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Network Working Group                                       D. Farinacci
Intended status: Informational                          22 December 2023
Expires: 24 June 2024

 LISP NAT-Traversal Implementation Report


   This memo documents the implementation of LISP NAT
   traversal functionality.  The document describes message formats and
   protocol semantics necessary to interoperate with the implementation.
   This memo is not a standard and does not reflect IETF consensus.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   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 24 June 2024.

Copyright Notice

   Copyright (c) 2023 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 (
   license-info) in effect on the date of publication of this document.
   Please review these documents carefully, as they describe your rights
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   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Definition of Terms . . . . . . . . . . . . . . . . . . . . .   4
   3.  Overview  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Protocol Messages . . . . . . . . . . . . . . . . . . . . . .   6
   5.  xTR Map-Registering and Map-Server Proxy Map-Replying . . . .  10
   6.  Packet Flow from ITR-behind-NAT to RTR  . . . . . . . . . . .  11
   7.  Packet Flow from Remote ITR to RTR  . . . . . . . . . . . . .  11
   8.  Packet Flow from RTR to ETR-behind-NAT  . . . . . . . . . . .  11
   9.  Decentralized NAT . . . . . . . . . . . . . . . . . . . . . .  12
   10. Design Observations . . . . . . . . . . . . . . . . . . . . .  13
   11. Security Considerations . . . . . . . . . . . . . . . . . . .  14
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  14
   13. Code-Point Considerations . . . . . . . . . . . . . . . . . .  15
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     14.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Appendix A.  Acknowledgments  . . . . . . . . . . . . . . . . . .  17
   Appendix B.  Document Change Log  . . . . . . . . . . . . . . . .  17
     B.1.  Changes to draft-farinacci-lisp-lispers-net-nat-07  . . .  17
     B.2.  Changes to draft-farinacci-lisp-lispers-net-nat-06  . . .  17
     B.3.  Changes to draft-farinacci-lisp-lispers-net-nat-05  . . .  17
     B.4.  Changes to draft-farinacci-lisp-lispers-net-nat-04  . . .  18
     B.5.  Changes to draft-farinacci-lisp-lispers-net-nat-03  . . .  18
     B.6.  Changes to draft-farinacci-lisp-lispers-net-nat-02  . . .  18
     B.7.  Changes to draft-farinacci-lisp-lispers-net-nat-01  . . .  18
     B.8.  Changes to draft-farinacci-lisp-lispers-net-nat-00  . . .  18
     B.9.  Changes to draft-farinacci-lisp-simple-nat-06 . . . . . .  19
     B.10. Changes to draft-farinacci-lisp-simple-nat-05 . . . . . .  19
     B.11. Changes to draft-farinacci-lisp-simple-nat-04 . . . . . .  19
     B.12. Changes to draft-farinacci-lisp-simple-nat-03 . . . . . .  19
     B.13. Changes to draft-farinacci-lisp-simple-nat-02 . . . . . .  19
     B.14. Changes to draft-farinacci-lisp-simple-nat-01 . . . . . .  19
     B.15. Changes to draft-farinacci-lisp-simple-nat-00 . . . . . .  19
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   This document is an implementation report of a simple mechanism for
   LISP NAT-Traversal functionality developed by  Many
   ideas in the implementation are taken from
   [I-D.ermagan-lisp-nat-traversal].  This design was first implemented
   in the LISP implementation dating back to January 2014.

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   This implementation of NAT-traversal is not intended to interoperate
   with [I-D.ermagan-lisp-nat-traversal].  Parts of the implementation
   may interoperate with ITRs but likely to not
   interoperate with ETRs.  See details about this later
   in the document.

   The implementation takes an approach to use an RLOC-name set to
   "" in RLOC records to identify RLOC addresses of RTRs
   by Map-Registering xTRs and Map-Replying Map-Servers.  In
   releases prior to January 2024, a shortcut approach, not specified in
   [RFC9300] and [RFC9301], is used for identifying RTR RLOCs with a
   unicast priority of 254 and RLOC-name of "RTR".  This works among
   consenting implementations when no one else is using
   priority 254 in any other way, and therefore do not recommend it for
   arbitrary deployments.  This approach is in the process of being

   The procedures described in this document are performed by LISP
   compliant [RFC9300] [RFC9301] xTRs that reside on the private side of
   one or more NAT devices that connect them to the public side of the

   The solution is applicable to the following xTR deployments:

   *  A physical ITR/ETR device that is directly connected or multiple
      hops away from a NAT device.

   *  A LISP-MN acting as an ITR/ETR device on an cellular service where
      a mobile provider is providing a NAT function.

   *  A logical ITR/ETR that resides in a VM that is behind a NAT device
      managed by a hypervisor or cloud provider.

   *  A logical ITR/ETR that resides in a container where a NAT function
      is provided by the container service.

   *  The above xTR deployments can operate through multiple levels of

   *  The above deployments are also applicable to RTR and PxTR devices
      that may reside behind NAT devices.

   *  The lig [RFC6835] implementation uses the protocol
      messaging defined in this draft so any system behind a NAT (either
      running as a LISP xTR or not running LISP at all), can query the
      mapping system to obtain mappings for network maintenance and

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2.  Definition of Terms

   This document uses terms defined in [RFC9300] and [RFC9301].  The
   definitions are extended in this section to provide context and
   details for NAT-Traversal uses.

   Routing Locator (RLOC):  an RLOC address is a routable address on the
      public Internet.  It is used by LISP to locate where EIDs are
      topologically located and appears in the outer header of LISP
      encapsulated packets.  With respect to this design, an RLOC can be
      a private or public address.  Private RLOCs can be registered to
      the LISP mapping system so they can be used by other LISP xTRs
      which reside in the same private network.  Public RLOCs can be
      registered to the LISP mapping system and are used by LISP xTRs
      that are on the public side of the network.

   Network Address Translator (NAT):  is a router type device that
      isolates a private network from a public network.  The addresses
      used on the private side of a network are known as private
      addresses and are not routable on the public side of the network.
      Therefore, a NAT device must translate private addresses to public
      addresses.  In this document, xTRs that reside on the private side
      of the network use private RLOCs.  These RLOCs must be translated
      to public addresses so they can be registered in the LISP mapping
      system.  Details on NAT operation can be found in [RFC3022].

   Private RLOC:  is the IP address of the interface of an xTR that
      faces outbound towards a NAT device.  This address is typically
      translated to a public RLOC address before the packet appears on
      the public side of the network.

   Ephemeral Port:  is the UDP source port in a LISP data-plane or
      control-plane message.  This port number is typically translated
      by a NAT device when the packet goes from the private side of the
      NAT device to the public side of the network.

   Global RLOC:  is an address that has been translated by a NAT device.
      The Private RLOC is translated to a Global RLOC and is registered
      to the mapping system.  This RLOC will be the source address in
      LISP encapsulated packets on the public side of the network.

   Translated Port:  is the Ephemeral Port that is translated by a NAT
      device.  For an xTR outgoing packet, the source Ephemeral Port is
      translated to a source Translated Port seen by the public side of
      the network.  For an incoming packet, the NAT device translates
      the destination Translated Port to the destination Ephemeral Port.

   Re-encapsulating Tunnel Router (RTR):  is a LISP network element that

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      receives a LISP encapsulated packet, strips the outer header and
      prepends a new outer header.  With respect to this NAT-Traversal
      design, an ITR (either behind a NAT device or on the public
      network) encapsulates a packet to the RTR's RLOC address.  The RTR
      strips this ITR prepended header and then prepends a its own new
      outer header and sends packet to the RLOC address of an ETR that
      registered the EID that appears as the destination address from
      the inner header.

   NAT Info Cache:  is a data structure managed by an RTR to track xTR
      hostname, Global RLOC and Translated Port information.  The RTR
      uses this table so it knows what is the destination port to be
      used for LISP encapsulated packets that go through a NAT device.

   Address Family Identifier (AFI):  a term used to describe an address
      encoding in a packet [AFI] and [RFC1700].  All LISP control
      messages use AFI encoded addresses.  The AFI value is 16-bits in
      length and precedes all LISP encoded addresses.  In this document,
      the design calls for AFI encodings for IPv4 and IPv6 addresses as
      well as Distinguished-Name [I-D.ietf-lisp-name-encoding] and LCAF
      [RFC8060] address formats.

3.  Overview

   The following sequence of actions describes at a high-level how the implementation performs NAT-Traversal and is the basis
   for a simplified NAT-Traversal protocol design.

   1.   An xTR sends a Info-Request message to port 4342 to its
        configured Map-Servers so it can get a list of RTRs to be used
        for NAT-Traversal.

   2.   The Map-Servers return an Info-Reply message with the list of

   3.   The xTR then sends an Info-Request message to port 4341 to each

   4.   Each RTR caches the translated RLOC address and port in a NAT
        Info Cache.  At this point, the NAT device has created state to
        allow the RTR to send encapsulated packets from port 4341 to the
        translated port.

   5.   The RTR returns an Info-Reply message so the xTR can learn its
        translated Global RLOC address and Translated Port.

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   6.   The xTR registers its EID-prefixes with an RLOC-set that
        contains all its global RLOCs as well as the list of RTRs it has
        learned from Info-Reply messages.

   7.   The Map-Servers are configured to proxy Map-Reply for these
        registered EID-prefixes.

   8.   When a remote ITR sends a Map-Request for an EID that matches
        one of these EID-prefixes, the Map-Server returns a partial
        RLOC-set which contain only the list of RTRs.  The remote ITR
        encapsulates packets to the RTRs.

   9.   When one of the RTRs send a Map-Request for an EID that matches
        one of these EID-prefixes, the Map-Server returns a partial
        RLOC-set which contain only the global RLOCs so the RTR can
        encapsulate packets that will make it through the NAT device to
        the xTR.

   10.  The xTR behind a NAT device only stores default map-cache
        entries with an RLOC-set that contain the list of RTRs the Map-
        Server supplied it with.  The xTR load-splits traffic across the
        RTRs based on the 5-tuple hash algorithm detailed in [RFC9300].

4.  Protocol Messages

   The implementation uses the Info-Request and Info-Reply
   messages from [I-D.ermagan-lisp-nat-traversal] as well as the NAT-
   Traversal LISP Canonical Address Format (LCAF) from [RFC8060].  This
   section indicates how these messages are used by the implementation.

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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 |0|            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>     |

              Figure 1 - LISP Info-Request Message Format

   The implementation will send an Info-Request message to
   each configured Map-Server.  The message is sent to UDP destination
   port 4342 which is the control-plane port for LISP [RFC9301] from a
   UDP ephemeral source port.  The source address is its Private RLOC.
   When the xTR is multi-homed to more than one NAT device, it sends the
   Info-Request on all interfaces facing NAT devices.

   A randomized 64-bit nonce is selected for the message and no
   authentication is used.  The EID-prefix AFI is 17 according to the
   encoding format in [I-D.ietf-lisp-name-encoding] and the EID-prefix
   is the hostname of the xTR encoded as a string null terminated.  Name
   collisions are dealt with according to procedures in

   An Info-Request is sent out each outgoing interface, with the address
   of that interface as the Private RLOC, leading to a NAT device.  The
   port pair in the UDP message is the same for each outgoing interface.

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   When the xTR receives an Info-Reply message from the Map-Server in
   response to this control-plane Info-Request, it caches a list of RTRs
   from the Info-Reply.  If the list of RTRs are different from each
   Map-Server, the lists are merged.  The xTR stores the merged list as
   the RLOC-set for 4 default map-cache entries.  The map-cache entries
   have the following EID-prefixes:

           IPv4 unicast:
           IPv4 multicast:    (,
           IPv6 unicast:       0::/0
           IPv6 multicast:    (0::/0, ff00::/8)

   Now that the xTR has a list of RTRs, it sends a data-plane Info-
   Request to each RTR to UDP destination port 4341 from a UDP ephemeral
   source port.  The data-plane Info-Request is sent out each interface
   just like the control-plane Info-Request was sent for the multi-homed
   NAT device case.

   When Map-Servers and RTRs return an Info-Reply message to xTRs behind
   NAT devices, the format of the Info-Reply message is the following.

   Info-Request messages are sent periodically every 15 seconds to both
   the configured set of Map-Servers and the discovered set of RTRs to
   keep state alive in NAT devices.

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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 |1|               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 ...  |

                 Figure 2 - LISP Info-Reply Message Format

   The information returned is the same information that was sent in the
   Info-Request message except the Info-Reply bit is set (the bit next
   to Type=7) and the NAT Traversal LCAF encoding is appended.

   When a Map-Server returns the Info-Reply, the MS UDP Port Number and
   ETR UDP Port Number is set to 0.  All Address fields are empty by
   using AFI equal to 0.  Except for the RTR RLOC address fields which
   the Map-Server is configured to return to xTRs behind NAT devices.

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   When an RTR returns the Info-Reply, the MS UDP Port Number is set to
   0 and the ETR UDP Port Number is set to the UDP source port the RTR
   received from the Info-Request message.  The Global ETR RLOC Address
   is set to the source address received by the RTR in the Info-Request
   message.  All other address fields are empty by using AFI equal to 0.

5.  xTR Map-Registering and Map-Server Proxy Map-Replying

   EID-prefixes registered by an xTR behind a NAT include all the global
   RLOCs and reachable RTR RLOCs it learns.  The xTR can use the unicast
   priority to control ingress packet flow as described in [RFC9301].
   The RTR RLOCs must be registered with with an RLOC name of
   "" so the Map-Server can identify xTR global RLOCs
   from RTR RLOCs when proxy Map-Replying.  Each RTR RLOC weight is set
   to 1 so ITRs can load-split traffic across them.

   The Global RLOCs are encoded in a RLOC-record using the AFI-List LCAF
   encoding [RFC8060].  There are two AFI encoded addresses in the list,
   one being AFI=1 which encodes the IPv4 translated NAT address and
   other being the Distinguished-Name AFI=17
   [I-D.ietf-lisp-name-encoding] which encodes the hostname of the xTR.
   When the xTR is multi-homed, the hostname is appended by a unique
   interface name.  For example, for an xTR behind a NAT that has two
   interfaces facing the same or two different NAT devices, the
   Distinguished-Name for each RLOC-record could be "dino-xtr-eth0" and
   "dino-xtr-eth1" for an xTR configured to be named "dino-xtr".

   Encoding a Distinguished-Name in an RLOC-record is important so an
   RTR can use the Global RLOC registered to the mapping system with the
   translated port stored in its NAT Info Cache.  See Section 8 for more

   When a remote ITR sends a Map-Request for a unicast or multicast EID
   registered by a xTR behind a NAT, the Map-Server returns a partial
   RLOC-set that contains all the RTRs (RLOC-records with RLOC-name
   "") in the proxied Map-Reply message.

   When a RTR sends a Map-Request for a unicast or multicast EID
   registered by a xTR behind a NAT, the Map-Server returns a partial
   RLOC-set that contains all the Global RLOCs of the xTR behind the NAT
   in the proxied Map-Reply message.

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6.  Packet Flow from ITR-behind-NAT to RTR

   All packets received by the ITR from the private side of the NAT will
   use one of the 4 default map-cache entries.  There is a unicast and
   multicast IPv4 default EID-prefix and a unicast and multicast IPv6
   default EID-prefix.  The RLOC-set is the same for all 4 entries.  The
   RLOC-set contains the globally reachable RLOCs of the RTRs. 5-tuple
   hashing is used to load-split traffic across the RTRs.  RLOC-Probing
   is used to avoid encapsulating to unreachable RTRs.

7.  Packet Flow from Remote ITR to RTR

   A remote ITR will get a list of RTRs from the mapping system in a
   proxy Map-Reply when it sends a Map-Request for a unicast or
   multicast EID that is registered by an xTR behind a NAT device.  The
   remote ITR will load split traffic across the RTRs from the RLOC-set.
   Those RTRs can get packets through the NAT devices destined for the
   xTR behind the NAT since an Info-Request/Info-Reply exchange had
   already happened between the xTR behind the NAT and the list of RTRs.

   There can be a reachability situation where an RTR cannot reach the
   xTR behind a NAT but a remote ITR may 5-tuple hash to this RTR.
   Which means packets can travel from the remote ITR to the RTR but
   then get dropped on the path from the RTR to the xTR behind the NAT.
   To avoid this situation, the xTR behind the NAT RLOC-probes RTRs and
   when they become unreachable, they are not included in the xTR

8.  Packet Flow from RTR to ETR-behind-NAT

   The RTR will receive a list of Global RLOCs in a proxy Map-Reply from
   the mapping system for the xTR behind the NAT.  The RTR 5-tuple load-
   splits packets across the RLOC-set of Global RLOCs that can travel
   through one or more NAT devices along the path to the ETR behind the
   NAT device.

   When the RTR selects a Global RLOC to encapsulate to it must select
   the correct Translated Port for the UDP destination port in the
   encapsulation header.  The RTR needs to use the same Translated
   Address and Translated Port pair a NAT device used to translate the
   Info-Request message otherwise the encapsulated packet will be
   dropped.  The NAT Info Cache contains an entry for every hostname
   (and optionally appended interface name), translated address and port
   cached when processing Info-Request messages.  The RTR obtains the
   correct Translated Port from the NAT Info Cache by using the Global
   RLOC and RLOC-record hostname from the registered RLOC-set.

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   The RTR can test reachability for xTRs behind NATs by encapsulating
   RLOC-Probe requests in data packets where the UDP source port is set
   to 4341 and the UDP destination port is set to the Translated Port.
   The outer header destination address is the Global RLOC for the xTR.

9.  Decentralized NAT

   A decentralized version of this design is also supported in the implementation.  See [DECENT-NAT] for an overview.  The
   design allows direct encapsulation from an ITR to an ETR when they
   both reside behind NAT devices.  Packets do not have to take a sub-
   optimal path through the RTR.  The RTR does play a role in informing
   the ETRs about their translated address and port number just as it
   does for the centralized version.  Here are some details of the

   *  Like the centralized version, each ETR registers its global RLOC
      address by sending a Map-Register message using an RLOC-Record
      name of its hostname.  In addition, for Decentralized-NAT, the
      translated port number is part of the RLOC-Record name, for
      example "dino-macbook@tp-34265".

   *  When an ITR sends a Map-Request, it sets the Decent-NAT bit so the
      Map-Server returns the entire RLOC-set so the ITR can encapsulate
      directly to the ETR or through the RTR for cases the ETR goes path
      unreachable.  The Map-Request N-bit below is used for Decent-NAT:

       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=1 |A|M|P|S|p|s|m|I|  Rsvd |N|L|D|   IRC   | Record Count  |

   *  When the ITR receives a proxy Map-Reply from the Map-Server, it
      stores the entire RLOC-set in a map-cache entry.  From the RLOC-
      record, the global translated address and the translated port
      number from the RLOC-record name is stored and used for

   *  The ITR will next send a NAT probe Info-Request to the global
      translated RLOC and translated port for the remote xTR using UDP
      source port 4341 opening up the NAT to allow packets to be
      received through the local NAT.

   *  The ITR encapsulates packets with a private source address and UDP
      source port 4341 to a global destination address with a UDP
      destination translated port.

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   *  At this point if the ITR encapsulates packets to the ETR that it
      cannot receive.  The ETR will not receive packets because it has
      not opened up its NAT.  It can only do this when it decides to
      encapsulate packets back.  If bidirectional traffic begins by an
      initiating application client which causes a response packet from
      the application server, the response packet can not be sent
      because the remote side has not opened up its NAT to receive the
      client packet.  To solve this circular dependency problem, the ITR
      will send a few packets to the RTR that can get through the NAT to
      the ETR.  Then response packets can now be returned using the same
      process as described above.

   *  At this point, when both xTRs have map-cache entries and have sent
      NAT Info-Request probes, packets can flow in both directions
      directly from local ITR to remote ETR and from remote-ITR to
      local-ETR.  This increases packet delivery performance since there
      is no packet hair-pinning.

   *  Both sides can RLOC-probe directly to obtain reachability status
      and underlay telemetry statistics.

   Your feature mileage may vary depending on the type of NAT or
   firewall deployed.  There is an assumption that the translated port
   for an xTR that sends to the RTR is the same translated port used for
   other destinations.

10.  Design Observations

   The following benefits and observations can be attributed to this

   *  An ITR behind a NAT virtually runs no control-plane and a very
      simple data-plane.  All it does is RLOC-probe the RTRs in the
      common RLOC-set for each default map-cache entry.  And maintains a
      very small map-cache of 4 entries per instance-ID it supports.

   *  An xTR behind a NAT can tell if another xTR is behind the same set
      of NAT devices and use Private RLOCs to reach each other on a
      short-cut path.  It does this by comparing the Global RLOC
      returned from RTRs in Info-Reply messages.

   *  An xTR behind a NAT is free to send a Map-Request to the mapping
      system for any EID to test to see if there is a direct path to the
      LISP site versus potentially using a sub-optimal path through an
      RTR.  This happens when xTRs exist that are not behind NAT devices
      where their RLOCs are global RLOCs.

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   *  By sending Info-Requests to Map-Servers, an xTR behind a NAT can
      tell if they are reachable and if those Map-Servers also act as
      Map-Resolvers, the xTR behind the NAT can avoid sending Map-
      Requests to unreachable Map-Resolvers.

   *  Enhanced data-plane security can be used via LISP-Crypto
      mechanisms detailed in [RFC8061] using this NAT-Traversal design
      so both unicast and multicast traffic are encrypted.

   *  This design allows for the minimum amount of NAT device state
      since only RTRs are encapsulating to ETRs behind NAT devices.
      Therefore, the number of ITRs sending packets to EIDs behind NAT
      devices is aggregated out for scale.  Scale is also achieved when
      xTRs behind NATs roam and RLOC-set changes need to update only RTR

   *  The protocol procedures in this document can be used when a LISP
      site has multiple xTRs each connected via separate NAT devices to
      the public network.  Each xTR registers their Global RLOCs and
      RTRs with merge semantics to the mapping system so remote ITRs can
      load-split traffic across a merged RTR set as well as RTRs across
      each xTR behind different NAT devices.

11.  Security Considerations

   There are no additional security considerations the implementation
   provides for NAT-Traversal.  However, the general
   implementation does adhere to the recommendations from [RFC9300] and

   This implementation does not support [RFC9303] at the current time.
   It can be implemented as requirements change.

   The implementation is exposed to several threats described in
   [RFC7835].  An attacker may spoof Info-Request messages.  This
   implementation does not mitigate that attack, but it could be done in
   future work by authenticating xTRs like the way key management is
   used for Map-Register messages according to [RFC9301].

   The implementation does not set or use the authentication data fields
   in the Info-Request and Info-Reply messages.  However, this will
   become future work.

12.  IANA Considerations

   This implementation makes a single request for IANA.

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   The N-bit in the Map-Request header specified in this document has
   been used in this implementation.  This document requests assignment
   for this N-bit at the bit position in the Map-Request header
   indicated below.

   Registry: Locator/ID Separation Protocol (LISP) Parameters, Sub-
   Registry: Map-Request Header Bits:

      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=1 |A|M|P|S|p|s|R|R|  Rsvd |N|L|D|   IRC   | Record Count  |

     | Spec Name | IANA Name     | Bit Position | Description       |
     | N         | map-request-N | 16           | NAT-Traversal Bit |

                  Table 1: LISP Map-Request Header Bits

13.  Code-Point Considerations

   The code-point values in this specification are already allocated in
   [AFI] or [RFC8060].

   An RLOC name set to "", encoded in Distinguished-Name
   AFI format [I-D.ietf-lisp-name-encoding], is used in the
   implementation to identify an RTR RLOC-record.  This is not an IANA
   registry code-point value and is not being requested to be reserved.

14.  References

14.1.  Normative References

   [AFI]      "Address Family Identifier (AFIs)", ADDRESS FAMILY
              NUMBERS, February 2007.

              Farinacci, D., "LISP Distinguished Name Encoding", Work in
              Progress, Internet-Draft, draft-ietf-lisp-name-encoding-
              04, 14 December 2023,

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   [RFC1700]  Reynolds, J. and J. Postel, "Assigned Numbers", RFC 1700,
              DOI 10.17487/RFC1700, October 1994,

   [RFC3022]  Srisuresh, P. and K. Egevang, "Traditional IP Network
              Address Translator (Traditional NAT)", RFC 3022,
              DOI 10.17487/RFC3022, January 2001,

   [RFC6835]  Farinacci, D. and D. Meyer, "The Locator/ID Separation
              Protocol Internet Groper (LIG)", RFC 6835,
              DOI 10.17487/RFC6835, January 2013,

   [RFC7835]  Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID
              Separation Protocol (LISP) Threat Analysis", RFC 7835,
              DOI 10.17487/RFC7835, April 2016,

   [RFC8060]  Farinacci, D., Meyer, D., and J. Snijders, "LISP Canonical
              Address Format (LCAF)", RFC 8060, DOI 10.17487/RFC8060,
              February 2017, <>.

   [RFC8061]  Farinacci, D. and B. Weis, "Locator/ID Separation Protocol
              (LISP) Data-Plane Confidentiality", RFC 8061,
              DOI 10.17487/RFC8061, February 2017,

   [RFC9300]  Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
              Cabellos, Ed., "The Locator/ID Separation Protocol
              (LISP)", RFC 9300, DOI 10.17487/RFC9300, October 2022,

   [RFC9301]  Farinacci, D., Maino, F., Fuller, V., and A. Cabellos,
              Ed., "Locator/ID Separation Protocol (LISP) Control
              Plane", RFC 9301, DOI 10.17487/RFC9301, October 2022,

   [RFC9303]  Maino, F., Ermagan, V., Cabellos, A., and D. Saucez,
              "Locator/ID Separation Protocol Security (LISP-SEC)",
              RFC 9303, DOI 10.17487/RFC9303, October 2022,

14.2.  Informative References

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              "Decentralized-NAT", Decentralized-NAT Slide: https://gith
              832e76461ae69a86/docs/lisp-decent-nat.pdf, January 2023.

              Ermagan, V., Farinacci, D., Lewis, D., Maino, F.,
              Portoles-Comeras, M., Skriver, J., White, C., Brescó, A.
              L., and A. Cabellos-Aparicio, "NAT traversal for LISP",
              Work in Progress, Internet-Draft, draft-ermagan-lisp-nat-
              traversal-19, 7 May 2021,

Appendix A.  Acknowledgments

   The author would like to thank the authors of the LISP NAT-Traversal
   specification [I-D.ermagan-lisp-nat-traversal] for their initial
   ideas and prototyping to allow a simpler form of NAT-Traversal to be
   designed.  A special grateful thank you to the members of who have been involved in testing the

Appendix B.  Document Change Log

B.1.  Changes to draft-farinacci-lisp-lispers-net-nat-07

   *  Posted December 2023.

   *  Add to abstract that this document is not a IETF standard.

B.2.  Changes to draft-farinacci-lisp-lispers-net-nat-06

   *  Posted December 2023.

   *  Made document changes to reflect implementation changes to
      identify an RTR in a locator-set.  No longer will the presence of
      unicast priority 254 identify an RTR for NAT-traversal purposes.
      The new approach is to set the RLOC-name in an RLOC-record to
      "".  This will happen in starting in
      releases January 2024.

B.3.  Changes to draft-farinacci-lisp-lispers-net-nat-05

   *  Posted November 2023.

   *  Update references and document timer.

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B.4.  Changes to draft-farinacci-lisp-lispers-net-nat-04

   *  Posted May 2023.

   *  Made changes based on WG comments, particularly from Luigi and

B.5.  Changes to draft-farinacci-lisp-lispers-net-nat-03

   *  Posted February 2023.

   *  Added "Code-Point Considersations" section.

   *  Indicate that Info-Requests are also used to keep state alive in
      NAT deivces.

B.6.  Changes to draft-farinacci-lisp-lispers-net-nat-02

   *  Posted February 2023.

   *  Made changes to reflect comments from Eliot Lear, the ISE..

B.7.  Changes to draft-farinacci-lisp-lispers-net-nat-01

   *  Posted February 2023.

   *  Made changes to reflect comments from Luigi Iannone, LISP WG

B.8.  Changes to draft-farinacci-lisp-lispers-net-nat-00

   *  Posted January 2023.

   *  Changed document title and filename to reflect that the draft
      documents an existing implementation and not specifying a proposed
      protocol solution.

   *  Made recommended changes from the ISE to make document eligble for
      Informational RFC publication.

   *  Add text about LISP-SEC and priority 254 per Luigi's comments.

   *  Indicate how this draft does not interoperate with

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B.9.  Changes to draft-farinacci-lisp-simple-nat-06

   *  Posted January 2023.

   *  Add section on how Decentralized-NAT works.

   *  Update references for RFC9300 and RFC9301.

B.10.  Changes to draft-farinacci-lisp-simple-nat-05

   *  Posted September 2022.

   *  Update draft-ietf-lisp-name-encdoing reference.

B.11.  Changes to draft-farinacci-lisp-simple-nat-04

   *  Posted May 2022.

   *  Update document timer.

B.12.  Changes to draft-farinacci-lisp-simple-nat-03

   *  Posted November 2021.

   *  Update document timer.

B.13.  Changes to draft-farinacci-lisp-simple-nat-02

   *  Posted May 2021.

   *  Update document timer.

B.14.  Changes to draft-farinacci-lisp-simple-nat-01

   *  Posted November 2020.

   *  Update document timer.

B.15.  Changes to draft-farinacci-lisp-simple-nat-00

   *  Posted May 2020.

   *  Initial posting.

Author's Address

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   Dino Farinacci
   San Jose, CA
   United States of America

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