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RFC 6011, "Session Initiation Protocol (SIP) User Agent Configuration", October 2010

Source of RFC: IETF - NON WORKING GROUP
Area Assignment: rai
See Also: RFC 6011 w/ inline errata

Errata ID: 2622
Status: Verified
Type: Technical
Publication Format(s) : TEXT
Reported By: Alfred Hoenes
Date Reported: 2010-11-11
Verifier Name: Gonzalo Camarillo
Date Verified: 2013-04-03

Section 2.3.1.2 says: 

   If the DNS request to resolve the Configuration Service Domain name
   to a request URL does not receive any response, the UA should follow
   standard DNS retry procedures.

   If the DNS request to resolve the Configuration Service Domain name
|  to a host name returns a response that indicates that no matching
|  result is available (NXDOMAIN), the UA SHOULD attempt to obtain
   another Configuration Service Domain name using the procedures in
   Section 2.2, "Obtaining the Configuration Service Domain".

It should say:

   If the DNS request to resolve the Configuration Service Domain name
   to a request URL does not receive any response, the UA should follow
   standard DNS retry procedures.

   If the DNS request to resolve the Configuration Service Domain name
|  to a request URL returns a response that indicates that the queried
|  domain does not exist (NXDomain), that no matching result is
|  available at that domain (NoError response with an empty NAPTR RRset
|  in the Answer section), or that a permanent error condition exists
|  (other non-zero RCODE value, e.g., ServFail), the UA SHOULD attempt
   to obtain another Configuration Service Domain name using the
   procedures in Section 2.2, "Obtaining the Configuration Service
   Domain".

Notes:

Rationale:
a) This section discusses the U-NAPTR usage; therefore, as in the first
paragraph, the second paragraph should not erroneously indicate
a "host name" return, it also should precisely indicate that it
talks about U-NAPTR lookup; hence s/host name/request URL/ .

b) It is an unfortunately widespread misconception that a DNS query
for a RR type that does not exists at a particular domain name
returns a NXDomain response. This is not the case. An empty RRset
is a valid response returned with RCODE=0 (NoError). Further, the
RFC text omits the important error cases that also need to be dealt
with by the SIP UA configuration procedure.
The replacement text tries to clarify the different situations
where no NAPTR record can be obtained.

c) Use the standard version spelling of DNS RCODE names as registered
in the "DNS RCODEs" sub-registry -- part of
http://www.IANA.ORG/assignments/dns-parameters.

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