Re: [dnsext] Question on characters in DNS lookups?

[Edward Lewis <[e-mail]>]

At 9:05 +1100 3/5/11, Mark Andrews wrote:

>More correctly the DNS does not place restrictions.  The DNS is
>a storage device.  The users of the DNS may place restrictions.
>
>Hostnames have restrictions RFC 952.
>Mail domains have restrictions RFC 822 and its successors.

Mark,

What's your take on this:

In some places an RR's RDATA needs a domain name and in some places 
it calls for a host name.  The value of CNAME record is a domain 
name.  The value of an NS record is a host name.  The "target" of an 
MX record is a host name.

The difference in these three cases is - in a CNAME the target is a 
location in the tree, not a host.  For a NS, the target is a host but 
one that is being accessed by DNS implementations.  For the latter, 
the MX, the target is a host to be contacted by a SMTP implementation 
- which seem to be quite finicky things when it comes to host syntax.

In light of this, I choose to limit the RDATA of MX records to host 
name rules, and NS too for convenience but let the CNAME be any 8-bit 
value.

The original question mentioned questions - the owner name in a 
question (and all sections) can have any 8-bit value.  I'm asking if 
you think there should be restrictions on what's in RDATA.

I checked STD 13 and found this, this is where I got my idea years ago:

#                CNAME           a domain name.
#
#                MX              a 16 bit preference value (lower is
#                                better) followed by a host name willing
#                                to act as a mail exchange for the owner
#                                domain.
#
#                NS              a host name.

In this case, the NS is said to be a host, not domain, name. From 
that, I would say that the DNS does place restrictions - but only 
within some RDATA specifications.


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Edward Lewis             
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