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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)
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IESG Responsible AD Brian Haberman
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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]