One document matched: draft-eastlake-dnsext-xnamercode-01.txt
Differences from draft-eastlake-dnsext-xnamercode-00.txt
Network Working Group Donald Eastlake 3rd
INTERNET-DRAFT Stellar Switches
Intended status: Proposed Standard
Expires: December 4, 2010 June 5, 2010
xNAME RCODE and Status Bits Clarification
<draft-eastlake-dnsext-xnamercode-01.txt>
Abstract
The Domain Name System (DNS) has long provided means, such as CNAME
(Canonical Name), where a query can be redirected to a different
name. A DNS response header has an RCODE (Response Code) field, used
for indicating errors, and response status bits. This document
clarifies, in the case of such redirected queries, how the RCODE and
status bits correspond to the initial query cycle (where the CNAME or
the like was detected) and subsequent or final query cycles.
Status of This Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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D. Eastlake [Page 1]
INTERNET-DRAFT xNAME RCODE Clarification
Table of Contents
1. Introduction............................................3
1.1 Conventions used in this document......................3
2. Status Bits.............................................4
2.1 The Authoritative Answer Bit...........................4
2.2 The Authentic Data Bit.................................4
3. RCODE Clarification.....................................5
3.A [Alternative A]........................................5
3.B [Alternative B]........................................5
4. Security Considerations.................................6
5. IANA Considerations.....................................6
6. References..............................................7
6.1 Normative References...................................7
6.2 Informative References.................................7
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INTERNET-DRAFT xNAME RCODE Clarification
1. Introduction
The Domain Name System (DNS) has long provided means, such as the
CNAME (Canonical Name [RFC1035]) and DNAME [RFC2672] RRs (Resource
Records), whereby a DNS query can be redirected to a different name.
In particular, CNAME normally causes a query to its owner name to be
redirected while DNAME normally causes a query to any lower level
name to be redirected. There has been a proposal for another
redirection RR. In addition, as specified in [RFC2672], redirection
through a DNAME also results in the synthesis of a CNAME RR in the
response. In this document, we will refer to all RRs causing such
redirection as xNAME RRs.
xNAME RRs can be explicitly retrieved by querying for the xNAME type.
When a different type is queried and an xNAME RR is encountered, the
xNAME RR (and possibly a synthesized CNAME) is added to the answer of
the response, DNSSEC RRs applicable to the xNAME RR may be added to
the response, and the query is restarted with the name to which it
was redirected.
An xNAME may redirect a query to a name at which there is another
xNAME and so on. In this document, we use "xNAME chain" to refer to a
series of one or more xNAMEs each of which refers to another xNAME
except the last, which refers to a non-xNAME or results in an error.
A DNS response header has an RCODE (Response Code) field, used for
indicating errors, and status bits that indicate whether an answer is
authoritative and/or authentic. This document clarifies, in the case
of such redirected queries, how the RCODE and status bits correspond
to the initial query cycle (where the (first) xNAME was detected) and
subsequent or final query cycles.
1.1 Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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INTERNET-DRAFT xNAME RCODE Clarification
2. Status Bits
There are two status bits returned in query responses for which a
question could arise as to how, in the case of an xNAME chain, they
relate to the first, possible intermediate, and/or last queries, as
follows:
2.1 The Authoritative Answer Bit
The AA, or Authoritative Answer bit, in the DNS response header
indicates that the answer returned is from a DNS server authoritative
for the zone containing that answer. For an xNAME chain, this
"authoritative" status could be different for each answer in that
chain.
[RFC1035] unambiguously states that the AA bit is to be set based on
whether the server providing the answer with the first owner name in
the answer section is authoritative. This specification of the AA
bit has not been changed.
2.2 The Authentic Data Bit
The AD, or Authentic Data bit, indicates that the response returned
is authentic according to the dictates of DNSSEC [RFC4035]. [RFC4035]
unambiguously states that the AD bit is to be set in a DNS response
header only if the DNSSEC enabled server believes all RRs in the
answer and authority sections of that response to be authentic. This
specification of the AD bit has not been changed.
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INTERNET-DRAFT xNAME RCODE Clarification
3. RCODE Clarification
The RCODE (Response Code) field in a DNS query response header is
non-zero to indicate an error. Section 4.3.2 of [RFC1034] has a
resolution algorithm thast includes CNAME processing but has been
found to be unclear concerning the ultimate setting of RCODE in the
case of such redirection. Section 2.1 of [RFC2308] implies that the
RCODE should be set based on the last query cycle in the case of an
xName chain but Section 2.2.1 of [RFC2308] says that some servers
don't do that!
When there is an xNAME chain, the RCODE field is set as follows:
3.A [Alternative A]
As with the AA bit, the RCODE MUST BE set based on the initial lookup
of the QNAME in the original DNS query. This means that, if this
initial lookup succeeds in finding an xNAME RR, which is then
inserted as the first RR in the answer section, necessarily the RCODE
in the ultimate DNS response will be zero, indicating no error.
3.B [Alternative B]
When an xNAME chain is followed, all but the last query cycle
necessarily had no error. The RCODE in the ultimate DNS response MUST
BE set based on the final query cycle leading to that response. If
the xNAME chain was terminated by an error, it will be that error
code. If the xNAME chain terminated without error, it will be zero.
D. Eastlake [Page 5]
INTERNET-DRAFT xNAME RCODE Clarification
4. Security Considerations
The header flag bits and RCODE are not protected by DNSSEC [RFC4033].
To secure them, secure communications are needed between the querying
resolver and the DNS server. Such security can be provided by DNS
transaction security, either TSIG [RFC2845] or SIG(0) [RFC2931].
5. IANA Considerations
This document requires no IANA actions. RFC Editor: please remove
this section on publication.
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INTERNET-DRAFT xNAME RCODE Clarification
6. References
Normative and informative references for this document are given
below.
6.1 Normative References
[RFC1034] - Mockapetris, P., "Domain Names - Concepts and
Facilities", STD 13, RFC 1034, November 1987.
[RFC1035] - Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, November 1987.
[RFC2119] - Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2672] - Crawford, M., "Non-Terminal DNS Name Redirection", RFC
2672, August 1999.
[RFC4035] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security Extensions",
RFC 4035, March 2005
6.2 Informative References
[RFC2308] - Andrews, M., "Negative Caching of DNS Queries (DNS
NCACHE)", RFC 2308, March 1998.
[RFC2845] - Vixie, P., Gudmundsson, O., Eastlake 3rd, D., and B.
Wellington, "Secret Key Transaction Authentication for DNS
(TSIG)", RFC 2845, May 2000.
[RFC2931] - Eastlake 3rd, D., "DNS Request and Transaction Signatures
( SIG(0)s )", RFC 2931, September 2000.
[RFC4033] - Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "DNS Security Introduction and Requirements", RFC 4033,
March 2005.
D. Eastlake [Page 7]
INTERNET-DRAFT xNAME RCODE Clarification
Authors' Addresses
Donald E. Eastlake 3rd
Stellar Switches
155 Beaver Street
Milford, MA 01757
Phone: +1-508-333-2270
email: d3e3e3@gmail.com
D. Eastlake [Page 8]
INTERNET-DRAFT xNAME RCODE Clarification
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D. Eastlake [Page 9]
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