On Jul 12, 2007, at 10:36 PM, Olivier Nicole wrote:
I'm using dynamicDNS, so I will able to specify the forward *AND*
reverse lookups?
Yes.
No, nobody else is going to see the results your local nameserver
sends since it isn't authoritative for the domains, and the
delegation for the IP block isn't going to point to your server but
to the actual nameserver. Take a look at what happens when someone
using an external nameserver does the same queries:
Forward DNS lookup: (alrw17.desktops.cs.ait.ac.th is dynamic DNS)
banyan<on>57: dig alrw17.desktops.cs.ait.ac.th
; <<>> DiG 9.3.1 <<>> alrw17.desktops.cs.ait.ac.th
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 15772
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 1,
ADDITIONAL: 1
;; QUESTION SECTION:
;alrw17.desktops.cs.ait.ac.th. IN A
;; ANSWER SECTION:
alrw17.desktops.cs.ait.ac.th. 3600 IN A 192.41.170.214
;; AUTHORITY SECTION:
desktops.cs.ait.ac.th. 43200 IN NS dns.cs.ait.ac.th.
;; ADDITIONAL SECTION:
dns.cs.ait.ac.th. 43200 IN A 192.41.170.15
;; Query time: 1 msec
;; SERVER: 192.41.170.15#53(192.41.170.15)
;; WHEN: Fri Jul 13 12:35:23 2007
;; MSG SIZE rcvd: 96
% dig alrw17.desktops.cs.ait.ac.th
; <<>> DiG 9.3.4 <<>> alrw17.desktops.cs.ait.ac.th
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NXDOMAIN, id: 30625
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 0
;; QUESTION SECTION:
;alrw17.desktops.cs.ait.ac.th. IN A
;; AUTHORITY SECTION:
desktops.cs.ait.ac.th. 10800 IN SOA dns.cs.ait.ac.th.
postmaster.cs.ait.ac.th. 2006139734 21600 1800 1209600 43200
;; Query time: 892 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Fri Jul 13 13:09:14 2007
;; MSG SIZE rcvd: 97
Notice the NXDOMAIN response...?
Reverse DNS lookup:
banyan<on>58: dig -x 192.41.170.214
; <<>> DiG 9.3.1 <<>> -x 192.41.170.214
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 14984
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 1,
ADDITIONAL: 1
;; QUESTION SECTION:
;214.170.41.192.in-addr.arpa. IN PTR
;; ANSWER SECTION:
214.170.41.192.in-addr.arpa. 43200 IN CNAME 214.170.41.192.rev-
dns.cs.ait.ac
.th.
214.170.41.192.rev-dns.cs.ait.ac.th. 3600 IN PTR
alrw17.desktops.cs.ait.ac.th.
;; AUTHORITY SECTION:
170.41.192.rev-dns.cs.ait.ac.th. 43200 IN NS dns.cs.ait.ac.th.
;; ADDITIONAL SECTION:
dns.cs.ait.ac.th. 43200 IN A 192.41.170.15
;; Query time: 9 msec
;; SERVER: 192.41.170.15#53(192.41.170.15)
;; WHEN: Fri Jul 13 12:35:31 2007
;; MSG SIZE rcvd: 158
% dig -x 192.41.170.214
; <<>> DiG 9.3.4 <<>> -x 192.41.170.214
;; global options: printcmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 53167
;; flags: qr rd ra; QUERY: 1, ANSWER: 2, AUTHORITY: 1, ADDITIONAL: 0
;; QUESTION SECTION:
;214.170.41.192.in-addr.arpa. IN PTR
;; ANSWER SECTION:
214.170.41.192.in-addr.arpa. 43200 IN CNAME 214.170.41.192.rev-
dns.cs.ait.ac.th.
214.170.41.192.rev-dns.cs.ait.ac.th. 3600 IN PTR
VAIO.desktops.cs.ait.ac.th.
;; AUTHORITY SECTION:
170.41.192.rev-dns.cs.ait.ac.th. 43200 IN NS dns.cs.ait.ac.th.
;; Query time: 438 msec
;; SERVER: 127.0.0.1#53(127.0.0.1)
;; WHEN: Fri Jul 13 13:09:49 2007
;; MSG SIZE rcvd: 140
The answer everyone else gets, VAIO.desktops.cs.ait.ac.th, doesn't
match alrw17.desktops.cs.ait.ac.th, so a double-reverse lookup check
would fail.
--
-Chuck
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