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Versions: (RFC 6834) 00

Network Working Group                                         L. Iannone
Internet-Draft                                         Telecom ParisTech
Intended status: Standards Track                               D. Saucez
Expires: November 18, 2018                        INRIA Sophia Antipolis
                                                          O. Bonaventure
                                        Universite catholique de Louvain
                                                            May 17, 2018


          Locator/ID Separation Protocol (LISP) Map-Versioning
                      draft-iannone-6834bis-00.txt

Abstract

   This document describes the LISP (Locator/ID Separation Protocol)
   Map-Versioning mechanism, which provides in-packet information about
   Endpoint ID to Routing Locator (EID-to-RLOC) mappings used to
   encapsulate LISP data packets.  The proposed approach is based on
   associating a version number to EID-to-RLOC mappings and the
   transport of such a version number in the LISP-specific header of
   LISP-encapsulated packets.  LISP Map-Versioning is particularly
   useful to inform communicating Ingress Tunnel Routers (ITRs) and
   Egress Tunnel Routers (ETRs) about modifications of the mappings used
   to encapsulate packets.  The mechanism is optional and transparent to
   implementations not supporting this feature, since in the LISP-
   specific header and in the Map Records, bits used for Map-Versioning
   can be safely ignored by ITRs and ETRs that do not support or do not
   want to use the mechanism.

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
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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 November 18, 2018.






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Copyright Notice

   Copyright (c) 2018 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Requirements Notation . . . . . . . . . . . . . . . . . . . .   4
   3.  Definitions of Terms  . . . . . . . . . . . . . . . . . . . .   4
   4.  EID-to-RLOC Map-Version Number  . . . . . . . . . . . . . . .   4
     4.1.  The Null Map-Version  . . . . . . . . . . . . . . . . . .   5
   5.  Dealing with Map-Version Numbers  . . . . . . . . . . . . . .   6
     5.1.  Handling Destination Map-Version Number . . . . . . . . .   7
     5.2.  Handling Source Map-Version Number  . . . . . . . . . . .   9
   6.  LISP Header and Map-Version Numbers . . . . . . . . . . . . .   9
   7.  LISP Generic Protocol Encapsulation (GPE) Header and Map-
       Version Numbers . . . . . . . . . . . . . . . . . . . . . . .  10
   8.  Map Record and Map-Version  . . . . . . . . . . . . . . . . .  11
   9.  Benefits and Case Studies for Map-Versioning  . . . . . . . .  12
     9.1.  Map-Versioning and Unidirectional Traffic . . . . . . . .  12
     9.2.  Map-Versioning and Interworking . . . . . . . . . . . . .  13
       9.2.1.  Map-Versioning and Proxy-ITRs . . . . . . . . . . . .  13
       9.2.2.  Map-Versioning and LISP-NAT . . . . . . . . . . . . .  14
       9.2.3.  Map-Versioning and Proxy-ETRs . . . . . . . . . . . .  14
     9.3.  RLOC Shutdown/Withdraw  . . . . . . . . . . . . . . . . .  14
     9.4.  Map-Version Additional Use Cases  . . . . . . . . . . . .  15
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  15
     10.1.  Map-Versioning against Traffic Disruption  . . . . . . .  16
     10.2.  Map-Versioning against Reachability Information DoS  . .  16
   11. Considerations  . . . . . . . . . . . . . . . . . . . . . . .  17
   12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  18
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     13.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19





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1.  Introduction

   This document describes the Map-Versioning mechanism used to provide
   information on changes in the EID-to-RLOC (Endpoint ID to Routing
   Locator) mappings used in the LISP (Locator/ID Separation Protocol
   [I-D.ietf-lisp-rfc6830bis][I-D.ietf-lisp-rfc6833bis]) context to
   perform packet encapsulation.  The mechanism is totally transparent
   to xTRs (Ingress and Egress Tunnel Routers) not supporting or not
   using such functionality.

   The basic mechanism is to associate a Map-Version number to each LISP
   EID-to-RLOC mapping and transport such a version number in the LISP-
   specific header.  When a mapping changes, a new version number is
   assigned to the updated mapping.  A change in an EID-to-RLOC mapping
   can be a change in the RLOCs set, by adding or removing one or more
   RLOCs, but it can also be a change in the priority or weight of one
   or more RLOCs.

   When Map-Versioning is used, LISP-encapsulated data packets contain
   the version number of the two mappings used to select the RLOCs in
   the outer header (i.e., both source and destination).  These version
   numbers are encoded in the 24 low-order bits of the first longword of
   the LISP header and indicated by a specific bit in the flags (first 8
   high-order bits of the first longword of the LISP header).  Note that
   not all packets need to carry version numbers.

   When an ITR (Ingress Tunnel Router) encapsulates a data packet, with
   a LISP header containing the Map-Version numbers, it puts in the
   LISP-specific header two version numbers:

   1.  The version number assigned to the mapping (contained in the EID-
       to-RLOC Database) used to select the source RLOC.

   2.  The version number assigned to the mapping (contained in the EID-
       to-RLOC Cache) used to select the destination RLOC.

   This operation is two-fold.  On the one hand, it enables the ETR
   (Egress Tunnel Router) receiving the packet to know if the ITR is
   using the latest mapping version that any ETR at the destination EID
   site would provide to the ITR in a Map-Reply.  If this is not the
   case, the ETR can send to the ITR a Map-Request containing the
   updated mapping or solicit a Map-Request from the ITR (both cases are
   already defined in [I-D.ietf-lisp-rfc6833bis]).  In this way, the ITR
   can update its EID-to-RLOC Cache.  On the other hand, it enables an
   ETR receiving such a packet to know if it has in its EID-to-RLOC
   Cache the latest mapping for the source EID (in the case of
   bidirectional traffic).  If this is not the case, a Map-Request can
   be sent.



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   COnsiderations about the deployment of LISP Map-Versioning for
   Internet traffic are discussed in Section 11.

2.  Requirements Notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  Definitions of Terms

   This document uses terms already defined in the main LISP
   specification (, [I-D.ietf-lisp-rfc6830bis]
   [I-D.ietf-lisp-rfc6833bis]).  Here, we define the terms that are
   specific to the Map-Versioning mechanism.  Throughout the whole
   document, Big Endian bit ordering is used.

   Map-Version number:  An unsigned 12-bit integer is assigned to an
     EID-to-RLOC mapping, not including the value 0 (0x000).

   Null Map-Version:  The 12-bit null value of 0 (0x000) is not used as
     a Map-Version number.  It is used to signal that no Map-Version
     number is assigned to the EID-to-RLOC mapping.

   Source Map-Version number:  This Map-Version number of the EID-to-
     RLOC mapping is used to select the source address (RLOC) of the
     outer IP header of LISP-encapsulated packets.

   Destination Map-Version number:  This Map-Version number of the EID-
     to-RLOC mapping is used to select the destination address (RLOC) of
     the outer IP header of LISP-encapsulated packets.

4.  EID-to-RLOC Map-Version Number

   The EID-to-RLOC Map-Version number consists of an unsigned 12-bit
   integer.  The version number is assigned on a per-mapping basis,
   meaning that different mappings have a different version number,
   which is also updated independently.  An update in the version number
   (i.e., a newer version) consists of incrementing by one the older
   version number.

   The space of version numbers has a circular order where half of the
   version numbers are greater (i.e., newer) than the current Map-
   Version number and the other half of the version numbers are smaller
   (i.e., older) than the current Map-Version number.  In a more formal
   way, assuming that we have two version numbers V1 and V2 and that the
   numbers are expressed in N bits, the following steps MUST be




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   performed (in the same order as shown below) to strictly define their
   order:

   1.  V1 = V2 : The map-version numbers are the same.

   2.  V2 > V1 : if and only if

         V2 > V1 AND (V2 - V1) <= 2**(N-1)

         OR

         V1 > V2 AND (V1 - V2) > 2**(N-1)

   3.  V1 > V2 : otherwise.

   Using 12 bits, as defined in this document, and assuming a Map-
   Version value of 69, Map-Version numbers in the range [70; 69 + 2048]
   are greater than 69, while Map-Version numbers in the range [69 +
   2049; (69 + 4096) mod 4096] are smaller than 69.

   Map-version numbers are assigned to mappings by configuration.  The
   initial Map-Version number of a new EID-to-RLOC mapping SHOULD be
   assigned randomly, but it MUST NOT be set to the Null Map-Version
   value (0x000), because the Null Map-Version number has a special
   meaning (see Section 4.1).

   Upon reboot, an ETR will use mappings configured in its EID-to-RLOC
   Database.  If those mappings have a Map-Version number, it will be
   used according to the mechanisms described in this document.  ETRs
   MUST NOT automatically generate and assign Map-Version numbers to
   mappings in the EID-to-RLOC Database.

4.1.  The Null Map-Version

   The value 0x000 (zero) is not a valid Map-Version number indicating
   the version of the EID-to-RLOC mapping.  Such a value is used for
   special purposes and is named the Null Map-Version number.

   The Null Map-Version MAY appear in the LISP-specific header as either
   a Source Map-Version number (cf.  Section 5.2) or a Destination Map-
   Version number (cf.  Section 5.1).  When the Source Map-Version
   number is set to the Null Map-version value, it means that no map
   version information is conveyed for the source site.  This means that
   if a mapping exists for the source EID in the EID-to-RLOC Cache, then
   the ETR MUST NOT compare the received Null Map-Version with the
   content of the EID-to-RLOC Cache.  When the Destination Map-version
   number is set to the Null Map-version value, it means that no map
   version information is conveyed for the destination site.  This means



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   that the ETR MUST NOT compare the value with the Map-Version number
   of the mapping for the destination EID present in the EID-to-RLOC
   Database.

   The other use of the Null Map-Version number is in the Map Records,
   which are part of the Map-Request, Map-Reply, and Map-Register
   messages (defined in [I-D.ietf-lisp-rfc6833bis]).  Map Records that
   have a Null Map-Version number indicate that there is no Map-Version
   number associated with the mapping.  This means that LISP-
   encapsulated packets destined to the EID-Prefix referred to by the
   Map Record MUST either not contain any Map-Version numbers (V bit set
   to 0) or, if they contain Map-Version numbers (V bit set to 1), then
   the destination Map-Version number MUST be set to the Null Map-
   Version number.  Any value different from zero means that Map-
   Versioning is supported and MAY be used.

   The fact that the 0 value has a special meaning for the Map-Version
   number implies that, when updating a Map-Version number because of a
   change in the mapping, if the next value is 0, then the Map-Version
   number MUST be incremented by 2 (i.e., set to 1, which is the next
   valid value).

5.  Dealing with Map-Version Numbers

   The main idea of using Map-Version numbers is that whenever there is
   a change in the mapping (e.g., adding/removing RLOCs, a change in the
   weights due to Traffic Engineering policies, or a change in the
   priorities) or a LISP site realizes that one or more of its own RLOCs
   are not reachable anymore from a local perspective (e.g., through
   IGP, or policy changes) the LISP site updates the mapping, also
   assigning a new Map-Version number.

   To each mapping, a version number is associated and changes each time
   the mapping is changed.  Note that Map-Versioning does not introduce
   new problems concerning the coordination of different ETRs of a
   domain.  Indeed, ETRs belonging to the same LISP site must return for
   a specific EID-prefix the same mapping, including the same Map-
   Version number.  This is orthogonal to whether or not Map-Versioning
   is used.  The synchronization problem and its implications on the
   traffic are out of the scope of this document.

   In order to announce in a data-driven fashion that the mapping has
   been updated, Map-Version numbers used to create the outer IP header
   of the LISP-encapsulated packet are embedded in the LISP-specific
   header.  This means that the header needs to contain two Map-Version
   numbers:





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   o  The Source Map-Version number of the EID-to-RLOC mapping in the
      EID-to-RLOC Database used to select the source RLOC.

   o  The Destination Map-Version number of the EID-to-RLOC mapping in
      the EID-to-RLOC Cache used to select the destination RLOC.

   By embedding both the Source Map-Version number and the Destination
   Map-Version number, an ETR receiving a LISP packet with Map-Version
   numbers can perform the following checks:

   1.  The ITR that has sent the packet has an up-to-date mapping in its
       EID-to-RLOC Cache for the destination EID and is performing
       encapsulation correctly.

   2.  In the case of bidirectional traffic, the mapping in the local
       ETR EID-to-RLOC Cache for the source EID is up to date.

   If one or both of the above conditions do not hold, the ETR can send
   a Map-Request either to make the ITR aware that a new mapping is
   available (see Section 5.1) or to update the mapping in the local
   EID-to-RLOC Cache (see Section 5.2).

5.1.  Handling Destination Map-Version Number

   When an ETR receives a packet, the Destination Map-Version number
   relates to the mapping for the destination EID for which the ETR is
   an RLOC.  This mapping is part of the ETR EID-to-RLOC Database.
   Since the ETR is authoritative for the mapping, it has the correct
   and up-to-date Destination Map-Version number.  A check on this
   version number can be done, where the following cases can arise:

   1.  The packet arrives with the same Destination Map-Version number
       stored in the EID-to-RLOC Database.  This is the regular case.
       The ITR sending the packet has in its EID-to-RLOC Cache an up-to-
       date mapping.  No further actions are needed.

   2.  The packet arrives with a Destination Map-Version number greater
       (i.e., newer) than the one stored in the EID-to-RLOC Database.
       Since the ETR is authoritative on the mapping, meaning that the
       Map-Version number of its mapping is the correct one, this
       implies that someone is not behaving correctly with respect to
       the specifications.  In this case, the packet carries a version
       number that is not valid; otherwise, the ETR would have the same
       number, and the packet SHOULD be silently dropped.

   3.  The packets arrive with a Destination Map-Version number smaller
       (i.e., older) than the one stored in the EID-to-RLOC Database.
       This means that the ITR sending the packet has an old mapping in



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       its EID-to-RLOC Cache containing stale information.  The ETR MAY
       choose to normally process the encapsulated datagram according to
       [I-D.ietf-lisp-rfc6830bis]; however, the ITR sending the packet
       has to be informed that a newer mapping is available.  This is
       done with a Map-Request message sent back to the ITR.  The Map-
       Request will either trigger a Map-Request back using the Solicit-
       Map-Request (SMR) bit or it will piggyback the newer mapping.
       These are not new mechanisms; how to use the SMR bit or how to
       piggyback mappings in Map-Request messages is already described
       in [I-D.ietf-lisp-rfc6833bis].  One feature introduced by Map-
       Version numbers is the possibility of blocking traffic not using
       the latest mapping.  Indeed, after a certain number of retries,
       if the Destination Map-Version number in the packets is not
       updated, the ETR MAY drop packets with a stale Map-Version number
       while strongly reducing the rate of Map-Request messages.  This
       is because either the ITR is refusing to use the mapping for
       which the ETR is authoritative, or (worse) it might be some form
       of attack.

   The rule in the third case MAY be more restrictive.  If the mapping
   has been the same for a period of time as long as the Time To Live
   (TTL) (defined in [I-D.ietf-lisp-rfc6833bis]) of the previous version
   of the mapping, all packets arriving with an old Map-Version SHOULD
   be silently dropped right away without issuing any Map-Request.  Such
   action is permitted because if the new mapping with the updated
   version number has been unchanged for at least the same time as the
   TTL of the older mapping, all the entries in the EID-to-RLOC Caches
   of ITRs must have expired.  Hence, all ITRs sending traffic should
   have refreshed the mapping according to [I-D.ietf-lisp-rfc6833bis].
   If packets with old Map-Version numbers are still received, then
   either someone has not respected the TTL or it is a form of spoof/
   attack.  In both cases, this is not valid behavior with respect to
   the specifications and the packet SHOULD be silently dropped.

   LISP-encapsulated packets with the V-bit set, when the original
   mapping in the EID-to-RLOC Database has the version number set to the
   Null Map-Version value, MAY be silently dropped.  As explained in
   Section 4.1, if an EID-to-RLOC mapping has a Null Map-Version, it
   means that ITRs, using the mapping for encapsulation, MUST NOT use a
   Map-Version number in the LISP-specific header.

   For LISP-encapsulated packets with the V-bit set, when the original
   mapping in the EID-to-RLOC Database has the version number set to a
   value different from the Null Map-Version value, a Destination Map-
   Version number equal to the Null Map-Version value means that the
   Destination Map-Version number MUST be ignored.





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5.2.  Handling Source Map-Version Number

   When an ETR receives a packet, the Source Map-Version number relates
   to the mapping for the source EID for which the ITR that sent the
   packet is authoritative.  If the ETR has an entry in its EID-to-RLOC
   Cache for the source EID, then a check can be performed and the
   following cases can arise:

   1.  The packet arrives with the same Source Map-Version number as
       that stored in the EID-to-RLOC Cache.  This is the correct
       regular case.  The ITR has in its EID-to-RLOC Cache an up-to-date
       copy of the mapping.  No further actions are needed.

   2.  The packet arrives with a Source Map-Version number greater
       (i.e., newer) than the one stored in the local EID-to-RLOC Cache.
       This means that the ETR has in its EID-to-RLOC Cache a mapping
       that is stale and needs to be updated.  A Map-Request SHOULD be
       sent to get the new mapping for the source EID.  This is a normal
       Map-Request message sent through the mapping system and MUST
       respect the specifications in [I-D.ietf-lisp-rfc6833bis],
       including rate-limitation policies.

   3.  The packet arrives with a Source Map-Version number smaller
       (i.e., older) than the one stored in the local EID-to-RLOC Cache.
       Such a case is not valid with respect to the specifications.
       Indeed, if the mapping is already present in the EID-to-RLOC
       Cache, this means that an explicit Map-Request has been sent and
       a Map-Reply has been received from an authoritative source.
       Assuming that the mapping system is not corrupted, the Map-
       Version in the EID-to-RLOC Cache is the correct one, while the
       one carried by the packet is stale.  In this situation, the
       packet MAY be silently dropped.

   If the ETR does not have an entry in the EID-to-RLOC Cache for the
   source EID, then the Source Map-Version number can be safely ignored.

   For LISP-encapsulated packets with the V-bit set, if the Source Map-
   Version number is the Null Map-Version value, it means that the
   Source Map-Version number MUST be ignored.

6.  LISP Header and Map-Version Numbers

   In order for the versioning approach to work, the LISP-specific
   header has to carry both the Source Map-Version number and
   Destination Map-Version number.  This is done by setting the V-bit in
   the LISP-specific header as defined in [I-D.ietf-lisp-rfc6830bis].
   When the V-bit is set and the P bit is reset (0), the low-order 24
   bits of the first longword are used to transport both the source and



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   destination Map-Version numbers.  In particular, the first 12 bits
   are used for the Source Map-Version number and the second 12 bits for
   the Destination Map-Version number.

   Below is an example of a LISP header carrying version numbers.

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |N|L|E|V|I|P|K|K|  Source Map-Version   |Destination Map-Version|
   LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                 Instance ID/Locator Status Bits               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Source Map-Version number (12 bits):  Map-Version of the mapping used
     by the ITR to select the RLOC present in the "Source Routing
     Locator" field.  Section 5.2 describes how to set this value on
     transmission and handle it on reception.

   Destination Map-Version number (12 bits):  Map-Version of the mapping
     used by the ITR to select the RLOC present in the "Destination
     Routing Locator" field.  Section 5.1 describes how to set this
     value on transmission and handle it on reception.

   Not all of the LISP-encapsulated packets need to carry version
   numbers.  When Map-Version numbers are carried in these packets, the
   V-bit MUST be set to 1.  All permissible combinations of the flags
   when the V-bit is set to 1 are described in
   [I-D.ietf-lisp-rfc6830bis] and [I-D.ietf-lisp-gpe].

7.  LISP Generic Protocol Encapsulation (GPE) Header and Map-Version
    Numbers

   [I-D.ietf-lisp-gpe] extends the Locator/ID Separation Protocol (LISP)
   Data-Plane, changing the LISP header, to support multi-protocol
   encapsulation.  A flag in the LISP header, called the P-bit, is used
   to signal the presence of the Next Protocol field in the low-order 8
   bits of the first lognword.  When the V-bit and P-bit are both set,
   the middle-order 16 bits of the first longword are used to transport
   both the source and destination Map-Version numbers.  In particular,
   the first 8 bits are used for the Source Map-Version number and the
   second 8 bits for the Destination Map-Version number.

   Below is an example of a LISP header carrying version numbers.







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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |N|L|E|V|I|P|K|K|Src Map-Version|Dst Map-Version| Next Protocol |
   LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                 Instance ID/Locator Status Bits               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The Source Map-Version number and the Destination Map-Version number
   are used exactly in the same way previously described.  There are
   only three differences:

   o  When filling the LISP-GPE-specific header only the low order 8
      bits are copied in the Source and Destination Map-Version Number
      (out of the original 12 bits).

   o  When comparing a Map-Version retrieved from the LISP-GPE-specific
      header (either Source or Destination Map-Version number) with the
      version number of a mapping (stored in the LISP Cache or LISP
      Database) only the low-order 8 bits of the latter are used for the
      comparison.

   o  When trimming a Map-Version number from 12 to 8 bits it may happen
      that it is converted to a Null Map-Version number, which will
      chnage the way Map-Version number is interpreted as described in
      Section 4.1.  To avoid such wrong behavior, Map-Version number
      with the low-order 8 bits all equal to zero SHOULD be avoided on
      xTRs using LISP-GPE.

8.  Map Record and Map-Version

   To accommodate the proposed mechanism, the Map Records that are
   transported in Map-Request/Map-Reply/Map-Register messages need to
   carry the Map-Version number as well.  For this purpose, the 12 bits
   before the EID-AFI field in the Record that describes a mapping are
   used (see [I-D.ietf-lisp-rfc6833bis] and reported here as an example.















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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
   +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |   |                          Record TTL                           |
   |   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   R   | Locator Count | EID mask-len  | ACT |A|      Reserved         |
   e   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   c   | Rsvd  |  Map-Version Number   |       EID-Prefix-AFI          |
   o   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   r   |                          EID-Prefix                           |
   d   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  /|    Priority   |    Weight     |  M Priority   |   M Weight    |
   | L +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | o |        Unused Flags     |L|p|R|           Loc-AFI             |
   | c +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  \|                             Locator                           |
   +-> +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Map-Version Number:  Map-Version of the mapping contained in the
     Record.  As explained in Section 4.1, this field can be zero (0),
     meaning that no Map-Version is associated to the mapping; hence,
     packets that are LISP encapsulated using this mapping MUST NOT
     contain Map-Version numbers in the LISP-specific header, and the
     V-bit MUST be set to 0.

   This packet format works perfectly with xTRs that do not support Map-
   Versioning, since they can simply ignore those bits.

9.  Benefits and Case Studies for Map-Versioning

   In the following sections, we provide more discussion on various
   aspects and uses of Map-Versioning.  Security observations are
   grouped in Section 10.

9.1.  Map-Versioning and Unidirectional Traffic

   When using Map-Versioning, the LISP-specific header carries two Map-
   Version numbers, for both source and destination mappings.  This can
   raise the question on what will happen in the case of unidirectional
   flows, for instance, in the case presented in Figure 1, since the
   LISP specification does not mandate that the ETR have a mapping for
   the source EID.









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    +-----------------+            +-----------------+
    | Domain A        |            | Domain B        |
    |       +---------+            +---------+       |
    |       | ITR A   |----------->| ETR B   |       |
    |       +---------+            +---------+       |
    |                 |            |                 |
    +-----------------+            +-----------------+

          Figure 1: Unidirectional traffic between LISP domains.

   In the case of the ITR, the ITR is able to put both the source and
   destination version number in the LISP header, since the Source Map-
   Version number is in the ITR's database, while the Destination Map-
   Version number is in the ITR's cache.

   In the case of the ETR, the ETR simply checks only the Destination
   Map-Version number in the same way as that described in Section 5,
   ignoring the Source Map-Version number.

9.2.  Map-Versioning and Interworking

   Map-Versioning is compatible with the LISP interworking between LISP
   and non-LISP sites as defined in [RFC6832].  LISP interworking
   defines three techniques to make LISP sites and non-LISP sites,
   namely Proxy-ITR, LISP-NAT, and Proxy-ETR.  The following text
   describes how Map-Versioning relates to these three mechanisms.

9.2.1.  Map-Versioning and Proxy-ITRs

   The purpose of the Proxy-ITR (PITR) is to encapsulate traffic
   originating in a non-LISP site in order to deliver the packet to one
   of the ETRs of the LISP site (cf.  Figure 2).  This case is very
   similar to the unidirectional traffic case described in Section 9.1;
   hence, similar rules apply.

    +----------+                             +-------------+
    | LISP     |                             | non-LISP    |
    | Domain A |                             | Domain B    |
    |  +-------+        +-----------+        |             |
    |  | ETR A |<-------| Proxy ITR |<-------|             |
    |  +-------+        +-----------+        |             |
    |          |                             |             |
    +----------+                             +-------------+

   Figure 2: Unidirectional traffic from non-LISP domain to LISP domain.

   The main difference is that a Proxy-ITR does not have any mapping,
   since it just encapsulates packets arriving from the non-LISP site



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   and thus cannot provide a Source Map-Version.  In this case, the
   proxy-ITR will just put the Null Map-Version value as the Source Map-
   Version number, while the receiving ETR will ignore the field.

   With this setup, LISP Domain A is able to check whether or not the
   PITR is using the latest mapping.

9.2.2.  Map-Versioning and LISP-NAT

   The LISP-NAT mechanism is based on address translation from non-
   routable EIDs to routable EIDs and does not involve any form of
   encapsulation.  As such, Map-Versioning does not apply in this case.

9.2.3.  Map-Versioning and Proxy-ETRs

   The purpose of the Proxy-ETR (PETR) is to decapsulate traffic
   originating in a LISP site in order to deliver the packet to the non-
   LISP site (cf.  Figure 3).  One of the main reasons to deploy PETRs
   is to bypass uRPF (Unicast Reverse Path Forwarding) checks on the
   provider edge.

    +----------+                             +-------------+
    | LISP     |                             | non-LISP    |
    | Domain A |                             | Domain B    |
    |  +-------+        +-----------+        |             |
    |  | ITR A |------->| Proxy ETR |------->|             |
    |  +-------+        +-----------+        |             |
    |          |                             |             |
    +----------+                             +-------------+

   Figure 3: Unidirectional traffic from LISP domain to non-LISP domain.

   A Proxy-ETR does not have any mapping, since it just decapsulates
   packets arriving from the LISP site.  In this case, the ITR will just
   put the Null Map-Version value as the Destination Map-Version number,
   while the receiving Proxy-ETR will ignore the field.

   With this setup, the Proxy-ETR is able to check whether or not the
   mapping has changed.

9.3.  RLOC Shutdown/Withdraw

   Map-Versioning can also be used to perform a graceful shutdown or
   withdraw of a specific RLOC.  This is achieved by simply issuing a
   new mapping, with an updated Map-Version number where the specific
   RLOC to be shut down is withdrawn or announced as unreachable (via
   the R bit in the Map Record; see [I-D.ietf-lisp-rfc6833bis]), but
   without actually turning it off.



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   Once no more traffic is received by the RLOC, it can be shut down
   gracefully, because all sites actively using the mapping have updated
   it.

9.4.  Map-Version Additional Use Cases

   The use of Map-Versioning can help in developing a lightweight
   implementation of LISP.  However, this comes with the price of not
   supporting the Loc-Status-Bit, which is useful in some contexts.

   In the current LISP specifications, the set of RLOCs must always be
   maintained ordered and consistent with the content of the Loc Status
   Bits ([I-D.ietf-lisp-rfc6830bis]).  With Map-Versioning, such types
   of mechanisms can be avoided.  When a new RLOC is added to a mapping,
   it is not necessary to "append" new locators to the existing ones as
   explained in [I-D.ietf-lisp-rfc6830bis].  A new mapping with a new
   Map-Version number will be issued, and since the old locators are
   still valid, the transition will occur with no disruptions.  The same
   applies for the case where an RLOC is withdrawn.  There is no need to
   maintain holes in the list of locators, as is the case when using
   Locator Status Bits, for sites that are not using the RLOC that has
   been withdrawn; in this case, the transition will occur with no
   disruptions.

   All of these operations, as already stated, do not need to maintain
   any consistency among Locator Status Bits and in the way that the
   RLOCs are stored in the EID-to-RLOC Cache.

   Map-Versioning can be used as a substitute for the "clock sweep"
   operation described in Section 6.6.1 of [I-D.ietf-lisp-rfc6833bis].
   Indeed, every LISP site communicating to a specific LISP site that
   has updated the mapping will be informed of the available new mapping
   in a data-driven manner.

10.  Security Considerations

   Map-Versioning does not introduce any security issues concerning both
   the data plane and the control plane.  On the contrary, as described
   below, if Map-Versioning may also be used to update mappings in the
   case of change in the reachability information (i.e., instead of the
   Locator Status Bits), it is possible to reduce the effects of some
   DoS or spoofing attacks that can happen in an untrusted environment.

   Robustness of the Map-Versioning mechanism leverages on a trusted
   Mapping Distribution System.  A thorough security analysis of LISP is
   documented in [RFC7835].





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10.1.  Map-Versioning against Traffic Disruption

   An attacker can try to disrupt ongoing communications by creating
   LISP-encapsulated packets with wrong Locator Status Bits.  If the xTR
   blindly trusts the Locator Status Bits, it will change the
   encapsulation accordingly, which can result in traffic disruption.

   This does not happen in the case of Map-Versioning.  As described in
   Section 5, upon a version number change the xTR first issues a Map-
   Request.  The assumption is that the mapping distribution system is
   sufficiently secure that Map-Request and Map-Reply messages and their
   content can be trusted.  Security issues concerning specific mapping
   distribution systems are out of the scope of this document.  In the
   case of Map-Versioning, the attacker should "guess" a valid version
   number that triggers a Map-Request as described in Section 5;
   otherwise, the packet is simply dropped.  Nevertheless, guessing a
   version number that generates a Map-Request is easy; hence, it is
   important to follow the rate-limitation policies described in
   [I-D.ietf-lisp-rfc6833bis] in order to avoid DoS attacks.

   Note that a similar level of security can be obtained with Loc Status
   Bits by simply making it mandatory to verify any change through a
   Map-Request.  However, in this case Locator Status Bits lose their
   meaning, because it does not matter anymore which specific bits have
   changed; the xTR will query the mapping system and trust the content
   of the received Map-Reply.  Furthermore, there is no way to perform
   filtering as in Map-Versioning in order to drop packets that do not
   carry a valid Map-Version number.  In the case of Locator Status
   Bits, any random change can trigger a Map-Request (unless rate
   limitation is enabled, which raises another type of attack as
   discussed in Section 10.2).

10.2.  Map-Versioning against Reachability Information DoS

   Attackers can try to trigger a large amount of Map-Requests by simply
   forging packets with random Map-Versions or random Locator Status
   Bits.  In both cases, the Map-Requests are rate-limited as described
   in [I-D.ietf-lisp-rfc6833bis].  However, in contrast to the Locator
   Status Bit, where there is no filtering possible, in the case of Map-
   Versioning it is possible to filter invalid version numbers before
   triggering a Map-Request, thus helping to reduce the effects of DoS
   attacks.  In other words, the use of Map-Versioning enables a fine
   control on when to update a mapping or when to notify someone that a
   mapping has been updated.

   It is clear that Map-Versioning does not protect against DoS and DDoS
   attacks, where an xTR loses processing power when doing checks on the




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   LISP header of packets sent by attackers.  This is independent of
   Map-Versioning and is the same for Loc Status Bits.

11.  Considerations

   Even without Map-Versioning, LISP requires ETRs to announce the same
   mapping for the same EID-Prefix to a requester.  The implications
   that a temporary lack of synchronization may have on the traffic are
   yet to be fully explored.

   Map-Versioning does not require additional synchronization mechanisms
   as compared to the normal functioning of LISP without Map-Versioning.
   Clearly, all the ETRs have to reply with the same Map-Version number;
   otherwise, there can be an inconsistency that creates additional
   control traffic, instabilities, and traffic disruptions.  It is the
   same without Map-Versioning, with ETRs that have to reply with the
   same mapping; otherwise, the same problems can arise.

   There are two ways Map-Versioning is helpful with respect to the
   synchronization problem.  On the one hand, assigning version numbers
   to mappings helps in debugging, since quick checks on the consistency
   of the mappings on different ETRs can be done by looking at the Map-
   Version number.  On the other hand, Map-Versioning can be used to
   control the traffic toward ETRs that announce the latest mapping.

   As an example, let's consider the topology of Figure 4 where ITR A.1
   of Domain A is sending unidirectional traffic to Domain B, while A.2
   of Domain A exchanges bidirectional traffic with Domain B.  In
   particular, ITR A.2 sends traffic to ETR B, and ETR A.2 receives
   traffic from ITR B.

    +-----------------+              +-----------------+
    | Domain A        |              | Domain B        |
    |       +---------+              |                 |
    |       | ITR A.1 |---           |                 |
    |       +---------+    \         +---------+       |
    |                 |      ------->| ETR B   |       |
    |                 |      ------->|         |       |
    |       +---------+    /         |         |       |
    |       | ITR A.2 |---      -----| ITR B   |       |
    |       |         |       /      +---------+       |
    |       | ETR A.2 |<-----        |                 |
    |       +---------+              |                 |
    |                 |              |                 |
    +-----------------+              +-----------------+

                        Figure 4: Example topology.




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   Obviously, in the case of Map-Versioning, both ITR A.1 and ITR A.2 of
   Domain A must use the same value; otherwise, the ETR of Domain B will
   start to send Map-Requests.

   The same problem can, however, arise without Map-Versioning, for
   instance, if the two ITRs of Domain A send different Locator Status
   Bits.  In this case, either the traffic is disrupted if ETR B trusts
   the Locator Status Bits, or if ETR B does not trust the Locator
   Status Bits it will start sending Map-Requests to confirm each change
   in reachability.

   So far, LISP does not provide any specific synchronization mechanism
   but assumes that synchronization is provided by configuring the
   different xTRs consistently.  The same applies for Map-Versioning.
   If in the future any synchronization mechanism is provided, Map-
   Versioning will take advantage of it automatically, since it is
   included in the Record format, as described in Section 8.

12.  Acknowledgments

   This work hbenefited support from NewNet@Paris, Cisco's Chair
   "Networks for the Future" at Telecom ParisTech
   (http://newnet.telecom-paristech.fr).  Any opinions, findings or
   recommendations expressed in this material are those of the author(s)
   and do not necessarily reflect the views of partners of the Chair.

13.  References

13.1.  Normative References

   [I-D.ietf-lisp-gpe]
              Maino, F., Lemon, J., Agarwal, P., Lewis, D., and M.
              Smith, "LISP Generic Protocol Extension", draft-ietf-lisp-
              gpe-03 (work in progress), April 2018.

   [I-D.ietf-lisp-rfc6830bis]
              Farinacci, D., Fuller, V., Meyer, D., Lewis, D., and A.
              Cabellos-Aparicio, "The Locator/ID Separation Protocol
              (LISP)", draft-ietf-lisp-rfc6830bis-12 (work in progress),
              March 2018.

   [I-D.ietf-lisp-rfc6833bis]
              Fuller, V., Farinacci, D., and A. Cabellos-Aparicio,
              "Locator/ID Separation Protocol (LISP) Control-Plane",
              draft-ietf-lisp-rfc6833bis-10 (work in progress), March
              2018.





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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

13.2.  Informative References

   [RFC6832]  Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
              "Interworking between Locator/ID Separation Protocol
              (LISP) and Non-LISP Sites", RFC 6832,
              DOI 10.17487/RFC6832, January 2013,
              <https://www.rfc-editor.org/info/rfc6832>.

   [RFC7835]  Saucez, D., Iannone, L., and O. Bonaventure, "Locator/ID
              Separation Protocol (LISP) Threat Analysis", RFC 7835,
              DOI 10.17487/RFC7835, April 2016,
              <https://www.rfc-editor.org/info/rfc7835>.

Authors' Addresses

   Luigi Iannone
   Telecom ParisTech

   EMail: ggx@gigix.net


   Damien Saucez
   INRIA Sophia Antipolis

   EMail: damien.saucez@inria.fr


   Olivier Bonaventure
   Universite catholique de Louvain

   EMail: olivier.bonaventure@uclouvain.be















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