draft-ietf-dnsext-nsid-01.txt
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Network Working Group R. AusteinInternet-Draft ISCExpires: July 15, 2006 January 11, 2006 DNS Name Server Identifier Option (NSID) draft-ietf-dnsext-nsid-01Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 July 15, 2006.Copyright Notice Copyright (C) The Internet Society (2006).Abstract With the increased use of DNS anycast, load balancing, and other mechanisms allowing more than one DNS name server to share a single IP address, it is sometimes difficult to tell which of a pool of name servers has answered a particular query. While existing ad-hoc mechanism allow an operator to send follow-up queries when it is necessary to debug such a configuration, the only completely reliable way to obtain the identity of the name server which responded is to have the name server include this information in the response itself. This note defines a protocol extension to support this functionality.Austein Expires July 15, 2006 [Page 1] Internet-Draft DNS NSID January 2006Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Reserved Words . . . . . . . . . . . . . . . . . . . . . . 3 2. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Resolver Behavior . . . . . . . . . . . . . . . . . . . . 4 2.2. Name Server Behavior . . . . . . . . . . . . . . . . . . . 4 2.3. The NSID Option . . . . . . . . . . . . . . . . . . . . . 4 2.4. Presentation Format . . . . . . . . . . . . . . . . . . . 5 3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. The NSID Payload . . . . . . . . . . . . . . . . . . . . . 6 3.2. NSID Is Not Transitive . . . . . . . . . . . . . . . . . . 8 3.3. User Interface Issues . . . . . . . . . . . . . . . . . . 8 3.4. Truncation . . . . . . . . . . . . . . . . . . . . . . . . 9 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 11 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13 7.1. Normative References . . . . . . . . . . . . . . . . . . . 13 7.2. Informative References . . . . . . . . . . . . . . . . . . 13 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14 Intellectual Property and Copyright Statements . . . . . . . . . . 15Austein Expires July 15, 2006 [Page 2] Internet-Draft DNS NSID January 20061. Introduction With the increased use of DNS anycast, load balancing, and other mechanisms allowing more than one DNS name server to share a single IP address, it is sometimes difficult to tell which of a pool of name servers has answered a particular query. Existing ad-hoc mechanisms allow an operator to send follow-up queries when it is necessary to debug such a configuration, but there are situations in which this is not a totally satisfactory solution, since anycast routing may have changed, or the server pool in question may be behind some kind of extremely dynamic load balancing hardware. Thus, while these ad-hoc mechanisms are certainly better than nothing (and have the advantage of already being deployed), a better solution seems desirable. Given that a DNS query is an idempotent operation with no retained state, it would appear that the only completely reliable way to obtain the identity of the name server which responded to a particular query is to have that name server include identifying information in the response itself. This note defines a protocol enhancement to achieve this.1.1. Reserved Words 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].Austein Expires July 15, 2006 [Page 3] Internet-Draft DNS NSID January 20062. Protocol This note uses an EDNS [RFC2671] option to signal the resolver's desire for information identifying the name server and to hold the name server's response, if any.2.1. Resolver Behavior A resolver signals its desire for information identifying a name server by sending an empty NSID option (Section 2.3) in an EDNS OPT pseudo-RR in the query message. The resolver MUST NOT include any NSID payload data in the query message. The semantics of an NSID request are not transitive. That is: the presence of an NSID option in a query is a request that the name server which receives the query identify itself. If the name server side of a recursive name server receives an NSID request, the client is asking the recursive name server to identify itself; if the resolver side of the recursive name server wishes to receive identifying information, it is free to add NSID requests in its own queries, but that is a separate matter.2.2. Name Server Behavior A name server which understands the NSID option and chooses to honor a particular NSID request responds by including identifying information in a NSID option (Section 2.3) in an EDNS OPT pseudo-RR in the response message. The name server MUST ignore any NSID payload data that might be present in the query message. The NSID option is not transitive. A name server MUST NOT send an NSID option back to a resolver which did not request it. In particular, while a recursive name server may choose to add an NSID option when sending a query, this has no effect on the presence or absence of the NSID option in the recursive name server's response to the original client. As stated in Section 2.1, this mechanism is not restricted to authoritative name servers; the semantics are intended to be equally applicable to recursive name servers.2.3. The NSID Option The OPTION-CODE for the NSID option is [TBD].Austein Expires July 15, 2006 [Page 4] Internet-Draft DNS NSID January 2006 The OPTION-DATA for the NSID option is an opaque byte string the semantics of which are deliberately left outside the protocol. See Section 3.1 for discussion.2.4. Presentation Format User interfaces MUST read and write the content of the NSID option as a sequence of hexadecimal digits, two digits per payload octet. The NSID payload is binary data. Any comparison between NSID payloads MUST be a comparison of the raw binary data. Copy operations MUST NOT assume that the raw NSID payload is null- terminated. Any resemblance between raw NSID payload data and any form of text is purely a convenience, and does not change the underlying nature of the payload data. See Section 3.3 for discussion.Austein Expires July 15, 2006 [Page 5] Internet-Draft DNS NSID January 20063. Discussion This section discusses certain aspects of the protocol and explains considerations that led to the chosen design.3.1. The NSID Payload The syntax and semantics of the content of the NSID option is deliberately left outside the scope of this specification. This section describe some of the kinds of data that server administrators might choose to provide as the content of the NSID option, and explains the reasoning behind choosing a simple opaque byte string. There are several possibilities for the payload of the NSID option: o It could be the "real" name of the specific name server within the name server pool. o It could be the "real" IP address (IPv4 or IPv6) of the name server within the name server pool. o It could be some sort of pseudo-random number generated in a predictable fashion somehow using the server's IP address or name as a seed value. o It could be some sort of probabilisticly unique identifier initially derived from some sort of random number generator then preserved across reboots of the name server. o It could be some sort of dynamicly generated identifier so that only the name server operator could tell whether or not any two queries had been answered by the same server. o It could be a blob of signed data, with a corresponding key which might (or might not) be available via DNS lookups. o It could be a blob of encrypted data, the key for which could be restricted to parties with a need to know (in the opinion of the server operator). o It could be an arbitrary string of octets chosen at the discretion of the name server operator. Each of these options has advantages and disadvantages: o Using the "real" name is simple, but the name server may not have a "real" name.Austein Expires July 15, 2006 [Page 6] Internet-Draft DNS NSID January 2006 o Using the "real" address is also simple, and the name server almost certainly does have at least one non-anycast IP address for maintenance operations, but the operator of the name server may not be willing to divulge its non-anycast address. o Given that one common reason for using anycast DNS techniques is an attempt to harden a critical name server against denial of service attacks, some name server operators are likely to want an identifier other than the "real" name or "real" address of the name server instance. o Using a hash or pseudo-random number can provide a fixed length value that the resolver can use to tell two name servers apart without necessarily being able to tell where either one of them "really" is, but makes debugging more difficult if one happens to be in a friendly open environment. Furthermore, hashing might not add much value, since a hash based on an IPv4 address still only involves a 32-bit search space, and DNS names used for servers that operators might have to debug at 4am tend not to be very random. o Probabilisticly unique identifiers have similar properties to hashed identifiers, but (given a sufficiently good random number generator) are immune to the search space issues. However, the strength of this approach is also its weakness: there is no algorithmic transformation by which even the server operator can associate name server instances with identifiers while debugging, which might be annoying. This approach also requires the name server instance to preserve the probabilisticly unique identifier across reboots, but this does not appear to be a serious restriction, since authoritative nameservers almost always have some form of nonvolatile storage in any case, and in the rare case of a name server that does not have any way to store such an identifier, nothing terrible will happen if the name server just generates a new identifier every time it reboots. o Using an arbitrary octet string gives name server operators yet another thing to configure, or mis-configure, or forget to configure. Having all the nodes in an anycast name server constellation identify themselves as "My Name Server" would not be particularly useful. Given all of the issues listed above, there does not appear to be a single solution that will meet all needs. Section 2.3 therefore defines the NSID payload to be an opaque byte string and leaves the choice up to the implementor and name server operator. The following guidelines may be useful to implementors and server operators:Austein Expires July 15, 2006 [Page 7] Internet-Draft DNS NSID January 2006 o Operators for whom divulging the unicast address is an issue could use the raw binary representation of a probabilisticly unique random number. This should probably be the default implementation behavior. o Operators for whom divulging the unicast address is not an issue could just use the raw binary representation of a unicast address for simplicity. This should only be done via an explicit configuration choice by the operator. o Operators who really need or want the ability to set the NSID payload to an arbitrary value could do so, but this should only be done via an explicit configuration choice by the operator. This approach appears to provide enough information for useful debugging without unintentionally leaking the maintenance addresses of anycast name servers to nogoodniks, while also allowing name server operators who do not find such leakage threatening to provide more information at their own discretion.3.2. NSID Is Not Transitive As specified in Section 2.1 and Section 2.2, the NSID option is not transitive. This is strictly a hop-by-hop mechanism. Most of the discussion of name server identification to date has⌨️ 快捷键说明
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