Neighbor Unreachability Detection Is Too Impatient
RFC 7048
Document | Type |
RFC
- Proposed Standard
(January 2014)
Updates RFC 4861
|
|
---|---|---|---|
Authors | Erik Nordmark , Igor Gashinsky | ||
Last updated | 2015-10-14 | ||
RFC stream | Internet Engineering Task Force (IETF) | ||
Formats | |||
Additional resources | Mailing list discussion | ||
IESG | Responsible AD | Brian Haberman | |
Send notices to | (None) |
RFC 7048
Network Working Group R. Austein Request for Comments: 5001 ISC Category: Standards Track August 2007 DNS Name Server Identifier (NSID) Option 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. Copyright Notice Copyright (C) The IETF Trust (2007). 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 mechanisms 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 that 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 Standards Track [Page 1] RFC 5001 DNS NSID August 2007 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Reserved Words . . . . . . . . . . . . . . . . . . . . . . 3 2. Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Resolver Behavior . . . . . . . . . . . . . . . . . . . . 3 2.2. Name Server Behavior . . . . . . . . . . . . . . . . . . . 3 2.3. The NSID Option . . . . . . . . . . . . . . . . . . . . . 4 2.4. Presentation Format . . . . . . . . . . . . . . . . . . . 4 3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. The NSID Payload . . . . . . . . . . . . . . . . . . . . . 4 3.2. NSID Is Not Transitive . . . . . . . . . . . . . . . . . . 7 3.3. User Interface Issues . . . . . . . . . . . . . . . . . . 7 3.4. Truncation . . . . . . . . . . . . . . . . . . . . . . . . 8 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 5. Security Considerations . . . . . . . . . . . . . . . . . . . 9 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 7.1. Normative References . . . . . . . . . . . . . . . . . . . 9 7.2. Informative References . . . . . . . . . . . . . . . . . . 10 1. 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 that 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. Austein Standards Track [Page 2] RFC 5001 DNS NSID August 2007 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]. 2. 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 that 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. Austein Standards Track [Page 3] RFC 5001 DNS NSID August 2007 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 3. 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 contents 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. 3. 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 are deliberately left outside the scope of this specification. Choosing the NSID content is a prerogative of the server administrator. The server administrator might choose to encode the NSID content in such a way that the server operator (or clients authorized by the server operator) can decode the NSID content to obtain more information than other clients can. Alternatively, the server operator might choose unencoded NSID content that is equally meaningful to any client. This section describes 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 specifying a simple opaque byte string in Section 2.3. Austein Standards Track [Page 4] RFC 5001 DNS NSID August 2007 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 probabilistically 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 dynamically 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. 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 "Operational Neighbor Discovery Problems", RFC 6583, March 2012. Authors' Addresses Erik Nordmark Arista Networks Santa Clara, CA USA EMail: nordmark@acm.org Igor Gashinsky Yahoo! 45 W 18th St New York, NY USA EMail: igor@yahoo-inc.com Nordmark & Gashinsky Standards Track [Page 8]