Network Working Group V. Fuller
Internet-Draft
Intended status: Experimental D. Lewis
Expires: March 12, 2017 V. Ermagan
Cisco Systems
A. Jain
Juniper Networks
A. Smirnov
Cisco Systems
September 8, 2016
LISP Delegated Database Tree
draft-ietf-lisp-ddt-08
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 12, 2017.
Copyright Notice
Copyright (c) 2016 IETF Trust and the persons identified as the
document authors. All rights reserved.
Fuller, et al. Expires March 12, 2017 [Page 1]
Internet-Draft LISP Delegated Database Tree September 2016
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. EID-prefix tree structure and instance IDs . . . . . . . 7
4.2. Configuring prefix delegation . . . . . . . . . . . . . . 7
4.2.1. The root DDT node . . . . . . . . . . . . . . . . . . 7
5. DDT Map-Request . . . . . . . . . . . . . . . . . . . . . . . 8
6. The Map-Referral message . . . . . . . . . . . . . . . . . . 8
6.1. Action codes . . . . . . . . . . . . . . . . . . . . . . 9
6.2. Referral set . . . . . . . . . . . . . . . . . . . . . . 9
6.3. Incomplete flag . . . . . . . . . . . . . . . . . . . . . 10
6.4. Map-Referral Message Format . . . . . . . . . . . . . . . 10
6.4.1. SIG section . . . . . . . . . . . . . . . . . . . . . 12
7. DDT network elements and their operation . . . . . . . . . . 13
7.1. DDT node . . . . . . . . . . . . . . . . . . . . . . . . 14
7.1.1. Match of a delegated prefix (or sub-prefix) . . . . . 14
7.1.2. Missing delegation from an authoritative prefix . . . 14
7.2. DDT Map Server . . . . . . . . . . . . . . . . . . . . . 14
7.3. DDT Map Resolver . . . . . . . . . . . . . . . . . . . . 15
7.3.1. Queuing and sending DDT Map-Requests . . . . . . . . 15
7.3.2. Receiving and following referrals . . . . . . . . . . 16
7.3.3. Handling referral errors . . . . . . . . . . . . . . 18
7.3.4. Referral loop detection . . . . . . . . . . . . . . . 18
8. Pseudo Code and Decision Tree diagrams . . . . . . . . . . . 19
8.1. Map Resolver processing of ITR Map-Request . . . . . . . 19
8.1.1. Pseudo-code summary . . . . . . . . . . . . . . . . . 19
8.1.2. Decision tree diagram . . . . . . . . . . . . . . . . 19
8.2. Map Resolver processing of Map-Referral message . . . . . 20
8.2.1. Pseudo-code summary . . . . . . . . . . . . . . . . . 20
8.2.2. Decision tree diagram . . . . . . . . . . . . . . . . 22
8.3. DDT Node processing of DDT Map-Request message . . . . . 24
8.3.1. Pseudo-code summary . . . . . . . . . . . . . . . . . 24
8.3.2. Decision tree diagram . . . . . . . . . . . . . . . . 25
9. Example topology and request/referral following . . . . . . . 25
9.1. Lookup of 2001:db8:0103:1::1/128 . . . . . . . . . . . . 27
Fuller, et al. Expires March 12, 2017 [Page 2]
Internet-Draft LISP Delegated Database Tree September 2016
9.2. Lookup of 2001:db8:0501:8:4::1/128 . . . . . . . . . . . 28
9.3. Lookup of 2001:db8:0104:2::2/128 . . . . . . . . . . . . 29
9.4. Lookup of 2001:db8:0500:2:4::1/128 . . . . . . . . . . . 30
9.5. Lookup of 2001:db8:0500::1/128 (non-existent EID) . . . . 30
10. Securing the database and message exchanges . . . . . . . . . 31
10.1. XEID-prefix Delegation . . . . . . . . . . . . . . . . . 31
10.2. DDT node operation . . . . . . . . . . . . . . . . . . . 32
10.2.1. DDT public key revocation . . . . . . . . . . . . . 32
10.3. Map Server operation . . . . . . . . . . . . . . . . . . 33
10.4. Map Resolver operation . . . . . . . . . . . . . . . . . 33
11. Open Issues and Considerations . . . . . . . . . . . . . . . 34
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 34
13. Security Considerations . . . . . . . . . . . . . . . . . . . 34
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 35
14.1. Normative References . . . . . . . . . . . . . . . . . . 35
14.2. Informative References . . . . . . . . . . . . . . . . . 35
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 36
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
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.
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.
The DBID is provided for possible use in case a need evolves for
another, higher level in the hierarchy, to allow the creation of
multiple, separate database trees.
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-
Fuller, et al. Expires March 12, 2017 [Page 3]
Internet-Draft LISP Delegated Database Tree September 2016
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.
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 Map Server (sometimes termed a "terminal DDT node") 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].
Fuller, et al. Expires March 12, 2017 [Page 4]
Internet-Draft LISP Delegated Database Tree September 2016
3. Definition of Terms
Extended EID (XEID): a LISP EID, optionally extended with a non-
zero Instance ID (IID) if the EID is intended for use in a context
where it may not be a unique value, 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.
XEID-prefix: a LISP EID-prefix with 16-bit LISP-DDT DBID (provided
to allow the definition of multiple databases; currently always
zero in this version of DDT, with other values reserved for future
use), 32-bit IID and 16-bit AFI prepended. Encoding of the
prefix, its AFI and the instance ID (IID) are specified by
[I-D.ietf-lisp-lcaf]. An XEID-prefix is used as a key index into
the database.
DDT node: a network infrastructure component responsible for
specific XEID-prefix and for delegation of more-specific sub-
prefixes to other DDT nodes.
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,
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 Resolver: a network infrastructure element that accepts a
Map-Request, adds the XEID to its pending request list, then
queries one or more DDT nodes for the requested EID, 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 original sender. A DDT
Map Resolver maintains both a cache of Map-Referral message
results containing RLOCs for DDT nodes responsible for XEID-
prefixes of interest (termed the "referral cache") and a pending
request list of XEIDs that are being resolved through iterative
querying of DDT nodes.
Encapsulated Map-Request: a LISP Map-Request carried within an
Encapsulated Control Message, which has an additional LISP header
Fuller, et al. Expires March 12, 2017 [Page 5]
Internet-Draft LISP Delegated Database Tree September 2016
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 more information about the
sub-prefix; 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 a 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: 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 a DDT
client for an XEID. Each entry in the list contains additional
state needed by the referral following process, including the
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 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,
Fuller, et al. Expires March 12, 2017 [Page 6]
Internet-Draft LISP Delegated Database Tree September 2016
and Map Resolver, please consult the LISP specification [RFC6830] and
the LISP Mapping Service specification [RFC6833].
4. Database organization
4.1. EID-prefix tree structure and instance IDs
LISP-DDT defines a tree structure that is indexed by a 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. The index into this structure is also referred to as an
Extended EID-prefix (XEID-prefix).
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 (Map Servers and their registered EIDs) 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.
4.2. 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.
4.2.1. The root DDT node
The root DDT node is the logical "top" of the database hierarchy:
DBID=0, IID=0, AFI=0, EID-prefix=0/0. 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
Fuller, et al. Expires March 12, 2017 [Page 7]
Internet-Draft LISP Delegated Database Tree September 2016
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].
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.
Fuller, et al. Expires March 12, 2017 [Page 8]
Internet-Draft LISP Delegated Database Tree September 2016
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 Map Resolver 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 a 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.
NOT-AUTHORITATIVE (5): indicates that the replying DDT node received
a Map-Request for an XEID-request for which it is not
authoritative. This can occur if a cached referral has become
invalid due to a change in the database hierarchy.
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 Map Resolver uses this information to contact one of those DDT
nodes as it "follows" a referral.
Fuller, et al. Expires March 12, 2017 [Page 9]
Internet-Draft LISP Delegated Database Tree September 2016
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 Map
Resolver 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 does
not have configuration for other "peer" DDT nodes that are also
authoritative for the matched XEID-prefix.
o If it is setting action code NOT-AUTHORITATIVE.
6.4. Map-Referral Message Format
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/LCAF-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 6 action types. The values for the action types are:
Fuller, et al. Expires March 12, 2017 [Page 10]
Internet-Draft LISP Delegated Database Tree September 2016
NODE-REFERRAL (0): Sent by a DDT node with a child delegation, which
is authoritative for the EID.
MS-REFERRAL (1): Sent by a DDT node that has information about Map
Server(s) for the EID but it is not one of the Map Servers listed,
i.e. the DDT-Node sending the referral is not a Map Server.
MS-ACK (2): Sent by a DDT Map Server that has one or more ETR
registered for the EID.
MS-NOT-REGISTERED (3): Sent by a DDT Map Server that is configured
for the EID-prefix, but for which no ETRs are registered.
DELEGATION-HOLE (4): Sent by an intermediate DDT node with
authoritative configuration covering the requested EID but without
any child delegation for the EID. 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): Sent by a DDT node that does not have
authoritative configuration for the requested EID. The EID-prefix
returned MUST be the original requested EID and the TTL MUST be
set to 0. 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.
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:
-------------------------------------------------------------------
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
-------------------------------------------------------------------
Fuller, et al. Expires March 12, 2017 [Page 11]
Internet-Draft LISP Delegated Database Tree September 2016
*: The "Incomplete" flag setting on Map Server originated referral of
MS-REFERRAL 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 the
Map Server has not encoded the complete Map Server set
information.
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/LCAF-AFI: If this is a Loc AFI, keys SHOULD NOT be included in
the record. If this is a LCAF AFI, the contents of the LCAF depend
on the Type field of the LCAF. Security material are stored in LCAF
Type 11. DDT nodes and 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].
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.
Fuller, et al. Expires March 12, 2017 [Page 12]
Internet-Draft LISP Delegated Database Tree September 2016
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/| 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.
Sig-Algorithm: The identifier of the cryptographic algorithm used for
the signature. This specification defines only one algorithm: Sig-
Algorithm type 1 is RSA-SHA1 (see [RFC3447]).
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 record. The Record TTL and the sig fields are 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.
Fuller, et al. Expires March 12, 2017 [Page 13]
Internet-Draft LISP Delegated Database Tree September 2016
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 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.
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.
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 or
an authoritative XEID-prefix, 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:
Fuller, et al. Expires March 12, 2017 [Page 14]
Internet-Draft LISP Delegated Database Tree September 2016
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-
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 Map Resolver
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 uses an iterative process of
following referrals 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.
7.3.1. Queuing and sending DDT Map-Requests
When a DDT Map Resolver receives an 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
Map Resolver.
If a match is found, the DDT Map Resolver creates a pending request
list entry for the XEID and saves the 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 initialized to the null value since no referral has
yet been received. The Map Resolver 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 Map-
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 Map Resolver is not absolutely required to cache referrals, but
it doing so decreases latency and reduces lookup delays.
Fuller, et al. Expires March 12, 2017 [Page 15]
Internet-Draft LISP Delegated Database Tree September 2016
Note that in normal use on the public Internet, the statically-
configured initial referral cache for a DDT Map Resolver should
include a "default" entry with RLOCs for one or more DDT nodes that
can reach the DDT root node. If a Map Resolver 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.
7.3.2. Receiving and following referrals
After sending a DDT Map-Request, a DDT Map Resolver expects to
receive a Map-Referral response. If none occurs within the timeout
period, the DDT Map Resolver retransmits the request, sending to the
next RLOC in the referral cache entry if one is available. If the
maximum number of retransmissions has occurred and all RLOCs have
been tried, then the pending request list entry is dequeued.
A DDT Map Resolver processes a received Map-Referral message
according to each action code:
NODE-REFERRAL: The DDT Map Resolver checks for a possible referral
loop as as described in Section 7.3.4. If no loop is found, the
DDT Map Resolver 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 in the Referral Set; security information saved with the
original Map-Request SHOULD NOT be included.
MS-REFERRAL: The DDT Map Resolver follows 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
Map Resolver 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
Fuller, et al. Expires March 12, 2017 [Page 16]
Internet-Draft LISP Delegated Database Tree September 2016
can be discarded. Otherwise, LISP-SEC information is required and
has not yet been sent to the authoritative DDT Map-Server; the DDT
Map Resolver 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 Map Resolver 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 Map Resolver MUST return a negative
Map-Reply to the original Map-Request sender; this Map-Reply
contains the non-registered XEID-prefix 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 Map Resolver MUST return a
negative Map-Reply to the original Map-Request sender; this Map-
Reply SHOULD indicate the least-specific XEID-prefix matching the
requested 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 Map Resolver 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.
Fuller, et al. Expires March 12, 2017 [Page 17]
Internet-Draft LISP Delegated Database Tree September 2016
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
Map Resolver; they should be considered errors and logged as such.
It is not clear exactly what else the DDT Map Resolver should do in
such cases; one possibility is to remove the pending request list
entry and send a negative Map-Reply to the original Map-Request
sender. Alternatively, if a DDT Map Resolver 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 Map-
Resolver 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 Map Resolver 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 Map Resolver 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 Map Resolver saves the most recently
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 Map Resolver 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 Map Resolver 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 Map Resolvers.
Fuller, et al. Expires March 12, 2017 [Page 18]
Internet-Draft LISP Delegated Database Tree September 2016
8. Pseudo Code and Decision Tree diagrams
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
Fuller, et al. Expires March 12, 2017 [Page 19]
Internet-Draft LISP Delegated Database Tree September 2016
+------------+
| 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
+------------+ 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 ( no request pending matched by referral nonce ) {
silently drop
}
if ( pfx in referral less specific than last referral used ) {
Fuller, et al. Expires March 12, 2017 [Page 20]
Internet-Draft LISP Delegated Database Tree September 2016
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:
if ( security material stripped ) {
resend request with security material
if { !incomplete } {
cache
Fuller, et al. Expires March 12, 2017 [Page 21]
Internet-Draft LISP Delegated Database Tree September 2016
}
}
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
Fuller, et al. Expires March 12, 2017 [Page 22]
Internet-Draft LISP Delegated Database Tree September 2016
+------------+
| 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
| | | | | 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
Fuller, et al. Expires March 12, 2017 [Page 23]
Internet-Draft LISP Delegated Database Tree September 2016
8.3. DDT Node processing of DDT Map-Request message
8.3.1. Pseudo-code summary
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
Fuller, et al. Expires March 12, 2017 [Page 24]
Internet-Draft LISP Delegated Database Tree September 2016
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
Fuller, et al. Expires March 12, 2017 [Page 25]
Internet-Draft LISP Delegated Database Tree September 2016
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
+---------------------+ +---------------------+
| root1: 192.0.2.1 | | 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|
+---------------------------+ +---------------------------+
Fuller, et al. Expires March 12, 2017 [Page 26]
Internet-Draft LISP Delegated Database Tree September 2016
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.
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
Fuller, et al. Expires March 12, 2017 [Page 27]
Internet-Draft LISP Delegated Database Tree September 2016
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
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)
Fuller, et al. Expires March 12, 2017 [Page 28]
Internet-Draft LISP Delegated Database Tree September 2016
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
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
Fuller, et al. Expires March 12, 2017 [Page 29]
Internet-Draft LISP Delegated Database Tree September 2016
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-
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
Fuller, et al. Expires March 12, 2017 [Page 30]
Internet-Draft LISP Delegated Database Tree September 2016
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.
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 the 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.
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
Fuller, et al. Expires March 12, 2017 [Page 31]
Internet-Draft LISP Delegated Database Tree September 2016
authenticating the public keys associated with the children nodes,
and authorizing them to be used by the children DDT nodes to provide
origin authentication and integrity protection for further
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
Fuller, et al. Expires March 12, 2017 [Page 32]
Internet-Draft LISP Delegated Database Tree September 2016
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.
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.
Fuller, et al. Expires March 12, 2017 [Page 33]
Internet-Draft LISP Delegated Database Tree September 2016
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.
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.
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
Fuller, et al. Expires March 12, 2017 [Page 34]
Internet-Draft LISP Delegated Database Tree September 2016
and the path between Map-Resolver and Map-Server needs to be
protected, DDT security should be enabled as well.
14. References
14.1. 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,
<http://www.rfc-editor.org/info/rfc2119>.
[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
[I-D.ietf-lisp-lcaf]
Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
Address Format (LCAF)", draft-ietf-lisp-lcaf-13 (work in
progress), May 2016.
[I-D.ietf-lisp-sec]
Maino, F., Ermagan, V., Cabellos-Aparicio, A., and D.
Saucez, "LISP-Security (LISP-SEC)", draft-ietf-lisp-sec-10
(work in progress), April 2016.
[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>.
Fuller, et al. Expires March 12, 2017 [Page 35]
Internet-Draft LISP Delegated Database Tree September 2016
[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>.
[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>.
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.
Authors' Addresses
Vince Fuller
Email: vaf@vaf.net
Darrel Lewis
Cisco Systems
Email: darlewis@cisco.com
Fuller, et al. Expires March 12, 2017 [Page 36]
Internet-Draft LISP Delegated Database Tree September 2016
Vina Ermagan
Cisco Systems
Email: vermagan@cisco.com
Amit Jain
Juniper Networks
Email: atjain@juniper.net
Anton Smirnov
Cisco Systems
Email: as@cisco.com
Fuller, et al. Expires March 12, 2017 [Page 37]
