I configured a dns server formy own use recently, such that I can control everything on dns.

There are two dns server and configured in master-slave
master and slave dns server are located in different location (i.e. different subnet)
the master dns will relocate to another data centre soon, then it may be down for a while.

Do Internet people still able to query and resolve my domain name ? against on slave dns server ?

I configured primary and secondary name server on the domain hosting company where
primary name server is pointed to master dns server
secondary name server is pointed to slave dns server

so if master dns down, slave dns will pick up the job of dns response ?

I asked one of my friend, he said that it will not work. He said he tried shutdown the primary dns server and however secondary will not response dns query.

No, you domain will continue working, as long as there's at least 1 dns server alvailable. The 2nd dns will be used as a backup dns. When the 1st one is down, the dns query will get the result from the 2nd dns server. This will make your domain more reliable (about 99% uptime).
Moreover, you can purchase 2 more DNS to make sure that your domain is 100% uptime

Since you've done it... could you please tell me what the procedure is for this? I asked my domain hoster, he told me that I should ask the DENIC (German domain distributor) to do this. Anyone experienced this? Will the the central distributor charge for these "changing favours"?
I have to say that I am a virgin when it comes to domains, because I'm a poor guy and I only have one, that I didn't even buy myself. This one "redirects" to other hosts, but it's actually only a stupid frame with the host in it. Quite unprofessional.
When I set up nameserver it will look as if my hoster was directly on my domain, right?
Can I set up a .de-Domain to use a .com (astahost.com) nameserver? Sounds strange to me..
Any answers appreciated, thanks,
Ruben

Yep you can do it - but you'll need to have a dns server running at your end 24/7, as also you'll need a STATIC IP associated with this dns server.

Secondly you'll need, what is known as a "SOA" or Start Of Authority. Usually this can be purchased for a small one-time fee and this allows you to be a DNS Authority and run your own DNS Server. Without SOA, your own DNS wouldn't function properly, as it won't be linked properly with the root nameservers.

Sorry, this was too much technic talk for me :-/
What I got: A domain hosted at a professional hoster, but without webspace. The domain currently just frames my webspace (not the best solution, is it?).
I talked to them, they told me to talk to the DENIC. I'm the domain owner. My hoster hosts my domain 24/7 so this should be no problem right?
Can you figure out if the DENIC will charge me for the redirection?
I'm not that good with internet theory, I'm sorry :-( the only thing I really understood is that .de-Domain to .com-Nameserver is possible.
Thanks a lot.