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Thread: DNS TXT records > 255 characters

  1. #1
    Join Date
    Jul 2005
    Location
    Netherlands
    Posts
    58

    DNS TXT records > 255 characters

    according to rfc 4408 a TXT records can contain more than 255 characters, it just needs to be split into multiple strings.
    rfc...
    3.1.3. Multiple Strings in a Single DNS record As defined in [RFC1035] sections 3.3.14 and 3.3, a single text DNS record (either TXT or SPF RR types) can be composed of more than one string. If a published record contains multiple strings, then the record MUST be treated as if those strings are concatenated together without adding spaces. For example: IN TXT "v=spf1 .... first" "second string..." MUST be treated as equivalent to IN TXT "v=spf1 .... firstsecond string..." SPF or TXT records containing multiple strings are useful in constructing records that would exceed the 255-byte maximum length of a string within a single TXT or SPF RR record...

    I've noticed that DirectAdmin splits records after 149 characters.
    I made some txt records to test

    150.soko.nl text =

    "12345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789"
    "0"


    Is there a reason why the string is split that short?
    Of course this is totally legit. Multple strings in a TXT record is ok. But can't the character count have an higher number, so that strings < 250 characters aren't split?

    maybe there is an other reason for splitting the record @ 150 characters, I'd like to know it.

  2. #2
    Join Date
    Apr 2005
    Location
    GMT +7.00
    Posts
    12,195
    Hello,

    My wild guess is it is done because of a need to show records correct in the Enhanced skin in WebUI

  3. #3
    Join Date
    Jul 2005
    Location
    Netherlands
    Posts
    58
    Nah, I don't think so. because the webinterface is showing it as one string. the splitting happens in the background and is inserted into the .db file.

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