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On 12 Sep 2000, at 16:32, Michael T. Babcock wrote:
> cf. http://www.faqs.org/rfcs/rfc974.html
>
> This is the only mention of the non-use of CNAMEs in the mail
> standards.
I beg to differ. Please have a look at RFC1912, called "Common
DNS errors". Quoting section 2.4:
> Don't use CNAMEs in combination with RRs which point to other names
> like MX, CNAME, PTR and NS. (PTR is an exception if you want to
> implement classless in-addr delegation.) For example, this is
> strongly discouraged:
>
> podunk.xx. IN MX mailhost
> mailhost IN CNAME mary
> mary IN A 1.2.3.4
>
>
> [RFC 1034] in section 3.6.2 says this should not be done, and [RFC
> 974] explicitly states that MX records shall not point to an alias
> defined by a CNAME. This results in unnecessary indirection in
> accessing the data, and DNS resolvers and servers need to work more
> to get the answer. If you really want to do this, you can
> accomplish the same thing by using a preprocessor such as m4 on
> your host files.
>
> Also, having chained records such as CNAMEs pointing to CNAMEs may
> make administration issues easier, but is known to tickle bugs in
> some resolvers that fail to check loops correctly. As a result
> some hosts may not be able to resolve such names.
>
> Having NS records pointing to a CNAME is bad and may conflict badly
> with current BIND servers. In fact, current BIND implementations
> will ignore such records, possibly leading to a lame delegation.
> There is a certain amount of security checking done in BIND to
> prevent spoofing DNS NS records. Also, older BIND servers
> reportedly will get caught in an infinite query loop trying to
> figure out the address for the aliased nameserver, causing a
> continuous stream of DNS requests to be sent.
Other questions? :-)
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--
Petr Novotny, ANTEK CS
[EMAIL PROTECTED]
http://www.antek.cz
PGP key ID: 0x3BA9BC3F
-- Don't you know there ain't no devil there's just God when he's drunk.
[Tom Waits]
