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Currently I have the following setup with two hostnames and two ips:

cheeze1.mydomain.com    IN  A   123.123.123.111
111.123.123.123.in-addr.arpa    IN  PTR cheeze1.mydomain.com

cheeze2.mydomain.com    IN  A   123.123.123.222
222.123.123.123.in-addr.arpa    IN  PTR cheeze2.mydomain.com

I want to change to having a round-robin dns for a single hostname using the two ips. Are the following PTR records valid? Can a host have multiple IPs and with each having valid reverse dns resolution?

cheezeonly.mydomain.com IN  A   123.123.123.111
cheezeonly.mydomain.com IN  A   123.123.123.222
111.123.123.123.in-addr.arpa    IN  PTR cheezeonly.mydomain.com
222.123.123.123.in-addr.arpa    IN  PTR cheezeonly.mydomain.com

EDIT: Please note that this question isn't asking the same as suggested in comments.

I'm going to answer this one myself, you guys are no help marking it as duplicate and not reading the question properly. Hopefully this answer will help others.

ANSWER:::

Yes, it is valid, and yes it will pass a FcRDNS check.

From the "Pro DNS and BIND" book: http://www.zytrax.com/books/dns/ch9/rr.html

An alternate approach is to define multiple A records with the same mail server name:
; zone file fragment
        IN  MX  10  mail.example.com.
....
mail    IN  A       192.168.0.4
        IN  A       192.168.0.5
        IN  A       192.168.0.6

In this case the load-balancing effect is under the control of BIND and the rrset-order record. In order to avoid problems if the receiving mail system does reverse look-up as a spam check then the PTR records for 192.168.0.4, 192.168.0.5, 192.168.0.6 above must all define (resolve to) mail.example.com.

And from RFC1912: Common DNS Operational and Configuration Errors

"For every IP address, there should be a matching PTR record in the in-addr.arpa domain. If a host is multi-homed, (more than one IP address) make sure that all IP addresses have a corresponding PTR record (not just the first one). Failure to have matching PTR and A records can cause loss of Internet services similar to not being registered in the DNS at all. " –

Therefor this configuration is valid and passes FcRDNS checks.

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  • 2
    re: dups:: no, those aren't what I'm asking. The first is about multiple PTR for a single IP and the second is about having having two different IPs resolve to a single host, which the A record only resolves to one IP, failing fcrdns check.
    – dandan
    May 12, 2015 at 6:10
  • could you please post your answer as an answer to your own question, rather than in the question itself?
    – dbr
    May 12, 2015 at 19:47
  • you guys don't give up. I can't answer my own question, no option to add an answer since douches marked it as duplicate. @dbr at the top of the screen it says "This question already has an answer here:" .... it's disabled the add answer feature for me.
    – dandan
    May 13, 2015 at 15:59
  • 1
    i got way more freaking hassle from the community then help to solve this question.
    – dandan
    May 13, 2015 at 16:01

1 Answer 1

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Yes, it's valid. But...

Some programs do a "double-reverse lookup" or as Wikipedia calls it, Forward-confirmed reverse DNS. Quoting from the wikipedia entry, "RFC 1912 and RFC 1033 (Informational) recommend it as a best practice, but it is not a requirement of standard defining RFCs governing operation of the DNS." (emphasis, mine). The programs that do this will complain or refuse service to/from that IP/hostname.

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  • 1
    this would pass a FcRDNS check though...
    – dandan
    May 12, 2015 at 6:05

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