timer to waiting for forwarding result

[Merton Campbell Crockett]

On 12 Jun 2006, at 22:54 , Hanrong Jiang wrote:

> Hello,
>
> in named.conf the option "forward first" is used, according to ARM,  
> DNS will
> lookup the forwarders in list to get the result first, when failed/ 
> timeout,
> DNS will lookup record in local.

I don't believe that this is the proper interpretation for "forward  
first".  My interpretation is the following:

(1)  If the request can be  answered with cached data, return the  
cached response.

(2)   If there is no cached data for the response, forward the  
request to the name servers identified in "forwarders".

(3)  If the "forwarders" fail to respond, send a query to the root  
name servers for the name servers authoritative for the domain.

Observation of DNS traffic on my network supports the above  
interpretation.

> Can you give me details about the failure conditions and timer for  
> timeout ?

A SERVFAIL or timeout would advance you to the next forwarder or next  
step.  I can't remember, of the top of my head, the default timeout  
period.  Although I tend to think that it is rather large, on the  
order of 60 sec.

Merton Campbell Crockett
m.c.crockett at adelphia.net