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Network Working Group M. Kosters
Internet-Draft Network Solutions, Inc.
Expires: May 18, 2001 November 17, 2000
DNSSEC Opt-in for Large Zones
draft-kosters-dnsext-dnssec-opt-in-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
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 documents
at any time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on May 18, 2001.
Copyright Notice
Copyright (C) The Internet Society (2000). All Rights Reserved.
Abstract
In order for DNSSEC to be deployed operationally with large zones
and little operational impact, there needs to be included a
mechanism that allows for the separation of secure versus unsecure
views of zones. This needs to be done in a transparent fashion that
allows DNSSEC to be deployed in an incremental manner. This
document proposes the use of an extended RCODE to signify that a
DNSSEC-aware requestor may have to re-query for the information, if
and only if, the delegation is not yet secure. Thus, one can
maintain two views of the zone and expand the DNSSEC zone as demand
warrants.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Rationale . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Protocol Additions . . . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 8
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1. Introduction
DNS is an unsecure system. The key features that gives DNS its power
can also be its chief weaknesses. One feature is the facility to
delegate branches of information from one set of servers to another.
Currently, this is done in a non-cryptographically verified way that
allows spoofing attacks. For example, Eugene Kashpureff exploited
this vulnerability to redirect www.netsol.com and www.internic.net
to his own website. If this delegated information had been
cryptographically verified, this attack would not have been able to
occur.
In recent years, there has been much work within the IETF regarding
DNS security. There are a number of RFCs that integrate public key
technology within DNS to enable cryptographically-verified answers.
To this end, three new resource record types (RR's) have been
defined:
o KEY -- a public key of the zone
o SIG - a signature of an accompanying RR
o NXT - a negative response record
Within the zone, each authoritative RR will have accompanying SIG
RR's that can be verified with the KEY RR of the zone. Each KEY RR
can be verified hierarchically with a SIG RR from the direct parent
zone. For unsecure delegations, a null-KEY RR is inserted in the
parent zone. Finally, NXT RR's and their accompanying SIG RR's are
issued in the case of a negative reply.
As a zone maintainer, transitioning to a secure zone has a high
overhead in the following areas:
KEY RR
At a delegation point, the zone maintainer needs to place a NULL
key and accompanying SIG RR's when the child zone is not known to
be secure.
NXT RR
Each delegation needs to be lexigraphically ordered so that a NXT
RR can be generated and signed with SIG RR's. For large zone
operators, generating the zone file is a very time consuming
process. In the resolution process, NXT lookups require that the
server replace efficient hash structures with a lexigraphically
ordered search structure which degrades lookup performance. This
lookup performance is a critical element for a high-query rate
DNS server.
Thus, the net effect is when one initially secures a zone as defined
in RFC2535[4], the net overhead is massive because of the following
factors:
Kosters Expires May 18, 2001 [Page 3]
1. Zone ordering and maintenance for large zones is difficult and
expensive.
2. Adding null-KEY RR's, NXT RR's and their accompanying SIG RR's
for unsecure delegations will consume large amounts of memory
(6x the current memory requirements).
3. Having a less efficient look-up algorithm to provide answers to
queries will degrade overall performance.
4. Very little initial payoff (anticipate only a small fraction of
delegations to be signed. This equates to less than 1% over the
first six months).
5. Unsecured delegations are more expensive at the parent than
secure delegations (NULL KEY).
2. Rationale
As DNSSEC is initially deployed, it is anticipated that DNSSEC
adoption will be slow to materialize. It is also anticipated that
DNSSEC security resolution will be top down. Thus for DNSSEC to be
widely adopted, the root zone and GTLD zones will need to be signed.
Based on the implications previously listed, a large zone maintainer
such as the administrator of COM, needs to create an infrastructure
that is an order of magnitude larger than its current state with
very little initial benefit.
This document proposes an alternative opt-in approach that minimizes
the expense and complexity to ease adoption of DNSSEC for large
zones by allowing for an alternate view of secured only delegations.
3. Protocol Additions
The opt-in proposal allows for a zone operator to maintain two views
of its delegations - one being non-DNSSEC and the other being
DNSSSEC aware. The non-DNSSEC view will have all delegations - both
secured and non-secured. The DNSSEC aware view will only have
secured delegations. It is assumed that neither view will have any
innate knowledge of the other's delegations. Thus, the cost of
securing a zone is proportional to the demand of its delegations
with the added benefit of no longer having to maintain NULL KEY RRs
for unsecure delegations.
To determine which view each DNS query packet is to be queried
against, there is a simple algorithm to be followed:
1. The DNSSEC view is to be queried when the DO bit is set within
the EDNS0 OPT meta RR as indicated in [6].
2. The DNSSEC view is to be queried when the query type is SIG,
KEY, or NXT and the RRs added match the query name and query
type.
If the query does not follow either case (1) or (2), the non-DNSSEC
view MUST be consulted by default.
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Since the DNSSEC view will have a subset of the actual delegations
of that zone, it will not be able to respond to an unsecured
delgation. To that end, a new extended RCODE MUST be set within the
EDNS OPT RR for the resolver to retry again with the DO bit not set.
This RCODE is referred to as "RETRY-NO-SEC" (RS). In the context of
the EDNS0 OPT meta-RR, the RS value will be determined by IANA.
Setting the RS RCODE in a response indicates to the resolver that
the resolver is retrying the query again without the DO bit set. The
behavior of the authority and additional records section being
populated should be the same using the RS RCODE as the the RCODE
being set to NXDOMAIN. Therefore, the resolver will be able to
verify that the answer does not exist within the secure zone since
the NXT RR will be sent in the Authority section. To avoid caching,
the server SHOULD set the TTL on the NXT RR to 0.
Example:
Consider a zone with the secure names 3, 6, and 9, and unsecure
names 2, 4, 5, 7, and 8.
Unsecured zone Contents:
@ SOA
2 NS
3 NS
4 NS
5 NS
6 NS
7 NS
8 NS
9 NS
Secured zone Contents:
@ SOA, SIG SOA, NXT(3), SIG NXT
3 NS, SIG NS, NXT(6), SIG NXT
6 NS, SIG NS, NXT(9), SIG NXT
9 NS, SIG NS, NXT(@), SIG NXT
1. Query for 5 RR type A with EDNS0 DO bit set, the response would
return with the extended RCODE RS bit set:
RCODE=RS
Authority Section:
SOA, SIG SOA, 3 NXT(6), SIG NXT
Additional Section:
KEY, SIG KEY
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The source would then retry without the EDNS0 DO bit set which
would return an answer as defined in RFC1035[2].
2. Query for 55 RR type A with EDNS0 DO bit set, the response would
return with the extended RCODE RS bit set:
RCODE=RS
Authority Section:
SOA, SIG SOA, 3 NXT(6), SIG NXT
Additional Section:
KEY, SIG KEY
The source would then retry without the EDNS0 DO bit set which
would return an answer as defined in RFC1035[2].
3. Query for 33 RR type KEY without EDNS DO bit set. The response
would return with an answer as defined in RFC2535[4].
4. Query for 3 RR type A, with EDNS0 DO bit set, the response would
be the same as defined in RFC2535[4].
4. Security Considerations
This draft is different and separate from RFC2535[4] in that it
allows for secured delegation paths to exist but does not allow for
secure answers to unsecured delegations at the parent level.
Increased exposure will be marginal given that the children are
unsecure.
5. IANA Considerations
Allocation of the most significant bit of the RCODE field in the
EDNS0 OPT meta-RR is required.
6. Acknowledgements
This document is based on a rough draft by Brian Wellington, and
input from Olafur Gudmundsson.
References
[1] Mockapetris, P.V., "Domain names - concepts and facilities",
RFC 1034, STD 13, Nov 1987.
[2] Mockapetris, P.V., "Domain names - implementation and
specification", RFC 1035, STD 13, Nov 1987.
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[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, BCP 14, March 1997.
[4] Eastlake, D., "Domain Name System Security Extensions", RFC
2535, March 1999.
[5] Vixie, P., "Extension Mechanisms for DNS (EDNS0)", RFC 2671,
August 1999.
[6] Conrad, D. R., "Indicating Resolver Support of DNSSEC (work in
progress)", August 2000.
Author's Address
Mark Kosters
Network Solutions, Inc.
505 Huntmar Park Drive
Herndon, VA 22070
US
Phone: +1 703 948-3362
EMail: markk@netsol.com
URI: http://www.netsol.com
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Full Copyright Statement
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph
are included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC editor function is currently provided by the
Internet Society.
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INTERNET-DRAFT M. Sawyer
A. Gustafsson
M. Graff
Nominum
<draft-msawyer-dnsext-edns-attributes-00.txt> 15 November 2000
Handling of unknown EDNS0 attributes
Status of this Memo
This document is an Internet-Draft and is in full conformance with
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 documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as ``work in progress.''
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html
This draft expires on May 15, 2001.
Abstract
This document provides a clarification of the EDNS0 protocol,
specifying the behavior of servers when they receive unknown EDNS
options.
1.1 - Introduction
Familiarity with DNS [RFC1034, RFC1035] and DNS Extension Mechanisms
[RFC2671] is helpful.
EDNS0 [RFC2671] specifies a general framework for extending the
packet format used by the Domain Name System protocol. The framework
provides for a series of additional options, identified by a 16 bit
attribute ID and arbitrary sized payload. Any number of these
additional options can be specified in the DNS packet. As specified,
the current scheme has drawbacks:
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- It provides no way for implementers to deploy test systems with
experimental features prior to approval of the feature and assignment
of an attribute ID.
- It provides no specification on what an application should do when
receiving unrecognized options.
This draft proposes to clarify the original EDNS0 draft [RFC2671],
addressing these drawbacks.
1.2 - Requirements
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].
2 - Protocol changes:
This document updates [RFC2671]. Conformance to this specification
is claimed by specifying EDNS version 1.
2.1 - Advisory and Required Options:
Some potential uses of EDNS options are advisory in nature, For
example, a hypothetical option indicating that "I understand frobozz
compression in responses" can be safely ignored by the recipient,
which will then simply not use frobozz compression. Others uses of
options, such as a hypothetical "send only cryptographically verified
data in responses" option, cannot be safely ignored, and should cause
the request to fail if not understood by the receiver.
This suggests that we need two types of options, "advisory" options
(that can be ignored) and "required" options (that can not). Because
a server needs to classify options as advisory or required even if
they were not yet defined when the server was implemented, the type
of an option must be evident without knowing its internal structure.
This is achieved by splitting the option type codes into two ranges:
options with type code 0x0000-0x7FFF are considered "advisory", and
options with type code 0x8000-0xFFFF are considered "required".
2.2 - Handling of Unknown and Unsupported EDNS Option Types
When a server receives an unknown or unsupported advisory option in a
request or response message, it MUST ignore the unknown option and
process the message as if the option was not present. In the reply,
it SHOULD include an advisory UNSUPPORTED option (TBD).
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When a server receives an unknown or unsupported required option in a
request message, it MUST NOT act on the request, and it MUST return
an error response with the extended result code BADOPT (TBD). In the
reply, it SHOULD include an advisory UNSUPPORTED option.
When a server receives an unknown or unsupported required option in a
response message, it MUST ignore the response. The server SHOULD
continue to parse options after the unknown option, including a list
of all unsupported options in the UNSUPPORTED option in the reply.
Servers MAY include SUPPORTED options in replies to messages, listing
option codes which they understand. This message SHOULD contain all
option codes the server understands. This facility MAY NOT be used
in place of the UNSUPPORTED option to identify unsupported options in
replies.
Clients MAY include SUPPORTED or UNSUPPORTED options in queries.
UNSUPPORTED options SHOULD only list those option codes which the
client has received in previous replies from the server, not an
inclusive list of all unsupported option codes.
2.3 - Use of Reserved Options for Development
Option codes in the range of 0x7FF0 to 0x7FFF and 0xFFF0 to 0xFFFF
are considered "reserved" and shall not be assigned to new protocols.
Software vendors SHOULD use these options for testing of protocols
under development, provided the following conditions are met:
- Vendors MUST NOT ship any versions of the software which use option
codes in this range. They MUST delay shipping software with the new
options until IANA has assigned permanent option codes.
- Vendors MUST NOT place development servers on the live internet
which send options in this range to remote servers or which
understand options in this range as having any meaning.
3.1 - SUPPORTED and UNSUPPORTED options
The SUPPORTED and UNSUPPORTED options contain a list of option codes
which the server or client does or doesn't support. The list
contains, in network byte order, the supported or unsupported 16 bit
option codes:
1 1 1 1 1 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| SUPPORTED or UNSUPPORTED (TBD) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
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| LENGTH (number of options * 2) |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
/ OPTION CODE(s) /
/ /
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Sending a SUPPORTED option with a zero-length payload indicates that
the server or client supports no EDNS options, so none should be
used. UNSUPPORTED options with zero-length payloads SHOULD NOT be
sent, as such a message is meaningless.
4 - IANA considerations
When allocating EDNS Option Codes, the IANA shall henceforth require
the RFC defining the new option to specify whether the option is an
"advisory" or a "required" option. The option code for an advisory
option shall be allocated from the range 0x0000-0x7FEF, and the code
for a required option shall be allocated from the range
0x8000-0xFFEF.
Option codes in the ranges of 0x7FF0 to 0x7FFF and 0xFFF0 to 0xFFFF
are considered "reserved."
The IANA is hereby requested to assign EDNS Version Number 1 to this
specification, to assign a new extended RCODE value for BADOPT, and
to assign advisory option codes for UNSUPPORTED and SUPPORTED.
5 - Security considerations
This document provides a mechanism for users to override the default
behavior of the server when accessing data from its internal zone
databases. Software developers and administrators should use some
care when enabling these options, as they may provide outside users
the ability to retrieve information otherwise not available.
6 - Acknowledgments
The authors would like to thank Olafur Gudmundsson for his input on
this draft.
7 - References
[RFC2119] S. Brander, ``Key words for use in RFCs to Indicate
Requirement Levels,'' RFC 2119, ISI, November 1997.
[RFC2671] P. Vixie, ``Extension Mechanisms for DNS (EDNS0),'' RFC
2671, ISI, August, 1999
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Author's Address
Michael Sawyer
Nominum, Inc.
950 Charter St.
Redwood City, CA 94063
Phone: +1-650-779-6021
michael.sawyer@nominum.com
Andreas Gustafsson
Nominum, Inc.
950 Charter St.
Redwood City, CA 94063
Phone: +1-650-779-6004
andreas.gustafsson@nominum.com
Michael Graff
Nominum, Inc.
950 Charter St.
Redwood City, CA 94063
Phone: +1-650-779-6034
michael.graff@nominum.com
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