Network Working Group                                      B. Wellington
Request for Comments: 3655                                O. Gudmundsson
Updates: 2535                                              November 2003
Category: Standards Track
Network Working Group                                      B. Wellington
Request for Comments: 3655                                O. Gudmundsson
Updates: 2535                                              November 2003
Category: Standards Track

Redefinition of DNS Authenticated Data (AD) bit


Status of this Memo


This document specifies an Internet standards track protocol for the Internet community, and requests discussion and suggestions for improvements. Please refer to the current edition of the "Internet Official Protocol Standards" (STD 1) for the standardization state and status of this protocol. Distribution of this memo is unlimited.

本文件规定了互联网社区的互联网标准跟踪协议,并要求进行讨论和提出改进建议。有关本协议的标准化状态和状态,请参考当前版本的“互联网官方协议标准”(STD 1)。本备忘录的分发不受限制。

Copyright Notice


Copyright (C) The Internet Society (2003). All Rights Reserved.




This document alters the specification defined in RFC 2535. Based on implementation experience, the Authenticated Data (AD) bit in the DNS header is not useful. This document redefines the AD bit such that it is only set if all answers or records proving that no answers exist in the response has been cryptographically verified or otherwise meets the server's local security policy.

本文件修改了RFC 2535中定义的规范。根据实施经验,DNS报头中的身份验证数据(AD)位没有用处。本文档重新定义AD位,以便仅当证明响应中不存在答案的所有答案或记录已通过加密验证或符合服务器的本地安全策略时,才设置AD位。

1. Introduction
1. 介绍

Familiarity with the DNS system [RFC1035] and DNS security extensions [RFC2535] is helpful but not necessary.


As specified in RFC 2535 (section 6.1), the AD (Authenticated Data) bit indicates in a response that all data included in the answer and authority sections of the response have been authenticated by the server according to the policies of that server. This is not especially useful in practice, since a conformant server SHOULD never reply with data that failed its security policy.

如RFC 2535(第6.1节)所述,AD(认证数据)位在响应中表示响应的应答和授权部分中包含的所有数据已由服务器根据该服务器的策略进行认证。这在实践中并不特别有用,因为一致性服务器永远不应该使用未通过其安全策略的数据进行回复。

This document redefines the AD bit such that it is only set if all data in the response has been cryptographically verified or otherwise meets the server's local security policy. Thus, neither a response containing properly delegated insecure data, nor a server configured without DNSSEC keys, will have the AD set. As before, data that failed to verify will not be returned. An application running on a host that has a trust relationship with the server performing the


recursive query can now use the value of the AD bit to determine whether the data is secure.


1.1. Motivation
1.1. 动机

A full DNSSEC capable resolver called directly from an application can return to the application the security status of the RRsets in the answer. However, most applications use a limited stub resolver that relies on an external recursive name server which incorporates a full resolver. The recursive nameserver can use the AD bit in a response to indicate the security status of the data in the answer, and the local resolver can pass this information to the application. The application in this context can be either a human using a DNS tool or a software application.


The AD bit SHOULD be used by the local resolver if and only if it has been explicitly configured to trust the remote resolver. The AD bit SHOULD be ignored when the recursive name server is not trusted.


An alternate solution would be to embed a full DNSSEC resolver into every application, but this has several disadvantages.


- DNSSEC validation is both CPU and network intensive, and caching SHOULD be used whenever possible.

- DNSSEC验证是CPU和网络密集型验证,应尽可能使用缓存。

- DNSSEC requires non-trivial configuration - the root key must be configured, as well as keys for any "islands of security" that will exist until DNSSEC is fully deployed. The number of configuration points should be minimized.

- DNSSEC需要非常重要的配置—必须配置根密钥以及在DNSSEC完全部署之前存在的任何“安全孤岛”的密钥。应尽量减少配置点的数量。

1.2. Requirements
1.2. 要求

The key words "MAY", "MAY NOT" "MUST", "MUST NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", in this document are to be interpreted as described in BCP 14, RFC 2119 [RFC2119].

本文件中的关键词“可能”、“不可能”、“必须”、“不得”、“应该”、“不应该”、“建议”应按照BCP 14、RFC 2119[RFC2119]中的说明进行解释。

1.3. Updated documents and sections
1.3. 更新的文件和章节

The definition of the AD bit in RFC 2535, Section 6.1, is changed.

RFC 2535第6.1节中AD位的定义已更改。

2. Setting of AD bit
2. AD位的设置

The presence of the CD (Checking Disabled) bit in a query does not affect the setting of the AD bit in the response. If the CD bit is set, the server will not perform checking, but SHOULD still set the AD bit if the data has already been cryptographically verified or


complies with local policy. The AD bit MUST only be set if DNSSEC records have been requested via the DO bit [RFC3225] and relevant SIG records are returned.


2.1. Setting of AD bit by recursive servers
2.1. 通过递归服务器设置AD位

Section 6.1 of RFC 2535 says:

RFC 2535第6.1节规定:

"The AD bit MUST NOT be set on a response unless all of the RRs in the answer and authority sections of the response are either Authenticated or Insecure."


The replacement text reads:


"The AD bit MUST NOT be set on a response unless all of the RRsets in the answer and authority sections of the response are Authenticated."


"The AD bit SHOULD be set if and only if all RRs in the answer section and any relevant negative response RRs in the authority section are Authenticated."


A recursive DNS server following this modified specification will only set the AD bit when it has cryptographically verified the data in the answer.


2.2. Setting of AD bit by authoritative servers
2.2. 由权威服务器设置AD位

A primary server for a secure zone MAY have the policy of treating authoritative secure zones as Authenticated. Secondary servers MAY have the same policy, but SHOULD NOT consider zone data Authenticated unless the zone was transferred securely and/or the data was verified. An authoritative server MUST only set the AD bit for authoritative answers from a secure zone if it has been explicitly configured to do so. The default for this behavior SHOULD be off.


Note that having the AD bit clear on an authoritative answer is normal and expected behavior.


2.2.1. Justification for setting AD bit w/o verifying data
2.2.1. 设置AD位(无验证数据)的理由

The setting of the AD bit by authoritative servers affects only the small set of resolvers that are configured to directly query and trust authoritative servers. This only affects servers that function as both recursive and authoritative. Iterative resolvers SHOULD ignore the AD bit.


The cost of verifying all signatures on load by an authoritative server can be high and increases the delay before it can begin


answering queries. Verifying signatures at query time is also expensive and could lead to resolvers timing out on many queries after the server reloads zones.


Organizations requiring that all DNS responses contain cryptographically verified data will need to separate the authoritative name server and signature verification functions, since name servers are not required to validate signatures of data for which they are authoritative.


3. Interpretation of the AD bit
3. 广告位的解读

A response containing data marked Insecure in the answer or authority section MUST never have the AD bit set. In this case, the resolver SHOULD treat the data as Insecure whether or not SIG records are present.


A resolver MUST NOT blindly trust the AD bit unless it communicates with a recursive nameserver over a secure transport mechanism or using a message authentication such as TSIG [RFC2845] or SIG(0) [RFC2931] and is explicitly configured to trust this recursive name server.


4. Applicability statement
4. 适用性声明

The AD bit is intended to allow the transmission of the indication that a resolver has verified the DNSSEC signatures accompanying the records in the Answer and Authority section. The AD bit MUST only be trusted when the end consumer of the DNS data has confidence that the intermediary resolver setting the AD bit is trustworthy. This can only be accomplished via an out of band mechanism such as:


- Fiat: An organization that can dictate whether it is OK to trust certain DNS servers.

- Fiat:一个可以决定是否可以信任某些DNS服务器的组织。

- Personal: Because of a personal relationship or the reputation of a recursive nameserver operator, a DNS consumer can decide to trust that recursive nameserver.

- 个人:由于个人关系或递归名称服务器操作员的声誉,DNS使用者可以决定信任该递归名称服务器。

- Knowledge: If a recursive nameserver operator posts the configured policy of a recursive nameserver, a consumer can decide that recursive nameserver is trustworthy.

- 知识:如果递归名称服务器操作员发布递归名称服务器的配置策略,则使用者可以确定递归名称服务器是可信的。

In the absence of one or more of these factors AD bit from a recursive name server SHOULD NOT be trusted. For example, home users frequently depend on their ISP to provide recursive DNS service; it


is not advisable to trust these recursive nameservers. A roaming/traveling host SHOULD not use recursive DNS servers offered by DHCP when looking up information where security status matters.


In the latter two cases, the end consumer must also completely trust the path to the trusted recursive name servers, or a secure transport must be employed to protect the traffic.


When faced with a situation where there are no satisfactory recursive nameservers available, running one locally is RECOMMENDED. This has the advantage that it can be trusted, and the AD bit can still be used to allow applications to use stub resolvers.


5. Security Considerations
5. 安全考虑

This document redefines a bit in the DNS header. If a resolver trusts the value of the AD bit, it must be sure that the responder is using the updated definition, which is any DNS server/resolver supporting the DO bit [RFC3225].


Authoritative servers can be explicitly configured to set the AD bit on answers without doing cryptographic checks. This behavior MUST be off by default. The only affected resolvers are those that directly query and trust the authoritative server, and this functionality SHOULD only be used on servers that act both as authoritative and recursive name servers.


Resolvers (full or stub) that blindly trust the AD bit without knowing the security policy of the server generating the answer can not be considered security aware.


A resolver MUST NOT blindly trust the AD bit unless it communicates such as IPsec, or using message authentication such as TSIG [RFC2845] or SIG(0) [RFC2931]. In addition, the resolver must have been explicitly configured to trust this recursive name server.


6. IANA Considerations
6. IANA考虑



7. Internationalization Considerations
7. 国际化考虑

None. This document does not change any textual data in any protocol.


8. Intellectual Property Rights Notice
8. 知识产权公告

The IETF takes no position regarding the validity or scope of any intellectual property or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. Copies of claims of rights made available for publication and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementors or users of this specification can be obtained from the IETF Secretariat.


The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights which may cover technology that may be required to practice this standard. Please address the information to the IETF Executive Director.


9. Acknowledgments
9. 致谢

The following people have provided input on this document: Robert Elz, Andreas Gustafsson, Bob Halley, Steven Jacob, Erik Nordmark, Edward Lewis, Jakob Schlyter, Roy Arends, Ted Lindgreen.


10. Normative References
10. 规范性引用文件

[RFC1035] Mockapetris, P., "Domain Names - Implementation and Specification", STD 13, RFC 1035, November 1987.

[RFC1035]Mockapetris,P.,“域名-实现和规范”,STD 13,RFC 1035,1987年11月。

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2119]Bradner,S.,“RFC中用于表示需求水平的关键词”,BCP 14,RFC 2119,1997年3月。

[RFC2535] Eastlake, D., "Domain Name System Security Extensions", RFC 2535, March 1999.


[RFC2845] Vixie, P., Gudmundsson, O., Eastlake 3rd, D. and B. Wellington, "Secret Key Transaction Authentication for DNS (TSIG)", RFC 2845, May 2000.

[RFC2845]Vixie,P.,Gudmundsson,O.,Eastlake 3rd,D.和B.Wellington,“DNS秘密密钥交易认证(TSIG)”,RFC 28452000年5月。

[RFC2931] Eastlake, D., "DNS Request and Transaction Signatures (SIG(0))", RFC 2931, September 2000.

[RFC2931]Eastlake,D.,“DNS请求和事务签名(SIG(0))”,RFC 29312000年9月。

[RFC3225] Conrad, D., "Indicating Resolver Support of DNSSEC", RFC 3225, December 2001.

[RFC3225]Conrad,D.“指示DNSSEC的分解器支持”,RFC 3225,2001年12月。

11. Authors' Addresses
11. 作者地址

Brian Wellington Nominum Inc. 2385 Bay Road Redwood City, CA, 94063 USA

Brian Wellington Nominum Inc.美国加利福尼亚州红木市海湾路2385号,邮编94063


Olafur Gudmundsson 3821 Village Park Drive Chevy Chase, MD, 20815 USA


12. Full Copyright Statement
12. 完整版权声明

Copyright (C) The Internet Society (2003). 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 assignees.






Funding for the RFC Editor function is currently provided by the Internet Society.