dig @server foobar +trace +recurse

John Miller johnmill at brandeis.edu
Thu Jul 9 17:35:37 UTC 2015


Even after flushing Google's cache (
>> https://developers.google.com/speed/public-dns/cache), I still get the
>> same response.  Does anyone have insight on +showsearch, other than the
>> following ;-)
>>
>> ...
>
> "showsearch" has nothing to do with iteration or recursion.  "showsearch"
> is related to the "search list" that is used if the domain name you are
> searching for is not fully qualified (does not end in a dot).  Only useful
> if /etc/resolv.conf has a "search" list (or "domain" has more than two
> labels which creates an implied search list).   See man page for
> resolv.conf for more.
>

Thanks for the clarification, Bob.  I definitely didn't make the connection
between "search" and "showsearch," so your response helped.  Otherwise,
some careful reading and educated guessing's definitely required to figure
this out:

       +[no]showsearch
           Perform [do not perform] a search showing intermediate results.

This doesn't say anything about resolv.conf.  "search," however, is
clear-cut: use the list in resolv.conf or don't (default):

       +[no]search
           Use [do not use] the search list defined by the searchlist or
domain directive in resolv.conf (if any). The
           search list is not used by default.

and it's easy to see the difference:

me at mybox ~ $ grep search /etc/resolv.conf
search brandeis.edu

me at mybox ~ $ dig alumni
;; QUESTION SECTION:
;alumni.                IN    A

jmiller at 100degN ~ $ dig +search alumni
;; QUESTION SECTION:
;alumni.brandeis.edu.        IN    A
;; ANSWER SECTION:
alumni.brandeis.edu.    11396    IN    A    129.64.101.157

Because it uses resolv.conf , it gives the same results as using the "host"
command.

And "showsearch" shows the full chain of queries made based on your search
path -- "+showsearch" has an implied "+search" in it:

(server fqdn: dns-rec-xs-dev1.unet.brandeis.edu; search path: brandeis.edu
unet.brandeis.edu)

[me at server ~]$ dig dns-rec-xs-dev1
;; QUESTION SECTION:
;dns-rec-xs-dev1.        IN    A

[me at server ~]$ dig +search dns-rec-xs-dev1
;; QUESTION SECTION:
;dns-rec-xs-dev1.unet.brandeis.edu. IN    A
;; ANSWER SECTION:
dns-rec-xs-dev1.unet.brandeis.edu. 11306 IN A    129.64.100.67

[me at server ~]$ dig +showsearch dns-rec-xs-dev1
;; QUESTION SECTION:
;dns-rec-xs-dev1.brandeis.edu.    IN    A
;; AUTHORITY SECTION:
brandeis.edu.        1437    IN    SOA    dns-master.brandeis.edu.
hostmaster.brandeis.edu. 1436381401 3600 1800 1209600 1800

;; QUESTION SECTION:
;dns-rec-xs-dev1.unet.brandeis.edu. IN    A
;; ANSWER SECTION:
dns-rec-xs-dev1.unet.brandeis.edu. 10655 IN A    129.64.100.67

_Two_ question and answer sections here: it shows both queries that dig
makes.  Same results as running host -v; just a different format.

I'd suggest substituting:

       +[no]showsearch
           Perform [do not perform] a search showing intermediate results.

with

       +[no]showsearch
           Similar to +search, but show [do not show] results for each
domain in the searchlist.  Automatically enables
          +search.

I'll read through the contributors' guide and submit a patch.

John
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