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RDNS CNAME for MX Record Issue

Okay, so I'm not sure if this is by design or if it is indeed an issue. Just encountered a third-party that's using a CNAME for their MX PTR record and the UTM (9.209-8) rejects it with "RDNS invalid".

"Dig" returns a valid response and checking their domain on various DNS validation sites, everything reports "OK" with their MX and PTR setup.

From what I can gather, it's generally considered "not the best" to use CNAMEs for MX PTR records but there also doesn't appear to be any hard and fast RFC rules that forbid it. So, on to my question; do I just deal with it and create an exception for these people or is this something that should go into a "feature request" list or is this a bug that needs to be fixed?

Thanks!

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0 scorpionking over 10 years ago
Are you talking about the PTR record of the public IP or about the MX record? These are different types.

An MX record has to point to an A record, pointing to a CNAME is a non-standard configuration (as stated in RFC 974).

So if you can't convince that third party to correct their DNS zone you will have to define an exception excluding RDNS check for this domain.
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Private Setup:

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UTM: 2 vCPUs, 2GB RAM, 50GB vHDD, 2 vNICs on vServer (KVM) | UTM 9.7 (Home License) with: Email Protection, Webserver Protection, RED-Tunnel (server)
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0 GoAboutYourBusiness over 10 years ago in reply to scorpionking

Are you talking about the PTR record of the public IP or about the MX record? These are different types.

Sorry, I guess that wasn't very clear. Their forward lookup MX record is fine; the PTR record is using a CNAME:

~$ dig millenniumpartners.net MX +nocomments



; <>> DiG 9.3.6-P1-RedHat-9.3.6-20.P1.el5_8.6 <>> millenniumpartners.net MX +nocomments

;; global options:  printcmd

;millenniumpartners.net.                IN      MX

millenniumpartners.net. 7121    IN      MX      10 mail.millenniumpartners.net.

millenniumpartners.net. 165202  IN      NS      ns87.worldnic.com.

millenniumpartners.net. 165202  IN      NS      ns88.worldnic.com.

mail.millenniumpartners.net. 7121 IN    A       12.226.35.115

ns87.worldnic.com.      7121    IN      A       207.204.40.144

ns88.worldnic.com.      7121    IN      A       206.188.198.44



~$ dig mail.millenniumpartners.net A +nocomments



; <>> DiG 9.3.6-P1-RedHat-9.3.6-20.P1.el5_8.6 <>> mail.millenniumpartners.net A +nocomments

;; global options:  printcmd

;mail.millenniumpartners.net.   IN      A

mail.millenniumpartners.net. 6954 IN    A       12.226.35.115

millenniumpartners.net. 165035  IN      NS      ns88.worldnic.com.

millenniumpartners.net. 165035  IN      NS      ns87.worldnic.com.

ns87.worldnic.com.      6954    IN      A       207.204.40.144

ns88.worldnic.com.      6954    IN      A       206.188.198.44



~$ dig -x 12.226.35.115 +nocomments



; <>> DiG 9.3.6-P1-RedHat-9.3.6-20.P1.el5_8.6 <>> -x 12.226.35.115 +nocomments

;; global options:  printcmd

;115.35.226.12.in-addr.arpa.    IN      PTR

115.35.226.12.in-addr.arpa. 78693 IN    CNAME   115.112-28.35.226.12.in-addr.arpa.

115.112-28.35.226.12.in-addr.arpa. 78693 IN PTR mail.millenniumpartners.net.

112-28.35.226.12.in-addr.arpa. 78693 IN NS      cbru.br.ns.els-gms.att.net.

112-28.35.226.12.in-addr.arpa. 78693 IN NS      cmtu.mt.ns.els-gms.att.net.

cbru.br.ns.els-gms.att.net. 78693 IN    A       68.94.156.132

cmtu.mt.ns.els-gms.att.net. 78693 IN    A       99.99.99.132



~$ host 12.226.35.115

115.35.226.12.in-addr.arpa is an alias for 115.112-28.35.226.12.in-addr.arpa.

115.112-28.35.226.12.in-addr.arpa domain name pointer mail.millenniumpartners.net.

Reply

0 GoAboutYourBusiness over 10 years ago in reply to scorpionking

Are you talking about the PTR record of the public IP or about the MX record? These are different types.

Sorry, I guess that wasn't very clear. Their forward lookup MX record is fine; the PTR record is using a CNAME:

~$ dig millenniumpartners.net MX +nocomments



; <>> DiG 9.3.6-P1-RedHat-9.3.6-20.P1.el5_8.6 <>> millenniumpartners.net MX +nocomments

;; global options:  printcmd

;millenniumpartners.net.                IN      MX

millenniumpartners.net. 7121    IN      MX      10 mail.millenniumpartners.net.

millenniumpartners.net. 165202  IN      NS      ns87.worldnic.com.

millenniumpartners.net. 165202  IN      NS      ns88.worldnic.com.

mail.millenniumpartners.net. 7121 IN    A       12.226.35.115

ns87.worldnic.com.      7121    IN      A       207.204.40.144

ns88.worldnic.com.      7121    IN      A       206.188.198.44



~$ dig mail.millenniumpartners.net A +nocomments



; <>> DiG 9.3.6-P1-RedHat-9.3.6-20.P1.el5_8.6 <>> mail.millenniumpartners.net A +nocomments

;; global options:  printcmd

;mail.millenniumpartners.net.   IN      A

mail.millenniumpartners.net. 6954 IN    A       12.226.35.115

millenniumpartners.net. 165035  IN      NS      ns88.worldnic.com.

millenniumpartners.net. 165035  IN      NS      ns87.worldnic.com.

ns87.worldnic.com.      6954    IN      A       207.204.40.144

ns88.worldnic.com.      6954    IN      A       206.188.198.44



~$ dig -x 12.226.35.115 +nocomments



; <>> DiG 9.3.6-P1-RedHat-9.3.6-20.P1.el5_8.6 <>> -x 12.226.35.115 +nocomments

;; global options:  printcmd

;115.35.226.12.in-addr.arpa.    IN      PTR

115.35.226.12.in-addr.arpa. 78693 IN    CNAME   115.112-28.35.226.12.in-addr.arpa.

115.112-28.35.226.12.in-addr.arpa. 78693 IN PTR mail.millenniumpartners.net.

112-28.35.226.12.in-addr.arpa. 78693 IN NS      cbru.br.ns.els-gms.att.net.

112-28.35.226.12.in-addr.arpa. 78693 IN NS      cmtu.mt.ns.els-gms.att.net.

cbru.br.ns.els-gms.att.net. 78693 IN    A       68.94.156.132

cmtu.mt.ns.els-gms.att.net. 78693 IN    A       99.99.99.132



~$ host 12.226.35.115

115.35.226.12.in-addr.arpa is an alias for 115.112-28.35.226.12.in-addr.arpa.

115.112-28.35.226.12.in-addr.arpa domain name pointer mail.millenniumpartners.net.

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