Cache only nameserver...

[Ladislav Vobr]

> The state of the link has no effect on whether it uses its cache or not.
> It always responds from the cache if the answer is in there and its TTL
> hasn't expired.  If not, it has to go out to the Internet to get the
> answer; if the link is saturated, this may take a while to succeed.

the state of the link has an impact on bind performance generally. If 
under load from the recursion desired clients, bind might become 
completely nonresposive, be it either cached or non-recursive requests.

it's recursive request queue gets full and starts dropping the recursive 
requests, which are not cached, and the the cached or authoritative 
requests might not be answered, since the whole system is busy 
continuosly retrying and following up every uncached recursive requests 
several times again and again. The load on such a servers goes up 
dramatically.

I used to disable recursion and do ndc reload, this will stop this 
"ridiculous activity, when it's clear that uplinks are down" and starts 
answering from the cache only + athorative requests.

Ladislav