On Sat, Sep 14, 2019 at 8:38 AM Stephane Bortzmeyer <bortzmeyer@xxxxxx> wrote: > > On Wed, Sep 11, 2019 at 11:55:04AM -0700, > S Moonesamy <sm+ietf@xxxxxxxxxxxx> wrote > a message of 18 lines which said: > > > There is the following recommendation in Section 4: "When returning > > a response containing stale records, a recursive resolver MUST set > > the TTL of each expired record in the message to a value greater > > than 0, with 30 seconds RECOMMENDED". Where does the "30 seconds" > > come from? > > It comes from the fact that it is the upper recommended value between > retrials by the resolver (section 5). So, a downstream client has no > reason to try again before 30 seconds. > > The reasons of this choice (why 30) are in section 6: "Other very > short TTLs could lead to congestive collapse as TTL-respecting clients > rapidly try to refresh. The recommended value of 30 seconds not only > sidesteps those potential problems with no practical negative > consequences, it also rate limits further queries from any client that > honors the TTL, such as a forwarding resolver." Thanks Stephane. Added a reference to section 6 here.
