All this TTL talk makes me think. Why not have two ttls - a 'must-recheck' (does not expire the record but forces a recheck; updates record if server replies & serial has incremented) and a 'must-delete' (cache will be stale at this point)? On October 23, 2016 3:42:58 PM PDT, Mark Andrews <marka@isc.org> wrote:
On Oct 21, 2016, at 6:35 PM, Eitan Adler <lists@eitanadler.com>
wrote:
[...]
In practice TTLs tend to be ignored on the public internet. In
research I've been involved with browser[0] behavior was effectively random despite the TTL set.
[0] more specifically, the chain of DNS resolution and caching down to the browser.
Yes, but that it can be both better and worse than your TTLs does not mean that you can ignore properly working implementations.
If the other end device chain breaks you that's their fault and out of your control. If your own settings break you that's your fault.
+1 to what George wrote that we should make efforts to improve our
the network. There are ISPs that ignore TTL settings and only update
In message <CADJJukkadFbOYvWVan_8pdR=fxenqGRsyisiKBH6vpyDse6JrQ@mail.gmail.com> , Masood Ahmad Shah writes: past part of their
cached records every two to three days or even more (particularly the smaller ones). OTOH, this results in your DNS data being inconsistent but it���s very common to cache DNS records at multiple levels. It's an effort that everyone needs to contribute to.
For TTL there is a tension between being able to update with new data and resiliance when servers are unreachable. For zone transfers we have 3 timers refesh, retry and expire to deal with this tension. If we were doing DNS from scratch there would be at least two ttl values one for freshness and one for don't use past.
Additionally a lot of the need for small TTL's is because clients don't fail over to second addresses in a reasonable amount of time. There is no reason for this other than poorly designed clients. A client can failover using sub-second timers. We do this for Happy Eyeballs. This strategy is viable for ALL connection attempts.
Mark
-- Sent from my Android device with K-9 Mail. Please excuse my brevity.