what is the behavior of global forwarders

[Kevin Darcy]

kalyanasundaram S wrote:
> Hi,
>   I have a problem regarding forwarders. I configured /etc/named.conf global option with the following
>  global {
>   forward only;
>   forwarders {1.2.3.4; };
>   ......
>   ....
>  }
>
> ..
> ..
> zone "example.com" in {
>    type forward;
>    forward first;
>    forwarders { 3.3.3.3; };
> };
>
> this 3.3.3.3 does not exist. (it is a stand alone setup- so there is no root server access,and 1.2.3.4 is alive in that stand alone setup) I queried for some client in example.com. What i expected was that it is not able to contact 3.3.3.3 so it should go for global forwarders(in this case 1.2.3.4) . But it looks for root server and said connection time out.
>
> then again i had 
> zone "example.com" in {
>    type forward;
> };
> i expected atleast now it should go for global forwarders. But again the same.
>
> what is default behaviour of global forwarders. Where it is used? how do i configure my dns to go for global forwarders when the forward zone forwarders is not available?
>
> is it a bug or am i missing some option to set
>   
Forwarders are not cumulative. The list of forwarders you define at a 
given zone level overrides any forwarders you may or may not have 
defined at ancestor zone levels which in turn override the global 
forwarders. If you want the global forwarders to be used 
*in*addition*to* some set of zone-specific forwarders, then add them to 
the list.

Note that some versions of BIND 9 work through the forwarders list 
*sequentially*, so if you're running one of those versions, you might 
want to give some thought as to the order of the list. Other versions of 
BIND 9 choose forwarders based on an adaptive algorithm which keeps 
track of how quickly the respective forwarders respond to queries. For 
those versions, the order in which the forwarders are defined is irrelevant.

- Kevin