timer to waiting for forwarding result
Merton Campbell Crockett
m.c.crockett at adelphia.net
Wed Jun 14 02:00:44 UTC 2006
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
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