Checking forward and reverse dns

Very often problems like  ‘my website is not working’ or ‘I did not get any emails’ are caused by improperly set up dns records or expired domain. At my work, I’m permanently dealing  with incorrectly set up dns records. There are available services like intodns.com which you can use to check dns records for domain.  But what to do, if you have problem with reverse dns? Or you want to check, if your reverse delegation is set up correctly?


Here dig command with +trace options comes to help:

+trace
Toggle tracing of the delegation path from the root name servers for the name being looked up. Tracing is disabled
by default. When tracing is enabled, dig makes iterative queries to resolve the name being looked up. It will
follow referrals from the root servers, showing the answer from each server that was used to resolve the lookup.

For example, to check reverse delegation for ip 93.184.71.5


dig +trace 5.71.184.93.in-addr.arpa PTR

prints


; <<>> DiG 9.5.1-P2.1 <<>> +trace 5.71.184.93.in-addr.arpa PTR
;; global options:  printcmd
.                       341417  IN      NS      e.root-servers.net.
.                       341417  IN      NS      k.root-servers.net.
.                       341417  IN      NS      a.root-servers.net.
.                       341417  IN      NS      h.root-servers.net.
.                       341417  IN      NS      g.root-servers.net.
.                       341417  IN      NS      d.root-servers.net.
.                       341417  IN      NS      f.root-servers.net.
.                       341417  IN      NS      j.root-servers.net.
.                       341417  IN      NS      c.root-servers.net.
.                       341417  IN      NS      m.root-servers.net.
.                       341417  IN      NS      i.root-servers.net.
.                       341417  IN      NS      b.root-servers.net.
.                       341417  IN      NS      l.root-servers.net.
;; Received 500 bytes from 10.0.0.1#53(10.0.0.1) in 1 ms

93.in-addr.arpa.        86400   IN      NS      SNS-PB.ISC.ORG.
93.in-addr.arpa.        86400   IN      NS      NS-PRI.RIPE.NET.
93.in-addr.arpa.        86400   IN      NS      SEC1.APNIC.NET.
93.in-addr.arpa.        86400   IN      NS      SUNIC.SUNET.SE.
93.in-addr.arpa.        86400   IN      NS      SEC3.APNIC.NET.
93.in-addr.arpa.        86400   IN      NS      NS2.LACNIC.NET.
93.in-addr.arpa.        86400   IN      NS      NS3.NIC.FR.
93.in-addr.arpa.        86400   IN      NS      TINNIE.ARIN.NET.
;; Received 246 bytes from 2001:503:ba3e::2:30#53(a.root-servers.net) in 129 ms

71.184.93.in-addr.arpa. 172800  IN      NS      ns.vnet.sk.
71.184.93.in-addr.arpa. 172800  IN      NS      ns2.vnet.sk.
;; Received 84 bytes from 2001:500:13::c7d4:35#53(TINNIE.ARIN.NET) in 156 ms

5.71.184.93.in-addr.arpa. 43200 IN      CNAME   5.0/26.71.184.93.in-addr.arpa.
0/26.71.184.93.in-addr.arpa. 43200 IN   NS      ns3.lanechange.net.
0/26.71.184.93.in-addr.arpa. 43200 IN   NS      e.ns.lanechange.info.
0/26.71.184.93.in-addr.arpa. 43200 IN   NS      ns2.lanechange.net.
0/26.71.184.93.in-addr.arpa. 43200 IN   NS      ns4.lanechange.net.
0/26.71.184.93.in-addr.arpa. 43200 IN   NS      ns1.lanechange.net.
;; Received 183 bytes from 217.73.16.2#53(ns2.vnet.sk) in 14 ms

Looks good. We have reply, that 5.71.184.93.in-addr.arpa is CNAME to 5.0/26.71.184.93.in-addr.arpa

So we try


dig +trace 5.0/26.71.184.93.in-addr.arpa PTR

which will output

; <<>> DiG 9.5.1-P2.1 <<>> +trace 5.0/26.71.184.93.in-addr.arpa PTR
;; global options:  printcmd
.                       341057  IN      NS      f.root-servers.net.
.                       341057  IN      NS      j.root-servers.net.
.                       341057  IN      NS      i.root-servers.net.
.                       341057  IN      NS      h.root-servers.net.
.                       341057  IN      NS      b.root-servers.net.
.                       341057  IN      NS      m.root-servers.net.
.                       341057  IN      NS      k.root-servers.net.
.                       341057  IN      NS      a.root-servers.net.
.                       341057  IN      NS      g.root-servers.net.
.                       341057  IN      NS      l.root-servers.net.
.                       341057  IN      NS      e.root-servers.net.
.                       341057  IN      NS      c.root-servers.net.
.                       341057  IN      NS      d.root-servers.net.
;; Received 500 bytes from 10.0.0.1#53(10.0.0.1) in 1 ms

93.in-addr.arpa.        86400   IN      NS      SEC1.APNIC.NET.
93.in-addr.arpa.        86400   IN      NS      SEC3.APNIC.NET.
93.in-addr.arpa.        86400   IN      NS      NS3.NIC.FR.
93.in-addr.arpa.        86400   IN      NS      SUNIC.SUNET.SE.
93.in-addr.arpa.        86400   IN      NS      NS-PRI.RIPE.NET.
93.in-addr.arpa.        86400   IN      NS      SNS-PB.ISC.ORG.
93.in-addr.arpa.        86400   IN      NS      TINNIE.ARIN.NET.
93.in-addr.arpa.        86400   IN      NS      NS2.LACNIC.NET.
;; Received 251 bytes from 192.112.36.4#53(g.root-servers.net) in 49 ms

71.184.93.in-addr.arpa. 172800  IN      NS      ns2.vnet.sk.
71.184.93.in-addr.arpa. 172800  IN      NS      ns.vnet.sk.
;; Received 89 bytes from 2001:500:13::c7d4:35#53(TINNIE.ARIN.NET) in 157 ms

0/26.71.184.93.in-addr.arpa. 43200 IN   NS      e.ns.lanechange.info.
0/26.71.184.93.in-addr.arpa. 43200 IN   NS      ns2.lanechange.net.
0/26.71.184.93.in-addr.arpa. 43200 IN   NS      ns4.lanechange.net.
0/26.71.184.93.in-addr.arpa. 43200 IN   NS      ns1.lanechange.net.
0/26.71.184.93.in-addr.arpa. 43200 IN   NS      ns3.lanechange.net.
;; Received 167 bytes from 217.73.16.2#53(ns2.vnet.sk) in 7 ms

5.0/26.71.184.93.in-addr.arpa. 86400 IN PTR     dl5.eset.com.
0/26.71.184.93.in-addr.arpa. 259200 IN  NS      e.ns.lanechange.info.
0/26.71.184.93.in-addr.arpa. 259200 IN  NS      ns1.lanechange.net.
0/26.71.184.93.in-addr.arpa. 259200 IN  NS      ns2.lanechange.net.
0/26.71.184.93.in-addr.arpa. 259200 IN  NS      ns3.lanechange.net.
0/26.71.184.93.in-addr.arpa. 259200 IN  NS      ns4.lanechange.net.
;; Received 273 bytes from 64.79.219.248#53(ns1.lanechange.net) in 121 ms

It seems, all is OK :)

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