17

I realize how some might think this isn't exactly constructive, buuuut, I was wondering how come you can't resolve com, org, us, ru, or any other top level domain? I am taking this is as a learning exercise because there might be some holes in my understanding of how DNS works. For example, I tried;

nslookup com
Server:    dns.server.com
Address:   123.123.123.123

*** dns.server.com cant find com: Non-existent domain

I always thought that all other sites under the .com top level domain depended on the existence of an actual domain name called com. At the very least, I thought it kept track of existing domains under the .com domain. What am I missing?

Chad Harrison
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    Thats not how DNS works. You can't query .COM and get a list of anything. If you want to know whats there look into http://IANA.org to see the Root Zone Management – Brent Pabst Aug 17 '12 at 13:46
  • @BrentPabst I must have been asleep for that part of the lecture because this is new iformation for meh. Thanx! – Chad Harrison Aug 17 '12 at 13:56
  • So this is a homework question then? Read the FAQ please. – Brent Pabst Aug 17 '12 at 13:57
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    Is it considered homework if I'm not in school? I was just making reference to the few telecom classes I took a while back. – Chad Harrison Aug 17 '12 at 13:58
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    Not all TLDs behave this way though, I know http://ws/ has an A record (it redirects you to `www.website.ws`) – DerfK Aug 17 '12 at 14:11
  • Just because someone slept through classes when they were taking those classes does not mean they are taking them now. OTOH, maybe that would be a good idea. – Skaperen Aug 17 '12 at 14:46

2 Answers2

24

They do depend on com. - but it does not have an A record and you can't look it up like that. Try looking for the NS record instead: 

 nslookup
> set type=NS
> com.
Server:     12.12.12.12
Address:    12.12.12.12#53

Non-authoritative answer:
com nameserver = b.gtld-servers.net.
com nameserver = f.gtld-servers.net.
com nameserver = j.gtld-servers.net.
com nameserver = g.gtld-servers.net.
com nameserver = k.gtld-servers.net.
com nameserver = e.gtld-servers.net.
com nameserver = l.gtld-servers.net.
com nameserver = d.gtld-servers.net.
com nameserver = i.gtld-servers.net.
com nameserver = m.gtld-servers.net.
com nameserver = a.gtld-servers.net.
com nameserver = h.gtld-servers.net.
com nameserver = c.gtld-servers.net.

Authoritative answers can be found from:
b.gtld-servers.net  internet address = 192.33.14.30
b.gtld-servers.net  has AAAA address 2001:503:231d::2:30
f.gtld-servers.net  internet address = 192.35.51.30
j.gtld-servers.net  internet address = 192.48.79.30
g.gtld-servers.net  internet address = 192.42.93.30
k.gtld-servers.net  internet address = 192.52.178.30
e.gtld-servers.net  internet address = 192.12.94.30
l.gtld-servers.net  internet address = 192.41.162.30
d.gtld-servers.net  internet address = 192.31.80.30
i.gtld-servers.net  internet address = 192.43.172.30
m.gtld-servers.net  internet address = 192.55.83.30
a.gtld-servers.net  internet address = 192.5.6.30
a.gtld-servers.net  has AAAA address 2001:503:a83e::2:30
h.gtld-servers.net  internet address = 192.54.112.30
c.gtld-servers.net  internet address = 192.26.92.30

This will give you the gtld-servers which are authoritative for com. and on which you are directed to next set of nameservers for a domain.

If you have dig, try dig +trace com. if not, then visit http://www.digwebinterface.com/?hostnames=com.&type=&trace=on&ns=resolver&useresolver=8.8.4.4&nameservers= which will show you the output and the route from root level (.) until the NS that gives you the NXDOMAIN response.

Frands Hansen
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17

You're not missing anything. Domain 'com' exists, but has no A records. If you look for NS records (domain server records), you get results (as expected).

; <<>> DiG 9.9.1-P2 <<>> NS com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 25150
;; flags: qr rd ra; QUERY: 1, ANSWER: 13, AUTHORITY: 0, ADDITIONAL: 16

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;com.                               IN      NS

;; ANSWER SECTION:
com.                        8396    IN      NS      d.gtld-servers.net.
com.                        8396    IN      NS      l.gtld-servers.net.
com.                        8396    IN      NS      g.gtld-servers.net.
com.                        8396    IN      NS      f.gtld-servers.net.
com.                        8396    IN      NS      m.gtld-servers.net.
com.                        8396    IN      NS      k.gtld-servers.net.
com.                        8396    IN      NS      h.gtld-servers.net.
com.                        8396    IN      NS      e.gtld-servers.net.
com.                        8396    IN      NS      c.gtld-servers.net.
com.                        8396    IN      NS      j.gtld-servers.net.
com.                        8396    IN      NS      i.gtld-servers.net.
com.                        8396    IN      NS      a.gtld-servers.net.
com.                        8396    IN      NS      b.gtld-servers.net.

;; ADDITIONAL SECTION:
a.gtld-servers.net. 94680   IN      A       192.5.6.30
a.gtld-servers.net. 94680   IN      AAAA    2001:503:a83e::2:30
b.gtld-servers.net. 94680   IN      A       192.33.14.30
b.gtld-servers.net. 94680   IN      AAAA    2001:503:231d::2:30
c.gtld-servers.net. 94680   IN      A       192.26.92.30
d.gtld-servers.net. 94680   IN      A       192.31.80.30
e.gtld-servers.net. 94680   IN      A       192.12.94.30
f.gtld-servers.net. 94680   IN      A       192.35.51.30
g.gtld-servers.net. 94680   IN      A       192.42.93.30
h.gtld-servers.net. 94680   IN      A       192.54.112.30
i.gtld-servers.net. 94680   IN      A       192.43.172.30
j.gtld-servers.net. 94680   IN      A       192.48.79.30
k.gtld-servers.net. 94680   IN      A       192.52.178.30
l.gtld-servers.net. 94680   IN      A       192.41.162.30
m.gtld-servers.net. 94680   IN      A       192.55.83.30

;; Query time: 35 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Fri Aug 17 15:50:18 2012
;; MSG SIZE  rcvd: 520
mulaz
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    There is also an SOA record, as well as DNSKEY, NSEC3PARAM, and RRSIG records. Zone transfers are disabled, of course. – Skaperen Aug 17 '12 at 14:49