invalidate cache on cache-only resolver?

[Frank Cusack]

Is it possible to invalidate the cache for a zone on a cache-only
resolver?

On a resolver that is master or slave for a zone, I can run
`ndc reload <zone>'.

Anything like this for cache-only?

Or, how about letting cache-only servers listen to NOTIFY messages and
invalidate their cache based on receiving such a message? Yes, there
are security (performance) implications, but something similar to
how NOTIFY works with slaves could happen:

  -- master sends NOTIFY to cache-only
  -- cache-only sends notify-response to master
  -- cache-only requests soa record and checks serial
     -- if serial is newer, cache-only invalidates cache for that zone

This would be useful in our environment, if anyone else thinks this is
a useful item I'd be willing to work on a BIND patch. Also a patch
for ndc and BIND that adds an invalidate message.

~frank

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