On Sunday, February 13, 2005, 8:56:32 AM, Alain wrote:
But the good news is : The more users, the more caching. So the burden on the nameservers will grow slower.
The SURBL zone files have a minimal 15 minute TTL, so in order for ISP resolver hits to be cached, the queries will need to occur within some 15 minutes, which seems less likely at MUA download time than at MTA processing time. MTAs probably see similar spam over a short period of time whereas MUA clients can download at any later time.
In this case, I don't think your argument applies. For something like caching yahoo domains, or any with "normal" longer TTLs, it probably applies more strongly.
While not having experience with DNS TTL's, wouldn't it be possible to give individual ttl? For example start with 10 minutes and add one 1 minute for the days the entry is inside the list? (Recalculation can be done one's a day.), this is only usefull if older entries would have significantly less FP's. Given the very low FP's already, this is probably difficult to measure. Well just an idea and probably not needed for performance.
We keep the TTLs low to both speed up the addition of new records to the list and speed up the deletion of old records. The 15 minute TTL was chosen because it experimentally maximized speed of these changes and minimized DNS server traffic. (It turns out that some other RBLs also settled on 15 minute TTLs as optimal.)
TTLs for normal domains would be more like 1 day.
Jeff C. -- "If it appears in hams, then don't list it."