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Versions: 00 01 02 03 04 05 06 07 08 09 RFC 6834

Network Working Group                                         L. Iannone
Internet-Draft                              TU Berlin - Deutsche Telekom
Intended status: Experimental                            Laboratories AG
Expires: April 15, 2012                                        D. Saucez
                                                          O. Bonaventure
                                        Universite catholique de Louvain
                                                        October 13, 2011


                          LISP Map-Versioning
                 draft-ietf-lisp-map-versioning-05.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 transport
   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 transparent to legacy
   implementations, 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 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 April 15, 2012.

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the



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   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements 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.  Map Record and Map-Version . . . . . . . . . . . . . . . . . . 10
   8.  Benefits and case studies for Map-Versioning . . . . . . . . . 11
     8.1.  Synchronization of different xTRs  . . . . . . . . . . . . 11
     8.2.  Map-Versioning and unidirectional traffic  . . . . . . . . 12
     8.3.  Map-Versioning and interworking  . . . . . . . . . . . . . 13
       8.3.1.  Map-Versioning and Proxy-ITRs  . . . . . . . . . . . . 13
       8.3.2.  Map-Versioning and LISP-NAT  . . . . . . . . . . . . . 14
       8.3.3.  Map-Versioning and Proxy-ETRs  . . . . . . . . . . . . 14
     8.4.  RLOC shutdown/withdraw . . . . . . . . . . . . . . . . . . 15
     8.5.  Map-Version for lightweight LISP implementation  . . . . . 15
   9.  Incremental deployment and implementation status . . . . . . . 16
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 16
     10.1. Map-Versioning against traffic disruption  . . . . . . . . 16
     10.2. Map-Versioning against reachability information DoS  . . . 17
   11. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 17
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 17
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 18
     13.2. Informative References . . . . . . . . . . . . . . . . . . 18
   Appendix A.  Estimation of time before Map-Version wrap-around . . 18
   Appendix B.  Document Change Log . . . . . . . . . . . . . . . . . 19
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21





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1.  Introduction

   This document describes the Map-Versioning mechanism used to provide
   information on changes in the EID-to-RLOC mappings used in the LISP
   ([I-D.ietf-lisp]) context to perform packet encapsulation.  The
   mechanism is totally transparent to xTRs not supporting such
   functionality.  It is not meant to replace any existing LISP
   mechanism, but rather to extend them providing new functionalities.
   If for any unforseen reason a normative conflict between the present
   document and the LISP main specifications is found, the latter
   ([I-D.ietf-lisp]) has precedence on the present document.

   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 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
   receiving the packet to know if the ITR has the latest version number
   that any ETR at the destination EID site has provided to the ITR in a
   Map-Reply.  If it is not the case the ETR can send to the ITR a Map-
   Request containing the updated mapping or soliciting a Map-Request
   from the ITR (both cases are already defined in [I-D.ietf-lisp]).  In
   this way the ITR can update its 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 case of bidirectional
   traffic).  If it is not the case a Map-Request can be sent.



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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

   The present document uses terms already defined in main LISP
   specification [I-D.ietf-lisp].  Hereafter are defined only 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-bits assigned to an EID-to-RLOC
      mapping, not including the value 0 (0x000).

   Null Map-Version:  The 12-bits null value of 0 (0x000) is not used as
      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:  Map-Version number of the EID-to-RLOC
      mapping used to select the source address (RLOC) of the outer IP
      header of LISP-encapsulated packets.

   Destination Map-Version number:  Map-Version number of the EID-to-
      RLOC mapping 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 in an unsigned 12-bits
   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 in incrementing by one the older
   version number.  Appendix A contains a rough estimation of the wrap-
   around time for the Map-Version number.

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




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   1.  V1 = V2 : The map-version number 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 number 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 it 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 mechnisms 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
   Source Map-Version number (cf. Section 5.2) or 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 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,



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   which are part of the Map-Request, Map-Reply and Map-Register
   messages (defined in [I-D.ietf-lisp]).  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 the Map Record refers to, MUST
   either not contain any Map-Version numbers (V bit set to 0), or if it
   contains 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 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 TE 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.  In principle this is orthogonal to whether or not
   map-versioning is used.  The synchronization problem and its
   implication on the traffic is 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:

   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.



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   By embedding both Source Map-Version number and 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
       cache for the destination EID and is performing encapsulation
       correctly.

   2.  In 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
   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 a
   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 packets arrive 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,
       and 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
       its EID-to-RLOC Cache containing stale information.  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 SMR or



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       piggyback mappings in Map-Request messages is already described
       in [I-D.ietf-lisp], while their security is discussed in
       [I-D.ietf-lisp-threats].  These Map-Request messages should be
       rate limited (rate limitation policies are also described in
       [I-D.ietf-lisp]).  The 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 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.
       Another case might be that the control-plane is experiencing
       transient failures so the Map-Requests cannot reach that ITR.  By
       keeping sending Map-Requests at very low rate it is possible to
       recover from this situation.

   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 TTL (defined in
   [I-D.ietf-lisp]) 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.  The reason that allows such
   action is the fact that 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 caches of ITRs must have
   expired.  Hence, all ITRs sending traffic should have refreshed the
   mapping according to [I-D.ietf-lisp].  If packets with old Map-
   Version number 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 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
   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 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 stored
       in the EID-to-RLOC Cache.  This is the correct regular case.  The
       ITR has in its 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 ETR has in its 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], 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 anyhow, 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 (e.g., in case of unidirectional traffic) 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 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] Section 5.3.  When the



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   V-bit is set the low-order 24-bits of the first longword are used to
   transport both source and destination Map-Version numbers.  In
   particular the first 12 bits are used for Source Map-Version number
   and the second 12 bits for the Destination Map-Version number.

   Hereafter is the example of LISP header carrying version numbers in
   the case of IPv4-in-IPv4 encapsulation.  The same setting can be used
   for any other case (IPv4-in-IPv6, IPv6-in-IPv4, and IPv6-in-IPv6).

        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|flags|  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.  How to set on transmission and handle on
      reception this value is described in Section 5.2.

   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.  How to set on transmission and handle on
      reception this value is described in Section 5.1.

   The present document just specifies how to use the low-order 24-bits
   of the first longword of the LISP-specific header when the V-bit is
   set to 1.  All other cases, including the bit fields of the rest of
   the LISP-specific header and the whole LISP packet format are
   specified in [I-D.ietf-lisp].  Not all of the LISP encapsulated
   packets need to carry version numbers.  When Map-Version numbers are
   carried the V-bit MUST be set to 1.  All legal combinations of the
   flags, when the V-bit is set to 1, are described in [I-D.ietf-lisp].


7.  Map Record and Map-Version

   To accommodate the proposed mechanism, the Map Records that are
   transported on 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 describe a mapping is
   used.  This is defined in Section 6.1.4 of [I-D.ietf-lisp] and
   reported here as 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.


8.  Benefits and case studies for Map-Versioning

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

8.1.  Synchronization of different xTRs

   Map-Versioning does not require additional synchronization mechanism
   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, 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.

   As an example, let's consider the topology of Figure 1 where ITR A.1
   of domain A is sending unidirectional traffic to the domain B, while
   A.2 of domain A exchange bidirectional traffic with domain B. In



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   particular, ITR A.2 send 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 1

   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 Loc Status Bits.
   In this case either the traffic is disrupted, if the ETR B trusts the
   Locator Status Bits, or if ETR B does not trusts the Locator Status
   Bits it will start sending Map-Requests to confirm the each change in
   the 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 7.

8.2.  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, like for instance in the case presented in Figure 2, since
   LISP specification do not mandate for ETR to have a mapping for the
   source EID.




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

                                 Figure 2

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

   For what concerns the ETR, it simply checks only the Destination Map-
   Version number in the same way as described in Section 5, ignoring
   the Source Map-Version number.

8.3.  Map-Versioning and interworking

   Map-Versioning is compatible with the LISP interworking between LISP
   and non-LISP sites as defined in [I-D.ietf-lisp-interworking].  LISP
   interworking defines three techniques to make LISP sites and non-LISP
   sites, namely Proxy-ITR, LISP-NAT, and Proxy-ETR.  Hereafter it is
   described how Map-Versioning relates to these three mechanisms.

8.3.1.  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 3).  This case is very
   similar to the unidirectional traffic case described in Section 8.2,
   hence similar rules apply.

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

                                 Figure 3

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



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

   With this setup the LISP Domain A is able to check whether or not the
   PITR is using the latest mapping.  If this is not the case the
   mapping for LISP Domain A on the PITR can be updated using one of the
   mechanisms defined in [I-D.ietf-lisp] and
   [I-D.ietf-lisp-interworking].

8.3.2.  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.

8.3.3.  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 4).  One of the main reasons of 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 4

   A Proxy-ETR does not have any mapping, since it just decapsulates
   packets arriving from LISP site.  In this case, the ITR will just put
   the Null Map-Version value as 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.  If this is the case the mapping for LISP Domain
   A on the PETR can be updated using one of the mechanisms defined in
   [I-D.ietf-lisp] and [I-D.ietf-lisp-interworking].







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8.4.  RLOC shutdown/withdraw

   Map-Versioning can be even 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 (R bit
   in the Map Record, see [I-D.ietf-lisp]), but without actually turning
   it off.

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

   It should be pointed out that for frequent up/down changes such a
   mechanism should not be used since this can generate excessive load
   on the Mapping System.

8.5.  Map-Version for lightweight LISP implementation

   The use of Map-Versioning can help in developing a lightweight
   implementation of LISP.  This comes with the price of not supporting
   Loc-Status-Bit, which are 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 (see section 6.5 of [I-D.ietf-lisp]).  With Map-Versioning such
   type 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 Section 6.5 of [I-D.ietf-lisp].  A new mapping
   with a new Map-Version number will be issued, and since the old
   locators are still valid the transition will be with no disruptions.
   The same applies for the case a 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 the transition will be with no disruptions.

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

   Further, Map-Version can be used to substitute the "clock sweep"
   operation described in Section 6.5.1 of [I-D.ietf-lisp].  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.

   Note that what is proposed in the present section is just an example
   and MUST NOT be considered as specifications for a lightweight LISP



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   implementation.  In case the IETF decides to undertake such a work,
   it will be documented elsewhere.


9.  Incremental deployment and implementation status

   Map-Versioning can be incrementally deployed without any negative
   impact on existing LISP elements (e.g., xTRs, Map-Servers, Proxy-
   ITRs, etc).  Any LISP element that does not support Map-Versioning
   can safely ignore them.  Further, there is no need of any specific
   mechanism to discover if an xTR supports or not Map-Versioning.  This
   information is already included in the Map Record.

   Map-Versioning is currently implemented in OpenLISP
   [I-D.iannone-openlisp-implementation].

   Note that the reference document for LISP implementation and
   interoperability tests remains [I-D.ietf-lisp].


10.  Security Considerations

   Map-Versioning does not introduce any security issue concerning both
   the data-plane and the control-plane.  On the contrary, as described
   in the following, if Map-Versioning may be used also to update
   mappings in 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 [I-D.ietf-lisp-threats].

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 system are out of the scope of this document.  In the
   case of Map-Versioning the attacker should "guess" a valid version



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   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 limitations policies described in
   [I-D.ietf-lisp] in order to avoid DoS attacks.

   Note that a similar level of security can be obtained with Loc Status
   Bits, by simply making mandatory to verify any change through a Map-
   Request.  However, in this case Locator Status Bits loose their
   meaning, because, it does not matter anymore which specific bits has
   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 the 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 raise another type of attack discussed in
   Section 10.2).

10.2.  Map-Versioning against reachability information DoS

   Attackers can try to trigger a large amount of Map-Request by simply
   forging packets with random Map-Version or random Locator Status
   Bits.  In both cases the Map-Requests are rate limited as described
   in [I-D.ietf-lisp].  However, differently from Locator Status Bit
   where there is no filtering possible, in the case of Map-Versioning
   is possible to filter not valid version numbers before triggering a
   Map-Request, thus helping in reducing 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 that a mapping has been
   updated.

   It is clear, that Map-Versioning does not protect against DoS and
   DDoS attacks, where an xTR looses processing power doing checks on
   the LISP header of packets sent by attackers.  This is independent
   from Map-Versioning and is the same for Loc Status Bits.


11.  IANA Considerations

   This document has no actions for IANA.


12.  Acknowledgements

   The authors would like to thank Alia Atlas, Jesper Skriver, Pierre
   Francois, Noel Chiappa, Dino Farinacci for their comments and review.

   This work has been partially supported by the INFSO-ICT-216372



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   TRILOGY Project (www.trilogy-project.org).


13.  References

13.1.  Normative References

   [I-D.ietf-lisp]
              Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
              "Locator/ID Separation Protocol (LISP)",
              draft-ietf-lisp-15 (work in progress), July 2011.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

13.2.  Informative References

   [I-D.iannone-openlisp-implementation]
              Iannone, L., Saucez, D., and O. Bonaventure, "OpenLISP
              Implementation Report",
              draft-iannone-openlisp-implementation-01 (work in
              progress), July 2008.

   [I-D.ietf-lisp-alt]
              Fuller, V., Farinacci, D., Meyer, D., and D. Lewis, "LISP
              Alternative Topology (LISP+ALT)", draft-ietf-lisp-alt-09
              (work in progress), September 2011.

   [I-D.ietf-lisp-interworking]
              Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
              "Interworking LISP with IPv4 and IPv6",
              draft-ietf-lisp-interworking-02 (work in progress),
              June 2011.

   [I-D.ietf-lisp-ms]
              Fuller, V. and D. Farinacci, "LISP Map Server",
              draft-ietf-lisp-ms-11 (work in progress), August 2011.

   [I-D.ietf-lisp-threats]
              Saucez, D., Iannone, L., and O. Bonaventure, "LISP Threats
              Analysis", draft-ietf-lisp-threats-00 (work in progress),
              July 2011.


Appendix A.  Estimation of time before Map-Version wrap-around

   The present section proposes an estimation of the wrap-around time
   for the proposed 12 bits size for the Map-Version number.  Using a



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   granularity of seconds and assuming as worst-case that a new version
   is issued each second, it takes slightly more than 1 hour before the
   version wraps around.  Note that the granularity of seconds is in
   line with the rate limitation policy for Map-Request messages, as
   proposed in the LISP main specifications ([I-D.ietf-lisp]).
   Alternatively a granularity of minutes can also be used, as for the
   TTL of the Map-Reply ([I-D.ietf-lisp]).  In this case the worst
   scenario is when a new version is issued every minute, leading to a
   much longer time before wrap-around.  In particular, when using 12
   bits, the wrap-around time is almost 3 days.

   For general information, hereafter there is a table with a rough
   estimation of the time before wrap-around in the worst-case scenario,
   considering different sizes (bits length) of the Map-Version number
   and different time granularity.

   +---------------+--------------------------------------------+
   |Version Number |           Time before wrap around          |
   |  Size (bits)  +---------------------+----------------------+
   |               |Granularity: Minutes | Granularity: Seconds |
   |               | (mapping changes    | (mapping changes     |
   |               |  every 1 minute)    |  every 1 second)     |
   +-------------------------------------+----------------------+
   |          32   |   8171   Years      |  136   Years         |
   |          30   |   2042   Years      |   34   Years         |
   |          24   |     31   Years      |  194   Days          |
   |          16   |     45   Days       |   18   Hours         |
   |          15   |     22   Days       |    9   Hours         |
   |          14   |     11   Days       |    4   Hours         |
   |          13   |      5.6 Days       |    2.2 Hours         |
   |          12   |      2.8 Days       |    1.1 Hours         |
   +---------------+---------------------+----------------------+

              Figure 5: Estimation of time before wrap-around


Appendix B.  Document Change Log

   o  Version 05 Posted October 2011.

      *  Added sentence in Section 3 on the use of Big Endian, as for
         comment of P. Resnick.

      *  Extended the end of Section 4 in order to clarify that Map-
         Version numbers are assigned to mappings by configuration and
         not automatically generated by ETRs, as for comments of R.
         Sparks




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      *  Changed formal definition of Map-Version order (greater vs.
         smaller) in Section 4 as for comments from R. Housley and R.
         Sparks.

      *  Added disclaimer in Section 1 stating that in case of unforseen
         conflict with the main spec the base document has precedence on
         the present one, as for comment from Sthephen Farrell.

   o  Version 04 Posted September 2011.

      *  Added clarifications in Section 1, Section 4, Section 5.2, and
         Section 5.1 to address Stephen Farrell's comments.

      *  Used the term LISP Site instead of ISP in Section 5 as
         suggested by Stephen Farrell.

      *  Deleted "(usually contains the nonce)" from Section 6 because
         confusing, as suggested by Stephen Farrell.

      *  Fixed several typos pointed out by Stephen Farrell.

   o  Version 03 Posted September 2011.

      *  Added reference in Section 7 toward the main lisp documents
         specifying the section, as requested by Jari Arkko.

      *  Fixed all typos and editorial issues pointed out by Jari Arkko.

      *  Added clarification in Section 8.4 as requested by Jari Arkko.

      *  Extentend all acronyms in the abstract as requested by Jari
         Arkko.

      *  Clarified silent drop polocy in Section 5.2 as requested by
         both Richard Barnes and Jari Arkko.

      *  Fixed typos pointed out by Richard Barnes.

   o  Version 02 Posted July 2011.

      *  Added text in Section 5 about ETR synchronization, as suggested
         by Alia Atlas.

      *  Modified text in Section 8.5 concerning lightweight LISP
         implementation, as suggested by Alia Atlas.

      *  Deleted text concerning old versions of [I-D.ietf-lisp-ms] and
         [I-D.ietf-lisp-alt] in Section 7, as pointed out by Alia Atlas.



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      *  Fixed section 4.1 to be less restrictive, as suggested by
         Jesper Skriver.

   o  Version 01 Posted March 2011.

      *  Changed the wording from "Map-Version number 0" to "Null Map-
         Version.

      *  Clarification of the use of the Null Map-Version value as
         Source Map-Version Number and Destination Map-Version Number.

      *  Extended the section describing Map-Versioning and LISP
         Interworking co-existence.

      *  Reduce packet format description to avoid double definitions
         with the main specs.

   o  Version 00 Posted September 2010.

      *  Added Section "Definitions of Terms".

      *  Editorial polishing of all sections.

      *  Added clarifications in section "Dealing with Map-Version
         numbers" for the case of the special Map-Version number 0.

      *  Rename of draft-iannone-mapping-versioning-02.txt.


Authors' Addresses

   Luigi Iannone
   TU Berlin - Deutsche Telekom Laboratories AG
   Ernst-Reuter Platz 7
   Berlin
   Germany

   Email: luigi@net.t-labs.tu-berlin.de


   Damien Saucez
   Universite catholique de Louvain
   Place St. Barbe 2
   Louvain-la-Neuve
   Belgium

   Email: damien.saucez@uclouvain.be




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   Olivier Bonaventure
   Universite catholique de Louvain
   Place St. Barbe 2
   Louvain-la-Neuve
   Belgium

   Email: olivier.bonaventure@uclouvain.be












































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