Minimum TTL?

John Levine johnl at
Fri Feb 9 18:10:50 UTC 2018

In article <mailman.451.1518194253.749.bind-users at> you write:
>As long as you understand the implications of what you're doing?
>The zone owner may be using short TTLs to implement load balancing 
>and/or quick failover. If you extend the TTLs, your users may experience 
>poor performance when they try to go to these sites using out-of-date 
>cache entries.

The zone in question is a DNSBL.  When an address is added to or
removed from a dynamically maintained BL, the short TTL means clients
pick it the change promptly.  If you want your mail filtering to work
reliably, you pay attention to that.  Some of Spamhaus' BLs have
minimum TTLs of 10 seconds, and they do update that fast (not using
BIND, of course.)

The person who asked the original question made it quite clear that
his goal is use a commercial DNSBL but avoid paying for it, so I don't
see any need to offer further help.


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