I am running two name servers (bind 9.2.4) on linux servers.
I am using delegation for some entries of the first name server
to the second name server.

name NS server2.domain.

name A

So if a client asks the first name server for a delegated name,
the first name server uses recursion and asks the second
name server. Then it sends the answer to the client.

On both name servers only ipv4 is in use, there are no
ipv6 records.

When a client starts an ipv4 query for a delegated name to
the first name server it gets the right answer containing the ip address.

But when the client sends an ipv6 query, the first name server
answers with SERVFAIL, although the second name server
(with the delegated name) answers with NOERROR (with
an empty answer section) to the first name server.

The ipv6 client then waits serveral seconds
before it asks again. So each name resolution causes delay.
There is no way to turn off ipv6 on the client.

For a name which is not delegated, the answer of the first
name server to the ipv6 query is NOERROR with empty
answer section. This is ok and causes no delay at the

Does anybody know why a SERVFAIL appears?
Is this a bug or a feature?
Is there a way to change the behaviour?