LISP Working Group D. Saucez, Ed.
Internet-Draft Inria
Obsoletes: 8111 (if approved) L. Iannone, Ed.
Updates: 9301 (if approved) Huawei
Intended status: Standards Track 3 March 2025
Expires: 4 September 2025
Locator/ID Separation Protocol Delegated Database Tree (LISP-DDT)
draft-saucez-lisp-8111bis-01
Abstract
This document describes the Locator/ID Separation Protocol Delegated
Database Tree (LISP-DDT), a hierarchical distributed database that
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 control plane elements generically 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.
This document obsoletes RFC 8111 and updates RFC 9301.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 4 September 2025.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5
3. Definitions of Terms . . . . . . . . . . . . . . . . . . . . 5
4. Delegated Database Tree Organization . . . . . . . . . . . . 7
4.1. XEID-Prefixes . . . . . . . . . . . . . . . . . . . . . . 7
4.2. Structure of the DDT Database . . . . . . . . . . . . . . 7
4.3. Configuring Prefix Delegation . . . . . . . . . . . . . . 8
4.3.1. The Root DDT Node . . . . . . . . . . . . . . . . . . 8
5. The DDT Map-Referral Message . . . . . . . . . . . . . . . . 9
5.1. Map-Referral Message Format . . . . . . . . . . . . . . . 9
5.2. Action Codes . . . . . . . . . . . . . . . . . . . . . . 11
5.3. Referral Set . . . . . . . . . . . . . . . . . . . . . . 12
5.4. "Incomplete" Flag . . . . . . . . . . . . . . . . . . . . 12
5.5. Signature Section . . . . . . . . . . . . . . . . . . . . 12
6. DDT Network Elements and Their Operation . . . . . . . . . . 14
6.1. DDT Node . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1.1. XEID Match . . . . . . . . . . . . . . . . . . . . . 14
6.1.2. XEID Miss . . . . . . . . . . . . . . . . . . . . . . 15
6.2. DDT Map-Server . . . . . . . . . . . . . . . . . . . . . 15
6.3. DDT Client . . . . . . . . . . . . . . . . . . . . . . . 16
6.3.1. Queuing and Sending DDT Map-Requests . . . . . . . . 16
6.3.2. Receiving and Following DDT Map-Referrals . . . . . . 17
6.3.3. Handling Referral Errors . . . . . . . . . . . . . . 19
6.3.4. Referral Loop Detection . . . . . . . . . . . . . . . 19
7. Securing the Database and Message Exchanges . . . . . . . . . 19
7.1. XEID-Prefix Delegation . . . . . . . . . . . . . . . . . 20
7.2. DDT Node Operation . . . . . . . . . . . . . . . . . . . 21
7.2.1. DDT Public Key Revocation . . . . . . . . . . . . . . 21
7.3. Map-Server Operation . . . . . . . . . . . . . . . . . . 22
7.4. Map-Resolver Operation . . . . . . . . . . . . . . . . . 22
8. Security Considerations . . . . . . . . . . . . . . . . . . . 22
9. Deployment Experience . . . . . . . . . . . . . . . . . . . . 23
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
10.1. LISP DDT Map-Referral Packet Type . . . . . . . . . . . 23
10.2. LISP DDT Action Codes . . . . . . . . . . . . . . . . . 23
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
11.1. Normative References . . . . . . . . . . . . . . . . . . 24
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11.2. Informative References . . . . . . . . . . . . . . . . . 25
Appendix A. Pseudo-code and Decision Tree Diagrams . . . . . . . 26
A.1. Map-Resolver Processing of Map-Request . . . . . . . . . 26
A.1.1. Pseudo-code Summary . . . . . . . . . . . . . . . . . 26
A.1.2. Decision Tree Diagram . . . . . . . . . . . . . . . . 26
A.2. Map-Resolver Processing of Map-Referral Message . . . . . 27
A.2.1. Pseudo-code Summary . . . . . . . . . . . . . . . . . 27
A.2.2. Decision Tree Diagram . . . . . . . . . . . . . . . . 29
A.3. DDT Node Processing of DDT Map-Request Message . . . . . 30
A.3.1. Pseudo-code Summary . . . . . . . . . . . . . . . . . 30
A.3.2. Decision Tree Diagram . . . . . . . . . . . . . . . . 31
Appendix B. Generic DDT Example . . . . . . . . . . . . . . . . 33
B.1. Reference DDT Tree Topology . . . . . . . . . . . . . . . 33
B.2. Lookup EID registered at with Map-Server1 . . . . . . . . 34
B.3. Lookup EID registered at with Map-Server3 . . . . . . . . 35
B.4. Lookups using cached DDT Map-Referrals to Map-Servers . . 36
B.5. Lookup using cached DDT Map-Referrals to DDT Nodes . . . 37
B.6. Lookup of a non-existent EID . . . . . . . . . . . . . . 37
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 39
1. Introduction
The Locator/ID Separation Protocol (LISP), defined in [RFC9300] and
[RFC9301], specifies an architecture to create overlays networks
leveraging on two separate namespaces, namely the Endpoint
Identifiers (EIDs) used for end-to-end communications, and the
Routing Locators (RLOCs) used for routing and forwarding.
[RFC9301] specifies an interface between a database storing EID-to-
RLOC mappings and LISP devices that need such information to forward
packets. The internal organization of such a database is beyond the
scope of [RFC9301]. Multiple architectures of the database have been
proposed, each having its advantages and disadvantages (see, for
example, [RFC6836] and [RFC6837]).
This document specifies an architecture for a scalable distributed
database of LISP EID-to-RLOC mappings: the LISP Delegated Database
Tree (LISP-DDT). LISP-DDT is a hierarchical distributed database
that 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 perform EID-to-RLOC mappings lookups. A
Map-Resolver that requests a given mapping will follow a path through
the tree-structured database and will contact, one after another, the
nodes along that path, until it reaches the leaf node(s)
authoritative for the mapping it is seeking.
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In organizing a database of EID-to-RLOC mappings, this specification
extends the definition of the EID numbering space by logically
concatenating the following attributes in order to define the
database index key:
* Database-ID (DBID) (16 bits)
* Instance Identifier (IID) (24 bits)
* Address Family Identifier (AFI) (16 bits)
* EID-Prefix (variable, according to the 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 is
also 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 (MS) 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 [RFC9301]
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 the Map-Referral LISP message type, 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 5 for the definition of the Map-Referral message.
To find an EID-to-RLOC mapping, a LISP-DDT Client, usually a Map-
Resolver, starts by sending an Encapsulated Map-Request to a pre-
configured DDT Node RLOC. The DDT Node responds with a Map-Referral
message indicating that either (1) it will find the requested mapping
to complete processing of the request or (2) the DDT Client should
contact another DDT Node that has more-specific information; in the
latter case, the DDT Node then sends a new 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
[RFC1035].
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This document obsoletes [RFC8111] and updates [RFC9301].
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Definitions of Terms
This documents assumes that the reader is familiar with LISP and the
LISP terminology. For definitions of terms like Map-Request,
Encapsulated Map-Request, Map-Reply, ITR, ETR, Map-Server, and Map-
Resolver, please consult the LISP Data Plane specification [RFC9300]
and the LISP Control Plane specification [RFC9301].
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.
DDT Client: a network infrastructure component that sends Map-
Request messages and implements the iterative following of Map-
Referral results. Typically, a DDT Client will be a Map-Resolver
(as defined by [RFC9301]), but it is also possible for an Ingress
Tunnel Router (ITR) to implement DDT Client functionality.
DDT 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 DDT Map-Referral includes a "referral" consisting
in a set of RLOCs for DDT Nodes that have information about the
more-specific XEID-Prefix covering the requested XEID. See
Section 5 for a complete definition of the message and Section 6.1
and Section 6.3 for details on its processing.
DDT Map-Referral Cache: Data structure to temporarily maintain
previously received Map-Referral message results, containing RLOCs
for DDT Nodes responsible for XEID-Prefixes.
DDT Map-Request: an ECM Map-Request sent by a DDT Client to a DDT
Node, with the "DDT-originated" flag set. Section 6.3.1 describes
how DDT Map-Requests are sent. [RFC9301] defines the position of
the "DDT-originated" flag in the Encapsulated Control Message
header.
DDT Map-Resolver: a Map-Resolver that also implements DDT Client
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functionality. Map-Resolver functionality is defined by
[RFC9301]. A DDT Map-Resolver accepts Map-Requests from ITRs,
sends Map-Requests to DDT Nodes, and implements the iterative
following of Map-Referrals. Note that Map-Resolvers, as of
[RFC9301], do not respond to clients that sent Map-Requests; they
only ensure that the Map-Request has been forwarded to a LISP
device (ETR or proxy Map-Server) that will provide an
authoritative response to the original requester. This document
uses the terms "DDT Map-Resolver" and "Map-Resolver"
interchangeably.
DDT Map-Server: a Map-Server that also implements DDT functionality.
Map-Server functionality is defined in [RFC9301]. This document
uses the terms "DDT Map-Server" and "Map-Server" interchangeably.
DDT Map-Server peers: a 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 the returned reply as potentially incomplete.
DDT Node: a network infrastructure component responsible for
specific XEID-Prefix(es) and for the delegation of more-specific
sub-prefixes to other DDT Nodes.
Extended EID (XEID): a LISP EID extended with data uniquely
identifying the address space to which it belongs (LISP IID,
address family, etc.). See Section 4.1 for a detailed description
of XEID data.
Extended EID-Prefix (XEID-Prefix): 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-Prefixes.
Negative DDT Map-Referral: A 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 Requests List: Data structure storing the set of outstanding
requests for which a DDT Map-Resolver has received ECM Map-
Requests from its clients seeking EID-to-RLOC mapping for an XEID.
Each entry in the list contains additional state needed by the
referral-following process, including the XEID, requester(s) of
the XEID (typically one or more ITRs), saved information about the
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last referral received and followed (matching XEID-Prefix, action
code, RLOC set, index of the last RLOC queried in the RLOC set),
and any LISP-Security (LISP-SEC) information [RFC9303] that was
included in the DDT Client Map-Request. An entry in the list may
be interchangeably termed a "pending requests list entry" or
simply a "pending request".
4. Delegated Database Tree Organization
This section firstly defines the DDT database index key, namely XEID-
Prefixes, and then details of the DDT database organization and how
to configure prefix delegation.
4.1. XEID-Prefixes
A DDT database is indexed by Extended EID-Prefixes (XEID-Prefixes).
An XEID-Prefix is a LISP EID-Prefix that includes additional data to
uniquely identify the address space associated with the prefix. An
XEID-Prefix is composed of four binary-encoded concatenated
attributes:
* DBID (16 bits),
* Instance ID (24 bits),
* AFI (16 bits),
* and EID-Prefix (variable, according to the AFI value).
The DBID is the LISP-DDT Database-ID, a 16-bit attribute that allows
the definition of multiple databases. Implementations that are
compliant with this document must always set this field to 0. Other
values of the DBID are reserved for future use.
The Instance ID (IID) is a 24-bit value describing the context of the
EID-Prefix, see Section 8 of [RFC9300] for more discussion of
Instance IDs.
The AFI is a 16-bit value defining the syntax of the EID-Prefix. AFI
values are assigned by IANA [AFI].
4.2. Structure of the DDT Database
The LISP-DDT Database is organized as a prefix tree structure that is
indexed by XEID-Prefixes, where each node of the tree is a DDT Node
which has delegated for a set of sub-prefixes (see Section 4.3 for
details regarding delegation).
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DDT Map-Requests sent by DDT Clients to DDT Nodes always contain
specific values for the DBID, IID, and AFI; unspecified values or
ranges of values MUST NOT be used for any of these attributes.
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 that
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 that 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. A delegation 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 regarding security
information exchange and its use, see Section 7). Those RLOCs are
returned in Map-Referral messages when the DDT Node receives a DDT
Map-Request with an XEID that matches a delegation.
DDT Nodes may also have a list of "hints", which are XEID-Prefixes,
for which it is no authoritative. Each of such XEID-Prefixes "hints"
includes the list of RLOCs of the DDT Nodes authoritative for the
XEID-Prefix. The list of "hints" is statically configured similarly
to delegations.
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, namely, for
all valid 3-tuples (DBID, IID, AFI) and their EID-Prefixes.
The root DDT Nodes is the starting point for a XEID-Prefix lookup via
a DDT Map-Request. However, not all DDT Map-Request will go through
a root DDT Nodes thanks to the DDT Map-Referral Cache maintained by
intermediate nodes (see Section 6 for details). The root DDT Node in
a particular instantiation of LISP-DDT MUST be configured, at a
minimum, to cover all EID space of all <DBID, Instance IDs, AFI>
tuples defined in the instantiation.
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5. The DDT Map-Referral Message
This specification defines a new LISP message called the DDT Map-
Referral message. A DDT Map-Referral message is sent by a DDT Node
to a DDT Client in response to a DDT Map-Request message. The
message consists of an action code along with delegation information
about the XEID-Prefix that matches the requested XEID.
5.1. Map-Referral Message Format
The format of the Map-Referral message is depicted in Figure 1.
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-Prefix-AFI |
o +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
r | EID-Prefix ... |
d +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| /| Reserved |
| R +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| e | Reserved |R| Loc-AFI |
| f +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| \~ Locator ~
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ~ Signatures Section ~
+-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Map-Referral message format.
Type: DDT Map-Referral type 6, as allocated in [RFC9301].
Record Count: As defined in Section 5.4 of [RFC9301].
Nonce: As defined in Section 5.4 of [RFC9301].
Record TTL: As defined in Section 5.4 of [RFC9301].
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Referral Count: This is the number of referral records in this
message. A referral record is comprised of that portion of the
packet labeled "Ref" and occurs the number of times equal to
Referral Count.
EID mask-len: As defined in Section 5.4 of [RFC9301].
ACT: The DDT Action (ACT) field of the in a Map-Referral message
encodes one of the action types defined in Section 5.2. Note
that, despite the same position and same name as in Map-Reply
messages defined in [RFC9301], the actions in DDT Map-Referrals
message are different from the ones in Map-Replies.
A: The Authoritative bit CAN only be set to 1 by a DDT Node that is
authoritative for the XEID-Prefix.
I; Incomplete (I) bit indicating that a DDT Node's Referral Set of
locators is incomplete and the receiver of this message SHOULD NOT
cache the referral (see Section 5.2 for details).
SigCnt: Indicates the number of signatures sections present in the
Record. If SigCnt is larger than 0, the signature information
captured in a Signature section as described in Section 5.5 will
be appended to the Record. The number of Signature sections at
the end of the Record MUST match the SigCnt.
Map Version Number: As defined in [RFC9302].
EID-Prefix-AFI: As defined in Section 5.4 of [RFC9301].
XEID-Prefix: The requested XEID-Prefix. Uses the LCAF type 2
[RFC8060] to encode the IID and IP address prefix that form the
XEID. It can also use natively IPv4 or IPv6 addresses, in this
case the IID has the implicit default value of 0. The EID-Prefix-
AFI MUST be set accordingly.
R bit: As defined in Section 5.4 of [RFC9301].
Loc-AFI: AFI of the Locator field. Values for this field include
the value 16387 of the LISP Canonical Address Format (LCAF)
[RFC8060]. LCAF Security Key Type 11 is used to store security
material associated to the locator. DDT Nodes and DDT Map-Servers
uses this LCAF Type to include public keys associated with their
child DDT Nodes for an XEID-Prefix Map-Referral Record.
Locator: RLOC of a DDT Node to which the DDT Client is being
referred. This is a variable-length field; its length is
determined by the Loc-AFI setting.
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Signatures Section: When present this section contain one (or more)
signature sections containing a signature covering the whole DDT
Map-Referral message and the related information necessary for its
verification. See Section 5.5 for the details.
Fields marked as "reserved" MUST be sent as 0 (zero) and MUST be
ignored on reception.
5.2. Action Codes
The possible values of the action field are defined hereafter, where
the number in parenthesis indicated the decimal value of the 3-bit
ACT filed.
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 record
with additional information, most significantly, the set of RLOCs
to which the XEID-Prefix has been delegated, which 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 6.3.2).
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 a Map-
Reply 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
that 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 6.1.2 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. LI: Not coherent.
In this case an MS-Not-REGISTERED MUST be sent--.
NOT-AUTHORITATIVE (5): Indicates that the replying DDT Node received
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a Map-Request for an XEID for which it is not authoritative. This
can occur if a cached referral has become invalid due to a change
in the database hierarchy. However, if such a DDT Node has a
"hint" covering the requested EID, it MAY choose to return NODE-
REFERRAL or MS-REFERRAL as appropriate. When returning action
code NOT-AUTHORITATIVE, the DDT Node MUST provide the EID-Prefix
received in the request and the TTL MUST be set to 0.
5.3. 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.
5.4. "Incomplete" Flag
A DDT Node sets the "Incomplete" (I) flag in a Map-Referral message
if the Referral Set is incomplete; this is intended to prevent a DDT
Client from caching, in the DDT Map-Referral Cache, a referral with
incomplete information. A DDT node MUST set the "Incomplete" flag in
the following cases:
* If returned action code is MS-ACK or MS-NOT-REGISTERED, but the
matching XEID-Prefix is not flagged as "complete" in the
configuration DDT Map-Server. The XEID-Prefix configuration on
the DDT Map-Server SHOULD be marked as "complete" when the
configuration of the XEID-Prefix includes all DDT Map-Server peers
that are also authoritative for the same XEID-Prefix, or when a
DDT Map-Server is the only authoritative node for the XEID-Prefix
.
* If the returned action code is NOT-AUTHORITATIVE.
5.5. Signature Section
SigCnt counts the number of signature sections that appear at the end
of the Record. The format of the signature section is described
Figure 2.
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/| Original Record TTL |
/ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Signature Expiration |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
s | Signature Inception |
i +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
g | Key Tag | Sig Length |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | Sig-Algorithm | Reserved |
\ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ ~ Signature ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Map-Referral Signature Section format.
Original Record TTL: The original Record TTL for this Record that is
covered by the signature.
Signature Expiration and Signature Inception: Specify the validity
period for the signature. The signature MUST NOT be used for
authentication prior to the inception and MUST NOT be used for
authentication after the expiration. 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 (see Section 8).
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. Implementations conforming
to this specification MUST implement at least RSA-SHA256 for DDT
signing. Sig-Algorithm type 1 (RSA-SHA1) is deprecated and SHOULD
NOT be used.
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+===============+============+===========+============+
| Sig-Algorithm | Name | Reference | Notes |
+===============+============+===========+============+
| 1 | RSA-SHA1 | [RFC8017] | DEPRECATED |
+---------------+------------+-----------+------------+
| 2 | RSA-SHA256 | [RFC8017] | MANDATORY |
+---------------+------------+-----------+------------+
Table 1: Sig-Algorithm Values
Reserved: MUST be set to 0 on transmit and MUST be ignored on
receipt.
Signature: Contains the cryptographic signature that covers the
entire Map-Referral Record to which this signature belongs. For
the purpose of computing the signature, the Record TTL
(Section 5.1) value is set to the value of Original Record TTL and
the Signature field is filled with zeros.
6. DDT Network Elements and Their Operation
As described above, LISP-DDT introduces a new network element, namely
the DDT Node and extends the functionality of Map-Servers and Map-
Resolvers to send and receive DDT Map-Referral messages. The
operation of each of these devices is described below.
6.1. 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 depending on whether or not there is
a match, different actions are taken, as described in the following.
6.1.1. XEID Match
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 7 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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A DDT Node MAY also be configured with "hints" for XEID-Prefixes
anywhere in the database hierarchy and for which it can provide
referrals. This feature may be useful for reducing the number of
iterations needed to find an EID-to-RLOC Mapping, particularly for
private network deployments. However, the incorrect use of hints may
create circular dependencies (or "referral loops") between DDT Nodes.
A DDT Client MUST handle such circular referrals as described in
Section 6.3.4. Furthermore, the use of hints in DDT deployments that
span multiple administrative domains (i.e., different authorities
manage DDT Nodes in the same DDT database) may not be a reliable
information. Indeed, in this case, an 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.
6.1.2. XEID Miss
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, which 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 a Negative Map-Referral
with action code NOT-AUTHORITATIVE MUST be returned.
6.2. 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:
* If the requested XEID matches a registered XEID-Prefix, then the
Map-Request is forwarded to one of the ETR RLOCs associated to the
XEID-Prefix (or the Map-Server sends a Map-Reply, if it is
providing a proxy Map-Reply service), and a Map-Referral with
action code MS-ACK MUST be returned to the sender of the DDT Map-
Request.
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* 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. This Map-Reply contains the
least-specific XEID-Prefix in the range for which this DDT Map-
Server is authoritative and in which no registrations exist. In
order to avoid long periods of lack of connectivity, the TTL value
of the Negative Map-Reply should be short. The RECOMMENDED value
is of 1 minute.
6.3. 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 reached 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 is usually performed by DDT Map-Resolvers.
Just as would 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. However, a DDT Map-Resolver implements DDT Client
functionality to find the correct ETR to answer a Map-Request, which
in turns requires a DDT Map-Resolver to maintain additional state,
namely a DDT Map-Referral Cache and a Pending Requests List of XEIDs
that are going through the iterative referral process.
6.3.1. Queuing and Sending DDT Map-Requests
When a DDT Client receives a A DDT Map-Request to resolve an XEID, it
first performs a longest-prefix-match search for the XEID in its DDT
Map-Referral Cache. Note that in normal use, the statically
configured initial DDT Map-Referral Cache for a DDT Client should
include a "default" entry with RLOCs for either the root DDT Node or
one or more DDT Nodes that contain hints for the root DDT Node.
Without such configuration, a DDT client would return a Negative Map-
Reply for Map-Requests for an EID outside the subset of the mapping
database known to it. There is no need to configure the same set of
root DDT nodes on all DDT Clients. Additional entries are added when
referrals are followed, as described below. If the longest-prefix-
math for the XEID in the Map-Request does not return any result, or
if a negative entry is found, then a Negative Map-Reply MUST be
returned, and no further processing is performed by the DDT Client.
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If a match is found, the DDT Client creates an entry in the Pending
Requests LIst for the XEID, storing the original request (in the case
of a DDT Map-Resolver, this will be the original Map-Request minus
the encapsulation header) along with other information needed to
track progress through the iterative referral process; the referral
associated to the request is also initialized to indicate that no
referral has yet been received.
The DDT Client then creates a DDT Map-Request, which is an ECM 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 selected DDT Map-Referral Cache entry.
If DDT message exchanges are authenticated as described in Section 7,
then the 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 root DDT Node.
6.3.2. Receiving and Following DDT Map-Referrals
After sending a DDT Map-Request, a DDT Client expects to receive a
DDT Map-Referral response. If none occurs within the timeout period,
the DDT Client retransmits the request, sending it 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 discarded. In this
case, the DDT Client returns no response to the sender of the
original request.
When a DDT Client receives a DDT Map-Referral, it processes the
message according to the action code it contains:
NODE-REFERRAL: The DDT Client checks for a possible referral loop as
described in Section 6.3.4. If no loop is found, the DDT Client
saves the returned XEID-Prefix in the DDT Map-Referral Cache. It
also updates the XEID-Prefix and saved RLOCs in the corresponding
Pending Request List entry, and follows the referral by sending a
new DDT Map-Request to one of the DDT Node RLOCs listed 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 LISP-SEC security
information saved with the original Map-Request MUST be included
in the new DDT Map-Request sent to a Map-Server (see Section 7 for
details on security).
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MS-ACK: An MS-ACK is returned by a DDT Map-Server to indicate that
it has one or more registered ETRs that can answer the DDT Map-
Request for the XEID and the message has been forwarded to one of
them (or, if the Map-Server is providing a proxy service for the
prefix, then a reply has been sent to the querying ITR). If the
pending request did not include saved LISP-SEC information (i.e.,
LISP-SEC is not used) 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, when LISP-SEC information included in pending request,
but has not yet been sent to the authoritative DDT Map-Server, the
DDT Client MUST resend the DDT Map-Request with LISP-SEC
information included, and the Pending Request List entry remains
until another Map-Referral with action code MS-ACK is received.
Unless the "Incomplete" flag is set, the XEID-Prefix and its
referrals is saved in the DDT Map-Referral Cache.
MS-NOT-REGISTERED: The DDT Map-Server queried could not process the
request because no ETRs registered the XEID-Prefix and returned a
Negative DDT Map-Referral. If the DDT Client has not yet tried
all of the RLOCs saved with the Pending Request List, 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 the Negative Map-Reply
to the requester (or, in the case of a DDT Map-Resolver, to the
sender of the original Map-Request). A negative DDT Map-Referral
Cache entry is also created for the XEID-Prefix, whose TTL MUST be
set to the value in the Map-Referral message, and the processing
of the request stops.
DELEGATION-HOLE: The requested XEID-Prefix does not belong to the
EID space and the queried DDT Node returned a Negative DDT Map-
Referral. The DDT Client MUST return a Negative Map-Referral to
the requester (or, in the case of a DDT Map-Resolver, a Negative
Map-Reply to the sender of the original Map-Request);
NOT-AUTHORITATIVE: The DDT Node queried is not authoritative for the
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requested XEID-Prefix. This can occur, for instance, if a cached
referral has become invalid due to a change in the database
hierarchy. If the DDT Client receiving this message used a cached
information, it MAY choose to delete that cached information and
retry the original Map-Request, starting from its "root" DDT Map-
Referral Cache entry. If this action code is received in response
to a query that did not use cached referral information, then it
indicates a database synchronization problem or configuration
error. In this case the DDT Client SHOULD log the event and the
pending request MUST be silently discarded.
A DDT Client is not required to cache referrals, but doing so will
decrease latency and reduce lookup delays.
6.3.3. Handling Referral Errors
If a DDT Client detects unexpected behavior by a DDT node, it MAY
mark that node as unusable in its DDT Map-Referral Cache and update
the pending request to try a different DDT Node, if more than one is
listed. In any case, the DDT Client SHOULD log the error and any
prefix contained in a DDT Map-Referral message that causes a referral
error (including a referral loop) is not saved in the DDT Map-
Referral Cache.
6.3.4. 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 to see if 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 6.3.3.
7. 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.
Each DDT Node is configured with one or more public/private key pairs
that are used to digitally sign Map-Referral Records for XEID-
Prefix(es) for which the DDT Node is authoritative. In other words,
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each public/private key pair is associated with the combination of a
DDT Node and an XEID-Prefix for which it is authoritative. Every DDT
Node is also configured with the public keys of its child DDT Nodes.
By including the 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 refer sub-prefixes its authoritative
XEID-Prefixes for its child DDT nodes. A DDT Node configured to
provide hints must also have the public keys of the DDT Nodes to
which its hints point. 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. The revocation mechanism is described in
Section 7.2.1.
Map-Resolvers are configured with one or more DDT Nodes' 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 by either (1) having it configured
as a trust anchor or (2) 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's 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.
7.1. XEID-Prefix Delegation
In order to provide referrals to XEID sub-prefixes for its child DDT
Nodes, a parent DDT Node signs its DDT 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 DDT Node
delegated the specified XEID-Prefix to a given child DDT Node. The
signature is also authenticating the public keys associated with the
child DDT Nodes, and authorizing them to be used by the child DDT
nodes, to provide origin authentication and integrity protection 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.
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7.2. DDT Node Operation
Upon receiving a Map-Request, the DDT Node responds with a Map-
Referral as specified in Section 6. 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 child DDT Nodes.
Each Record contained in the Map-Referral is signed using the DDT
Node's private key.
7.2.1. DDT Public Key Revocation
The node that owns a public key can also revoke that public key. For
instance, if a parent DDT 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 mode, 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 Node is configured to
advertise that key, the parent DDT 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. (See Section 4.7 of [RFC8060] for details regarding
the R bit.) 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 MUST 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 MUST NOT 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
advertisement of the key was stopped by removal from the parent DDT
Node.
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7.3. 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 do not need to include keys in the Map-Referrals they
generate.
7.4. Map-Resolver Operation
Upon receiving a Map-Referral, the Map-Resolver MUST first verify the
signature(s) by using either 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 (Section 5.5)
of the signature can be used to select the correct 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 to verify
the signature with all matching keys. If a key is found, the Map-
Resolver MUST use it to verify the associated signature in the
Record. If (1) no matching key is found, or (2) 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
alternate node that is authoritative for the same prefix. If not,
the Map-Resolver CAN query the DDT Node's parent to retrieve a valid
key.
Once the signature is verified, the Map-Resolver has verified the
XEID-Prefix delegation in the Map-Referral. This also means that
public keys of the child DDT Nodes were authenticated; 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.
8. Security Considerations
This documents extends the LISP control plane defined in [RFC9301];
as such security considerations in that document apply here as well.
This document specifies how DDT security and LISP-SEC [RFC9303]
complement one another to secure the DDT infrastructure, Map-Referral
messages, and the Map-Request/Map-Reply protocols.
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,
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where the path between the Map-Resolver and Map-Server needs to be
protected. Such protection can be achieved with the mechanism
described in Section 7, which proposes a DDT security architecture
that provides data origin authentication, data integrity protection,
and XEID-Prefix delegation within the DDT infrastructure. DDT
security as described in Section 7 MUST be enabled by default.
9. Deployment Experience
TBD
10. IANA Considerations
10.1. LISP DDT Map-Referral Packet Type
IANA has made the an early temporary allocation for message type 6,
"LISP DDT Map-Referral", in the "LISP Packet Types" registry group.
IANA is requested to make the allocation permanent and modify the
"LISP Packet Types" as shown in Table 2.
+======+=======================+=================+
| Code | Message | Reference |
+======+=======================+=================+
| 6 | LISP DDT Map-Referral | [This document] |
+------+-----------------------+-----------------+
Table 2: LISP DDT Map-Referral Message Type
Allocation
10.2. LISP DDT Action Codes
IANA is asked to create a registry named "LISP DDT Action Codes"
under the "Locator/ID Separation Protocol (LISP) Parameters" group.
Such registry should be populated as shown in Table 3:
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+======+===================+=================+
| Code | DDT Action | Reference |
+======+===================+=================+
| 0 | NODE-REFERRAL | [This document] |
+------+-------------------+-----------------+
| 1 | MS-REFERRAL | [This document] |
+------+-------------------+-----------------+
| 2 | MS-ACK | [This document] |
+------+-------------------+-----------------+
| 3 | MS-NOT-REGISTERED | [This document] |
+------+-------------------+-----------------+
| 4 | DELEGATION-HOLE | [This document] |
+------+-------------------+-----------------+
| 5 | NOT-AUTHORITATIVE | [This document] |
+------+-------------------+-----------------+
| 6-7 | Unallocated | [This document] |
+------+-------------------+-----------------+
Table 3: LISP DDT Action Codes Allocation
Values can be assigned by IANA on the "IETF Review" basis according
to [RFC8126].
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC5011] StJohns, M., "Automated Updates of DNS Security (DNSSEC)
Trust Anchors", STD 74, RFC 5011, DOI 10.17487/RFC5011,
September 2007, <https://www.rfc-editor.org/rfc/rfc5011>.
[RFC8060] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060,
February 2017, <https://www.rfc-editor.org/rfc/rfc8060>.
[RFC8111] Fuller, V., Lewis, D., Ermagan, V., Jain, A., and A.
Smirnov, "Locator/ID Separation Protocol Delegated
Database Tree (LISP-DDT)", RFC 8111, DOI 10.17487/RFC8111,
May 2017, <https://www.rfc-editor.org/rfc/rfc8111>.
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[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC9300] Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
Cabellos, Ed., "The Locator/ID Separation Protocol
(LISP)", RFC 9300, DOI 10.17487/RFC9300, October 2022,
<https://www.rfc-editor.org/rfc/rfc9300>.
[RFC9301] Farinacci, D., Maino, F., Fuller, V., and A. Cabellos,
Ed., "Locator/ID Separation Protocol (LISP) Control
Plane", RFC 9301, DOI 10.17487/RFC9301, October 2022,
<https://www.rfc-editor.org/rfc/rfc9301>.
[RFC9302] Iannone, L., Saucez, D., and O. Bonaventure, "Locator/ID
Separation Protocol (LISP) Map-Versioning", RFC 9302,
DOI 10.17487/RFC9302, October 2022,
<https://www.rfc-editor.org/rfc/rfc9302>.
[RFC9303] Maino, F., Ermagan, V., Cabellos, A., and D. Saucez,
"Locator/ID Separation Protocol Security (LISP-SEC)",
RFC 9303, DOI 10.17487/RFC9303, October 2022,
<https://www.rfc-editor.org/rfc/rfc9303>.
11.2. Informative References
[AFI] IANA, "Address Family Numbers",
<http://www.iana.org/assignments/address-family-numbers/>.
[RFC1035] Mockapetris, P., "Domain names - implementation and
specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
November 1987, <https://www.rfc-editor.org/rfc/rfc1035>.
[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, <https://www.rfc-editor.org/rfc/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,
<https://www.rfc-editor.org/rfc/rfc6837>.
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[RFC8017] Moriarty, K., Ed., Kaliski, B., Jonsson, J., and A. Rusch,
"PKCS #1: RSA Cryptography Specifications Version 2.2",
RFC 8017, DOI 10.17487/RFC8017, November 2016,
<https://www.rfc-editor.org/rfc/rfc8017>.
Appendix A. Pseudo-code and Decision Tree Diagrams
To illustrate the DDT algorithms described in this document and to
aid in implementation, each of the major DDT Map-Server and DDT Map-
Resolver functions are described first using simple "pseudo-code" and
then in the form of a decision tree.
A.1. Map-Resolver Processing of Map-Request
A.1.1. Pseudo-code Summary
if (Map-Request already in Pending Request List) {
replace old Map-Request with new
use new Map-Request nonce
} else if ( no match in DDT Map-Referral Cache ) {
return Negative Map-Reply to requester
} else if ( match type DELEGATION-HOLE ) {
return Negative Map-Reply to requester
} else if ( match type MS-ACK ) {
forward DDT Map-Request to Map-Server
} else {
Add Map-Request to Pending Request List
Forward DDT Map-Request w/o security material
}
A.1.2. Decision Tree Diagram
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+---------------+
/ Map-Request in \ Yes
| Request Pending +--> Replace old Map-Request with new
\ List? / use new Map-Request Nonce
+------+--------+
|No
V
+---------------+
/ Match in DDT \ No
| Map-Referral +--> Send Negative Map-Reply
\ Cache? / (unlikely event, as root or hint
+------+--------+ configured on every Map-Resolver)
|Yes
V
+---------------+
/ Match type \ Yes
| DELEGATION-HOLE? +--> Send Negative Map-Reply
\ /
+------+--------+
|No
V
+---------------+
/ Match type \ Yes
| MS-ACK? +--> Forward DDT Map-Request to
\ / Map-Server
+------+--------+
|No
o
Add Map-Request to Pending Request List
Forward DDT Map-Request without security material
A.2. Map-Resolver Processing of Map-Referral Message
A.2.1. Pseudo-code Summary
if ( authentication signature validation failed ) {
silently drop
}
if ( no Pending Request List entry matched by Map-Referral Nonce ) {
silently drop
}
if ( XEID-Prefix in Map-Referral less specific than last used ) {
if ( gone through root ) {
silently drop
} else {
send Map-Request to root
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}
}
switch (map_referral_type) {
case NOT-AUTHORITATIVE:
if ( gone through root ) {
return Negative Map-Reply to requester
} else {
send Map-Request to root
}
case DELEGATION-HOLE:
Store in DDT Map-Referral Cache
send Negative Map-Reply to requester
case MS-REFERRAL:
if ( Map-Referral RLOC Set contains last used RLOC ) {
if ( gone through root ) {
return Negative Map-Reply to requester
} else {
send Map-Request to root
}
} else {
Store in DDT Map-Referral Cache
follow Map-Referral with LISP-SEC security material
}
case NODE-REFERRAL:
if ( Map-Referral RLOCs Set contains last used RLOC ) {
if ( gone through root ) {
return Negative Map-Reply to requester
} else {
send Map-Request to root
}
} else {
Store in DDT Map-Referral Cache
follow Map-Referral without LISP-SEC security material
}
case MS-ACK:
if ( Map-Referral has no LISP-SEC security material ) {
resend Map-Request with LISP-SEC security material
if { !incomplete } {
Store in DDT Map-Referral Cache
}
}
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case MS-NOT-REGISTERED:
if ( all Map-Server delegations not tried ) {
follow Map-Referral without LISP-SEC security material
if ( !incomplete ) {
Store in DDT Map-Referral Cache
}
} else {
send Negative Map-Reply to requester
if { !incomplete } {
Store in DDT Map-Referral Cache
}
}
case DEFAULT:
Silently Drop
}
A.2.2. Decision Tree Diagram
+------------+
/Authetication \ No
| signature +-> Silently Drop
\valid? /
+------+-----+
|Yes
v
+------------+
/ In Pending \ No
| Request +-> Silently Drop
\ List? /
+------+-----+
|Yes
v
+------------+
/ XEID-Pfx less\ Yes
| specific than +-> Silently Drop
\ last used? /
+------+-----+
|No
v
+----------------------------------------------+ Unkonwn
| What is the Map-Referral type? +---------+
+--+---------+------+-------+---------+------+-+ v
/ | | | | \ Silently
| | | | MS-ACK DEL-HOLE Drop
| | | | | \
| | NODE-REF MS-REF | v
| | | | | Cache & Return
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| | | | v Negative Map-Reply
| | | | +---------+
| NOT-AUTH | | / LISP-SEC \ Yes
| | v | | material +-> Resend Request
| | +-------+ \ \ stripped? / with LISP-SEC
| |Yes/Pfx equal\ \ +----+----+
| *--+ last used?| \ | No
| | \ / \ +
MS-NOT-REGISTERED| +---+---+ | \
| + |No | \
| / v | \
| + Cache & Follow | \
| v Map-Referral v \
| +----------+ +-------+ +
| /Gone through\ Yes/Pfx equal\ |
| | root? |<-------+ last used?| |
| \ / \ / |
| +----------+ +---+---+ |
| |No |Yes |No |
| v v | |
| Send Req Send Negative v |
| to root Map-Reply Cache & Follow |
| Map-Referral with/
| LISP-SEC / +-> Do Not Cache
v v |
+--------+ +--------+ Yes
/ Other MS \ Yes +-------------+ /Incomplete\
| not tried? +-->|Follow other MS|---->| bit set? |
\ / +-------------+ \ /
+----+---+ +--------+ No
|No +---------------------+ ^ |
+---->|Send Negative Map-Reply|----+ +-> Cache
+---------------------+
A.3. DDT Node Processing of DDT Map-Request Message
A.3.1. Pseudo-code Summary
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if ( I am not authoritative ) {
send Map-Referral NOT_AUTHORITATIVE & set "Incomplete" bit
} else if ( delegation exists ) {
if ( delegated Map-Servers ) {
send Map-Referral MS_REFERRAL
} else {
send Map-Referral NODE_REFERRAL
}
} else {
if ( EID in site ) {
if ( site registered ) {
forward Map-Request to ETR
if ( Map-Server peers configured ) {
send Map-Referral MS_ACK
} else {
send Map-Referral MS_ACK & set"Incomplete" bit
}
} else {
if ( Map-Server peers configured ) {
send Map-Referral MS_NOT_REGISTERED
} else {
send Map-Referral MS_NOT_REGISTERED & set"Incomplete" bit
}
}
} else {
send Map-Referral DELEGATION_HOLE
}
}
A.3.2. Decision Tree Diagram
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+------------+
/ Am I \ No
| authoritative? +-> Return NOT-AUTHORITATIVE &
\ / I-bit = 1
+------+-----+
|Yes
v
+------------+ +------------+
/ Delegation \ Yes / Delegations \ Yes
| exists? +--->| are +--> Return MS-REFERRAL
\ / \ Map-Servers? /
+------+-----+ +------+-----+
|No |No
v +-> Return NODE-REFERRAL
+------------+
/ EID in Site \ No
| configuration? +-> Return DELEGATION-HOLE
\ /
+------+-----+
|Yes
v
+------------+ +------------+
/ Site \ No / Map-Server \ Yes
| Registered? +--->| peers +--+
\ / \ configured? / v
+------+-----+ +------+-----+ Return MS-NOT-REGISTERED
|Yes |No
v v
+----------------+ Return MS-NOT-REGISTERED &
| Forward | I-bit=1
| Map-Request |
| to ETR |
+--------+-------+
|
v
+------------+
/ Map-Server \ No
| peers +-> Return MS-ACK &
\ configured / I-bit=1
+------+-----+
|Yes
v
Return MS-ACK
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Appendix B. Generic DDT Example
This section shows an example of DDT tree and several possible
scenarios of Map-Requests coming to a Map-Resolver and subsequent
iterative DDT referrals. In this example, RLOCs of DDT Nodes are
shown in the IPv4 address space while the EIDs are in the IPv6
address space.
B.1. Reference DDT Tree Topology
To show how referrals are followed to find the RLOCs for a number of
different requests, the DDT topology in Figure 3 is used.
+---------------------+ +---------------------+
| DDT-Root1: 192.0.2.1| | DDT-Root2: 192.0.2.2|
|authoritative: ::/0 | |authoritative: ::/0 |
+-----------+---------+ +---------+-----------+
| \/ |
| /\ |
| / \ |
V V V V
+-----------------------+ +-----------------------+
| DDT-Node1: 192.0.2.11 | | DDT-Node2: 192.0.2.12 |
| authoritative: | | authoritative: |
| 2001:db8::/32 | | 2001:db8::/32 |
+-------------+---------+ +---------+-------------+
| \/ |
| /\ |
| / \ |
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|
+---------------------------+ +---------------------------+
Figure 3: Reference DDT tree topology.
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DDT Root nodes are configured with IP addresses 192.0.2.1 and
192.0.2.2. DDT Map-Resolvers are configured with default referral
cache entries for these addresses.
The DDT Root nodes delegate 2001:db8::/32 to two DDT nodes, DDT-Node1
and DDT-Node2, having IP addresses 192.0.2.11 and 192.0.2.12
respectively.
DDT-Node1 and DDT-Node2 delegate 2001:db8:0100::/40 to a Map-Server1,
who has RLOC 192.0.2.101. Map-Server1 is configured to allow ETRs to
register the sub-prefixes 2001:db8:0103::/48 and 2001:db8:0104::/48.
DDT-Node1 and DDT-Node2 also delegate 2001:db8:0500::/40 to DDT-Node3
who uses the address 192.0.2.201. DDT-Node3 further delegates
2001:db8:0500::/48 to Map-Server2, who has RLOC 192.0.2.211, and
2001:db8:0501::/48 to Map-Server3, who has RLOC 192.0.2.221.
Map-Server2 is configured to allow ETRs to register the sub-prefixes
2001:db8:0500:1::/64 and 2001:db8:0500:2::/64.
Map-Server3 is configured to allow ETRs to register the sub-prefixes
2001:db8:0501:8::/64 and 2001:db8:0501:9::/64.
B.2. Lookup EID registered at with Map-Server1
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. The example assumes that DDT Map-Referral Caches contain
only the default configuration.
ITR1 sends an ECM 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 a 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 the DDT Map-Referral Cache) the Map-Referral
for EID-Prefix 2001:db8::/32, action code NODE-REFERRAL, RLOC set
(192.0.2.11, 192.0.2.12).
3. Send a DDT Map-Request to 192.0.2.11 or 192.0.2.12.
4. Receive (and save in the DDT Map-Referral Cache) the Map-Referral
for EID-Prefix 2001:db8:0100::/40, action code MS-REFERRAL, RLOC
set (192.0.2.101).
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5. Send a DDT Map-Request to 192.0.2.101; if the ITR-originated ECM
Map-Request had a LISP-SEC signature, it is included.
6. The DDT Map-Server1 (192.0.2.101) decapsulates the DDT Map-
Request and forwards the Map-Request to the registered Site1 ETR
for 2001:db8:0103::/48.
7. The DDT Map-Server1 (192.0.2.101) sends a DDT Map-Referral
message for EID-Prefix 2001:db8:0103::/48, action code MS-ACK, to
the DDT Map-Resolver.
8. The DDT Map-Resolver receives the Map-Referral message with
action code MS-ACK and removes the request for 2001:db8:0103:1::1
from the Pending Request List.
9. Site1's ETR for 2001:db8:0103::/48 receives the Map-Request
forwarded by Map-Server1 and sends a Map-Reply to ITR1.
B.3. Lookup EID registered at with Map-Server3
This example shows a three-level delegation: root to first DDT node,
first DDT Node to second DDT Node, and second DDT Node to DDT Map-
Server. The example assumes that DDT Map-Referral Caches contain
only the default configuration.
ITR2 sends an ECM 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 a 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 the DDT Map-Referral Cache) the Map-
Referral for EID-Prefix 2001:db8::/32, action code NODE-
REFERRAL, RLOC set (192.0.2.11, 192.0.2.12).
3. Send a DDT Map-Request to 192.0.2.11 or 192.0.2.12.
4. Receive (and save in the DDT Map-Referral Cache) the DDT Map-
Referral for EID-Prefix 2001:db8:0500::/40, action code NODE-
REFERRAL, RLOC set (192.0.2.201).
5. Send a DDT Map-Request to 192.0.2.201.
6. Receive (and save in the DDT Map-Referral Cache) the DDT Map-
Referral for EID-Prefix 2001:db8:0501::/48, action code MS-
REFERRAL, RLOC set (192.0.2.221).
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7. Send a DDT Map-Request to 192.0.2.221; if the ITR-originated ECM
Map-Request had a LISP-SEC signature, it is included.
8. Map-Server3 (192.0.2.221) decapsulates the DDT Map-Request and
forwards the Map-Request to a registered Site5 ETR for
2001:db8:0501:8::/64.
9. Map-Server3 (192.0.2.221) sends a DDT Map-Referral message for
EID-Prefix 2001:db8:0501:8::/64, action code MS-ACK, to the DDT
Map-Resolver.
10. The DDT Map-Resolver receives a Map-Referral message with action
code MS-ACK and removes the request for 2001:db8:0501:8:4::1
from the Pending Request List.
11. Site5's ETR for 2001:db8:0501:8::/64 receives the Map-Request
forwarded by Map-Server3 and sends a Map-Reply to ITR2.
B.4. Lookups using cached DDT Map-Referrals to Map-Servers
This example shows a lookup for 2001:db8:0104:2::2, where the DDT
Map-Resolver uses a saved DDT Map-Referral Cache entry to skip the
iterative referral process and go directly to a DDT Map-Server.
In this case, ITR1 uses the same Map-Resolver used in the example in
Appendix B.2. It sends an ECM 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 directly a DDT Map-Request (for 2001:db8:0104:2::2) to
192.0.2.101; if the ITR-originated ECM Map-Request had a LISP-SEC
signature, it is included.
2. Map-Server1 (192.0.2.101) decapsulates the DDT Map-Request and
forwards the Map-Request to the registered Site2 ETR for
2001:db8:0104::/48.
3. Map-Server1 (192.0.2.101) sends a DDT Map-Referral message for
EID-Prefix 2001:db8:0104::/48, action code MS-ACK, to the DDT
Map-Resolver.
4. The DDT Map-Resolver receives the DTT Map-Referral with action
code MS-ACK and removes the request for 2001:db8:0104:2::2 from
the Pending Request List.
5. Site2's ETR for 2001:db8:0104::/48 receives the Map-Request from
Map-Server1 and sends a Map-Reply to ITR1.
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B.5. Lookup using cached DDT Map-Referrals to DDT Nodes
This example shows how a DDT Map-Resolver uses a DDT Map-Referral
Cache entry to start the referral process at a non-root, intermediate
DDT node for the prefix 2001:db8:0500:2:4::1, which is similar to one
previously requested.
In this case, ITR2 uses the same Map-Resolver used in the example in
Appendix B.3. It sends an ECM Map-Request for 2001:db8:0500:2:4::1
to that DDT Map-Resolver, which finds a NODE-REFERRAL cache entry for
2001:db8:0500::/40 with RLOC set 192.0.2.201. It proceeds as
follows:
1. Send a DDT Map-Request (for 2001:db8:0500:2:4::1) to 192.0.2.201.
2. Receive (and save in the referral cache) the Map-Referral for
EID-Prefix 2001:db8:0500::/48, action code MS-REFERRAL, RLOC set
(192.0.2.211).
3. Send a DDT Map-Request to 192.0.2.211; if the ITR-originated
Encapsulated Map-Request had a LISP-SEC signature, it is
included.
4. Map-Server2 (192.0.2.211) decapsulates the DDT Map-Request and
forwards the Map-Request to the registered Site4 ETR for
2001:db8:0500:2::/64.
5. Map-Server3 (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. The DDT Map-Resolver receives the Map-Referral (MS-ACK) and
removes the request for 2001:db8:0500:2:4::1 from the Pending
Request List.
7. Site4's ETR for 2001:db8:0500:2::/64 receives the Map-Request and
sends a Map-Reply to ITR2.
B.6. Lookup of a non-existent EID
This example shows the lookup of 2001:db8:0500::1/128, which uses the
cached MS-REFERRAL for 2001:db8:0500::/48 learned because of previous
lookups at the DDT Map-Server at 192.0.2.211. The DDT Map-Resolver
proceeds as follows:
1. Send a DDT Map-Request for 2001:db8:0500::1 to 192.0.2.211; if
the ITR-originated ECM Map-Request has a LISP-SEC signature, it
is included.
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2. Map-Server2 (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 DDT 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 the configured delegations
(2001:db8:0500:1::/64 and 2001:db8:0500:2::/64).
3. The DDT Map-Resolver receives the delegation, adds a Negative DDT
Map-Referral Cache entry for 2001:db8:0500::/64, removes the
request for 2001:db8:0500::1 from the Pending Request list, and
returns a Negative Map-Reply to ITR2.
Contributors
Vince Fuller
VAF.NET Internet Consulting
Email: vince.fuller@gmail.com
Darrel Lewis
ICANN
Los Angeles, CA 90292
United States of America
Email: darrel.lewis@icann.org
Vina Ermagan
Google
United States of America
Email: ermagan@gmail.com
Amit Jain
Juniper Networks
Email: atjain@juniper.net
Anton Smirnov
Cisco Systems, Inc.
De Kleetlaan 6a
1831 Diegem
Belgium
Email: as@cisco.com
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Authors' Addresses
Damien Saucez (editor)
Inria
France
Email: damien.saucez@inria.fr
Luigi Iannone (editor)
Huawei Technologies France S.A.S.U.
18, Quai du Point du Jour
92100 Boulogne-Billancourt
France
Email: luigi.iannone@huawei.com
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