NAT traversal for LISP
draft-ermagan-lisp-nat-traversal-19
Network Working Group V. Ermagan
Internet-Draft Google
Intended status: Experimental D. Farinacci
Expires: November 8, 2021 lispers.net
D. Lewis
F. Maino
M. Portoles
Cisco Systems, Inc.
J. Skriver
Arista
C. White
Logicalelegance, Inc.
A. Lopez
A. Cabellos
UPC/BarcelonaTech
May 7, 2021
NAT traversal for LISP
draft-ermagan-lisp-nat-traversal-19
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 the
LISP Re-encapsulating Tunnel Router (RTR) network element, which acts
as an anchor point in the data plane, forwarding traffic from
unmodified LISP devices through the NAT.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on November 8, 2021.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definition of Terms . . . . . . . . . . . . . . . . . . . . . 3
3. Basic Overview . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. LISP NAT Traversal Overview . . . . . . . . . . . . . . . 6
4. LISP RTR Message Details . . . . . . . . . . . . . . . . . . 7
4.1. Info-Request Message . . . . . . . . . . . . . . . . . . 7
4.2. LISP Info-Reply . . . . . . . . . . . . . . . . . . . . . 9
4.3. LISP Map-Register Message . . . . . . . . . . . . . . . . 11
4.4. LISP Map-Notify . . . . . . . . . . . . . . . . . . . . . 12
4.5. LISP Data-Map-Notify Message . . . . . . . . . . . . . . 13
5. Protocol Operations . . . . . . . . . . . . . . . . . . . . . 15
5.1. xTR Processing . . . . . . . . . . . . . . . . . . . . . 15
5.1.1. ETR Registration . . . . . . . . . . . . . . . . . . 16
5.1.2. Map-Request and Map-Reply Handling . . . . . . . . . 17
5.1.3. xTR Sending and Receiving Data . . . . . . . . . . . 18
5.2. Map-Server Processing . . . . . . . . . . . . . . . . . . 18
5.3. RTR Processing . . . . . . . . . . . . . . . . . . . . . 19
5.3.1. RTR Data Forwarding . . . . . . . . . . . . . . . . . 21
5.4. Multi-homed xTRs . . . . . . . . . . . . . . . . . . . . 22
5.5. Updating contents of EID-to-RLOC Mappings . . . . . . . . 23
5.6. Example . . . . . . . . . . . . . . . . . . . . . . . . . 24
6. Security Considerations . . . . . . . . . . . . . . . . . . . 27
6.1. Acknowledgments . . . . . . . . . . . . . . . . . . . . . 27
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
8. Normative References . . . . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
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1. Introduction
The Locator/ID Separation Protocol [I-D.ietf-lisp-rfc6830bis]
[I-D.ietf-lisp-rfc6833bis]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. Depending on the type of the NAT
device, this mapping state may be address and port dependent. In
other words, the mapping state in the NAT device may be associated
with the 5 tuple that forms a specific flow, preventing incoming
traffic from any LISP router other than the one associated with the 5
tuple. A NAT traversal mechanism is needed to make the LISP device
behind a NAT reachable.
This document briefly discusses available NAT traversal options, and
then it introduces in detail 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
[I-D.ietf-lisp-rfc6830bis] 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
[I-D.ietf-lisp-rfc6833bis] is on the public side of the NAT.
2. Definition of Terms
LISP Info-Request: A LISP control message sent by a LISP device to
its Map-Server.
LISP Info-Reply: A LISP control message sent by a Map Server to a
LISP device in response to an Info-Request control message.
LISP Re-encapsulating Tunnel Router (RTR): An RTR is a re-
encapsulating LISP Router (see [I-D.ietf-lisp-rfc6830bis]). One
function that an RTR provides is enabling a LISP device to
traverse NATs.
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LISP Data-Map-Notify: A LISP Map-Notify message encapsulated in a
LISP data header.
LISP xTR-ID A 128-bit field that, together with a site-ID, 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. A value of all zeros
indicate the xTR-ID is unspecified.
LISP site-ID A 64-bit field that, together with a xTR-ID, can be
appended at the end of a Map-Register or Map-Notify message. A
site-ID is used as a unique identifier of a group of xTRs
belonging to the same site. A value of 0 indicate the site-ID is
unspecified.
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
are not modified by the NAPT.
In this document the general term NAT is used to refer to both Basic
NAT and NAPT.
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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. A NAT traversal mechanism for LISP-
MN is also proposed in [NAT-MN].
For definitions of other terms, notably Map-Request, Map-Reply,
Ingress Tunnel Router (ITR), and Egress Tunnel Router (ETR), please
consult the LISP specification [I-D.ietf-lisp-rfc6833bis].
3. Basic Overview
There are a variety of NAT devices and a variety of network
topologies utilizing NAT devices in deployments. Most NAT devices
deployed today are designed primarily around the client/server
paradigm, where client machines inside a private network initiate
connections to public servers with public IP addresses. As such, any
protocol requiring a device or host in a private network behind a NAT
to receive packets or accept sessions from destinations without first
initiating a session or sending packets towards those destinations,
will be challenged by deployed NAT devices.
NAT devices are loosely classified based on how restrictive they are.
These classifications are essentially identifying the type of mapping
state that the NAT device is requiring to allow incoming traffic.
For instance, the mapping state may be end-point independent: once
device A inside the private network sends traffic to a destination
outside, a mapping state in the NAT is created that only includes
information about device A, namely its IP address and perhaps its
port number. Once this mapping is established in the NAT device, any
external device with any IP address could send packets to device A.
More restrictive NAT devices could include the 5 tuple information of
the flow as part of the mapping state, in other words, the mapping
state in the NAT is dependent upon Source IP and Port, as well as
destination IP and port (symmetric NAT or Endpoint-dependent NAT).
Such a NAT only allows traffic from the specified destination IP and
port to reach the specified source device on the specified source
port. Traffic with a different 5 tuple signature will not be allowed
to pass. In general, in the case of less restrictive NATs it may be
possible to eventually establish direct peer-to-peer connections, by
means of various hole punching techniques and initial rendezvous
servers. However, in the case of symmetric NATs or NATs with
endpoint-address-and-port-dependent mappings, direct connection may
prove impossible. In such cases a relay device is required that is
in the public Network and can relay packets between the two
endpoints.
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Various methods have been designed to address NAT traversal
challenges, mostly in the context of peer-to-peer applications and
protocols. Among these, the Interactive Connectivity Establishment
(ICE) [ICE] seems the most comprehensive, which defines a protocol
that leverages other protocols such as Session Traversal Utilities
for NAT(STUN) [STUN] and Traversal Using Relays around NAT (TURN)
[TURN], as well as a rendezvous server to identify and exchange a
list of potential transport (IP and Port) addresses between the two
endpoints. All possible pairs of transport addresses are
exhaustively tested to find the best possible option for
communication, preferring direct connection to connections using a
relay. In the case of most restrictive NATs, ICE leads to use of
TURN servers as relay for the traffic. TURN requires a list of
allowed peer IP addresses defined as permissions, before allowing a
peer to use the relay server to reach a TURN client.
Common NAT traversal techniques such as ICE generally assume bi-
directional traffic with the same 5 tuple. LISP, however, requires
traffic to use destination UDP port 4341, without specifying the
source port. As a result, LISP traffic is generally uni-directional.
This means that, in the case of symmetric or endpoint-address-and-
port-dependent mapping NATs, even when an outgoing mapping is
established, still incoming traffic may not match the established
mapping and will not be allowed to pass. As a result, while ICE may
be used to traverse less restrictive NATs, use of standard TURN
servers as relays to traverse symmetric NATs for LISP protocol is not
possible. The rest of this document specifies a NAT traversal
technique for the LISP protocol that enables LISP protocol to
traverse multiple types of NATs including symmetric NATs.
3.1. LISP NAT Traversal 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. The NAT likely
has a restrictive translation table and forwarding policy, requiring
outbound packets to create state before the NAT accepts inbound
packets. Second, LISP protocol requires an xTR to receive traffic on
a specific UDP port 4341, so the random UDP port allocated by the NAT
on its public side to associate with a xTR behind the NAT can not be
used by other xTRs to send LISP traffic to. 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
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NAT. To do this, an ETR queries its Map-Server to discover the ETR's
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 LISP Re-encapsulating Tunnel Router (RTR) entity as an
anchor point for sending and receiving data plane 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 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. The ETR 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-encapsulate and forward the
ETR's traffic via the existing NAT state to the ETR.
Outbound LISP data traffic from the xTR should also be encapsulated
to the RTR, where the RTR de-capsulates the LISP packets, and then
re-encapsulates them or forwards them natively depending on their
destination.
In the next sections these procedures are discussed in more detail.
This document does not support different xTR-ID registering the same
EID prefix and using the same set of RTRs. Future versions of this
spec will explore this use-case.
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.
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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
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. Future version of this document will
discuss anti-replay mitigation mechanisms
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Descriptions for other fields can be found in the Map-Register
section of [I-D.ietf-lisp-rfc6833bis]. Field descriptions for the
LCAF AFI = 0 can be found in the LISP LCAF RFC [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 RFC [LCAF] .
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4.3. LISP Map-Register Message
The third bit after the Type field in the Map-Register message is
allocated as "I" bit. I bit indicates that a 128 bit xTR-ID and a 64
bit site-ID field are present at the end of the Map-Register message.
If an xTR is configured with an xTR-ID or site-ID, it MUST set the I
bit to 1 and include its xTR-ID and site-ID in the Map-Register
messages it generates. If either the xTR-ID or site-ID is not
configured an all zeros value is encoded for whichever ID that is not
configured.
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. A value
of all zeros indicate that an xTR-ID is not specified, though encoded
in the message. This is useful in the case where a site-ID is
specified, but no xTR-ID is configured. When a Map-Server receives a
Map-Register with an xTR-ID specified (I bit set and xTR-ID has a
non-zero value), 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.
site-ID is a 64 bit field at the end of the Map-Register message,
following the xTR-ID. site-ID is used by the Map-Server receiving the
Map-Register message to identify which xTRs belong to the same site.
A value of 0 indicate that a site-ID is not specified, though encoded
in the message. When a Map-Server receives a Map-Register with a
site-ID specified (I bit set and site-ID has non-zero value), it must
copy the site-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 site-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)
[I-D.ietf-lisp-rfc6833bis]. The 6th bit in the ECM LISP header is
allocated as the "R" bit. The R bit indicates that the encapsulated
Map-Register is to be processed by an RTR. The 7th bit in the ECM
header is allocated as the "N" bit. The N bit indicates that this
Map-Register is being relayed by an RTR. When an RTR relays the ECM-
ed Map-Register to a Map-Server, the N bit must be set to 1.
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
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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 and
64 bit site-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 and site-ID). A Map-Server MUST set the I bit in a
Map-Notify and include the xTR-ID and/or site-ID of the intended
recipient xTR if the associated Map-Register has an xTR-ID and/or
site-ID specified, or when the Map-Server has previously cached an
xTR-ID and/or site-ID for the destination xTR.
A LISP device that sends a Map-Notify to an RTR must encapsulate the
Map-Notify message using an ECM. The 6th bit in the ECM LISP header,
allocated as the "R" bit, must be set when the encapsulated Map-
Notify is to be processed by an RTR. If the S bit is also set in the
Map-Notify ECM header, it indicates that additional MS-RTR
authentication data is included after the LISP header in the ECM. If
the I bit is also set in the Map-Notify, the xTR-ID and site-ID
fields are included in the Map-Notify. If a Map-Server receiving an
ECM-ed Map-Register has a shared key associated with the sending RTR,
it must generate a Map-Notify message with the S bit in the ECM
header 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| AD Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MS-RTR Key ID | MS-RTR Auth. Data Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ MS-RTR Authentication Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Changes to LISP Map-Notify Message
AD Type: 2 (RTR Authentication Data)
MS-RTR Key ID: A configured ID to find the configured Message
Authentication Code (MAC) algorithm and key value used for the
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authentication function. See [I-D.ietf-lisp-rfc6833bis] section 12.5
for code point 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. 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 [I-D.ietf-lisp-rfc6833bis].
The outer header source RLOC of the ECM is set to the xTR's Map-
Server RLOC, and the outer header source port is set to 4342. The
outer header destination RLOC and port are set to RTR's RLOC and 4342
respectively. The inner header source RLOC is set to the xTR's Map-
Server RLOC, and the inner source port is set to 4342. The inner
header destination RLOC is set to the LISP device's local RLOC copied
from the Map-Register, and inner header destination port is set to
4342.
4.5. LISP Data-Map-Notify Message
When an RTR receives an ECM-ed Map-Notify message with R bit in the
ECM header set to 1, it has to relay the Map-Notify payload to the
registering LISP device. After removing the ECM header and
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 the LISP device's local RLOC.
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 RTR must be informed of the ETR's translated
global RLOC including the translated ephemeral port number(s) at
which the RTR can reach the LISP device.
5.1. xTR Processing
Upon receiving a new local 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 as it is visible to the Map-Server. The
ETR uses its new local 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
its new local 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 statefull devices (e.g. statefull firewalls) may also
use an RTR and the procedure specified here for traversing the
statefull device. Detecting existence of such devices are beyond
scope of this document.
It is worth noting that a STUN server can also be used to do NAT
detection and to discover the NAT-translated public IP address and
port number for the ETR behind NAT. If a STUN server is used, list
of RTR devices that can be used by the xTR for NAT traversal must be
provisioned to the xTR via other means which are outside the scope of
this document.
If there is no NAT on the path identified by an info-Request and an
Info-Reply, the ETR registers the associated RLOC with its Map-Server
as described in [I-D.ietf-lisp-rfc6833bis].
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A device that is not behind a NAT can still choose to use RTR as an
anchor point. In some deployments, devices can roam from NATed
connections to non-NATed connections. In such scenarios, the
deployer may choose to always use an RTR, thus avoiding frequent
notifications of RLOC changes. The main disadvantage of this policy
is that RTRs may increase path length.
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
header to the selected RTR(s). The Map-Register message is created
as specified in [I-D.ietf-lisp-rfc6833bis]. 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 the P bit (proxy Map-Reply) and
the M bit (want-Map-Notify) in Map-Register to 1, and it includes the
selected RTR RLOC(s) as the locators in the Map-Register message.
The ETR can also include its local RLOCs as locators in the Map-
Register, including weight and priorities, while setting the R bit to
0 for each local RLOC. This can be used by the RTR for load
balancing when forwarding data to a multi-homed xTR behind a NAT.
The R bit is set to 1 for all RTR locators included in the Map-
Register. The ETR must also set the I bit in the Map-Register
message to 1 and include its xTR-ID and site-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. The R bit in the ECM header is also set to
1, to indicate that this EDCM-ed Map-Register is to be processed by
an RTR.
This ECM-ed Map-Register is then sent to the RTR. The RTR removes
the ECM header, encapsulates the new Map-Register in a new ECM header
with R bit set to 0, 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 [I-D.ietf-lisp-rfc6833bis]. 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
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the Data-Map-Notify, the xTR also stores the RTR RLOC(s) as its data
plane proxy for the interface/RLOC behind the NAT.
If the xTR is not multi-homed, or if all its interfaces are behind
the NAT and will use the same RTR, then the xTR should map the EID
prefix 0/0 to this RTR RLOC(s) in its map-cache. This results in the
xTR encapsulating all LISP data plane traffic to this RTR, reducing
the state created in the NAT. Note that not installing the default
map-cache entry will lead to normal Map-Request and Map-Reply
messages for EID mapping lookups which is only supported if the xTR
has interfaces not behind NAT. If outgoing traffic is sent directly
to destinations without passing through the RTR, this will result in
additional state to be created in the NAT device.
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 a xTR-ID specified, but the
xTR-ID 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 keep alive in order to preserve the state in the NAT
device. RFC 2663 [NAT] points out that the period for sending the
keep alives 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 configurable.
5.1.2. Map-Request and Map-Reply Handling
To avoid the creation of extra status in the NAT devices due to the
Map-Replies send to requesting ITRs, the ETR set the proxy-bit of the
Map-Register to one in order the Map-Server proxy-reply the ETR as
described in [I-D.ietf-lisp-rfc6833bis]
When an ITR behind a NAT is encapsulating outbound LISP traffic, it
can 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 finding EID-to-RLOC mappings. However, if the ITR is
multihomed and has at least one interface not behind NAT, it can
choose to send Map-Requests. For this, the ITR specifies in the ITR-
RLOC field of the Map-Request the list of RLOCs that are not behind
NAT to receive the Map-Reply messages. It should be noted that
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sending packets directly to destination RLOCs through the interface
behind NAT will result in creating additional state in the NAT
device. Also, it should be noted that outgoing packets use a direct
path while the incoming packets are forwarded through an RTR.
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
[I-D.ietf-lisp-rfc6833bis], except that the LISP device behind a NAT
only needs to probe the RTR's RLOC.
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, the Map-Server 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 [I-D.ietf-lisp-rfc6830bis].
For sending outbound LISP data, an ITR behind a NAT SHOULD use the
RTR RLOC as the locator for all EIDs that it wishes to send data to
via the interface behind the NAT. 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 SHOULD 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
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RLOC and port of the triggering Info-Request. The Map-Server sets
the source port of the Info-Reply to 4342.
Upon receiving an ECM-ed Map-Register message with the N bit in the
ECM header set to 1, the Map-Server removes the ECM header and if the
M bit in the Map-Register is set, the Map-Server processes the Map-
Register message and generates the resulting Map-Notify as described
in [I-D.ietf-lisp-rfc6833bis]. The Map-Server encapsulates the Map-
Notify in an ECM header and sets the R bit in the ECM header to 1.
This indicates that the ECM-ed Map-Notify is to be processed by an
RTR. If the Map-Server has a shared secret configured with the RTR
sending the Map-Register, the Map-Server also sets the S bit in the
ECM header of the Map-Notify and includes the MS-RTR authentication
data after the ECM LISP header. See Security Considerations
Section for more details. If the I bit is set in the Map-Register
message, the Map-Server also locally stores the xTR-ID and site-ID
from the Map-Register, and sets the I bit in the corresponding Map-
Notify message and includes the same xTR-ID and site-ID in the Map-
Notify. The ECM-ed Map-Notify is then sent to the RTR sending the
corresponding Map-Register.
5.3. RTR Processing
Upon receiving an ECM-encapsulated Map-Register with the R bit set in
the ECM header, 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, the weight and priority
associated with the xTR's local RLOC that was used to send this Map-
Register if present, and the nonce field of the Map-Register in this
local map-cache entry. The RTR uses the inner header source address
to identify which xTR local RLOC (R bit =0) was used by the xTR to
send this Map-Register. 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 outer header destination RLOC is the RTR's RLOC used
by the ETR. The RTR can later use these fields as the source RLOC
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.
In the cases where the xTR has multiple RLOCs behind the NAT, and
requires the RTR to load balance the traffic across those interfaces,
the xTR must include the local RLOCs associated with each interface
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behind the NAT with the R bit in the locator record set to 0 in the
ECM-ed Map-Register sent to the RTR. The RTR uses the weight and
priority policies of the RLOCs with R=0 in the Map-Register to load
balance the traffic from the RTR to the xTR behind the NAT. The RTR
compares the RLOCs with the R bit set to 0 in the Map-Register to the
inner header source address of the Map-Register to find the matching
RLOC that the xTR used to send the Map-Register from. The RTR
associates the weight and priority policies of this local RLOC with
the NAT-translated RLOC and xTR-ID for this map-cache entry. For all
other local RLOCs included in the Map-Register, that the Map-Register
is not originating from, the RTR only updates previously cached
weight and priority policies if it already has those local RLOCs
previously stored for that EID prefix and xTR-ID. In other words,
the RTR only adds new local RLOCs and their weight and priority
policies to its cache if the Map-Register is actually originating
from that RLOC. The TTL for every map-cache is also only updated
when a Map-Register is originating from the same RLOC. However, the
weight and priorities of all previously cached local RLOCs will be
updated by every Map-Register, whether it is originating from that
RLOC or not. The xTR-ID is used to define the Merge domain for these
RLOCs. In other words, a Map-Register originating from a unique xTR-
ID will always overwrite previously stored policies for that xTR-ID.
However it does not modify in any way the policies indicated by any
other xTR-ID serving the same EID prefix. As a result, in the case
of a renumbering or xTR reboot, the xTR uses its unique xTR-ID to
send a new Map-Register, overwriting the previously stored policies
for that xTR. Using this method the xTR can immediately remove any
RLOCs from the RTR cache that are no longer active. In order to
implement this, the RTR must compare the list of local RLOCs in the
Map-Register (R=0) with the ones it has previously cached associated
with the same xTR-ID. If there is any RLOC previously cached that
does not appear in the newly received Map-Register, the RTR must
remove that RLOC together with the associated translated RLOC and
associated policies, because removal of a local (behind-the-NAT) RLOC
also invalidates the NAT-ed address associated with it. .
After filling the local map-cache entry, the RTR strips the outer
header and extracts the Map-Register message, encapsulated in a new
ECM header with the R bit set to 0, and N bit set to 1, and sends the
ECM-ed Map-Register to destination Map-Server.
Map-Server responds with a ECM-ed Map-Notify message to the RTR.
Upon receiving an ECM-ed Map-Notify message with R bit set to 1 in
the ECM header, if the S bit in ECM header is set to 1, RTR uses the
MS-RTR Key ID to verify the MS-RTR Authentication Data included after
the ECM header. If the MS-RTR authentication fails, the RTR must
drop the packet. Once the authenticity of the message is verified,
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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 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: 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 S bit is set to 0 in the ECM header of the Map-Notify, and the
RTR has a shared key configured locally with the sending Map-Server,
the RTR must drop the packet. If the S 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 S 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.
An RTR receiving an unsolicited Map-Notify for a registered EID
should check if any of the RTR's RLOCs is present in the received
record. If it does, the RTR rewrites the inner header destination
RLOC of the Map-Notify message to ETR's local RLOC obtained from the
associated map-cache entry of the EID. Then the RTR encapsulates and
forwards the Map-Notify in a LISP data packet as explained above. If
the record of the received Map-Notify doesn't contain any locator of
the RTR it should drop it and request the new mapping to the mapping
system. If the map reply record doesn't contain any RTR's locator,
the map-cache entry for the EID is replaced otherwise, the Map-Reply
is silently dropped.
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
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source EID is not a registered EID, the RTR can drop or process the
packets 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.
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. Multi-homed xTRs
In the case where an xTR has multiple interfaces and RLOCs, info-
Requests can be sent per each interface and NAT discovery is done per
each interface. NAT traversal is accomplished by following state and
processes described above per each interface/RLOC. In other words,
if multiple interfaces of an xTR are behind a NAT, the ECM-ed Map-
Register messages should be sent via each xTR interface behind NAT if
the xTR desires to receive traffic via that interface. This is
required to establish the state in the NAT device for that interface.
The M bit (want Map-Notify) must be set in ECM-ed Map-Register
messages sent from at least one of xTR interfaces behind the NAT. If
additional interfaces behind the NAT are using the same RTR for NAT
traversal, no Map-Notify processing is required for such interfaces
and M bit in Map-Register can be set to 0 for these to reduce
processing on the RTR and the Map-Server.
The RLOCs included in Map-Register messages when the xTR has multiple
interfaces SHOULD be the union of the locators (behind NAT or not)
resulting from the process defined above per each RLOC of the xTR,
according to the specifics of that interface (whether it is behind
the NAT or not).
In cases where some xTR interfaces are behind NAT while others are
not, ECM-ed Map-Register messages should be sent via interfaces
behind the NAT through the selected RTRs. xTR can receive traffic via
both types of interfaces by including the associated RLOCs (as well
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as the RTR RLOCs) in its ECM-ed Map-Register messages. The xTR can
choose to store RTR RLOCs in a default map-cache entry to forward all
the traffic through the RTR. If the xTR decides to populate its map-
cache, the xTR may configure the RTR as a proxy of the interface
behind NAT instead of sending the traffic directly to avoid generate
new state in the NAT device.
5.5. Updating contents of EID-to-RLOC Mappings
When an interface of a LISP device is configured with a new RLOC, it
needs to discover whether it is behind NAT by sending an Info-Request
message. If the modified interface was previously behind NAT and the
new RLOC is also behind NAT using the same RTRs association, the
cache of the RTR is updated through the ECM-ed Map-Register send by
the ETR. Otherwise, the change of the EID-to-RLOC mapping needs to
be notified to remote ITRs/PiTRs.
LISP defines several mechanisms to update mappings in the Data-Plane
[I-D.ietf-lisp-rfc6830bis] and in the control plane
[I-D.ietf-lisp-rfc6833bis]. Also an additional Control-Plane
mechanism based on the Publish/subscribe paradigm is specified in
[I-D.ietf-lisp-pubsub]. It is recommended to use
[I-D.ietf-lisp-pubsub] to notify mapping changes as it is a faster
mechanism and it avoids the temporal increase of the path length
associated with an ETR desassociating of an RTR.
In the case of Solicit-Map-Request mechanism, when an RTR receives a
Soliciting Map-Request for a cached EID-Prefix, the RTR should
request for the new mapping to the mapping system. If the Map-Reply
record contains any RTR's locator, the RTR silently discards the Map-
Reply; otherwise, the status of the map-cache entry used to punch the
NAT of the EID-Prefix would be lost. If the Map-Reply record doesn't
contain any RTR's locator, the RTR must update the cache entry.
A Map-Server receiving a new registration for an EID should send
unsolicited Map-Notify to the departure ETRs as specified in section
4.2.3 of [I-D.ietf-lisp-eid-mobility]. An RTR receiving an
unsolicited Map-Notify for a registered EID should process it as
described in Section 5.3.
An RTR that replace a registered cache entry through a Map-Request /
Map-Reply must forward traffic to the EID as described in
[I-D.ietf-lisp-rfc6833bis] until the map-cache entry expires.
Optionally, the RTR can send Data Driven SMRs to ITRs sending traffic
to the removed EID through the RTR as described in section 4.2.4 of
[I-D.ietf-lisp-eid-mobility].
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5.6. 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.
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.
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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 R bit in ECM header
is set to 1. 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 and the source port is set to (for example)
5002. In the Map-Register message 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 and site-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, adds a new ECM header with R=0, and N=1, and forwards
the Map-Register to the destination Map-Server.
10. The Map-Server receives the ECM-ed Map-Register with N bit set
to 1, removes the ECM header, and processes it according to
[I-D.ietf-lisp-rfc6833bis]. Since Map-Server has a shared
secret with the sending RTR, after registering the ETR, Map-
Server responds with a ECM-ed Map-Notify with the R bit and S
bit both set to 1 in the ECM header 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 and site-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 copied from the local source
address of the Map Register (192.168.1.2), and both source and
destination ports are set to 4342.
11. The RTR receives the ECM-ed 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
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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 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.
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
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outbound LISP data traffic in order to avoid creating excessive
state in the NAT.
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.
6.1. Acknowledgments
The authors would like to thank Noel Chiappa, Alberto Rodriguez
Natal, Lorand Jakab, Albert Cabellos, Dominik Klein, Matthias
Hartmann, and Michael Menth for their previous work, feedback and
helpful suggestions.
7. IANA Considerations
This document does not request any IANA actions.
8. Normative References
[I-D.ietf-lisp-eid-mobility]
Comeras, M. P., Ashtaputre, V., Moreno, V., Maino, F., and
D. Farinacci, "LISP L2/L3 EID Mobility Using a Unified
Control Plane", draft-ietf-lisp-eid-mobility-07 (work in
progress), January 2021.
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[I-D.ietf-lisp-pubsub]
Rodriguez-Natal, A., Ermagan, V., Cabellos, A., Barkai,
S., and M. Boucadair, "Publish/Subscribe Functionality for
LISP", draft-ietf-lisp-pubsub-08 (work in progress),
February 2021.
[I-D.ietf-lisp-rfc6830bis]
Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
Cabellos, "The Locator/ID Separation Protocol (LISP)",
draft-ietf-lisp-rfc6830bis-36 (work in progress), November
2020.
[I-D.ietf-lisp-rfc6833bis]
Farinacci, D., Maino, F., Fuller, V., and A. Cabellos-
Aparicio, "Locator/ID Separation Protocol (LISP) Control-
Plane", draft-ietf-lisp-rfc6833bis-30 (work in progress),
November 2020.
[ICE] Rosenberg, J., "Interactive Connectivity Establishment
(ICE)", RFC rfc5245, October 2008.
[LCAF] Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
Address Format (LCAF)", RFC 8060, December 2015.
[NAT] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations", RFC
2663, August 1999.
[NAT-MN] Klein, D., Hartmann, M., and M. Menth, "NAT traversal for
LISP mobile node, In Proceedings of the Re-Architecting
the Internet Workshop (ReARCH '10).", 2010.
[STUN] Rosenberg, J., Mahy, R., Matthews, P., and D. Wing,
"Session Traversal Utilities for NAT (STUN)", RFC rfc5389,
October 2008.
[TURN] Mahy, R., Matthews, P., and J. Rosenberg, "Traversal Using
Relays around NAT (TURN)", RFC rfc5766, April 2010.
Authors' Addresses
Vina Ermagan
Google
Email: ermagan@gmail.com
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Dino Farinacci
lispers.net
Email: farinacci@gmail.com
Darrel Lewis
Cisco Systems, Inc.
Email: darlewis@cisco.com
Fabio Maino
Cisco Systems, Inc.
Email: fmaino@cisco.com
Marc Portoles Comeras
Cisco Systems, Inc.
Email: mportole@cisco.com
Jesper Skriver
Arista
Email: jesper@skriver.dk
Chris White
Logicalelegance, Inc.
Email: chris@logicalelegance.com
Albert Lopez
UPC/BarcelonaTech
Email: alopez@ac.upc.edu
Albert Cabellos
UPC/BarcelonaTech
Email: acabello@ac.upc.edu
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