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Versions: (draft-fuller-lisp-ddt) 00 01 02 03 04 05 06 07 08 09

Network Working Group                                          V. Fuller
Internet-Draft
Intended status: Experimental                                   D. Lewis
Expires: July 22, 2017                                        V. Ermagan
                                                           Cisco Systems
                                                                 A. Jain
                                                        Juniper Networks
                                                              A. Smirnov
                                                           Cisco Systems
                                                        January 18, 2017


                      LISP Delegated Database Tree
                         draft-ietf-lisp-ddt-09

Abstract

   This document describes the LISP Delegated Database Tree (LISP-DDT),
   a hierarchical, distributed database which embodies the delegation of
   authority to provide mappings from LISP Endpoint Identifiers (EIDs)
   to Routing Locators (RLOCs).  It is a statically-defined distribution
   of the EID namespace among a set of LISP-speaking servers, called DDT
   nodes.  Each DDT node is configured as "authoritative" for one or
   more EID-prefixes, along with the set of RLOCs for Map Servers or
   "child" DDT nodes to which more-specific EID-prefixes are delegated.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on July 22, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   4
   3.  Definition of Terms . . . . . . . . . . . . . . . . . . . . .   5
   4.  Database organization . . . . . . . . . . . . . . . . . . . .   7
     4.1.  XEID prefixes . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  DDT database tree structure . . . . . . . . . . . . . . .   7
     4.3.  Configuring prefix delegation . . . . . . . . . . . . . .   8
       4.3.1.  The root DDT node . . . . . . . . . . . . . . . . . .   9
   5.  DDT Map-Request . . . . . . . . . . . . . . . . . . . . . . .   9
   6.  The Map-Referral message  . . . . . . . . . . . . . . . . . .  10
     6.1.  Action codes  . . . . . . . . . . . . . . . . . . . . . .  10
     6.2.  Referral set  . . . . . . . . . . . . . . . . . . . . . .  11
     6.3.  Incomplete flag . . . . . . . . . . . . . . . . . . . . .  11
     6.4.  Map-Referral Message Format . . . . . . . . . . . . . . .  11
       6.4.1.  SIG section . . . . . . . . . . . . . . . . . . . . .  14
   7.  DDT network elements and their operation  . . . . . . . . . .  15
     7.1.  DDT node  . . . . . . . . . . . . . . . . . . . . . . . .  15
       7.1.1.  Match of a delegated prefix (or sub-prefix) . . . . .  15
       7.1.2.  Missing delegation from an authoritative prefix . . .  16
     7.2.  DDT Map Server  . . . . . . . . . . . . . . . . . . . . .  16
     7.3.  DDT client  . . . . . . . . . . . . . . . . . . . . . . .  17
       7.3.1.  Queuing and sending DDT Map-Requests  . . . . . . . .  17
       7.3.2.  Receiving and following referrals . . . . . . . . . .  18
       7.3.3.  Handling referral errors  . . . . . . . . . . . . . .  20
       7.3.4.  Referral loop detection . . . . . . . . . . . . . . .  20
   8.  Pseudo Code and Decision Tree diagrams  . . . . . . . . . . .  21
     8.1.  Map Resolver processing of ITR Map-Request  . . . . . . .  21
       8.1.1.  Pseudo-code summary . . . . . . . . . . . . . . . . .  21
       8.1.2.  Decision tree diagram . . . . . . . . . . . . . . . .  21
     8.2.  Map Resolver processing of Map-Referral message . . . . .  22
       8.2.1.  Pseudo-code summary . . . . . . . . . . . . . . . . .  22
       8.2.2.  Decision tree diagram . . . . . . . . . . . . . . . .  24
     8.3.  DDT Node processing of DDT Map-Request message  . . . . .  25
       8.3.1.  Pseudo-code summary . . . . . . . . . . . . . . . . .  25
       8.3.2.  Decision tree diagram . . . . . . . . . . . . . . . .  27
   9.  Example topology and request/referral following . . . . . . .  27



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     9.1.  Lookup of 2001:db8:0103:1::1/128  . . . . . . . . . . . .  30
     9.2.  Lookup of 2001:db8:0501:8:4::1/128  . . . . . . . . . . .  31
     9.3.  Lookup of 2001:db8:0104:2::2/128  . . . . . . . . . . . .  32
     9.4.  Lookup of 2001:db8:0500:2:4::1/128  . . . . . . . . . . .  32
     9.5.  Lookup of 2001:db8:0500::1/128 (non-existent EID) . . . .  33
   10. Securing the database and message exchanges . . . . . . . . .  34
     10.1.  XEID-prefix Delegation . . . . . . . . . . . . . . . . .  34
     10.2.  DDT node operation . . . . . . . . . . . . . . . . . . .  35
       10.2.1.  DDT public key revocation  . . . . . . . . . . . . .  35
     10.3.  Map Server operation . . . . . . . . . . . . . . . . . .  36
     10.4.  Map Resolver operation . . . . . . . . . . . . . . . . .  36
   11. Open Issues and Considerations  . . . . . . . . . . . . . . .  37
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  37
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  37
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  38
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  38
     14.2.  Informative References . . . . . . . . . . . . . . . . .  38
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  39
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  40

1.  Introduction

   LISP [RFC6830] specifies an architecture and mechanism for replacing
   the addresses currently used by IP with two separate name spaces:
   Endpoint Identifiers (EIDs), used end-to-end for terminating
   transport-layer associations, and Routing Locators (RLOCs), which are
   bound to topological location, and are used for routing and
   forwarding through the Internet infrastructure.

   [RFC6833] specifies an interface between database storing EID-to-RLOC
   mappings and LISP devices which need this information for packet
   forwarding.  Internal organization of such database is out the scope
   of [RFC6833].  Multiple architectures of the database have been
   proposed, each having its advantages and disadvantages (see for
   example [RFC6836] and [RFC6837]).

   This document specifies architecture for database of LISP EID-to-RLOC
   mappings with emphasis on high scalability.  LISP-DDT is a
   hierarchical distributed database, which embodies the delegation of
   authority to provide mappings, i.e. its internal structure mirrors
   the hierarchical delegation of address space.  It also provides
   delegation information to Map Resolvers, which use the information to
   locate EID-to-RLOC mappings.  A Map Resolver, which needs to locate a
   given mapping, will follow a path through the tree-structured
   database, contacting, one after another, the DDT nodes along that
   path until it reaches the leaf DDT node(s) authoritative for the
   mapping it is seeking.




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   LISP offers a general-purpose mechanism for mapping between EIDs and
   RLOCs.  In organizing a database of EID to RLOC mappings, this
   specification extends the definition of the EID numbering space by
   logically prepending and appending several fields for purposes of
   defining the database index key: Database-ID (DBID, 16 bits),
   Instance identifier (IID, 32-bits), Address Family Identifier (16
   bits), and EID-prefix (variable, according to AFI value).  The
   resulting concatenation of these fields is termed an "Extended EID
   prefix" or XEID-prefix.

   LISP-DDT defines a new device type, the DDT node, that is configured
   as authoritative for one or more XEID-prefixes.  It also is
   configured with the set of more-specific sub-prefixes that are
   further delegated to other DDT nodes.  To delegate a sub-prefix, the
   "parent" DDT node is configured with the RLOCs of each child DDT node
   that is authoritative for the sub-prefix.  Each RLOC either points to
   a DDT Map Server to which an Egress Tunnel Router (ETR) has
   registered that sub-prefix or points to another DDT node in the
   database tree that further delegates the sub-prefix.  See [RFC6833]
   for a description of the functionality of the Map Server and Map
   Resolver.  Note that the target of a delegation must always be an
   RLOC (not an EID) to avoid any circular dependency.

   To provide a mechanism for traversing the database tree, LISP-DDT
   defines a new LISP message type, the Map-Referral, which is returned
   to the sender of a Map-Request when the receiving DDT node can refer
   the sender to another DDT node that has more detailed information.
   See Section 6 for the definition of the Map-Referral message.

   To find an EID-to-RLOC mapping, a LISP-DDT client, usually a DDT Map
   Resolver, starts by sending an Encapsulated Map-Request to a
   preconfigured DDT node RLOC.  The DDT node responds with a Map-
   Referral message that either indicates that it will find the
   requested mapping to complete processing of the request or that the
   DDT client should contact another DDT node that has more-specific
   information; in the latter case, the DDT node then sends a new
   Encapsulated Map-Request to the next DDT node and the process repeats
   in an iterative manner.

   Conceptually, this is similar to the way that a client of the Domain
   Name System (DNS) follows referrals (DNS responses that contain only
   NS records) from a series of DNS servers until it finds an answer.

2.  Requirements Language

   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].



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3.  Definition of Terms

   Extended EID (XEID):  a LISP EID extended with data uniquely
      identifying address space to which it belongs, such as LISP
      instance ID, Address Family etc.  See Section 4.1 for detailed
      description of XEID data.

   XEID-prefix:  Extended EID-prefix (XEID-prefix) is a LISP EID-prefix
      prepended with XEID data.  An XEID-prefix is used as a key index
      into the DDT database.  XEID prefixes are used to describe
      database organization and are not seen as a single entity in
      protocol messages, though messages contain individual fields
      constituting XEID prefix.

   DDT node:  a network infrastructure component responsible for
      specific XEID-prefix(es) and for delegation of more-specific sub-
      prefixes to other DDT nodes.

   DDT client:  a network infrastructure component that sends DDT Map-
      Request messages and implements the iterative following of Map-
      Referral results.  Typically, a DDT client will be a Map Resolver
      (as defined by [RFC6833]), but it is also possible for an ITR to
      implement DDT client functionality.

   DDT Map Server:  a DDT node that also implements Map Server
      functionality (forwarding Map-Requests and/or returning Map-
      Replies if offering proxy Map-Reply service) for a subset of its
      delegated prefixes.  Map Server functions including proxying Map-
      Replies are described in [RFC6833].

   DDT Map Server peers:  list of all DDT Map Servers performing Map
      Server functionality for the same prefix.  If peers are configured
      on a DDT Map Server then the latter will provide complete
      information about the prefix in its Map-Replies; otherwise the Map
      Server will mark returned reply as potentially incomplete.

   DDT Map Resolver:  a network infrastructure element which implements
      both the DDT client functionality and Map Resolver functionality
      as defined by [RFC6833].  DDT Map Resolver accepts Map-Requests
      from ITRs, sends DDT Map-Requests to DDT nodes and implements
      iterative following of Map-Referrals.  Note that Map Resolvers do
      not respond to clients which sent Map-Requests, they only ensure
      that the Map-Request has been forwarded to a LISP device (ETR or
      proxy Map-Server) which will provide authoritative response to the
      original requestor.  A DDT Map Resolver will typically maintain a
      cache of previously received Map-Referral message results
      containing RLOCs for DDT nodes responsible for XEID- prefixes of
      interest (termed the "referral cache").



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   Encapsulated Map-Request:  a LISP Map-Request carried within an
      Encapsulated Control Message, which has an additional LISP header
      prepended.  Sent to UDP destination port 4342.  The "outer"
      addresses are globally-routable IP addresses, also known as RLOCs.
      Used by an ITR when sending to a Map Resolver and by a Map Server
      when forwarding a Map-Request to an ETR as documented in LISP-MS
      [RFC6833].

   DDT Map-Request:  an Encapsulated Map-Request sent by a DDT client to
      a DDT node.  The "DDT-originated" flag is set in the encapsulation
      header indicating that the DDT node should return Map-Referral
      messages if the Map-Request EID matches a delegated XEID-prefix
      known to the DDT node.  Section 7.3.1 describes how DDT Map-
      Requests are sent.  Section 5 defines position of the "DDT-
      originated" flag in the Encapsulated Control Message header.

   Authoritative XEID-prefix:  an XEID-prefix delegated to a DDT node
      and for which the DDT node may provide further delegations of
      more-specific sub-prefixes.

   Map-Referral:  a LISP message sent by a DDT node in response to a DDT
      Map-Request for an XEID that matches a configured XEID-prefix
      delegation.  A non-negative Map-Referral includes a "referral", a
      set of RLOCs for DDT nodes that have information about the more
      specific XEID prefix covering requested XEID; a DDT client
      "follows the referral" by sending another DDT Map-Request to one
      of those RLOCs to obtain either an answer or another referral to
      DDT nodes responsible for even more specific XEID-prefix.  See
      Section 7.1 and Section 7.3.2 for details on the sending and
      processing of Map-Referral messages.

   Negative Map-Referral:  an answer from an authoritative DDT node that
      there is no mapping for the requested XEID.  Negative Map-Referral
      is a Map-Referral sent in response to a DDT Map-Request that
      matches an authoritative XEID-prefix but for which there is no
      delegation configured (or no ETR registration if sent by a DDT
      Map-Server).

   Pending Request List:  the set of outstanding requests for which a
      DDT Map Resolver has received encapsulated Map-Requests from its
      clients seeking EID-to-RLOC mapping for a XEID.  Each entry in the
      list contains additional state needed by the referral following
      process, including the XEID, requestor(s) of the XEID (typically,
      one or more ITRs), saved information about the last referral
      received and followed (matching XEID-prefix, action code, RLOC
      set, index of last RLOC queried in the RLOC set), and any LISP-SEC
      information ([I-D.ietf-lisp-sec]) that was included in the DDT
      client Map-Request.  An entry in the list may be interchangeably



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      termed a "pending request list entry" or simply a "pending
      request".

   For definitions of other terms, notably Map-Request, Map-Reply,
   Ingress Tunnel Router (ITR), Egress Tunnel Router (ETR), Map Server,
   and Map Resolver, please consult the LISP specification [RFC6830] and
   the LISP Mapping Service specification [RFC6833].

4.  Database organization

4.1.  XEID prefixes

   DDT database is indexed by Extended EID-prefixes (XEID-prefixes).
   XEID-prefix is LISP EID-prefix together with data extending it to
   uniquely identify address space of the prefix.  XEID-prefix is
   composed as binary encoding of five fields, in order of significance:
   DBID (16 bits), Instance Identifier (IID, 32 bits), Address Family
   Identifier (AFI, 16 bits), and EID-prefix (variable, according to AFI
   value).  The fields are concatenated, with the most significant
   fields as listed above.

   DBID is LISP-DDT database ID, a 16-bit field provided to allow the
   definition of multiple databases.  In this version of DDT DBID MUST
   always be set to zero.  Other values of DBID are reserved for future
   use.

   Instance ID (IID) is 32-bit value describing context of EID prefix if
   the latter is intended for use in an environment where addresses may
   not be unique, such as on a Virtual Private Network where [RFC1918]
   address space is used.  See "Using Virtualization and Segmentation
   with LISP" in [RFC6830] for more discussion of Instance IDs.
   Encoding of the instance ID (IID) is specified by
   [I-D.ietf-lisp-lcaf].

   Address Family Identifier (AFI) is a 16-bit value defining syntax of
   EID-prefix.  AFI values are assigned by IANA ([AFI].

4.2.  DDT database tree structure

   LISP-DDT database of each DDT node is organised as a tree structure
   that is indexed by XEID prefixes.  Leaves of the database tree
   describe delegation of authority between DDT nodes (see more on
   delegation and information kept in the database entries in
   Section 4.3).

   DDT Map-Requests sent by the DDT client to DDT nodes always contain
   specific values for DBID, IID and AFI; never a range or unspecified




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   value for any of these fields.  Thus XEID prefix used as key for
   search in the database tree will have length of at least 64 bits.

   DDT node may, for example, be authoritative for a consecutive range
   of 3-tuples (DBID, IID, AFI) and all associated EID prefixes; or only
   for a specific EID prefix of a single 3-tuple.  Thus XEID prefixes/
   keys of the database tree leaves may have length less, equal or more
   than 64 bits.

   It is important to note that LISP-DDT does not store actual EID-to-
   RLOC mappings; it is, rather, a distributed index that can be used to
   find the devices (ETRs which registered their EIDs with DDT Map
   Servers) that can be queried with LISP to obtain those mappings.
   Changes to EID-to-RLOC mappings are made on the ETRs which define
   them, not to any DDT node configuration.  DDT node configuration
   changes are only required when branches of the database hierarchy are
   added, removed, or modified.

4.3.  Configuring prefix delegation

   Every DDT node is configured with one or more XEID-prefixes for which
   it is authoritative along with a list of delegations of XEID-prefixes
   to other DDT nodes.  A DDT node is required to maintain a list of
   delegations for all sub-prefixes of its authoritative XEID-prefixes;
   it also may list "hints", which are prefixes that it knows about that
   belong to its parents, to the root, or to any other point in the
   XEID-prefix hierarchy.  A delegation (or hint) consists of an XEID-
   prefix, a set of RLOCs for DDT nodes that have more detailed
   knowledge of the XEID-prefix, and accompanying security information
   (for details of security infomation exchange and its use see
   Section 10).  Those RLOCs are returned in Map-Referral messages when
   the DDT node receives a DDT Map-Request with an XEID that matches a
   delegation.  A DDT Map Server will also have a set of sub-prefixes
   for which it accepts ETR mapping registrations and for which it will
   forward (or answer, if it provides proxy Map-Reply service) Map-
   Requests.

   XEID prefix (or prefixes) for which DDT node is authoritative and
   delegation of authority for sub-prefixes is provided as configuration
   of the DDT node.  Implementations will likely develop a language to
   express this prefix authority and delegation.  Since DDT
   configuration is static (i.e. not exchanged between DDT nodes as part
   of the protocol itself) such language is implementation-dependant and
   is outside the scope of this specification.







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4.3.1.  The root DDT node

   The root DDT node is the logical "top" of the distributed database
   hierarchy.  It is authoritative for all XEID prefixes, that is for
   all valid 3-tuples (DBID, IID, AFI) and their EID prefixes.  A DDT
   Map-Request that matches no configured XEID-prefix will be referred
   to the root node (see Section 8 for formal description of conditions
   when DDT Request is forwarded to the root node).  The root node in a
   particular instantiation of LISP-DDT therefore MUST be configured
   with delegations for at least all defined IIDs and AFIs.

5.  DDT Map-Request

   A DDT client (usualy a Map Resolver) uses LISP Encapsulated Control
   Message (ECM) to send Map-Request to a DDT node.  Format of the ECM
   is defined by [RFC6830].  This specification adds to ECM flag "DDT-
   originated".

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |                       IPv4 or IPv6 Header                     |
   OH  |                      (uses RLOC addresses)                    |
     \ |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |       Source Port = xxxx      |       Dest Port = 4342        |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   LH  |Type=8 |S|D|                Reserved                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |                       IPv4 or IPv6 Header                     |
   IH  |                  (uses RLOC or EID addresses)                 |
     \ |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |       Source Port = xxxx      |       Dest Port = yyyy        |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   LCM |                      LISP Control Message                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   D: The "DDT-originated" flag.  It is set by a DDT client to indicate
      that the receiver SHOULD return Map-Referral messages as
      appropriate.  Use of the flag is further described in
      Section 7.3.1.  This bit is allocated from LISP message header
      bits marked as Reserved in [RFC6830].




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6.  The Map-Referral message

   This specification defines a new LISP message, the Map-Referral.  It
   is sent by a DDT node to a DDT client in response to a DDT Map-
   Request message.  See Section 6.4 for a detailed layout of the Map-
   Referral message fields.

   The message consists of an action code along with delegation
   information about the XEID-prefix that matches the requested XEID.

6.1.  Action codes

   The action codes are as follows:

   NODE-REFERRAL (0):  indicates that the replying DDT node has
      delegated an XEID-prefix that matches the requested XEID to one or
      more other DDT nodes.  The Map-Referral message contains a "map-
      record" with additional information, most significantly the set of
      RLOCs to which the prefix has been delegated, that is used by a
      DDT client to "follow" the referral.

   MS-REFERRAL (1):  indicates that the replying DDT node has delegated
      an XEID-prefix that matches the requested XEID to one or more DDT
      Map Servers.  It contains the same additional information as a
      NODE-REFERRAL, but is handled slightly differently by the
      receiving DDT client (see Section 7.3.2).

   MS-ACK (2):  indicates that the replying DDT Map Server received a
      DDT Map-Request that matches an authoritative XEID-prefix for
      which it has one or more registered ETRs.  This means that the
      request has been forwarded to one of those ETRs to provide an
      answer to the querying ITR.

   MS-NOT-REGISTERED (3):  indicates that the replying DDT Map Server
      received a Map-Request for one of its configured XEID-prefixes
      which has no ETRs registered.

   DELEGATION-HOLE (4):  indicates that the requested XEID matches a
      non-delegated sub-prefix of the XEID space.  This is a non-LISP
      "hole", which has not been delegated to any DDT Map Server or ETR.
      See Section 7.1.2 for details.  Also sent by a DDT Map Server with
      authoritative configuration covering the requested EID, but for
      which no specific site ETR is configured.

   NOT-AUTHORITATIVE (5):  indicates that the replying DDT node received
      a Map-Request for an XEID for which it is not authoritative and
      has no configured matching hint referrals.  This can occur if a
      cached referral has become invalid due to a change in the database



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      hierarchy.  However, if such a DDT node has a "hint" delegation
      covering the requested EID, it MAY choose to return NODE-REFERRAL
      or MS-REFERRAL as appropriate.  When returning action code NOT-
      AUTHORITATIVE DDT node MUST provide EID-prefix received in the
      request and the TTL MUST be set to 0.

6.2.  Referral set

   For "positive" action codes (NODE-REFERRAL, MS-REFERRAL, MS-ACK), a
   DDT node MUST include in the Map-Referral message a list of RLOCs for
   DDT nodes that are authoritative for the XEID-prefix being returned;
   a DDT client uses this information to contact one of those DDT nodes
   as it "follows" a referral.

6.3.  Incomplete flag

   A DDT node sets the "Incomplete" flag in a Map-Referral message if
   the Referral Set is incomplete; this is intended to prevent a DDT
   client from caching a referral with incomplete information.  A DDT
   node MUST set the "incomplete" flag in the following cases:

   o  If it is setting action code MS-ACK or MS-NOT-REGISTERED but the
      matching XEID-prefix is not flagged in configuration as
      "complete".  XEID-prefix configuration on DDT Mapping Server
      SHOULD be marked as "complete" when configuration of the XEID-
      prefix lists all "peer" DDT nodes that are also authoritative for
      the same XEID-prefix or when it is known that local DDT node is
      the only one authoritative for the XEID-prefix.

   o  If it is setting action code NOT-AUTHORITATIVE.

6.4.  Map-Referral Message Format



















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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |Type=6 |                Reserved               | Record Count  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         Nonce . . .                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                         . . . Nonce                           |
   +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |                          Record  TTL                          |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   R   | Referral Count| EID mask-len  | ACT |A|I|     Reserved        |
   e   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   c   |SigCnt |   Map Version Number  |            EID-AFI            |
   o   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   r   |                          EID-prefix ...                       |
   d   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  /|    Priority   |    Weight     |  M Priority   |   M Weight    |
   | R +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | e |       Unused Flags      |L|p|R|            Loc-AFI            |
   | f +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  \|                             Locator ...                       |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   ~                          Sig section                          ~
   +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Type: Type value 6 was reserved for future use in RFC6830, this
   document allocates this value to identify Map-Referral messages.

   ACT: The "action" field of the mapping record in a Map-Referral
   message encodes one of the 6 action types: NODE-REFERRAL, MS-
   REFERRAL, MS-ACK, MS-NOT-REGISTERED, DELEGATION-HOLE, NOT-
   AUTHORITATIVE.  See Section 6.1 for description of their meaning.

   Incomplete: The "I" bit indicates that a DDT node's referral-set of
   locators is incomplete and the receiver of this message SHOULD NOT
   cache the referral.  A DDT sets the "incomplete" flag, the TTL, and
   the Action Type field as follows:













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   -------------------------------------------------------------------
    Type (Action field)          Incomplete Referral-set   TTL values
   -------------------------------------------------------------------
     0    NODE-REFERRAL              NO         YES           1440

     1    MS-REFERRAL                NO         YES           1440

     2    MS-ACK                     *          *             1440

     3    MS-NOT-REGISTERED          *          *             1

     4    DELEGATION-HOLE            NO         NO            15

     5    NOT-AUTHORITATIVE          YES        NO            0
   -------------------------------------------------------------------

   *: The "Incomplete" flag setting on Map Server originated referral of
      MS-ACK and MS-NOT-REGISTERED types depend on whether the Map
      Server has the full peer Map Server configuration for the same
      prefix and has encoded the information in the mapping record.
      Incomplete bit is not set when the Map Server has encoded the
      information, which means the referral-set includes all the RLOCs
      of all Map Servers that serve the prefix.  It MUST be set when
      configuration of the Map Server does not flag matching prefix as
      configured with the complete information about "peer" Map Servers
      or when the Map Server does not return all configured locators.

   Referral Count: number of RLOCs in the current Referral set, it is
   equal to the number of Ref sections in the message.

   SigCnt: Indicates the number of signatures (sig section) present in
   the Record.  If SigCnt is larger than 0, the signature information
   captured in a sig section as described in Section 6.4.1 will be
   appended to the end of the record.  The number of sig sections at the
   end of the Record MUST match the SigCnt.  Note that bits occupied by
   SigCnt were Reserved in Records embedded into messages defined by
   [RFC6830] and were required to be set to zero.

   Loc-AFI: AFI of the Locator field.  If AFI value is different from
   LCAF AFI, security keys are not included in the record.  If AFI is
   equal to the LCAF AFI, the contents of the LCAF depend on the Type
   field of the LCAF.  LCAF Type 11 is used to store security material
   along with the AFI of the locator.  DDT nodes and DDT Map Servers can
   use this LCAF Type to include public keys associated with their Child
   DDT nodes for a XEID-prefix referral record.  LCAF types and formats
   are defined in [I-D.ietf-lisp-lcaf].





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   Locator: RLOC of a DDT node the DDT client is being referred to.
   Lenght of this variable-length field is determined by the Loc-AFI.

   All other fields and their descriptions are equivalent to those in
   the Map-Reply message, as defined in LISP [RFC6830].  Note, though,
   that the set of RLOCs correspond to the DDT node to be queried as a
   result of the referral not the RLOCs for an actual EID-to-RLOC
   mapping.

6.4.1.  SIG section

   SigCnt counts the number of signature sections that appear at the end
   of the Record.  Format of the signature section is described below.

       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /|                      Original Record TTL                      |
     / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    /  |                      Signature Expiration                     |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   s   |                      Signature Inception                      |
   i   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   g   |            Key Tag            |           Sig Length          |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   \   | Sig-Algorithm |    Reserved   |            Reserved           |
    \  +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ ~                             Signature                         ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Original Record TTL: The original Record TTL for this record that is
   covered by the signature.  Record TTL is in minutes.

   Signature Expiration and Inception: Specify the validity period for
   the signature.  The signature MUST NOT be used for authentication
   prior to the inception date and MUST NOT be used for authentication
   after the expiration date.  Each field specifies a date and time in
   the form of a 32-bit unsigned number of seconds elapsed since 1
   January 1970 00:00:00 UTC, ignoring leap seconds, in network byte
   order.

   Key Tag: An identifier to specify which key is used for this
   signature if more than one valid key exists for the signing DDT node.

   Sig Length: The length of the Signature field in bytes.

   Sig-Algorithm: The identifier of the cryptographic algorithm used for
   the signature.  Sig-Algorithm values defined in this specification
   are listed in Table 1.  Implementation conforming to this




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   specification MUST implement at least RSA-SHA256 for DDT signing.
   Sig-Algorithm type 1 RSA-SHA1 is deprecated and SHOULD NOT be used.

          +---------------+------------+-----------+------------+
          | Sig-Algorithm |    Name    | Reference |   Notes    |
          +---------------+------------+-----------+------------+
          |       1       |  RSA-SHA1  | [RFC3447] | DEPRECATED |
          |               |            |           |            |
          |       2       | RSA-SHA256 | [RFC3447] | MANDATORY  |
          +---------------+------------+-----------+------------+

                       Table 1: Sig-Algorithm Values

   Reserved: This field MUST be set to 0 on transmit and MUST be ignored
   on receipt.

   Signature: Contains the cryptographic signature that covers the
   entire referral record that this signature belongs to.  The Record
   TTL is set to Original Record TTL and the sig fields are Signature
   field is set to zero for the purpose of computing the Signature.

7.  DDT network elements and their operation

   As described above, DDT introduces a new network element, the "DDT
   node", extends the functionality of Map Servers and Map Resolvers to
   send and receive Map-Referral messages.  The operation of each of
   these devices is described as follows.

7.1.  DDT node

   When a DDT node receives a DDT Map-Request, it compares the requested
   XEID against its list of XEID-prefix delegations and its list of
   authoritative XEID-prefixes and acts as follows:

7.1.1.  Match of a delegated prefix (or sub-prefix)

   If the requested XEID matches one of the DDT node's delegated
   prefixes, then a Map-Referral message is returned with the matching
   more-specific XEID-prefix and the set of RLOCs for the referral
   target DDT nodes including associated security information (see
   Section 10 for details on security).  If at least one DDT node of the
   delegation is known to be a DDT Map Server, then the Map-Referral
   message SHOULD be sent with action code MS-REFERRAL to indicate to
   the receiver that LISP-SEC information (if saved in the pending
   request) SHOULD be included in the next DDT Map-Request; otherwise,
   the action code NODE-REFERRAL SHOULD be used.





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   Note that a matched delegation does not have to be for a sub-prefix
   of an authoritative prefix; in addition to being configured to
   delegate sub-prefixes of an authoritative prefix, a DDT node may also
   be configured with other XEID-prefixes for which it can provide
   referrals to DDT nodes anywhere in the database hierarchy.  This
   capability to define "shortcut hints" is never required to be
   configured, but may be a useful heuristic for reducing the number of
   iterations needed to find an EID, particular for private network
   deployments.

   Referral hints, if used properly, may reduce number of referrals a
   DDT client needs to follow to locate DDT Map Server authoritative for
   XEID prefix being resolved.  On the other hand, incorrect use of
   hints may create circular dependencies between DDT nodes (or
   "referral loops").  DDT client MUST be prepared to handle such
   circular referrals.  See Section 7.3.4 for discussion of referral
   loops and measures DDT client must implement in order to detect
   circular referrals and prevent infinite looping.

   Another danger with use of hints is when DDT deployment spans
   multiple administrative domains (i.e. different authorities manage
   DDT nodes in the same DDT database).  In this case operator managing
   a DDT node may not be aware of the fact that the node is being
   referred to by hints.  Locator addresses in hints may become stale
   when referred DDT nodes are taken out of service or change their
   locator addresses.

7.1.2.  Missing delegation from an authoritative prefix

   If the requested XEID did not match a configured delegation but does
   match an authoritative XEID-prefix, then the DDT node MUST return a
   negative Map-Referral that uses the least-specific XEID-prefix that
   does not match any XEID-prefix delegated by the DDT node.  The action
   code is set to DELEGATION-HOLE; this indicates that the XEID is not a
   LISP destination.

   If the requested XEID did not match either a configured delegation,
   an authoritative XEID-prefix or a "hint", then negative Map-Referral
   with action code NOT-AUTHORITATIVE MUST be returned.

7.2.  DDT Map Server

   When a DDT Map Server receives a DDT Map-Request, its operation is
   similar to that of a DDT node with additional processing as follows:

   o  If the requested XEID matches a registered XEID-prefix, then the
      Map-Request is forwarded to one of the destination ETR RLOCs (or
      the Map Server sends a Map-Reply, if it is providing proxy Map-



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      Reply service) and a Map-Referral with the MS-ACK action MUST be
      returned to the sender of the DDT Map-Request.

   o  If the requested XEID matches a configured XEID-prefix for which
      no ETR registration has been received then a negative Map-Referral
      with action code MS-NOT-REGISTERED MUST be returned to the sender
      of the DDT Map-Request.

7.3.  DDT client

   A DDT client queries one or more DDT nodes and uses an iterative
   process of following returned referrals until it receives one with
   action code MS-ACK (or an error indication).  MS-ACK indicates that
   the Map-Request has been sent to a Map Server that will forward it to
   an ETR that, in turn, will provide a Map-Reply to the locator address
   in the Map-Request.

   DDT client functionality will typically be implemented by DDT Map
   Resolvers.  Just as any other Map Resolver, a DDT Map Resolver
   accepts Map-Requests from its clients (typically, ITRs) and ensures
   that those Map-Requests are forwarded to the correct ETR, which
   generates Map-Replies.  Unlike a Map Resolver that uses the ALT
   mapping system (see [RFC6836]), however, a DDT Map Resolver
   implements a DDT client functionality to find the correct ETR to
   answer a Map-Request; this requires a DDT Map Resolver to maintain
   additional state: a Map-Referral cache and pending request list of
   XEIDs that are going through the iterative referral process.

   DDT client functionality may be implemented on ITRs.  In this case
   the DDT client will not receive Map-Request from another network
   element; instead, equivalent information will be provided to the DDT
   client by the means of programming interface.

7.3.1.  Queuing and sending DDT Map-Requests

   When a DDT client receives a request to resolve XEID (in case of DDT
   Map Resolver this will be in the form of received encapsulated Map-
   Request), it first performs a longest-match search for the XEID in
   its referral cache.  If no match is found or if a negative cache
   entry is found, then the destination is not in the database; a
   negative Map-Reply MUST be returned and no further processing is
   performed by the DDT client.

   If a match is found, the DDT client creates a pending request list
   entry for the XEID and saves the original request (in case of DDT
   Map-Resolved, original Map-Request minus the encapsulation header)
   along with other information needed to track progress through the
   iterative referral process; the "referral XEID-prefix" is also



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   initialized to indicate that no referral has yet been received.  The
   DDT client then creates a DDT Map-Request (which is an encapsulated
   Map-Request with the "DDT-originated" flag set in the message header)
   for the XEID but without any authentication data that may have been
   included in the original request.  It sends the DDT Map-Request to
   one of the RLOCs in the chosen referral cache entry.  The referral
   cache is initially populated with one or more statically-configured
   entries; additional entries are added when referrals are followed, as
   described below.  A DDT client is not absolutely required to cache
   referrals, but it doing so decreases latency and reduces lookup
   delays.

   Note that in normal use on the public Internet, the statically-
   configured initial referral cache for a DDT client should include a
   "default" entry with RLOCs for either the DDT root node or one or
   more DDT nodes that contain hints for the DDT root node.  If a DDT
   client does not have such configuration, it will return a Negative
   Map-Reply if it receives a query for an EID outside the subset of the
   mapping database known to it.  While this may be desirable on private
   network deployments or during early transition to LISP when few sites
   are using it, this behavior is not appropriate when LISP is in
   general use on the Internet.  If DDT message exchange is
   authenticated as described in Section 10 then DDT client MUST also be
   configured with public keys of DDT nodes pointed to by the "default"
   cache entry.  In this case the "default" entry will typically be for
   the DDT root node.

7.3.2.  Receiving and following referrals

   After sending a DDT Map-Request, a DDT client expects to receive a
   Map-Referral response.  If none occurs within the timeout period, the
   DDT client retransmits the request, sending to the next RLOC in the
   referral cache entry if one is available.  If all RLOCs have been
   tried and the maximum number of retransmissions has occurred for
   each, then the pending request list entry is dequeued and discarded.
   In this case DDT client returns no response to sender of the original
   request.

   A DDT client processes a received Map-Referral message according to
   each action code:

   NODE-REFERRAL:  The DDT client checks for a possible referral loop as
      as described in Section 7.3.4.  If no loop is found, the DDT
      client saves the prefix returned in the Map-Referral message in
      the referral cache, updates the saved prefix and saved RLOCs in
      the pending request list entry, and follows the referral by
      sending a new DDT Map-Request to one of the DDT node RLOCs listed




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      in the Referral Set; security information saved with the original
      Map-Request SHOULD NOT be included.

   MS-REFERRAL:  The DDT client processes an MS-REFERRAL in the same
      manner as a NODE-REFERRAL except that security information saved
      with the original Map-Request MUST be included in the new Map-
      Request sent to a Map Server (see Section 10 for details on
      security).

   MS-ACK:  This is returned by a DDT Map Server to indicate that it has
      one or more registered ETRs that can answer a Map-Request for the
      XEID and the request has been forwarded to one of them (or if the
      Map Server is doing proxy service for the prefix then reply has
      been sent to the querying ITR).  If the pending request did not
      include saved LISP-SEC information or if that information was
      already included in the previous DDT Map-Request (sent by the DDT
      client in response to either an MS-REFERRAL or a previous MS-ACK
      referral), then the pending request for the XEID is complete;
      processing of the request stops and all request state can be
      discarded.  Otherwise, LISP-SEC information is required and has
      not yet been sent to the authoritative DDT Map-Server; the DDT
      client MUST re-send the DDT Map-Request with LISP-SEC information
      included and the pending request queue entry remains until another
      Map-Referral with MS-ACK action code is received.  If the
      "incomplete" flag is not set, the prefix is saved in the referral
      cache.

   MS-NOT-REGISTERED:  The DDT Map Server queried could not process the
      request because it did not have any ETRs registered for a
      matching, authoritative XEID-prefix.  If the DDT client has not
      yet tried all of the RLOCs saved with the pending request, then it
      sends a Map-Request to the next RLOC in that list.  If all RLOCs
      have been tried, then the destination XEID is not registered and
      is unreachable.  The DDT client MUST return a negative Map-Reply
      to the requester (in case of DDT Map Resolver to the sender of
      original Map-Request); this Map-Reply contains the least-specific
      XEID-prefix in the range for which this DDT Map Server is
      autoritative and no registrations exist and whose TTL value SHOULD
      be set to one minute.  A negative referral cache entry is created
      for the prefix (whose TTL also SHOULD be set to one minute) and
      processing of the request stops.

   DELEGATION-HOLE:  The DDT Map Server queried did not have an XEID-
      prefix defined that matched the requested XEID so it does not
      exist in the mapping database.  The DDT client MUST return a
      negative Map-Reply to the requester (in case of DDT Map Resolver
      to the sender of original Map-Request); this Map-Reply SHOULD
      indicate the least-specific XEID-prefix matching the requested



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      XEID for which no delegations exist and SHOULD have a TTL value of
      15 minutes.  A negative referral cache entry is created for the
      prefix (which also SHOULD have TTL of 15 minutes) and processing
      of the pending request stops.

   NOT-AUTHORITATIVE:  The DDT Map Server queried is not authoritative
      for the requested XEID.  This can occur if a cached referral has
      become invalid due to a change in the database hierarchy.  If the
      DDT client receiving this message can determine that it is using
      old cached information, it MAY choose to delete that cached
      information and re-try the original Map-Request, starting from its
      "root" cache entry.  If this action code is received in response
      to a query that did not use a cached referral information, then it
      indicates a database synchronization problem or configuration
      error.  The pending request is silently discarded, i.e. all state
      for the request that caused this answer is removed and no answer
      is returned to the original requestor.

7.3.3.  Handling referral errors

   Other states are possible, such as a misconfigured DDT node (acting
   as a proxy Map Server, for example) returning a Map-Reply to the DDT
   client; they should be considered errors and logged as such.  It is
   not clear exactly what else the DDT client should do in such cases;
   one possibility is to remove the pending request list entry and send
   a negative Map-Reply to the requester (in case of DDT Map Resolver to
   the sender of original Map-Request).  Alternatively, if a DDT client
   detects unexpected behavior by a DDT node, it could mark that node as
   unusable in its referral cache and update the pending request to try
   a different DDT node if more than one is listed in the referral
   cache.  In any case, any prefix contained in a Map-Referral message
   that causes a referral error (including a referral loop) is not saved
   in the DDT client referral cache.

7.3.4.  Referral loop detection

   In response to a Map-Referral message with action code NODE-REFERRAL
   or MS-REFERRAL, a DDT client is directed to query a new set of DDT
   node RLOCs that are expected to have more-specific XEID-prefix
   information for the requested XEID.  To prevent a possible "iteration
   loop" (following referrals back-and-forth among a set of DDT nodes
   without ever finding an answer), a DDT client saves the last received
   referral XEID-prefix for each pending request and checks that a newly
   received NODE-REFERRAL or MS-REFERRAL message contains a more-
   specific referral XEID-prefix; an exact or less-specific match of the
   saved XEID-prefix indicates a referral loop.  If a loop is detected,
   the DDT Map Resolver handles the request as described in
   Section 7.3.3.  Otherwise, the DDT client saves the most recently



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   received referral XEID-prefix with the pending request when it
   follows the referral.

   As an extra measure to prevent referral loops, it is probably also
   wise to limit the total number of referrals for any request to some
   reasonable number; the exact value of that number will be determined
   during experimental deployment of LISP-DDT, but is bounded by the
   maximum length of the XEID.

   Note that when a DDT client adds an entry to its lookup queue and
   sends an initial Map-Request for an XEID, the queue entry has no
   previous referral XEID-prefix; this means that the first DDT node
   contacted by a DDT Map Resolver may provide a referral to anywhere in
   the DDT hierarchy.  This, in turn, allows a DDT client to use
   essentially any DDT node RLOCs for its initial cache entries and
   depend on the initial referral to provide a good starting point for
   Map-Requests; there is no need to configure the same set of root DDT
   nodes on all DDT clients.

8.  Pseudo Code and Decision Tree diagrams

   To illustrate DDT algorithms described above and to aid in
   implementation, each of the major DDT Map Server and DDT Map Resolver
   functions are described below, first using simple "psuedo-code" and
   then in the form of a decision tree.

8.1.  Map Resolver processing of ITR Map-Request

8.1.1.  Pseudo-code summary

    if ( request pending i.e., (ITR,EID) of request same ) {
        replace old request with new & use new request nonce
         for future requests
    } else if ( no match in refcache ) {
        return negative map-reply to ITR
    } else if ( match type delegation hole ) {
        return negative map-reply to ITR
    } else if ( match type ms-ack ) {
        fwd DDT request to map-server
    } else {
        store & fwd DDT request w/o security material to node delegation
    }

8.1.2.  Decision tree diagram







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   +------------+
   | Is Request | Yes
   |            |----> Replace old request with
   |  Pending?  |      new nonce for future requests
   +------------+
         |
         |No
         |
         V
   +------------+
   | Match In   | No
   | Referral   |----> Send Negative Map-Reply
   | cache?     |      (not a likely event as root or
   +------------+       hint configured on every MR)
         |
         |Yes
         |
         V
   +------------+
   | Match Type | Yes
   | Delegation |----> Send Negative Map-Reply
   | Hole?     |
   +------------+
         |
         |No
         |
         V
   +------------+
   | Match Type | Yes
   | MS-ACK?    |----> Forward DDT Map-request to Map-Server
   |            |
   +------------+
         |
         |No
         |
         V
   Store request & Fwd DDT Request w/o security material
    to DDT node delegation

8.2.  Map Resolver processing of Map-Referral message

8.2.1.  Pseudo-code summary

      if ( authentication signature validation failed ) {
          silently drop
      }

      if ( no request pending matched by referral nonce ) {



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          silently drop
      }

      if ( pfx in referral less specific than last referral used ) {
          if ( gone through root ) {
              silently drop
          } else {
              send request to root
          }
      }

      switch (map_referral_type) {

          case NOT_AUTHORITATIVE :
              if ( gone through root ) {
                  return negative map-reply to ITR
              } else {
                  send request to root
              }

          case DELEGATION_HOLE:
              cache & send negative map-reply to ITR

          case MS_REFERRAL:
              if ( referral equal to last used ) {
                  if ( gone through root ) {
                      return negative map-reply to ITR
                  } else {
                      send request to root
                  }
              } else {
                  cache
                  follow the referral, include security material
              }

          case NODE_REFERRAL:
              if ( referral equal to last used ) {
                  if ( gone through root ) {
                      return negative map-reply to ITR
                  } else {
                      send request to root
                  }
              } else {
                  cache
                  follow the referral, strip security material
              }

          case MS_ACK:



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              if ( security material stripped ) {
                  resend request with security material
                  if { !incomplete } {
                      cache
                  }
              }

          case MS_NOT_REGISTERED:
              if { all map-server delegations not tried } {
                  follow delegations not tried
                  if ( !incomplete ) {
                      cache
                  }
              } else {
                  send negative map-reply to ITR
                  if { !incomplete } {
                      cache
                  }
              }

          case DEFAULT:
              drop
          }
      }

8.2.2.  Decision tree diagram

                          +----------------+
                          | Auth Signature | No
                          |     Valid?     |----> Silently drop
                          +----------------+
                                  | Yes
                                  V
                            +------------+
                            | Is Request | No
                            |  Pending?  |----> Silently drop
                            +------------+
                                  | Yes
                                  V
                    +------------------------------+ Yes
                    | Pfx less specific than last? |----> Silently drop
                    +------------------------------+
                                  |No
                                  V
       +---------------------------------------------------+
       |             What is Map-Referral Type?            |--UNKNOWN-+
       +---------------------------------------------------+          |
         |        |         |       |         |          |            V



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         |        |         |       |         |       DEL_HOLE      DROP
         |        |         |       |      MS_ACK        |
         |        |         |       |         |          V
         |        |     MS_REF   NODE_REF     |      Cache & return
         |        |         |       |         V      negative map-reply
         |        |         |       |    +---------+
         |   NOT_AUTH       |       |    | Was sec | Yes
         |        |         |       |    | material|
         |        |         |       |    |Stripped?|----> Done
         |        |         V       V    +---------+
         |        |       +------------+      | No
         |        |   Yes | Pfx equal  |      V
MS_NOT_REGISTERED |   +---| to last    |  +------------+
         |        |   |   | used?      |  | Incomplete | Yes
         |        |   |   +------------+  | bit set?   |---> Resend DDT
         |        V   V          |No      +------------+     request w
         |  +------------+       |               |No         security
         |  |  Gone      |       V               |           material
         |  |  Through   |   Cache & follow      V
         |  |  Root?     |   the referral     Cache & resend DDT
         |  +------------+                    request with
         |    |No      |Yes                   security material
         |    |        |
         |    V        V
         |  Send req   Send negative map-reply
         |  to root
         V
 +-----------+ Yes                        +-----------+ Yes
 | Other MS  |----Follow other MS-------->|Incomplete |----> Don't cache
 | not tried?|                            |bit set?   |
 |           |---Send negative map-reply->|           |----> Cache
 +-----------+ No                         +-----------+ No

8.3.  DDT Node processing of DDT Map-Request message

8.3.1.  Pseudo-code summary















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    if ( I am not authoritative ) {
        send map-referral NOT_AUTHORITATIVE with
         incomplete bit set and ttl 0
    } else if ( delegation exists ) {
        if ( delegated map-servers ) {
            send map-referral MS_REFERRAL with
              ttl 'Default_DdtNode_Ttl'
        } else {
            send map-referral NODE_REFERRAL with
              ttl 'Default_DdtNode_Ttl'
        }
    } else {
        if ( eid in site) {
            if ( site registered ) {
                forward map-request to etr
                if ( map-server peers configured ) {
                    send map-referral MS_ACK with
                     ttl 'Default_Registered_Ttl'
                } else {
                    send map-referral MS_ACK with
                     ttl 'Default_Registered_Ttl' and incomplete bit set
                }
            } else {
                if ( map-server peers configured ) {
                    send map-referral MS_NOT_REGISTERED with
                     ttl 'Default_Configured_Not_Registered_Ttl'
                } else {
                    send map-referral MS_NOT_REGISTERED with
                     ttl 'Default_Configured_Not_Registered_Ttl'
                     and incomplete bit set
                }
            }
        } else {
            send map-referral DELEGATION_HOLE with
             ttl 'Default_Negative_Referral_Ttl'
        }
    }

   where architectural constants for TTL are set as follows:

   Default_DdtNode_Ttl                   1440 minutes
   Default_Registered_Ttl                1440 minutes
   Default_Negative_Referral_Ttl         15 minutes
   Default_Configured_Not_Registered_Ttl 1 minute







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8.3.2.  Decision tree diagram

 +------------+
 |    Am I    | No
 |  Authori-  |----> Return NOT_AUTHORITATIVE
 |   tative?  |       Incomplete = 1
 +------------+       ttl = Default_DdtNode_Ttl
       |
       |Yes
       |
       V
 +------------+     +------------+
 | Delegation | Yes | Delegations| Yes
 |   Exists?  |---->| are map    |----> Return MS_REFERRAL
 |            |     | servers?   |       ttl = Default_DdtNode_Ttl
 +------------+     +------------+
       |                  \ No
       |No                 +--> Return NODE_REFERRAL
       |                        ttl = Default_DdtNode_Ttl
       V
 +------------+     +------------+                  +------------+
 | EID in     | Yes | Site       | Yes              | Map-server |
 |  Site      |---->| Registered?|----> Forward---->| peers      |
 | Config?    |     |            |      Map-request | configured?|
 +------------+     +------------+      to ETR      +------------+
       |                |                          |       |
       |                |No                      No|       |Yes
       |                |                          |       |
       |                |                          V       V
       |                |                Return MS_ACK    Return MS_ACK
       |                V                with INC=1
       |         +------------+          ttl=Default_Registered_Ttl
       |         | Map-server | Yes
       |         | peers      |----> Return MS_NOT_REGISTERED
       |         | configured?|      ttl = Default_Negative_Referral_Ttl
       |         +------------+
       |                \ No
       |No               +--> Return MS_NOT_REGISTERED
       |                      Incomplete = 1
       V                      ttl = Default_Negative_Referral_Ttl
 Return DELEGATION_HOLE
  ttl = Default_Negative_Referral_Ttl

9.  Example topology and request/referral following

   This chapter shows example DDT tree and several possible scenarios of
   Map-Requests coming to a Map Resolver and subsequent iterative DDT
   referrals.  For the sake of example RLOCs of DDT nodes are shown in



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   IPv4 address space while the EIDs are in IPv6 AF.  The same principle
   of hierarchical delegation and pinpointing referrals is equally
   applicable to any AF whose address hierarchy can be expressed as a
   bitstring with associated length.  DDT tree of IPv4 prefixes is
   another AF with immediate practical value.

   To show how referrals are followed to find the RLOCs for a number of
   EIDs, consider the following example EID topology for DBID=0, IID=0,
   AFI=2, and EID=0/0










































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      +---------------------+  +---------------------+
      |  root1: 192.0.2.1   |  |  root2: 192.0.2.2   |
      | authoritative: ::/0 |  | authoritative: ::/0 |
      +---------------------+  +---------------------+
                 |         \   /        |
                 |          \ /         |
                 |           X          |
                 |          / \         |
                 |         /   \        |
                 |        |     |       |
                 V        V     V       V
  +-------------------------+  +--------------------------+
  |  DDT node1: 192.0.2.11  |  |  DDT node2: 192.0.2.12   |
  |     authoritative:      |  |      authoritative:      |
  |      2001:db8::/32      |  |       2001:db8::/32      |
  +-------------------------+  +--------------------------+
                 |         \   /        |
                 |          \ /         |
                 |           X          |
                 |          / \         |
                 |         /   \        |
                 |        |     |       |
                 V        V     V       V
 +--------------------------+  +---------------------------+
 | Map-Server1: 192.0.2.101 |  |  DDT node3: 192.0.2.201   |
 |      authoritative:      |  |      authoritative:       |
 |    2001:db8:0100::/40    |  |    2001:db8:0500::/40     |
 | site1: 2001:db8:0103::/48|  +---------------------------+
 | site2: 2001:db8:0104::/48|     |                    |
 +--------------------------+     |                    |
                                  |                    |
                                  |                    |
                                  V                    V
           +---------------------------+   +---------------------------+
           | Map-Server2: 192.0.2.211  |   | Map-Server3: 192.0.2.221  |
           |      authoritative:       |   |      authoritative:       |
           |    2001:db8:0500::/48     |   |    2001:db8:0501::/48     |
           |site3: 2001:db8:0500:1::/64|   |site5: 2001:db8:0501:8::/64|
           |site4: 2001:db8:0500:2::/64|   |site6: 2001:db8:0501:9::/64|
           +---------------------------+   +---------------------------+

   DDT nodes are configured for this "root" at IP addresses 192.0.2.1
   and 192.0.2.2.  DDT Map Resolvers are configured with default
   referral cache entries to these addresses.

   The root DDT nodes delegate 2001:db8::/32 to two DDT nodes with IP
   addresses 192.0.2.11 and 192.0.2.12.




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   The DDT nodes for 2001:db8::/32 delegate 2001:db8:0100::/40 to a DDT
   Map Server with RLOC 192.0.2.101

   The DDT Map Server for 2001:db8:0100::/40 is configured to allow ETRs
   to register the sub-prefixes 2001:db8:0103::/48 and
   2001:db8:0104::/48

   The DDT nodes for 2001:db8::/32 also delegate 2001:db8:0500::/40 to a
   DDT node with RLOC 192.0.2.201

   The DDT node for 2001:db8:0500::/40 is further configured to delegate
   2001:db8:0500::/48 to a DDT Map Server with RLOC 192.0.2.211 and
   2001:db8:0501::/48 to a DDT Map Server with RLOC 192.0.2.221

   The DDT Map Server for 2001:db8:0500::/48 is configured to allow ETRs
   to register the sub-prefixes 2001:db8:0500:1::/64 and
   2001:db8:0500:2::/64

   The DDT Map Server for 2001:db8:0501::/48 is configured to allow ETRs
   to register the sub-prefixes 2001:db8:0501:8::/64 and
   2001:db8:0501:9::/64

9.1.  Lookup of 2001:db8:0103:1::1/128

   The first example shows a DDT Map Resolver following a delegation
   from the root to a DDT node followed by another delegation to a DDT
   Map Server.

   ITR1 sends an Encapsulated Map-Request for 2001:db8:0103:1::1 to one
   of its configured (DDT) Map Resolvers.  The DDT Map Resolver proceeds
   as follows:

   1.  Send DDT Map-Request (for 2001:db8:0103:1::1) to one of the root
       DDT nodes, 192.0.2.1 or 192.0.2.2

   2.  Receive (and save in referral cache) Map-Referral for EID-prefix
       2001:db8::/32, action code NODE-REFERRAL, RLOC set (192.0.2.11,
       192.0.2.12)

   3.  Send DDT Map-Request to 192.0.2.11 or 192.0.2.12

   4.  Receive (and save in referral cache) Map-Referral for EID-prefix
       2001:db8:0100::/40, action code MS-REFERRAL, RLOC set
       (192.0.2.101)

   5.  Send DDT Map-Request to 192.0.2.101; if the ITR-originated
       Encapsulated Map-Request had a LISP-SEC signature, it is included




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   6.  DDT Map Server at 192.0.2.101 decapsulates the DDT Map-Request
       and forwards to a registered site1 ETR for 2001:db8:0103::/48

   7.  DDT Map Server at 192.0.2.101 sends a Map-Referral message for
       EID-prefix 2001:db8:0103::/48, action code MS-ACK to the DDT Map
       Resolver

   8.  DDT Map Resolver receives Map-Referral message and dequeues the
       pending request for 2001:db8:0103:1::1

   9.  site1 ETR for 2001:db8:0103::/48 receives Map-Request forwarded
       by DDT Map Server and sends Map-Reply to ITR1

9.2.  Lookup of 2001:db8:0501:8:4::1/128

   The next example shows a three-level delegation: root to first DDT
   node, first DDT node to second DDT node, second DDT node to DDT Map
   Server.

   ITR2 sends an Encapsulated Map-Request for 2001:db8:0501:8:4::1 to
   one of its configured (DDT) Map Resolvers, which are different from
   those for ITR1.  The DDT Map Resolver proceeds as follows:

   1.   Send DDT Map-Request (for 2001:db8:0501:8:4::1) to one of the
        root DDT nodes, 192.0.2.1 or 192.0.2.2

   2.   Receive (and save in referral cache) Map-Referral for EID-prefix
        2001:db8::/32, action code NODE-REFERRAL, RLOC set (192.0.2.11,
        192.0.2.12)

   3.   Send DDT Map-Request to 192.0.2.11 or 192.0.2.12

   4.   Receive (and save in referral cache) Map-Referral for EID-prefix
        2001:db8:0500::/40, action code NODE-REFERRAL, RLOC set
        (192.0.2.201)

   5.   Send DDT Map-Request to 192.0.2.201

   6.   Receive (and save in referral cache) Map-Referral for EID-prefix
        2001:db8:0501::/48, action code MS-REFERRAL, RLOC set
        (192.0.2.221)

   7.   Send DDT Map-Request to 192.0.2.221; if the ITR-originated
        Encapsulated Map-Request had a LISP-SEC signature, it is
        included

   8.   DDT Map Server at 192.0.2.221 decapsulates the DDT Map-Request
        and forwards to a registered site5 ETR for 2001:db8:0501:8::/64



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   9.   DDT Map Server at 192.0.2.221 sends a Map-Referral message for
        EID-prefix 2001:db8:0501:8::/64, action code MS-ACK, to the DDT
        Map Resolver

   10.  DDT Map Resolver receives Map-Referral(MS-ACK) message and
        dequeues the pending request for 2001:db8:0501:8:4::1

   11.  site5 ETR for 2001:db8:0501:8::/64 receives Map-Request
        forwarded by DDT Map Server and sends Map-Reply to ITR2

9.3.  Lookup of 2001:db8:0104:2::2/128

   This example shows how a DDT Map Resolver uses a saved referral cache
   entry to skip the referral process and go directly to a DDT Map
   Server for a prefix that is similar to one previously requested.

   In this case, ITR1 uses the same Map Resolver used in example
   Section 9.1.  It sends an Encapsulated Map-Request for
   2001:db8:0104:2::2 to that (DDT) Map Resolver.  The DDT Map-Resolver
   finds an MS-REFERRAL cache entry for 2001:db8:0100::/40 with RLOC set
   (192.0.2.101) and proceeds as follows:

   1.  Send DDT Map-Request (for 2001:db8:0104:2::2) to 192.0.2.101; if
       the ITR-originated Encapsulated Map-Request had a LISP-SEC
       signature, it is included

   2.  DDT Map Server at 192.0.2.101 decapsulates the DDT Map-Request
       and forwards to a registered site2 ETR for 2001:db8:0104::/48

   3.  DDT Map Server at 192.0.2.101 sends a Map-Referral message for
       EID-prefix 2001:db8:0104::/48, action code MS-ACK to the DDT Map
       Resolver

   4.  DDT Map Resolver receives Map-Referral(MS-ACK) and dequeues the
       pending request for 2001:db8:0104:2::2

   5.  site2 ETR for 2001:db8:0104::/48 receives Map-Request and sends
       Map-Reply to ITR1

9.4.  Lookup of 2001:db8:0500:2:4::1/128

   This example shows how a DDT Map Resolver uses a saved referral cache
   entry to start the referral process at a non-root, intermediate DDT
   node for a prefix that is similar to one previously requested.

   In this case, ITR2 asks the same Map Resolver used in example
   Section 9.2.  It sends an Encapsulated Map-Request for
   2001:db8:0500:2:4::1 to that (DDT) Map Resolver, which finds a NODE-



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   REFERRAL cache entry for 2001:db8:0500::/40 with RLOC set
   (192.0.2.201).  It proceeds as follows:

   1.  Send DDT Map-Request (for 2001:db8:0500:2:4::1) to 192.0.2.201

   2.  Receive (and save in referral cache) Map-Referral for EID-prefix
       2001:db8:0500::/48, action code MS-REFERRAL, RLOC set
       (192.0.2.211)

   3.  Send DDT Map-Request to 192.0.2.211; if the ITR-originated
       Encapsulated Map-Request had a LISP-SEC signature, it is included

   4.  DDT Map Server at 192.0.2.211 decapsulates the DDT Map-Request
       and forwards to a registered site4 ETR for 2001:db8:0500:2::/64

   5.  DDT Map Server at 192.0.2.211 sends a Map-Referral message for
       EID-prefix 2001:db8:0500:2::/64, action code MS-ACK to the DDT
       Map Resolver

   6.  DDT Map Resolver receives Map-Referral(MS-ACK) and dequeues the
       pending request for 2001:db8:0500:2:4::1

   7.  site4 ETR for 2001:db8:0500:2::/64 receives Map-Request and sends
       Map-Reply to ITR2

9.5.  Lookup of 2001:db8:0500::1/128 (non-existent EID)

   This example uses the cached MS-REFERRAL for 2001:db8:0500::/48
   learned above to start the lookup process at the DDT Map-Server at
   192.0.2.211.  The DDT Map Resolver proceeds as follows:

   1.  Send DDT Map-Request (for 2001:db8:0500::1) to 192.0.2.211; if
       the ITR-originated Encapsulated Map-Request had a LISP-SEC
       signature, it is included

   2.  DDT Map Server at 192.0.2.211, which is authoritative for
       2001:db8:0500::/48, does not have a matching delegation for
       2001:db8:0500::1.  It responds with a Map-Referral message for
       2001:db8:0500::/64, action code DELEGATION-HOLE to the DDT Map
       Resolver.  The prefix 2001:db8:0500::/64 is used because it is
       the least-specific prefix that does match the requested EID, but
       does not match one of configured delegations
       (2001:db8:0500:1::/64 and 2001:db8:0500:2::/64).

   3.  DDT Map Resolver receives the delegation, adds a negative
       referral cache entry for 2001:db8:0500::/64, dequeues the pending
       request for 2001:db8:0500::1, and returns a negative Map-Reply to
       ITR2.



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10.  Securing the database and message exchanges

   This section specifies the DDT security architecture that provides
   data origin authentication, data integrity protection, and XEID-
   prefix delegation.  Global XEID-prefix authorization is out of the
   scope of this document.

   Each DDT node is configured with one or more public/private key
   pair(s) that are used to digitally sign referral records for XEID-
   prefix(es) that the DDT node is authoritative for.  In other words,
   each public/private key pair is associated with the combination of a
   DDT node and a XEID-prefix that it is authoritative for.  Every DDT
   node is also configured with the public keys of its children DDT
   nodes.  By including public keys of target child DDT nodes in the
   Map-Referral records, and signing each record with the DDT node's
   private key, a DDT node can securely delegate sub-prefixes of its
   authoritative XEID-prefixes to its children DDT nodes.  A DDT node
   configured to provide hints must also have the public keys of the DDT
   nodes that its hints point to.  DDT node keys can be encoded using
   LCAF type 11 to associate the key to the RLOC of the referred DDT
   node.  If a node has more than one public key, it should sign its
   records with at least one of these keys.  When a node has N keys, it
   can sustain up to N-1 key compromises.  Revocation mechanism is
   described in Section 10.2.1.

   Map Resolvers are configured with one or more trusted public keys
   referred to as trust anchors.  Trust anchors are used to authenticate
   the DDT security infrastructure.  Map Resolvers can discover a DDT
   node's public key either by having it configured as a trust anchor,
   or by obtaining it from the node's parent as part of a signed Map-
   Referral.  When a public key is obtained from a node's parent, it is
   considered trusted if it is signed by a trust anchor, or if it is
   signed by a key that was previously trusted.  Typically, in a Map
   Resolver, the root DDT node public keys should be configured as trust
   anchors.  Once a Map Resolver authenticates a public key it locally
   caches the key along with the associated DDT node RLOC and XEID-
   prefix for future use.

10.1.  XEID-prefix Delegation

   In order to delegate XEID sub-prefixes to its children, a parent DDT
   node signs its Map-Referrals.  Every signed Map-Referral MUST also
   include the public keys associated with each child DDT node.  Such a
   signature indicates that the parent node is delegating the specified
   XEID-prefix to a given child DDT node.  The signature is also
   authenticating the public keys associated with the children nodes,
   and authorizing them to be used by the children DDT nodes to provide
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   delegations and mapping information of the XEID-prefix allocated to
   the DDT node.

   As a result, for a given XEID-prefix, a Map Resolver can form an
   authentication chain from a configured trust anchor (typically the
   root DDT node) to the leaf nodes (Map Servers).  Map Resolvers
   leverage this authentication chain to verify the Map-Referral
   signatures while walking the DDT tree until they reach a Map Server
   authoritative for the given XEID-prefix.

10.2.  DDT node operation

   Upon receiving a Map-Request, the DDT node responds with a Map-
   Referral as specified in Section 7.  For every record present in the
   Map-Referral, the DDT node also includes the public keys associated
   with the record's XEID-prefix and the RLOCs of the children DDT
   nodes.  Each record contained in the Map-Referral is signed using the
   DDT node's private key.

10.2.1.  DDT public key revocation

   The node that owns a public key can also revoke that public key.  For
   instance if a parent node advertises a public key for one of its
   child DDT nodes, the child DDT node can at a later time revoke that
   key.  Since DDT nodes do not keep track of the Map Resolvers that
   query them, revocation is done in a pull model, where the Map
   Resolver is informed of the revocation of a key only when it queries
   the node that owns that key.  If the parent DDT is configured to
   advertise this key, the parent node must also be signaled to remove
   the key from the records it advertises for the child DDT node; this
   is necessary to avoid further distribution of the revoked key.

   To securely revoke a key, the DDT node creates a new Record for the
   associated XEID-prefix and locator, including the revoked key with
   the R bit set.  The DDT node must also include a signature in the
   Record that covers this record; this is computed using the private
   key corresponding to the key being revoked.  Such a record is termed
   a "revocation record".  By including this record in its Map-
   Referrals, the DDT node informs querying Map Resolvers about the
   revoked key.  A digital signature computed with a revoked key can
   only be used to authenticate the revocation, and SHOULD NOT be used
   to validate any data.  To prevent a compromised key from revoking
   other valid keys, a given key can only be used to sign a revocation
   for that specific key; it cannot be used to revoke other keys.  This
   prevents the use of a compromised key to revoke other valid keys as
   described in [RFC5011].  A revocation record MUST be advertised for a
   period of time equal to or greater than the TTL value of the Record
   that initially advertised the key, starting from the time that the



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   advertisement of the key was stopped by removal from the parent DDT
   node.

10.3.  Map Server operation

   Similar to a DDT node, a Map Server is configured with one (or more)
   public/private key pairs that it must use to sign Map-Referrals.

   However unlike DDT nodes, Map Servers do not delegate prefixes and as
   a result they do not need to include keys in the Map-Referrals they
   generate.

10.4.  Map Resolver operation

   Upon receiving a Map-Referral, the Map Resolver MUST first verify the
   signature(s) by using a trust anchor, or a previously authenticated
   public key, associated with the DDT node sending the Map-Referral.
   If multiple authenticated keys are associated with the DDT node
   sending this Map-Referral, the Key Tag field of the signature can be
   used to select the right public key for verifying the signature.  If
   the key tag matches more than one key associated with that DDT node,
   the Map Resolver MUST try verifying the signature with all matching
   keys.  For every matching key that is found the Map Resolver MUST
   also verify that the key is authoritative for the XEID-prefix in the
   Map-Referral record.  If such a key is found, the Map Resolver MUST
   use it to verify the associated signature in the record.  If no
   matching key is found, or if none of the matching keys is
   authoritative for the XEID-prefix in the Map-Referral record, or if
   such a key is found but the signature is not valid the Map-Referral
   record is considered corrupted and MUST be discarded.  This may be
   due to expired keys.  The Map Resolver MAY try other siblings of this
   node if there is an alternative node authoritative for the same
   prefix.  If not, the Map Resolver CAN query the DDT node's parent to
   retrieve a valid key.  It is good practice to use a counter or timer
   to avoid repeating this process if the resolver cannot verify the
   signature after several trials.

   Once the signature is verified, the Map Resolver has verified the
   XEID-prefix delegation in the Map-Referral, and authenticated the
   public keys of the children DDT nodes.  The Map Resolver must add
   these keys to the authenticated keys associated with each child DDT
   node and XEID-prefix.  These keys are considered valid for the
   duration specified in the record's TTL field.








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11.  Open Issues and Considerations

   There are a number of issues with the organization of the mapping
   database that need further investigation.  Among these are:

   o  Defining an interface to implement interconnection and/or
      interoperability with other mapping databases, such as LISP+ALT.

   o  Additional key structures for use with LISP-DDT, such as to
      support additional EID formats as defined in [I-D.ietf-lisp-lcaf]

   o  Management of the DDT Map Resolver referral cache, in particular,
      detecting and removing outdated entries.

   o  Best practices for configuring hint referrals (or vice verse
      avoiding using them).

   Operational experience will help answer open questions surrounding
   these and other issues.

12.  IANA Considerations

   This document makes no request of the IANA.

13.  Security Considerations

   Section 10 describes a DDT security architecture that provides data
   origin authentication, data integrity protection, and XEID-prefix
   delegation within the DDT Infrastructure.

   Global XEID-prefix authorization is beyond the scope of this
   document, but the SIDR working group [RFC6480] is developing an
   infrastructure to support improved security of Internet routing.
   Further work is required to determine if SIDR's public key
   infrastructure (PKI) and the distributed repository system it uses
   for storing and disseminating PKI data objects may also be used by
   DDT devices to verifiably assert that they are the legitimate holders
   of a set of XEID prefixes.

   This document specifies how DDT security and LISP-SEC
   ([I-D.ietf-lisp-sec]) complement one another to secure the DDT
   infrastructure, Map-Referral messages, and the Map-Request/Map-Reply
   protocols.  In the future other LISP security mechanisms may be
   developed to replace LISP-SEC.  Such future security mechanisms
   should describe how they can be used together with DDT to provide
   similar levels of protection.





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   LISP-SEC can use the DDT public key infrastructure to secure the
   transport of LISP-SEC key material (the One-Time Key) from a Map-
   Resolver to the corresponding Map-Server.  For this reason, when
   LISP-SEC is deployed in conjunction with a LISP-DDT mapping database
   and the path between Map-Resolver and Map-Server needs to be
   protected, DDT security as described in Section 10 should be enabled
   as well.

14.  References

14.1.  Normative References

   [I-D.ietf-lisp-lcaf]
              Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
              Address Format (LCAF)", draft-ietf-lisp-lcaf-22 (work in
              progress), November 2016.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC3447]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", RFC 3447, DOI 10.17487/RFC3447, February
              2003, <http://www.rfc-editor.org/info/rfc3447>.

   [RFC6830]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
              Locator/ID Separation Protocol (LISP)", RFC 6830,
              DOI 10.17487/RFC6830, January 2013,
              <http://www.rfc-editor.org/info/rfc6830>.

   [RFC6833]  Fuller, V. and D. Farinacci, "Locator/ID Separation
              Protocol (LISP) Map-Server Interface", RFC 6833,
              DOI 10.17487/RFC6833, January 2013,
              <http://www.rfc-editor.org/info/rfc6833>.

14.2.  Informative References

   [AFI]      "Address Family Identifier (AFIs)", IANA , Febuary 2007,
              <http://www.iana.org/assignments/address-family-numbers/
              address-family-numbers.xhtml>.

   [I-D.ietf-lisp-sec]
              Maino, F., Ermagan, V., Cabellos-Aparicio, A., and D.
              Saucez, "LISP-Security (LISP-SEC)", draft-ietf-lisp-sec-12
              (work in progress), November 2016.




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   [LISP-TREE]
              Jakab, L., Cabellos-Aparicio, A., Coras, F., Saucez, D.,
              and O. Bonaventure, "LISP-TREE: a DNS hierarchy to support
              the lisp mapping system", Selected Areas in
              Communications, IEEE Journal , 2010,
              <http://ieeexplore.ieee.org/xpls/
              abs_all.jsp?arnumber=5586446>.

   [RFC1918]  Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.,
              and E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, DOI 10.17487/RFC1918, February 1996,
              <http://www.rfc-editor.org/info/rfc1918>.

   [RFC5011]  StJohns, M., "Automated Updates of DNS Security (DNSSEC)
              Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011,
              September 2007, <http://www.rfc-editor.org/info/rfc5011>.

   [RFC6480]  Lepinski, M. and S. Kent, "An Infrastructure to Support
              Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
              February 2012, <http://www.rfc-editor.org/info/rfc6480>.

   [RFC6836]  Fuller, V., Farinacci, D., Meyer, D., and D. Lewis,
              "Locator/ID Separation Protocol Alternative Logical
              Topology (LISP+ALT)", RFC 6836, DOI 10.17487/RFC6836,
              January 2013, <http://www.rfc-editor.org/info/rfc6836>.

   [RFC6837]  Lear, E., "NERD: A Not-so-novel Endpoint ID (EID) to
              Routing Locator (RLOC) Database", RFC 6837,
              DOI 10.17487/RFC6837, January 2013,
              <http://www.rfc-editor.org/info/rfc6837>.

Appendix A.  Acknowledgments

   The authors would like to express their thanks to Lorand Jakab,
   Albert Cabellos-Asparicio, Florin Coras, Damien Saucez, and Olivier
   Bonaventure for their work on LISP-TREE [LISP-TREE] and LISP iterable
   mappings that inspired the hierarchical database structure and lookup
   iteration approach described in this document.  Thanks also go to
   Dino Farinacci and Isidor Kouvelas for their implementation work; to
   Selina Heimlich and Srin Subramanian for testing; to Fabio Maino for
   work on security processing; and to Job Snijders, Glen Wiley, Neel
   Goyal, and Mike Gibbs for work on operational considerations and
   initial deployment of a prototype database infrastructure.  Special
   thanks go to Jesper Skriver, Andrew Partan, and Noel Chiappa; all of
   whom have participated in (and put up with) seemingly endless hours
   of discussion of mapping database ideas, concepts, and issues.





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Authors' Addresses

   Vince Fuller

   Email: vaf@vaf.net


   Darrel Lewis
   Cisco Systems

   Email: darlewis@cisco.com


   Vina Ermagan
   Cisco Systems

   Email: vermagan@cisco.com


   Amit Jain
   Juniper Networks

   Email: atjain@juniper.net


   Anton Smirnov
   Cisco Systems

   Email: as@cisco.com






















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