Hi,
When relying on S-NAPTR (RFC3958), redirection is only possible inside
sub-domains of the original domain name.
I don't think that's true. RFC3958 has exactly this use case in it's
first example section (2.2): a domain example.com redirects service
"EM:protA" to another domain, namely someisp.example - with the
non-terminal flag, as I described in my original mail. This is
absolutely a different domain name.
This is a restriction compared to the use of normal NAPTR and REGEXP.
While making my own experiences with NAPTR, I learned that there is no
"normal" use of NAPTR. NAPTR records are not allowed to be used "in the
wild" without a valid DDDS specification defining its exact semantics.
That is precisely the reason why RFC3588 had to be revised in that
regard. RFC3958 provides that semantics, so it was a natural choice to
re-base Diameter's usage in an S-NAPTR.
The following recommendations can be also found in the RFC6733: "The domain
suffixes in the NAPTR replacement field SHOULD match the domain of the
original query." Actually, I don't even understand the "SHOULD" here without
any clarification on what to do if not... but it is another debate.
I now see that RFC6733 has put this IMHO arbitrary restriction in place.
It really serves no particular purpose; if there was some thinking
behind it, then that really should have been explained in the document.
I would tend to ignore that SHOULD if I were implementing Diameter (I'm
not :-) ). Different domain names are perfectly in scope for S-NAPTRs,
and you would have to consciously lobotomise libraries or code snippets
to *not* permit redirections to other domains.
We are also regularly using s-flag S-NAPTRs in eduroam and RADIUS
Dynamic Discovery to point to a delegate RADIUS server residing in a
different domain. It's just normal operations.
This limitation in RFC6733 is at best "funny" IMHO.
Therefore, my understanding is that the use of S-NAPTR is not suitable for
redirection when the target domain name is different from the original one.
And the current draft proposes to allow any kind of redirection without any
impact on existing DNS infra.
I would rather take a very good look at the section in RFC6733 that
discourages other domain names in the replacement. It's more like an
erratum for me; and if that restriction were away you would have a
working solution to your redirection problem with zero effort.
And anyway, it's a SHOULD without considerations or consequences
attached. Which makes it more of a DONTCARE anyway ;-)
But as I said, it is only based on my understanding and I'm not an expert on
DNS.
I don't think DNS is the problem here. It's more that Diameter butchers
its NAPTR usage unnecessarily.
Greetings,
Stefan Winter
Regards,
Lionel
-----Message d'origine-----
De : dime-bounces(_at_)ietf(_dot_)org
[mailto:dime-bounces(_at_)ietf(_dot_)org] De la part de Stefan Winter
Envoyé : lundi 19 août 2013 10:16
À : dime(_at_)ietf(_dot_)org; 'IETF Discussion Mailing List'
Objet : Re: [Dime] Last Call: <draft-ietf-dime-realm-based-redirect-11.txt>
(Realm-Based Redirection In Diameter) to Proposed Standard
Hello,
The IESG has received a request from the Diameter Maintenance and
Extensions WG (dime) to consider the following document:
- 'Realm-Based Redirection In Diameter'
<draft-ietf-dime-realm-based-redirect-11.txt> as Proposed Standard
Sorry for bringing this up so late, but as I was writing my own dynamic
discovery draft for RADIUS, it occured to me that the usage of S-NAPTR for
Diameter brings a built-in support to signal realm-based redirect
*if* S-NAPTR discovery is used.
That only affects this document periphally; it describes realm-based redirect
for agent-based redirects, not for DNS-based; but still, the wording in
section 2 implies that using a realm-based-redirect-aware Diameter agent is
the only choice, and I think that should be rectified.
The mechanism for S-NAPTR realm-based redirect is built into the S-NAPTR spec
by allowing for "non-terminal" lookups; this is signalled by having neither
an "s" flag (for SRV targets) nor an "a" flag (for A/AAAA targets); but
instead an "" (empty) flag. The replacement string in the NAPTR record is
then the label of /another/ NAPTR lookup; that lookup is then to be performed
with the same service/protocol tag.
That makes the whole realm-based redirect problem very easy protocol-wise.
Consider a realm "foo.example" who wants to tell its Diameter peers that its
realm's application ID 123 is from now on served from "example.com". It puts
into DNS
foo.example. 43200 IN NAPTR 100 10 "" "aaa+ap123:diameter.tls" ""
example.com
A client who got this answer would then query for
example.com NAPTR "aaa+ap123:diameter.tls"
and would get example.com's servers via SRV or A/AAAA records as configured
by the admins of example.com.
This is described in section 2.2.3 of RFC3958.
Now for the wording in the draft:
Sction 2: the first para needs a bit of a rewrite to factor in S-NAPTR's
capabilities.
I suggest something along the lines of:
"Realm-based redirection is implicitly a part of the Diameter base protocol,
but only where peer discovery using S-NAPTR is used (section
5.2 of [RFC6733], by using the non-terminal S-NAPTR flag). This allows for
both application-specific realm-based redirects, and for application-agnostic
(unconditional) realm-based redirects, and does not require any Diameter
agents.
For deployments which do not make use of S-NAPTR peer discovery, support of
realm-based redirection MUST be specified as part of functionality supported
by a Diameter application. (... continue with the rest of the section ...)
Greetings,
Stefan Winter
The IESG plans to make a decision in the next few weeks, and solicits
final comments on this action. Please send substantive comments to the
ietf(_at_)ietf(_dot_)org mailing lists by 2013-08-27. Exceptionally,
comments may
be sent to iesg(_at_)ietf(_dot_)org instead. In either case, please retain
the
beginning of the Subject line to allow automated sorting.
Abstract
Message redirection is a basic capability provided by the Diameter
base protocol. In its conventional form, message redirection is
performed by an application-independent "redirect agent", which
returns one or more individual hosts to the message sender as
possible destinations of the redirected message.
However, in some circumstances an operator may wish to redirect
messages to an alternate domain without specifying individual hosts.
This document specifies an application-specific mechanism by which
that can be achieved. New applications may incorporate this
capability by reference to the present document.
Because the redirection mechanism is application-specific, it must be
performed by a Diameter server or proxy rather than a basic redirect
agent as defined in the Diameter base protocol. A new term, "Realm-
based Redirect Server", is introduced in this document to
differentiate the application-specific nature of realm-based
redirection from the conventional Diameter redirection performed by a
basic redirect agent.
This memo updates Sections 6.13 and 6.14 of RFC6733 with respect to
the usage of the Redirect-Host-Usage and Redirect-Max-Cache-Time
AVPs.
The file can be obtained via
http://datatracker.ietf.org/doc/draft-ietf-dime-realm-based-redirect/
IESG discussion can be tracked via
http://datatracker.ietf.org/doc/draft-ietf-dime-realm-based-redirect/b
allot/
The following IPR Declarations may be related to this I-D:
http://datatracker.ietf.org/ipr/1254/
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--
Stefan WINTER
Ingenieur de Recherche
Fondation RESTENA - Réseau Téléinformatique de l'Education Nationale et de la
Recherche 6, rue Richard Coudenhove-Kalergi
L-1359 Luxembourg
Tel: +352 424409 1
Fax: +352 422473
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Stefan WINTER
Ingenieur de Recherche
Fondation RESTENA - Réseau Téléinformatique de l'Education Nationale et
de la Recherche
6, rue Richard Coudenhove-Kalergi
L-1359 Luxembourg
Tel: +352 424409 1
Fax: +352 422473
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