A question from RFC 3403

[sandoche BALAKRICHENAN]

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An example from RFC 3403

The URN might look like this:

urn:cid:1996061...@bar.example.com

This Application's First Well Known Rule is to extract the characters
between the first and second colon. For this URN that would be
'cid'. The Application also specifies that, in order to build a
Database-valid Key, the string 'urn.arpa' should be appended to the
result of the First Well Known Rule. The result is 'cid.urn.arpa'.
Next, the client queries the DNS for NAPTR records for the domain-
name 'cid.urn.arpa'. The result is a single record:

cid.urn.arpa. IN NAPTR 100 10 "" ""
"!^urn:cid:.+@([^\.]+\.)(.*)$!\2!i"

My question is when the application has already converted
"urn:cid:1996061...@bar.example.com" -> cid.urn.arpa.

==> why does the regexp string again searches for "urn:cid:" ?

The RFC says

REGEXP - A <character-string> containing a substitution expression that is applied to the original string

==> Anyone have an idea why it always should be applied to the original string?

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[Niall O'Reilly]

sandoche BALAKRICHENAN wrote:

> REGEXP - A <character-string> containing a substitution expression that
> is applied to the original string
>
> ==> Anyone have an idea why it always should be applied to the original
> string?

OT for bind-users, so I'll give the shortest answer I can:
what other string is available?

Let's find a better list for discussing the mysteries of DDDS.
It would be useful to have a broader community of understanding.

If anyone on this (bind-users) list knows of a natural home for
this discussion, I'ld appreciate a pointer.

ATB
/Niall

[Stephane Bortzmeyer]

On Wed, May 27, 2009 at 10:48:49AM +0100,
Niall O'Reilly <Niall....@ucd.ie> wrote
a message of 24 lines which said:

> OT for bind-users,

OK, but see later.

> what other string is available?

The domain name.

> Let's find a better list for discussing the mysteries of DDDS.
> It would be useful to have a broader community of understanding.
>
> If anyone on this (bind-users) list knows of a natural home for
> this discussion, I'ld appreciate a pointer.

I would like to know it, too.

IETF "DNS extensions" mailing list (namedroppers) is focused on future
protocols and trying to get insight on previous discussions seems
often frowned upon.

OARC dns-operations mailing list focus on... operations.

There is no "dns-talk" or "dns-i-want-to-learn" mailing list, as far
as I know.

[SM]

At 07:22 26-05-2009, sandoche BALAKRICHENAN wrote:
>An example from RFC 3403
>
>The URN might look like this:
>
> urn:cid:1996061...@bar.example.com
>
> This Application's First Well Known Rule is to extract the characters
> between the first and second colon. For this URN that would be
> 'cid'. The Application also specifies that, in order to build a
> Database-valid Key, the string 'urn.arpa' should be appended to the
> result of the First Well Known Rule. The result is 'cid.urn.arpa'.
> Next, the client queries the DNS for NAPTR records for the domain-
> name 'cid.urn.arpa'. The result is a single record:
>
>cid.urn.arpa. IN NAPTR 100 10 "" ""
>"!^urn:cid:.+@([^\.]+\.)(.*)$!\2!i"
>
>My question is when the application has already converted
>"urn:cid:1996061...@bar.example.com" -> cid.urn.arpa.
>
>==> why does the regexp string again searches for "urn:cid:" ?

Because it's not a terminal lookup.

>REGEXP - A <character-string> containing a substitution expression
>that is applied to the original string
>
>==> Anyone have an idea why it always should be applied to the
>original string?

The answer is in the paragraph that follows the one you quoted.

Regards,
-sm