Network Working Group V. Ermagan
Internet-Draft D. Farinacci
Intended status: Experimental D. Lewis
Expires: September 5, 2012 J. Skriver
F. Maino
Cisco Systems, Inc.
C. White
Logicalelegance, Inc.
March 4, 2012
NAT traversal for LISP
draft-ermagan-lisp-nat-traversal-00.txt
Abstract
This document describes a mechanism for IPv4 NAT traversal for LISP
tunnel routers (xTR) and LISP Mobile Nodes (LISP-MN) behind a NAT
device. A LISP device both detects the NAT and initializes its
state. Forwarding to the LISP device through a NAT is enabled by a
new network element, the LISP Re-encapsulating Tunnel Router (RTR),
which acts as an anchor point in the data plane, forwarding traffic
from unmodified LISP devices through the NAT.
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 September 5, 2012.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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(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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 4
3. Basic Overview . . . . . . . . . . . . . . . . . . . . . . . . 6
4. LISP RTR Message Details . . . . . . . . . . . . . . . . . . . 7
4.1. Info-Request Message . . . . . . . . . . . . . . . . . . . 7
4.2. LISP Info-Reply . . . . . . . . . . . . . . . . . . . . . 8
4.3. LISP Map-Register Message . . . . . . . . . . . . . . . . 9
4.4. LISP Map-Notify . . . . . . . . . . . . . . . . . . . . . 10
4.5. LISP Data-Map-Notify Message . . . . . . . . . . . . . . . 11
5. Protocol Operations . . . . . . . . . . . . . . . . . . . . . 13
5.1. xTR Processing . . . . . . . . . . . . . . . . . . . . . . 13
5.1.1. ETR Registration . . . . . . . . . . . . . . . . . . . 13
5.1.2. Map-Request and Map-Reply Handling . . . . . . . . . . 15
5.1.3. xTR Sending and Receiving Data . . . . . . . . . . . 16
5.2. Map-Server Processing . . . . . . . . . . . . . . . . . . 16
5.3. RTR Processing . . . . . . . . . . . . . . . . . . . . . . 17
5.3.1. RTR Data Forwarding . . . . . . . . . . . . . . . . . 18
5.4. Example . . . . . . . . . . . . . . . . . . . . . . . . . 19
6. Security Considerations . . . . . . . . . . . . . . . . . . . 23
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 24
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
9. Normative References . . . . . . . . . . . . . . . . . . . . . 26
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 27
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1. Introduction
The Locator/ID Separation Protocol [LISP] defines a set of functions
for encapsulating routers to exchange information used to map from
Endpoint Identifiers (EIDs) to routable Routing Locators (RLOCs).
The assumption that the LISP Tunnel Routers are reachable at their
RLOC breaks when a LISP device is behind a NAT. LISP relies on the
xTR being able to receive traffic at its RLOC on destination port
4341. However nodes behind a NAT are only reachable through the
NAT's public address and in most cases only after the appropriate
mapping state is set up in the NAT. A NAT traversal mechanism is
needed to make the LISP device behind a NAT reachable.
This document introduces a NAT traversal mechanism for LISP. Two new
LISP control messages - LISP Info-Request and LISP Info-Reply - are
introduced in order to detect whether a LISP device is behind a NAT,
and discover the global IP address and global ephemeral port used by
the NAT to forward LISP packets sent by the LISP device. A new LISP
component, the LISP Re-encapsulating Tunnel Router (RTR), acts as a
re-encapsulating LISP tunnel router [LISP] to pass traffic through
the NAT, to and from the LISP device. A modification to how the LISP
Map-Register messages are sent allows LISP device to initialize NAT
state to use the RTR services. This mechanism addresses the scenario
where the LISP device is behind the NAT, but the associated Map-
Server is on the public side of the NAT.
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2. Definition of Terms
LISP Info-Request: A LISP control packet sent by a LISP device to
its Map-Server.
LISP Info-Reply: A LISP control packet sent by a Map Server to a
LISP device in response to an Info-Request.
LISP Re-encapsulating Tunnel Router (RTR): An RTR is a re-
encapsulating LISP Router (see section 8 of the main LISP
specification) [LISP]. An RTR provides a LISP device the ability
to traverse NATs.
LISP Data-Map-Notify: A LISP Map-Notify message encapsulated in a
LISP data header.
LISP xTR-ID A 128 bit field that can be appended at the end of a
Map-Register or Map-Notify message. An xTR-ID is used as a unique
identifier of the xTR that is sending the Map-Register and is
especially useful for identifying multiple xTRs serving the same
site/EID-prefix.
NAT: "Network Address Translation is a method by which IP addresses
are mapped from one address realm to another, providing
transparent routing to end hosts". "Traditional NAT would allow
hosts within a private network to transparently access hosts in
the external network, in most cases. In a traditional NAT,
sessions are uni-directional, outbound from the private network."
--RFC 2663[NAT]. Basic NAT and NAPT are two varieties of
traditional NAT.
Basic NAT: "With Basic NAT, a block of external addresses are set
aside for translating addresses of hosts in a private domain as
they originate sessions to the external domain. For packets
outbound from the private network, the source IP address and
related fields such as IP, TCP, UDP and ICMP header checksums are
translated. For inbound packets, the destination IP address and
the checksums as listed above are translated." --RFC 2663[NAT].
NAPT: "NAPT extends the notion of translation one step further by
also translating transport identifier (e.g., TCP and UDP port
numbers, ICMP query identifiers). This allows the transport
identifiers of a number of private hosts to be multiplexed into
the transport identifiers of a single external address. NAPT
allows a set of hosts to share a single external address. Note
that NAPT can be combined with Basic NAT so that a pool of
external addresses are used in conjunction with port translation."
--RFC 2663[NAT]. Transport identifiers of the destination hosts
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are not modified by the NAPT.
In this document the general term NAT is used to refer to both Basic
NAT and NAPT.
While this document specifies LISP NAT Traversal for LISP tunnel
routers, a LISP-MN can also use the same procedure for NAT traversal.
The modifications attributed to a LISP-Device, xTR, ETR, and ITR must
be supported by a LISP-MN where applicable, in order to achieve NAT
traversal for such a LISP node.
For definitions of other terms, notably Map-Request, Map-Reply,
Ingress Tunnel Router (ITR), and Egress Tunnel Router (ETR), please
consult the LISP specification [LISP].
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3. Basic Overview
There are two attributes of a LISP device behind a typical NAT that
requires special consideration in LISP protocol behavior in order to
make the device reachable. First, the RLOC assigned to the device is
typically not globally unique nor globally routable. Second, the NAT
likely has a restrictive translation table and forwarding policy,
requiring outbound packets to create state before the NAT accepts
inbound packets. This section provides an overview of the LISP NAT
traversal mechanism which deals with these conditions. The following
sections specify the mechanism in more detail.
When a LISP device receives a new RLOC and wants to register it with
the mapping system, it needs to first discover whether it is behind a
NAT. To do this, an ETR uses its Map-Server to discover its
translated global RLOC and port via the two new LISP messages: Info-
Request and Info-Reply. Once an ETR detects that it is behind a NAT,
it uses a new LISP entity, a LISP Re-encapsulating Tunnel Router
(RTR) as a data plane 'anchor point' to send and receive traffic
through the NAT device. The ETR registers the RTR RLOC(s) to its
Map-Server using the RTR as a proxy for the Map-Register message.
The ETR encapsulates the Map-Register message in a LISP ECM header
destined to the RTR's RLOC. The RTR strips the LISP ECM header, re-
originates the Map-Register message, and sends it to the Map-Server.
This initializes state in the NAT device so the ETR can receive
traffic on port 4341 from the RTR. It also registers the RTR RLOC as
the RLOC where the ETR EID prefix is reachable. As a result, all
packets destined to the ETR's EID will go to its RTR. The RTR will
then re-encapsulates and forwards the ETR's traffic via the existing
NAT state to the ETR.
Outbound LISP data traffic from the xTR is also encapsulated to the
RTR, where the RTR re-encapsulated the LISP packets based on their
destination EIDs.
In the next sections the procedure is discussed in more detail.
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4. LISP RTR Message Details
The main modifications in the LISP protocol to enable LISP NAT
traversal via an RTR include: (1) two new messages used for NAT
discovery (Info-Request and Info-Reply), and (2) encapsulation of two
LISP control messages (Map-Register and Map-Notify) between the xTR
and the RTR. Map-Register is encapsulated in an ECM header while
Map-Notify is encapsulated in a LISP data header (Data-Map-Notify).
This section describes the message formats and details of the Info-
Request, Info-Reply, and Data-Map-Notify messages, as well as
encapsulation details and minor changes to Map-Register and Map-
Notify messages.
4.1. Info-Request Message
An ETR sends an Info-Request message to its Map-Server in order to
1. detect whether there is a NAT on the path to its Map-Server
2. obtain a list of RTR RLOCs that can be used for LISP data plane
NAT traversal.
An Info-Request message is a LISP control message, its source port is
chosen by the xTR and its destination port is set to 4342.
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=7 |R| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ID | Authentication Data Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Authentication Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | EID mask-len | EID-prefix-AFI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EID-prefix |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AFI = 0 | <Nothing Follows AFI=0> |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LISP Info-Request Message Format
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Type: 7 (Info-Request)
R: R bit indicates this is a reply to an Info-Request (Info-
Reply). R bit is set to 0 in an Info-Request. When R bit is set
to 0, the AFI field (following the EID-prefix field) must be set
to 0. When R bit is set to 1, the packet contents follow the
format for an Info-Reply as described below.
Reserved: Must be set to 0 on transmit and must be ignored on
receipt.
TTL: The time in minutes the recipient of the Info-Reply will
store the RTR Information.
Nonce: An 8-byte random value created by the sender of the Info-
Request. This nonce will be returned in the Info-Reply. The
nonce SHOULD be generated by a properly seeded pseudo-random (or
strong random) source.
Descriptions for other fields can be found in the Map-Register
section of the main LISP draft [LISP]. Field descriptions for the
LCAF AFI = 0 can be found in the LISP LCAF draft [LCAF] .
4.2. LISP Info-Reply
When a Map-Server receives an Info-Request message, it responds with
an Info-Reply message. The Info-Reply message source port is 4342,
and destination port is taken from the source port of the triggering
Info-Request. Map-Server fills the NAT LCAF (LCAF Type = 7) fields
according to their description. The Map-Server uses AFI=0 for the
Private ETR RLOC Address field in the NAT LCAF.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Type=7 |R| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Nonce . . . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . . . Nonce |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Key ID | Authentication Data Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Authentication Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | EID mask-len | EID-prefix-AFI |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| EID-prefix |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | AFI = 16387 | Rsvd1 | Flags |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | Type = 7 | Rsvd2 | 4 + n |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
N | MS UDP Port Number | ETR UDP Port Number |
A +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
T | AFI = x | Global ETR RLOC Address ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L | AFI = x | MS RLOC Address ... |
C +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A | AFI = x | Private ETR RLOC Address ... |
F +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | AFI = x | RTR RLOC Address 1 ... |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | AFI = x | RTR RLOC Address n ... |
+->+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LISP Info-Reply Message Format
Type: 7 , R = 1, (Info-Reply)
The format is similar to the Info-Request message. See Info-Request
section for field descriptions. Field descriptions for the NAT LCAF
section can be found in the LISP LCAF draft [LCAF] .
4.3. LISP Map-Register Message
The fourth bit after the Type field in the Map-Register message is
allocated as "R" bit. R bit indicates that the Map-Register is built
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for an RTR. R bit must be set in a Map-Register that a LISP device
sends to an RTR.
The third bit after the Type field in the Map-Register message is
allocated as "I" bit. I bit indicates that a xTR-ID field is present
at the end of the Map-Register message. If an xTR is configured with
an xTR-ID, it MUST set the I bit to 1 and include its xTR-ID in the
Map-Register messages it generates. If the R bit in the Map-Register
is set to 1, the I bit must also be set to 1, and an xTR-ID must be
included in the Map-Register message sent to an RTR.
xTR-ID is a 128 bit field at the end of the Map-Register message,
starting after the final Record in the message. The xTR-ID is used
to identify the intended recipient xTR for a Map-Notify message,
especially in the case where a site has more than one xTR. When a
Map-Server receives a Map-Register with the I bit set, it MUST copy
the XTR-ID from the Map-Register to the associated Map-Notify
message. When a Map-Server is sending an unsolicited Map-Notify to
an xTR to notify the xTR of a change in locators, the Map-Server must
include the xTR-ID for the intended recipient xTR, if it has one
stored locally.
A LISP device that sends a Map-Register to an RTR must encapsulate
the Map-Register message using an Encapsulated Control Message (ECM)
[LISP]. The outer header source RLOC of the ECM is set to the LISP
device's local RLOC, and the outer header source port is set to 4341.
The outer header destination RLOC and port are set to RTR RLOC and
4342 respectively. The inner header source RLOC is set to LISP
device's local RLOC, and the inner source port is picked at random.
The inner header destination RLOC is set to the xTR's Map-Server
RLOC, and inner header destination port is set to 4342.
4.4. LISP Map-Notify
The first bit after the Type field in a Map-Notify message is
allocated as the "I" bit. I bit indicates that a 128 bit xTR-ID
field is present at the end of the Map-Notify message, following the
final Record in the Map-Notify (See Section 4.3 for details on
xTR-ID). A Map-Server MUST set the I bit in a Map-Notify and include
the xTR-ID of the intended recipient xTR if the associated Map-
Register has the I bit set, or when the Map-Server has previously
cached an xTR-ID for the destination xTR.
The second bit after the Type field in Map-Notify is allocated as the
"R" bit. R bit in Map-Notify indicates that additional
authentication data is appended at the end of the Map-Notify message.
If the I bit is also set in the Map-Notify, the additional MS-RTR
authentication data must be appended after the xTR-ID field. If a
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Map-Server receiving a Map-Register with the R bit set, has a shared
key associated with the sending RTR, it must generate a Map-Notify
message with the R bit set to 1, and with the additional MS-RTR
authentication related fields described below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MS-RTR Key ID | MS-RTR Auth. Data Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ MS-RTR Authentication Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Changes to LISP Map-Notify Message
MS-RTR Key ID: A configured ID to find the configured Message
Authentication Code (MAC) algorithm and key value used for the
authentication function. See [LISP] section 14.4 for codepoint
assignments.
MS-RTR Authentication Data Length: The length in bytes of the MS-RTR
Authentication Data field that follows this field. The length of the
Authentication Data field is dependent on the Message Authentication
Code (MAC) algorithm used. The length field allows a device that
doesn't know the MAC algorithm to correctly parse the packet.
MS-RTR Authentication Data: The message digest used from the output
of the Message Authentication Code (MAC) algorithm. The entire Map-
Notify payload is authenticated with this field preset to 0. After
the MAC is computed, it is placed in this field. Implementations of
this specification MUST support HMAC-SHA-1-96 [RFC2404] and SHOULD
support HMAC-SHA-256-128 [RFC6234].
For a full description of all fields in the Map-Notify message refer
to Map-Notify section in the main LISP draft [LISP].
4.5. LISP Data-Map-Notify Message
When an RTR receives a Map-Notify message, it has to relay that
message to the registering LISP device. After processing the Map-
Notify message as described in Section 5.3, the RTR encapsulates the
Map-Notify in a LISP data header and sends it to the associated LISP
device. This Map-Notify inside a LISP data header is referred to as
a Data-Map-Notify message.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | IPv4 or IPv6 Header |
OH | (uses RLOC addresses) |
\ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Source Port = 4342 | Dest Port = xxxx |
UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | UDP Length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
L | LISP Header ~ |
I \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
S / | ~ LISP Header |
P +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | IPv4 or IPv6 Header |
IH | (uses RLOC or EID addresses) |
\ | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ | Source Port = 4342 | Dest Port = 4342 |
UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ | UDP Length | UDP Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LCM | LISP Map-Notify Message ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
LISP Data-Map-Notify Message
In a Data-Map-Notify, the outer header source RLOC is set to the
RTR's RLOC that was used in the associated Map-Register. This is
previously cached by the RTR. The outer header source port is set to
4342. The outer header destination RLOC and port are filled based on
the translated global RLOC and port of the registering LISP device
previously stored locally at the RTR. The inner header source
address is Map-Server's RLOC, and inner header source port is 4342.
The inner header destination address is set to the LISP device's
local RLOC also previously cached by the RTR (See Section 5.3 for
details.). The inner header destination port is 4342.
Since a Data-Map-Notify is a control message encapsulated in a LISP
data header, a special Instance ID is used as a signal for the xTR to
trigger processing of the control packet inside the data header. The
Instance ID value 0xFFFFFF is reserved for this purpose. The
Instance ID field in a Data-Map-Notify must be set to 0xFFFFFF.
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5. Protocol Operations
There are two main steps in the NAT traversal procedure. First, the
ETR's translated global RLOC must be discovered. Second, the NAT
translation table must be primed to accept incoming connections. At
the same time, the Map-Server and the RTR must be informed of the
ETR's translated global RLOC including the translated ephemeral port
number(s) at which the Map-Server and RTR can reach the LISP device.
5.1. xTR Processing
Upon receiving a new RLOC, an ETR first has to detect whether the new
RLOC is behind a NAT device. For this purpose the ETR sends an Info-
Request message to its Map-Server in order to discover the ETR's
translated global RLOC visible to the Map-Server. The ETR uses the
new RLOC as the source RLOC of the message. The Map-Server, after
authenticating the message, responds with an Info-Reply message. The
Map-Server includes the source RLOC and port from the Info-Request
message in the Global ETR RLOC Address and ETR UDP Port Number fields
of the Info-Reply. The Map Server also includes the destination RLOC
and port number of the Info-Request message in the MS RLOC Address
and MS UDP Port Number fields of the Info-Reply. In addition, the
Map-Server provides a list of RTR RLOCs that the ETR may use in case
it needs NAT traversal services. The source port of the Info-Reply
is set to 4342 and the destination port is copied from the source
port of the triggering Info-Request message.
Upon receiving the Info-Reply message, the ETR compares the source
RLOC and source port used for the Info-Request message with the
Global ETR RLOC Address and ETR UDP Port Number fields of the Info-
Reply message. If the two are not identical, the ETR concludes that
the new RLOC is behind a NAT and that it requires an RTR for NAT
traversal services in order to be reachable at that RLOC. An ETR
behind other stateful devices (e.g. stateful firewalls) may also use
an RTR and the procedure specified here for traversing the stateful
device. Detecting existence of such devices are beyond scope of this
document.
If there is no NAT on the path, the ETR registers to its Map-Server
as described in the main LISP draft [LISP].
5.1.1. ETR Registration
Once an ETR has detected that it is behind a NAT, based on local
policy the ETR selects one (or more) RTR(s) from the RTR RLOCs
provided in the Info-Reply and initializes state in the NAT device in
order to receive LISP data traffic on UDP port 4341 from the selected
RTR. To do so, the ETR sends a Map-Register encapsulated in an ECM
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header to the selected RTR(s). The Map-Register message is created
as specified in [LISP]. More specifically, the source RLOC of the
Map-Register is set to ETR's local RLOC, while the destination RLOC
is set to the ETR's Map-Server RLOC, and destination port is set to
4342. The ETR sets both the R bit and M bit in Map-Register to 1,
and it includes the selected RTR RLOC(s) as the locators in the Map-
Register message. The ETR must also set the I bit in the Map-
Register message to 1 and include its xTR-ID in the corresponding
field. In the ECM header of this Map-Register the source RLOC is set
to ETR's local RLOC and the source port is set to 4341, while the
destination RLOC is the RTR's RLOC and the destination port is set to
LISP control port 4342.
This ECM-ed Map-Register is then sent to the RTR. The RTR
reoriginates the Map-Register message and sends it to the associated
Map-Server. The RTR then encapsulates the corresponding Map-Notify
message in a LISP data header (Data-Map-Notify) and sends it back to
the xTR.
Upon receiving a Data-Map-Notify from the RTR, the ETR must strip the
outer LISP data header, and process the inner Map-Notify message as
described in [LISP]. Since outer header destination port in Data-
Map-Notify is set to LISP data port 4341, the Instance ID 0xFFFFFF in
the LISP header of the Data-Map-Notify is used by the ETR to detect
and process the Data-Map-Notify as a control message encapsulated in
a LISP data header. While processing the Data-Map-Notify, the xTR
also stores the RTR RLOC(s) as its data plane proxy, by storing a
default map-cache entry with the RTR RLOC(s) as its locator set. The
xTR may map the EID prefix 0/0 to this RTR RLOC(s). This results in
the xTR encapsulating all LISP data plane traffic to this RTR. At
this point the registration and state initialization is complete and
the xTR can use the RTR services. The state created in the NAT
device based on the ECM-ed Map-Register and corresponding Data-Map-
Notify is used by the xTR behind the NAT to send and receive LISP
control packets to/from the RTR, as well as for receiving LISP data
packets form the RTR.
If ETR receives a Data-Map-Notify with the I bit set, but with an
xTR-ID that is not equal to its local xTR-ID, it must log this as an
error. The ETR should discard such Data-Map-Notify message.
The ETR must periodically send ECM-ed Map-Register messages to its
RTR in order to both refresh its registration to the RTR and the Map-
Server, and as a keepalive in order to preserve the state in the NAT
device. Per recommendation in RFC 2663 [NAT] the period for sending
the keepalives can be set to default value of two minutes, however
since shorter timeouts may exist in some NAT deployments, the
interval for sending periodic ECM-ed Map-Registers must be
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configurable.
5.1.2. Map-Request and Map-Reply Handling
The ETR is in control of how to handle the Map-Requests and Map-
Replies. If the ETR wants the Map-Server to proxy-reply as described
in [LISP], it can register the RTR RLOC(s) as its locator via the
ECM-ed Map-Register message. In this case, if the proxy bit is set
in the Map-Register, the Map-Server will proxy reply with RTR's RLOC
to all Map-Requests for the ETR. As a result all traffic for the ETR
is encapsulated to its RTR(s).
If the proxy bit in the ECM-ed Map-Register message is not set, and
the ETR chooses to receive Map-Requests, the ETR must also initiate
and preserve state in the NAT device to receive LISP control packets
from its Map-Server. To do this, the ETR must periodically send
Info-Request messages to its Map-Server, and receive Info-Reply
messages from the Map-Server. Per recommendation in RFC 2663 [NAT]
the period for sending the keepalives can be set to default value of
two minutes, however since shorter timeouts may exist in some NAT
deployments, the interval for sending periodic Info-Requests must be
configurable. Furthermore, the ETR must also provide its Map-Server
with the ETR's translated global RLOC and port as visible to the Map-
Server. To do this, ETR includes a copy of the NAT LCAF section of
the Info-Reply message as one of the locators in its Map-Register
along with the RTR(s) RLOC(s). The ETR can set the priorities of RTR
RLOC(s) in this Map-Register to 255, resulting in the Map Server
encapsulating Map-Requests to the ETR's translated global RLOC and
port so it can receive them through the NAT device.
If an ETR behind a NAT chooses to receive Map-Requests from the Map-
Server, it must send Map-Replies to requesting ITRs. Note that this
configuration will result in excessive state in the NAT device and is
not recommended. ETR must include its RTR RLOC(s) as its locator set
in the Map-Reply in order to receive data through the NAT device.
When an ITR behind a NAT is encapsulating outbound LISP traffic, it
must use its RTR RLOC as the locator for all destination EIDs that it
wishes to send data to. As such, the ITR does not need to send Map-
Requests for the purpose of finding EID-to-RLOC mappings. For RLOC-
probing, the periodic ECM-ed Map-Register and Data-Map-Notify
messages between xTR and RTR can also serve the purpose of RLOC
probes. However, if RLOC-probing is used, no changes are required to
the RLOC-probing specification in [LISP], and the LISP device only
needs to probe the RTR's RLOC.
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5.1.3. xTR Sending and Receiving Data
When a Map-Request for a LISP device behind a NAT is received by its
Map-Server or the LISP device itself, the Map-Server, or the LISP
device (ETR), responds with a Map-Reply including RTR's RLOC as the
locator for the requested EID. As a result, all LISP data traffic
destined for the ETR's EID behind the NAT is encapsulated to its RTR.
The RTR re-encapsulates the LISP data packets to the ETR's translated
global RLOC and port number so the data can pass through the NAT
device and reach the ETR. As a result the ETR receives LISP data
traffic with outer header destination port set to 4341 as specified
in [LISP].
For sending outbound LISP data, an ITR behind a NAT must use the RTR
RLOC as the locator for all EIDs that it wishes to send data to
according to the installed default map-cache entry. The ITR then
encapsulates the LISP traffic in a LISP data header with outer header
destination set to RTR RLOC and outer header destination port set to
4341. This may create a secondary state in the NAT device. ITR must
set the outer header source port in all egress LISP data packets to a
random but static port number in order to avoid creating excessive
state in the NAT device.
If the ITR and ETR of a site are not collocated, the RTR RLOC must be
configured in the ITR via an out-of-band mechanism. Other procedures
specified here would still apply.
5.2. Map-Server Processing
Upon receiving an Info-Request message a Map-Server first verifies
the authenticity of the message. Next the Map-Server creates an
Info-Reply message and copies the source RLOC and port number of the
Info-Request message to the Global ETR RLOC Address and ETR UDP Port
Number fields of the Info-Reply message. The Map-Server also
includes a list of RTR RLOCs that the ETR may use for NAT traversal
services. The Map-Server sends the Info-Reply message to the ETR, by
setting the destination RLOC and port of the Info-Reply to the source
RLOC and port of the triggering Info-Request. The Map-Server sets
the source port of the Info-Reply to 4342.
Upon receiving a Map-Register message with the M bit set, the Map-
Server processes the Map-Register message and generates the resulting
Map-Notify as described in [LISP]. If the R bit is set in the Map-
Register message and the Map-Server has a shared secret configured
with the RTR sending the Map-Register, the Map-Server also sets the R
bit in the Map-Notify and includes the MS-RTR authentication data.
See Security Considerations Section for more details. If the I bit
is set in the Map-Register message, the Map-Server also locally
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stores the xTR-ID from the Map-Register, and sets the I bit in the
corresponding Map-Notify message and includes the same xTR-ID in the
Map-Notify. The Map-Notify is sent to the RTR sending the
corresponding Map-Register.
If a Map-Server is forwarding Map-Requests to an ETR which has
registered its RLOC in a NAT LCAF, Map-Server must use the ETR Global
RLOC Address and ETR UDP Port as the destination RLOC and port for
outer header of the encapsulated Map-Requests. If more than one NAT
LCAF is registered for the same EID prefix, the Map-Server must use
the NAT LCAF corresponding to the RLOC of this Map-Server.
5.3. RTR Processing
Upon receiving an ECM-encapsulated Map-Register, the RTR creates a
map-cache entry for the EID-prefix that was specified in the Map-
Register message. The RTR stores the outer header source RLOC and
outer header source port, the outer header destination RLOC (RTR's
own RLOC), the inner header source RLOC (xTR's local RLOC), the
xTR-ID, and the nonce field of the Map-Register in this local map-
cache entry. The outer header source RLOC and outer header source
port is the ETR's translated global RLOC and port number visible to
the RTR. Once the registration process is complete, this map-cache
entry can be used to send LISP data traffic to the ETR. The inner
header destination RLOC is the RTR's RLOC, and the inner header
source RLOC is the ETR's local RLOC behind the NAT, and the RTR can
later use these fields as the inner header source RLOC and
destination RLOC correspondingly, for sending data-encapsulated
control messages (Data-Map-Notify) back to the ETR. The nonce field
is used for security purposes and is matched with the nonce field in
the corresponding Map-Notify message. This map-cache entry is stored
as an "unverified" mapping, until the corresponding Map-Notify
message is received.
After filling the local map-cache entry, the RTR strips the outer
header and extracts the Map-Register message, re-originates the
message by rewriting the source RLOC of the Map-Register to RTR's
RLOC, and sends the Map-Register to destination Map-Server.
Map-Server responds with a Map-Notify message to the RTR.
Upon receiving a Map-Notify message from the Map-Server, if the R bit
in Map-Notify is set to 1, RTR uses the MS-RTR Key ID to verify the
MS-RTR Authentication Data included in the Map-Notify. If the MS-RTR
authentication fails, the RTR must drop the packet. Once the
authenticity of the message is verified, RTR can confirm that the
Map-Register message for the ETR with the matching xTR-ID was
accepted by the Map-Server. At this point the RTR can change the
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state of the associated map-cache entry to verified for the duration
of the Map-Register TTL.
The RTR then uses the information in the associated map-cache entry
to create a Data-Map-Notify message according to the following
procedure: RTR rewrites the inner header destination RLOC of the Map-
Notify message to ETR's local RLOC. Inner header destination port is
4342. The RTR encapsulates the Map-Notify in a LISP data header,
where the outer header destination RLOC and port number are set to
the ETR's translated global RLOC and port number. If more than one
ETR translated RLOC and port exists in the map-cache entry for the
same EID prefix specified in the Map-Notify, the RTR can use the
xTR-ID from the Map-Notify to identify which ETR is the correct
destination for the Data-Map-Notify. The RTR sets the outer header
source RLOC to RTR's RLOC from the map-cache entry and the outer
header source port is set to 4342. The RTR also sets the Instance ID
field in the LISP header of the Data-Map-Notify to 0xFFFFFF. The RTR
then sends the Data-Map-Notify to the ETR.
If the R bit is set to 0, and the RTR has a shared key configured
locally with the sending Map-Server, the RTR must drop the packet.
If the R bit is set to 0, and the RTR does not have a shared key
configured with the associated Map-Server, according to local policy,
the RTR may drop the packet. If the Map-Notify with R bit set to 0
is processed, the RTR must match the nonce field from this Map-Notify
with the nonce stored in the local map-cache entry with the matching
xTR-ID. If the nonces do not match, the RTR must drop the packet.
5.3.1. RTR Data Forwarding
For all LISP data packets encapsulated to RTR's RLOC and outer header
destination port 4341, the RTR first verifies whether the source or
destination EID is a previously registered EID. If so, the RTR must
process the packet according to the following. If the destination or
source EID is not a registered EID, the RTR can drop or process the
packet based on local policy.
In the case where the destination EID is a previously registered EID,
the RTR must strip the LISP data header and re-encapsulate the packet
in a new LISP data header. The outer header RLOCs and UDP ports are
then filled based on the matching map-cache entry for the associated
destination EID prefix. The RTR uses the RTR RLOC from the map-cache
entry as the outer header source RLOC. The outer header source port
is set to 4342. The RTR sets the outer header destination RLOC and
outer header destination port based on the ETR translated global RLOC
and port stored in the map-cache entry. Then the RTR forwards the
LISP data packet.
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In the case where the source EID is a previously registered EID, the
RTR process the packet as if it is a Proxy ETR (PETR). The RTR must
strip the LISP data header, and process the packet based on its inner
header destination address. The packet may be forwarded natively, it
may be LISP encapsulated to the destination ETR, or it may trigger
the RTR to send a LISP Map-Request.
5.4. Example
What follows is an example of an ETR initiating a registration of a
new RLOC to its Map-Server, when there is a NAT device on the path
between the ETR and the Map-Server.
In this example, the ETR (site1-ETR) is configured with the local
RLOC of 192.168.1.2. The NAT's global (external) addresses are from
2.0.0.1/24 prefix. The Map-Server is at 3.0.0.1. And one potential
RTR has an IP address of 1.0.0.1. The site1-ETR has an EID Prefix of
128.1.0.0/16.
An example of the registration process follows:
1. The Site1-ETR receives the private IP address, 192.168.1.2 as
its RLOC via DHCP.
2. The Site1-ETR sends an Info-Request message with the destination
RLOC of the Map-Server, 3.0.0.1, and source RLOC of 192.168.1.2.
This packet has the destination port set to 4342 and the source
port is set to (for example) 5001.
3. The NAT device translates the source IP from 192.168.1.2 to
2.0.0.1, and source port to (for example) 20001 global ephemeral
source port.
4. The Map-Server receives and responds to this Info-Request with
an Info-Reply message. This Info-Reply has the destination
address set to ETR's translated address of 2.0.0.1 and the
source address is the Map-Server's RLOC, namely 3.0.0.1. The
destination port is 20001 and the source port is 4342. Map-
Server includes a copy of the source address and port of the
Info-Request message (2.0.0.1:20001), and a list of RTR RLOCs
including RTR RLOC 1.0.0.1 in the Info-Reply contents.
5. The NAT translates the Info-Reply packet's destination IP from
2.0.0.1 to 192.168.1.2, and translates the destination port from
20001 to 5001, and forwards the Info-Reply to site1-ETR at
192.168.1.2.
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6. The Site1-ETR detects that it is behind a NAT by comparing its
local RLOC (192.168.1.2) with the Global ETR RLOC Address in the
Info-Reply (2.0.0.2) . Then site1-ETR picks the RTR 1.0.0.1
from the list of RTR RLOCs in the Info-Reply. ETR stores the
RTR RLOC in a default map-cache entry to periodically send
ECM-ed Map-Registers to.
7. The ETR sends an ECM encapsulated Map-Register to RTR at
1.0.0.1. The outer header source RLOC of this Map-Register is
set to 192.168.1.2 and the outer header source port is set to
4341. The outer header destination RLOC and port are set to RTR
RLOC at 1.0.0.1 and 4342 respectively. The inner header
destination RLOC is set to ETR's Map-Server 3.0.0.1, and the
inner header destination port is set to 4342. The inner header
source RLOC is set to ETR's local RLOC 192.168.1.2. In the Map-
Register message the R bit is set to 1, and the RTR RLOC 1.0.0.1
appears as the locator set for the ETR's EID prefix
(128.1.0.0/16). In this example ETR also sets the Proxy bit in
the Map-Register to 1, and sets I bit to 1, and includes its
xTR-ID in the Map-Register.
8. The NAT translates the source RLOC in the ECM header of the Map-
Register, by changing it from 192.168.1.2 to 2.0.0.2, and
translates the source port in the ECM header from 4341 to (for
example) 20002, and forwards the Map-Register to RTR.
9. The RTR receives the Map-Register and creates a map-cache entry
with the ETR's xTR-ID, EID prefix, and the source RLOC and port
of the ECM header of the Map-Register as the locator
(128.1.0.0/16 is mapped to 2.0.0.2:20002). RTR also caches the
inner header source RLOC of the Map-Register namely 192.168.1.2,
and the outer header destination RLOC of the ECM header in the
Map-Register (this would be RTR's RLOC 1.0.0.1 ) to use for
sending back a Data-Map-Notify. RTR then removes the outer
header, re-writes the source RLOC of the Map-Register message to
its own RLOC 1.0.0.1 and forwards the Map-Register to the
destination Map-Server.
10. The Map-Server receives the Map-Register and processes it
according to [LISP]. Since the R bit is set in the Map-Register
and Map-Server has a shared secret with the sending RTR, after
registering the ETR, Map-Server responds with a Map-Notify with
the R bit set and including the MS-RTR authentication data.
Since the I bit is set in the Map-Register, the Map-Server also
sets the I bit in the Map-Notify and copies the xTR-ID from the
Map-Register to the Map-Notify. The source address of this Map-
Notify is set to 3.0.0.1. The destination is RTR 1.0.0.1, and
both source and destination ports are set to 4342.
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11. The RTR receives the Map-Notify and verifies the MS-RTR
authentication data. The RTR data-encapsulates the Map-Notify
and sends the resulting Data-Map-Notify to site1-ETR with a
matching xTR-ID. The outer header source RLOC and port of the
Data-Map-Notify are set to 1.0.0.1:4342. The outer header
destination RLOC and port are retrieved from previously cached
map-cache entry in step 9 namely 2.0.0.2:20002. RTR also sets
the inner header destination address to site1-ETR's local
address namely 192.168.1.2. RTR sets the Instance ID in the
LISP header to 0xFFFFFF. At this point RTR marks ETR's EID
prefix as "Registered" status and forwards the Data-Map-Notify
to ETR.
12. The NAT device translates the destination RLOC and port of the
Data-Map-Notify to 192.168.1.2:4341 and forwards the packet to
ETR.
13. The Site1-ETR receives the packet with a destination port 4341,
and processes the packet as a control packet after observing the
Instance ID value 0xFFFFFF in the LISP header. At this point
ETR's registration to the RTR is complete.
Assume a requesting ITR in a second LISP (site2-ITR) site has an RLOC
of 74.0.0.1. The following is an example process of an EID behind
site2-ITR sending a data packet to an EID behind the site1-ETR:
1. The ITR sends a Map-Request which arrives via the LISP mapping
system to the ETR's Map Server.
2. The Map-Server sends a Map-Reply on behalf of the ETR, using the
RTR's RLOC (1.0.0.1) in the Map-Reply's Locator Set.
3. The ITR encapsulates a LISP data packet with ITR's local RLOC
(74.0.0.1) as the source RLOC and the RTR as the destination RLOC
(1.0.0.1) in the outer header.
4. The RTR decapsulates the packet, evaluates the inner header
against its map-cache and then re-encapsulates the packet. The
new outer header's source RLOC is the RTR's RLOC 1.0.0.1 and the
new outer header's destination RLOC is the Global NAT address
2.0.0.2. The destination port of the packet is set to 20002
(discovered above during the registration phase) and the source
port is 4342.
5. The NAT translates the LISP data packet's destination IP from to
2.0.0.2 to 192.168.1.2, and translates the destination port from
20002 to 4341, and forwards the LISP data packet to the ETR at
192.168.1.2.
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6. For the reverse path the ITR uses its local map-cache entry with
the RTR RLOC as the default locator and encapsulates the LISP
data packets using RTR RLOC, and 4341 as destination RLOC and
port. The ITR must pick a random source port to use for all
outbound LISP data traffic in order to avoid creating excessive
state in the NAT.
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6. Security Considerations
By having the RTR relay the ECM-ed Map-Register message from an ETR
to its Map-Server, the RTR can restrict access to the RTR services,
only to those ETRs that are registered with a given Map-Server. To
do so, the RTR and the Map-Server may be configured with a shared key
that is used to authenticate the origin and to protect the integrity
of the Map-Notify messages sent by the Map Server to the RTR. This
prevents an on-path attacker from impersonating the Map-Server to the
RTR, and allows the RTR to cryptographically verify that the ETR is
properly registered with the Map-Server.
Having the RTR re-encapsulate traffic only when the source or the
destination are registered EIDs, protects against the adverse use of
an RTR for EID spoofing.
Upon receiving a Data-Map-Notify, an xTR can authenticate the origin
of the Map-Notify message using the key that the ETR shares with the
Map-Server. This enables the ETR to verify that the ECM-ed Map-
Register was indeed forwarded by the RTR to the Map-Server, and was
accepted by the Map-Server.
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7. Acknowledgments
The authors would like to thank Noel Chiappa, Alberto Rodriguez
Natal, Lorand Jakab, and Albert Cabellos for their feedback and
helpful suggestions.
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8. IANA Considerations
This document does not request any IANA actions.
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9. Normative References
[LCAF] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
Address Format (LCAF)", draft-farinacci-lisp-lcaf-06 (work
in progress), October 2011.
[LISP] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
"Locator/ID Separation Protocol (LISP)",
draft-ietf-lisp-14 (work in progress), June 2011.
[NAT] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations", Request
for Comments: 2663, August 1999.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC4632] Fuller, V. and T. Li, "Classless Inter-domain Routing
(CIDR): The Internet Address Assignment and Aggregation
Plan", BCP 122, RFC 4632, August 2006.
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Authors' Addresses
Vina Ermagan
Cisco Systems, Inc.
Email: vermagan@cisco.com
Dino Farinacci
Cisco Systems, Inc.
Email: dino@cisco.com
Darrel Lewis
Cisco Systems, Inc.
Email: darlewis@cisco.com
Jesper Skriver
Cisco Systems, Inc.
Email: jesper@cisco.com
Fabio Maino
Cisco Systems, Inc.
Email: fmaino@cisco.com
Chris White
Logicalelegance, Inc.
Email: chris@logicalelegance.com
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