Server Fail and a non-recursive server

[Don Robertson]

I have questions about the "Server Fail" message from a non-recursive
server.

We are trying to set up a DNS server running BIND 8.2.3 that non-recursive.
It needs only be authoritive for its own zones, so we have recursion turned
off and no 'hints' file.

The problem is that we keep getting requests for domains that we are not
hosting. These requests are reoccuring and we believe this is because BIND
answers them with a "Server Fail" rather than a "NXDOMAIN" (name error).

My questions are:

1) Is there a way to configure BIND 8.2.3 so that it will be non-recursive,
yet not return server fail responses when it gets a domain name that it
doesn't know about, putting out NXDOMAIN instead?

2) Do these server fail messages really cause the requesting servers to keep
trying?

3) Any idea why we keep getting requests for these domains (with illegal
underscore characters in them)?:

_ldap._tcp.pdc._msdcs.eunju.com.
_ldap._tcp.434296fc-3d39-470e-a1eb-b60c0522e2a6.domains._msdcs.eunju.com.

Thanks, 
Don Robertson