S-NAPTR
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... Straightforward-NAPTR (S-NAPTR) Specification ...
... S-NAPTR DDDS Application Usage ...
... client examines the
SERVICE field to find a match. In the case of the S-NAPTR DDDS
application, this means a SERVICE field that includes the tags ...
... lookups are to be performed. Thus, to process a NAPTR
record with an empty FLAG field in S-NAPTR, the REPLACEMENT field is
used as the target of the next DNS lookup ...
... S-NAPTR and Successive Resolution ...
... is registered; or
o the S-NAPTR-designated DNS lookup fails to yield expected results
-- e.g., no A RR ...
... application client that supports more than one
protocol for a given application service, it MUST pursue S-NAPTR
resolution completely for one protocol, exploring all potential
terminal ...
... NAPTR RR set supports another of its preferred
protocols, and continue the S-NAPTR resolution based on that
protocol. For example, even if someisp.example offers the "EM"
service ...
...
The purpose of S-NAPTR is to provide application standards developers
with a more powerful framework (than SRV ...
... The rest of this section outlines the specific elements that protocol
developers must determine and document to make use of S-NAPTR.
...
...
Application protocol developers who wish to make use of S-NAPTR must
make provisions for registering any relevant application service and
...
... client
retry a target that was found via S-NAPTR? What should it consider a
failure that causes it to return to the S-NAPTR process to determine
...
... target that was found via S-NAPTR? What should it consider a
failure that causes it to return to the S-NAPTR process to determine
the next serviceable target, which by definition will have a lower
...
... server, should it retry for some (protocol-dependent) period of time?
Or should it try the next-preferred target in the S-NAPTR chain of
resolution? Should it only try the next-preferred target if it
...
...
The most important thing is to select one expected behaviour and
document it as part of the use of S-NAPTR.
As noted earlier, failure to provide appropriate credentials ...
...
Therefore, application protocol developers using S-NAPTR should
identify the mechanics of the expected identification handshake when
...
...
Although S-NAPTR aims to provide a "straightforward" application of
DDDS and use of NAPTR records ...
... Therefore, domain administrators are called upon to use S-NAPTR with
as much restraint as possible while still achieving their service
...
... application cannot successfully connect to one target, the
application will be expected to continue through the S-NAPTR tree to
try the (less preferred) alternatives.
...
...
The basic intended use cases for which S-NAPTR has been developed are
as follows
...
... Note that the above sections assume that there was one service
available (via S-NAPTR) per domain. Often, this will not be the
case. Assuming that thinkingcat.example had the CredReg service ...
... IANA has established and will maintain a registry for S-NAPTR
Application Service Tags, listing at least the following information
...
... clients to unintended destinations. This problem is hardly
unique to S-NAPTR (or NAPTR in general). A full discussion of the
...
... credential naming fields, nor the name-
matching semantics. Definitions of S-NAPTR for particular
application protocols MUST define these.
...
... Appendix A. Pseudo-Pseudocode for S-NAPTR ...
... pseudocode above does not permit retries -- once complete, it
sheds all context of where in the S-NAPTR tree it finished.
Therefore, client software ...
... S-NAPTR processing; or
o use an S-NAPTR resolution routine that finds *all* valid servers
for the required application service ...
...
Sample Python code for S-NAPTR resolution is available from
http://www.verisignlabs.com/pysnaptr-0.1.tgz
...