back and forth in email with a "vendor." They finally believed me and restarted their app server.
  - zhfliz 4y ago
    that's what i meant. the resolvers (which those apps talk to) are (afaik) generally rfc-conforming and respect ttl, though they may have lower max ttl values, allowing faster refreshes in some cases. certain bad applications however just don't bother dealing with ttls at all and assume dns is static and never changes.
  - paranoidrobot 4y ago
    > Also, older Java apps would cache DNS lookups forever, until you restarted the JVM. I remember arguing back and forth in email with a "vendor." They finally believed me and restarted their app server. New JVM-based apps do the same thing. I've had the same conversations with a "partner".
    - icedchai 4y ago
      I figured, after all these years, the JVM would switch to a sane default for DNS caching. Sadly that is not the case...
Snawoot 4y ago
That definitely takes place just because on the internet you can find any anomaly you can think of. But it's not widespread. Also, AWS Route53 also relies on fairly low TTL, so it's a non-issue.
donavanm 4y ago
Ive run a major CDN and authoritative nameservice. Its small enough to not matter in most cases. A quick swag is Id expect 95% of traffic to respect the ttl. Another 4% will appear to have some sort of minimum ttl on the order of single digit minutes. The last 1% transitions over the next hours. There will be a super long tail with measurable, but insignificant, traffic using the previous RDATA effectively forever. Im sure someone from DNS OARC has more recent and well quantified numbers.

zhfliz 4y ago

isn't it usually the opposite, except for client applications that ignore the ttl they got from their recursive resolver as they don't want to bother with keeping track of ttls?

icedchai 4y ago
When I ran a small web hosting provider, we had some clients (mostly bots, I think) hitting old IPs for months. We had kept the TTL below 5 minutes for a very long time before migration. Also, older Java apps would cache DNS lookups forever, until you restarted the JVM. I remember arguing back and forth in email with a "vendor." They finally believed me and restarted their app server.
- zhfliz 4y ago
  that's what i meant. the resolvers (which those apps talk to) are (afaik) generally rfc-conforming and respect ttl, though they may have lower max ttl values, allowing faster refreshes in some cases. certain bad applications however just don't bother dealing with ttls at all and assume dns is static and never changes.
- paranoidrobot 4y ago
  > Also, older Java apps would cache DNS lookups forever, until you restarted the JVM. I remember arguing back and forth in email with a "vendor." They finally believed me and restarted their app server. New JVM-based apps do the same thing. I've had the same conversations with a "partner".
  - icedchai 4y ago
    I figured, after all these years, the JVM would switch to a sane default for DNS caching. Sadly that is not the case...

Snawoot 4y ago

That definitely takes place just because on the internet you can find any anomaly you can think of. But it's not widespread. Also, AWS Route53 also relies on fairly low TTL, so it's a non-issue.

donavanm 4y ago

Ive run a major CDN and authoritative nameservice. Its small enough to not matter in most cases. A quick swag is Id expect 95% of traffic to respect the ttl. Another 4% will appear to have some sort of minimum ttl on the order of single digit minutes. The last 1% transitions over the next hours. There will be a super long tail with measurable, but insignificant, traffic using the previous RDATA effectively forever. Im sure someone from DNS OARC has more recent and well quantified numbers.