Detecting a non-existent domain

Dominic J. Eidson sauron at the-infinite.org
Tue Sep 23 21:24:32 UTC 2003


On Tue, 23 Sep 2003, Kee Hinckley wrote:

> Getting practical for a minute.  What is the optimal way now to see
> if a given host truly exists?  Assume that I can't control the DNS

Look for a SOA record for the domain - this should be the proper way to
check for the existance of a domain, instead of looking for A, NS or MX
records..

  box:~# dig assvsvsdcacdasc.com SOA
  ; <<>> DiG 9.1.3 <<>> assvsvsdcacdasc.com SOA
  ;; global options:  printcmd
  ;; Got answer:
  ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 47940
  ;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0

  ;; QUESTION SECTION:
  ;assvsvsdcacdasc.com.           IN      SOA

  ;; AUTHORITY SECTION:
  com.                    10800   IN      SOA     a.gtld-servers.net. nstld.verisign-grs.com. 2003092300 1800 900 604800 86400


  box:~# dig yahoo.com SOA
  ; <<>> DiG 9.1.3 <<>> yahoo.com SOA
  ;; global options:  printcmd
  ;; Got answer:
  ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 50827
  ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 5, ADDITIONAL: 0

  ;; QUESTION SECTION:
  ;yahoo.com.                     IN      SOA

  ;; ANSWER SECTION:
  yahoo.com.              1800    IN      SOA     hidden-master.yahoo.com. hostmaster.yahoo-inc.com. 2003092304 900 300 604800 600


Note the difference in QUERY and ANSWER numbers for the two...


 - d.

-- 
Dominic J. Eidson
                                        "Baruk Khazad! Khazad ai-menu!" - Gimli
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