draft-ietf-dnsext-dnssec-2535typecode-change-06.txt

bind 源码 最新实现 linux/unix/windows平台

INTERNET-DRAFT                                             Samuel Weiler
Expires: June 2004                                     December 15, 2003
Updates: RFC 2535, [DS]

	 Legacy Resolver Compatibility for Delegation Signer
	 draft-ietf-dnsext-dnssec-2535typecode-change-06.txt

Status of this Memo

   This document is an Internet-Draft and is subject to all provisions
   of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as
   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other
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   as reference material or to cite them other than as "work in
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   The list of current Internet-Drafts can be accessed at
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   The list of Internet-Draft Shadow Directories can be accessed at
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   Comments should be sent to the author or to the DNSEXT WG mailing
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Abstract

   As the DNS Security (DNSSEC) specifications have evolved, the
   syntax and semantics of the DNSSEC resource records (RRs) have
   changed.  Many deployed nameservers understand variants of these
   semantics.  Dangerous interactions can occur when a resolver that
   understands an earlier version of these semantics queries an
   authoritative server that understands the new delegation signer
   semantics, including at least one failure scenario that will cause
   an unsecured zone to be unresolvable.  This document changes the
   type codes and mnemonics of the DNSSEC RRs (SIG, KEY, and NXT) to
   avoid those interactions.

Changes between 05 and 06:

   Signifigantly reworked the IANA section -- went back to one
   algorithm registry.

   Removed Diffie-Hellman from the list of zone-signing algorithms
   (leaving only DSA, RSA/SHA-1, and private algorithms).

   Added a DNSKEY flags field registry.

Changes between 04 and 05:

   IESG approved publication.

   Cleaned up an internal reference in the acknowledgements section.

   Retained KEY and SIG for TKEY, too.  Added TKEY (2930) reference.

   Changed the names of both new registries.  Added algorithm
   mnemonics to the new zone signing algorithm registry.  Minor
   rewording in the IANA section for clarity.

   Cleaned up formatting of references.  Replaced unknown-rr draft
   references with RFC3597.  Bumped DS version number.

Changes between 03 and 04:

   Clarified that RRSIG(0) may be defined by standards action.

   Created a new algorithm registry and renamed the old algorithm
   registry for SIG(0) only.  Added references to the appropriate
   crypto algorithm and format specifications.

   Several minor rephrasings.

Changes between 02 and 03:

   KEY (as well as SIG) retained for SIG(0) use only.

Changes between 01 and 02:

   SIG(0) still uses SIG, not RRSIG.  Added 2931 reference.

   Domain names embedded in NSECs and RRSIGs are not compressible and
   are not downcased.  Added unknown-rrs reference (as informative).

   Simplified the last paragraph of section 3 (NSEC doesn't always
   signal a negative answer).

   Changed the suggested type code assignments.

   Added 2119 reference.

   Added definitions of "unsecure delegation" and "unsecure referral",
   since they're not clearly defined elsewhere.

   Moved 2065 to informative references, not normative.

1. Introduction

   The DNSSEC protocol has been through many iterations whose syntax
   and semantics are not completely compatible.  This has occurred as
   part of the ordinary process of proposing a protocol, implementing
   it, testing it in the increasingly complex and diverse environment
   of the Internet, and refining the definitions of the initial
   Proposed Standard.  In the case of DNSSEC, the process has been
   complicated by DNS's criticality and wide deployment and the need
   to add security while minimizing daily operational complexity.

   A weak area for previous DNS specifications has been lack of detail
   in specifying resolver behavior, leaving implementors largely on
   their own to determine many details of resolver function.  This,
   combined with the number of iterations the DNSSEC spec has been
   through, has resulted in fielded code with a wide variety of
   behaviors.  This variety makes it difficult to predict how a
   protocol change will be handled by all deployed resolvers.  The
   risk that a change will cause unacceptable or even catastrophic
   failures makes it difficult to design and deploy a protocol change.
   One strategy for managing that risk is to structure protocol
   changes so that existing resolvers can completely ignore input that
   might confuse them or trigger undesirable failure modes.

   This document addresses a specific problem caused by Delegation
   Signer's [DS] introduction of new semantics for the NXT RR that are
   incompatible with the semantics in RFC 2535 [RFC2535].  Answers
   provided by DS-aware servers can trigger an unacceptable failure
   mode in some resolvers that implement RFC 2535, which provides a
   great disincentive to sign zones with DS.  The changes defined in
   this document allow for the incremental deployment of DS.

1.1 Terminology

   In this document, the term "unsecure delegation" means any
   delegation for which no DS record appears at the parent.  An
   "unsecure referral" is an answer from the parent containing an NS
   RRset and a proof that no DS record exists for that name.

   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].

1.2 The Problem

   Delegation Signer introduces new semantics for the NXT RR that are
   incompatible with the semantics in RFC 2535.  In RFC 2535, NXT
   records were only required to be returned as part of a
   non-existence proof.  With DS, an unsecure referral returns, in
   addition to the NS, a proof of non-existence of a DS RR in the form
   of an NXT and SIG(NXT).  RFC 2535 didn't specify how a resolver was
   to interpret a response with both an NS and an NXT in the authority
   section, RCODE=0, and AA=0.  Some widely deployed 2535-aware
   resolvers interpret any answer with an NXT as a proof of
   non-existence of the requested record.  This results in unsecure
   delegations being invisible to 2535-aware resolvers and violates
   the basic architectural principle that DNSSEC must do no harm --
   the signing of zones must not prevent the resolution of unsecured
   delegations.

2. Possible Solutions

   This section presents several solutions that were considered.
   Section 3 describes the one selected.

2.1. Change SIG, KEY, and NXT type codes

   To avoid the problem described above, legacy (RFC2535-aware)
   resolvers need to be kept from seeing unsecure referrals that
   include NXT records in the authority section.  The simplest way to
   do that is to change the type codes for SIG, KEY, and NXT.

   The obvious drawback to this is that new resolvers will not be able
   to validate zones signed with the old RRs.  This problem already
   exists, however, because of the changes made by DS, and resolvers
   that understand the old RRs (and have compatibility issues with DS)
   are far more prevalent than 2535-signed zones.

2.2. Change a subset of type codes

   The observed problem with unsecure referrals could be addressed by
   changing only the NXT type code or another subset of the type codes
   that includes NXT.  This has the virtue of apparent simplicity, but
   it risks introducing new problems or not going far enough.  It's
   quite possible that more incompatibilities exist between DS and
   earlier semantics.  Legacy resolvers may also be confused by seeing
   records they recognize (SIG and KEY) while being unable to find
   NXTs.  Although it may seem unnecessary to fix that which is not
   obviously broken, it's far cleaner to change all of the type codes
   at once.  This will leave legacy resolvers and tools completely
   blinded to DNSSEC -- they will see only unknown RRs.

2.3. Replace the DO bit

   Another way to keep legacy resolvers from ever seeing DNSSEC
   records with DS semantics is to have authoritative servers only
   send that data to DS-aware resolvers.  It's been proposed that
   assigning a new EDNS0 flag bit to signal DS-awareness (tentatively
   called "DA"), and having authoritative servers send DNSSEC data
   only in response to queries with the DA bit set, would accomplish
   this.  This bit would presumably supplant the DO bit described in
   RFC 3225.

   This solution is sufficient only if all 2535-aware resolvers zero
   out EDNS0 flags that they don't understand.  If one passed through
   the DA bit unchanged, it would still see the new semantics, and it
   would probably fail to see unsecure delegations.  Since it's
   impractical to know how every DNS implementation handles unknown
   EDNS0 flags, this is not a universal solution.  It could, though,
   be considered in addition to changing the RR type codes.

2.4. Increment the EDNS version

   Another possible solution is to increment the EDNS version number
   as defined in RFC 2671 [RFC2671], on the assumption that all
   existing implementations will reject higher versions than they
   support, and retain the DO bit as the signal for DNSSEC awareness.