Today I have installed a nameserver using bind. After configuring the first clients I noticed a problem when logging of. Each logoff causes a delay from about 10 seconds.

I tried to identify the problem using tcpdump. And I could see that with each logoff and DNS query "." is running.

Code:
16:07:23.373217 IP fcbsrv03.36468 > fcbxen53.domain: 18357+ A? . (17)
So the first question is "what is the reason for the dot query"?

I checked a nameserver in an other environment and this server answers the query with a quick

Code:
pagdns001:/var/lib/named/master # nslookup .
Server:         172.23.0.8
Address:        172.23.0.8#53

Non-authoritative answer:
*** Can't find .: No answer
But the new nameserver is forwarding the query to his forwarders and ends with a timeout after 10 to 15 seconds. Which is causing the delay when logging off.

Code:
fcbsrv03:~ # time nslookup .
;; connection timed out; no servers could be reached


real    0m15.026s
user    0m0.008s
sys     0m0.004s
I have double-checked the configuration but I could not find a difference. So why does the new server forward the request and the other one not?