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Please Clarify rDNS

Discussion in 'Bind / DNS / Nameserver Issues' started by markb14391, Jul 1, 2008.

  1. markb14391

    markb14391 Well-Known Member

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    Hi,

    I'm wondering if cPanel or anyone else can clarify reverse DNS. The cPanel documentation is a bit spotty in some places, and I've seen bits and pieces about rDNS but not enough information to feel comfortable setting it up.

    Can someone please clarify:

    1) Why do I need reverse DNS?
    2) I've heard that it's a problem when e-mail is sent from the client IP, not the client domain. If this is true, is there any way to easily (hopefully automatically) set up rDNS for each client so their e-mail works properly?
    3) Do I really need my data center's permission and/or cooperation to set up reverse DNS?
    4) How do I set up rDNS, step-by-step?

    Thanks in advance!
     
  2. hydra

    hydra Well-Known Member

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    Hi,

    1. From the wiki:
    * One e-mail anti-spam technique is to check the domain names in the rDNS to see if they are likely from dialup users, dynamically assigned addresses, or other inexpensive internet services. Owners of such IP addresses typically assign them generic rDNS names such as "1-2-3-4-dynamic-ip.example.com." Since the vast majority, but by no means all, of e-mail that originates from these computers is spam, many spam filters refuse e-mail with such rDNS names. [3] [4]

    * A Forward Confirmed reverse DNS (FCrDNS) verification can create a form of authentication showing a valid relationship between the owner of a domainname and the owner of the server that has been given an IP address. While not very thorough, this validation is strong enough to often be used for whitelisting purposes, mainly because spammers and phishers usually can't pass verification for it when they use zombie computers to forge domains.

    2. also from the wiki:
    While most rDNS entries only have one PTR record, it is perfectly legal to have many different PTR records[2]. However, having multiple PTR records for the same IP address is generally not recommended unless there is a specific need. For example, if a webserver supports many virtual hosts, there can be one PTR record for each host and some versions of name server software will automatically add a PTR record for each host. Multiple PTR records can cause a couple of problems, including triggering bugs in programs that only expect there to ever be a single PTR record and, in the case of a large webserver, having hundreds of PTR records can cause the DNS packets to be much larger than normal.

    3. Only the owner of the ip (range) can set the PTR record. Usually this is the datacenter. So yes, you need the cooperation of the owner of the ip.

    4. U need to request it from your datacenter/server provider. maybe they have a panel or some form.

    Ronald.
     
    #2 hydra, Jul 1, 2008
    Last edited: Jul 1, 2008
  3. markb14391

    markb14391 Well-Known Member

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    Thanks.

    How can this be set up in cPanel (if it can at all)?

    Also, can automation be set up? If rDNS needs to be set up for each new account, I'd like that to happen automatically during the setup process. My goal is no manual setup.

    Also, if I work with my datacenter do I have to work with them regarding every cPanel account I have (to make sure each account's e-mail works), or can I just set something up once?

    I'd love to see a step-by-step "how-to" from cPanel.
     
  4. markb14391

    markb14391 Well-Known Member

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    cPanel, please provide this information. This is especially important considering the recent changes regarding sending e-mail from users' IP addresses.
     
  5. hydra

    hydra Well-Known Member

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    Hi,

    There is no way to set it with cpanel.
    If you send from your mail server IP you only need to set it for that IP.
    Then you do not need to set it for each cpanel account.

    If you need to send mail from client IP you will need to set the rDNS for that IP to.
    Just ask your ip provider. (datacenter/ co-locater )

    Ronald.
     
    #5 hydra, Jul 2, 2008
    Last edited: Jul 2, 2008
  6. hydra

    hydra Well-Known Member

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  7. markb14391

    markb14391 Well-Known Member

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    Yeah, but does that mean that all my hosting accounts have to be done this way, for example if I have a hundred customers hosting their domains on my server? I want to automate everything, not have to contact my DC to set up rDNS for every single customer domain on my server.

    Am I missing something?
     
  8. cPanelDavidG

    cPanelDavidG Technical Product Specialist

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    Reverse DNS is typically set by the data center, not individual machines. Not saying it isn't technologically possible - just that the vast majority data centers prefer to handle such things themselves rather than letting their customers have control over such things.
     
    #8 cPanelDavidG, Jul 7, 2008
    Last edited: Jul 7, 2008
  9. chirpy

    chirpy Well-Known Member

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    Go on, have a guess
    You also only have one rDNS PTR record for each IP address, not each domain.
     
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