switching query-source address on timeout and exhaustion of available servers

[Giuliano Gavazzi]

Hello, on one server I run BIND 9.3.1 as /sbin/named -4 on MacOSX10.3.9.

In the last few days I have seen failures in resolving some domains,  
just a couple I believe. This failure happens only when the query- 
source is changed from one line (ADSL) to another (HDSL) on a  
different provider.
I have traced the problem to a routing problem between the HDSL  
provider network and the secondaries of the domain(s) in question.
This is what happens: the first name server queried gives a SERVFAIL  
(should not!) and then the secondaries are interrogated, but they are  
reachable only from the ADSL line. So when originated from the HDSL  
line instead, the query times out.

I hope this is not a FAQ: it would be interesting to be able to switch  
query-source after a timeout or error has been hit on all nameservers  
so that the these temporary (hopefully) network problems can be  
circumvented (at least for DNS...).

Thanks

Giuliano