I've noticed that
some email servers are having a hard time looking up our reverse dns pointers,
so i started looking into why this is. When i used dnsstuff.com, its
output shows the following for one of the ip addresses on one of my email
servers:
Preparation:
The reverse DNS entry for an IP is found by reversing the IP, adding it to "in-addr.arpa", and looking up the PTR record.
So, the reverse DNS entry for 207.170.239.65 is found by looking up the PTR record for
65.239.170.207.in-addr.arpa.
All DNS requests start by asking the root servers, and they let us know what to do next.
See How Reverse DNS Lookups Work for more information.
How I am searching:
Asking f.root-servers.net for 65.239.170.207.in-addr.arpa PTR record:
f.root-servers.net says to go to henna.arin.net. (zone: 207.in-addr.arpa.)
Asking henna.arin.net. for 65.239.170.207.in-addr.arpa PTR record:
henna.arin.net [192.26.92.32] says to go to ns1.iplt.twtelecom.net. (zone: 239.170.207.in-addr.arpa.)
Asking ns1.iplt.twtelecom.net. for 65.239.170.207.in-addr.arpa PTR record:
ns1.iplt.twtelecom.net [64.132.94.250] says to go to ns1.choicenet1.com. (zone: 239.170.207.in-addr.arpa.)
WARNING: Duplicate zone found (239.170.207.in-addr.arpa. is repeated). This can prevent the lookup from continuing
(BIND8 and BIND9 will cause a 'server failure' response). Although I will continue, be aware that
most DNS servers will not see your reverse DNS entry.
Asking ns1.choicenet1.com. for 65.239.170.207.in-addr.arpa PTR record: Reports mail.silerpatrol.com. [from 207.170.239.10]
Answer:
207.170.239.65 PTR record: mail.silerpatrol.com. [TTL 3600s] [A=None] *ERROR* A record does not point back to original IP.
The reverse DNS entry for an IP is found by reversing the IP, adding it to "in-addr.arpa", and looking up the PTR record.
So, the reverse DNS entry for 207.170.239.65 is found by looking up the PTR record for
65.239.170.207.in-addr.arpa.
All DNS requests start by asking the root servers, and they let us know what to do next.
See How Reverse DNS Lookups Work for more information.
How I am searching:
Asking f.root-servers.net for 65.239.170.207.in-addr.arpa PTR record:
f.root-servers.net says to go to henna.arin.net. (zone: 207.in-addr.arpa.)
Asking henna.arin.net. for 65.239.170.207.in-addr.arpa PTR record:
henna.arin.net [192.26.92.32] says to go to ns1.iplt.twtelecom.net. (zone: 239.170.207.in-addr.arpa.)
Asking ns1.iplt.twtelecom.net. for 65.239.170.207.in-addr.arpa PTR record:
ns1.iplt.twtelecom.net [64.132.94.250] says to go to ns1.choicenet1.com. (zone: 239.170.207.in-addr.arpa.)
WARNING: Duplicate zone found (239.170.207.in-addr.arpa. is repeated). This can prevent the lookup from continuing
(BIND8 and BIND9 will cause a 'server failure' response). Although I will continue, be aware that
most DNS servers will not see your reverse DNS entry.
Asking ns1.choicenet1.com. for 65.239.170.207.in-addr.arpa PTR record: Reports mail.silerpatrol.com. [from 207.170.239.10]
Answer:
207.170.239.65 PTR record: mail.silerpatrol.com. [TTL 3600s] [A=None] *ERROR* A record does not point back to original IP.
I can see that it
follows the path correctly and gets to my DNS server ok, but what i am confused
about is the "duplicate zone" that is found. I have double and triple
checked and only have one reverse zone for that class C range. I have also
double and triple checked to make sure there wasn't duplicate entries for .65 in
that reverse zone.
Can anyone enlighten
me as to what this might indicate?
Thank you for your
time,
David
