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Network Working Group                                         L. Iannone
Internet-Draft                              TU Berlin - Deutsche Telekom
Intended status: Experimental                            Laboratories AG
Expires: January 13, 2011                                      D. Saucez
                                                          O. Bonaventure
                                        Universite catholique de Louvain
                                                           July 12, 2010


                          LISP Map-Versioning
              draft-iannone-lisp-mapping-versioning-02.txt

Abstract

   This document describes the LISP Map-Versioning mechanism.  This is
   mechanism to provide in-packet information about 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 xTRs about modification of the mappings used to
   encapsulate packets.  Note that, in the LISP encapsulation and in the
   Map Records, bits used for Map-Versioning can be safely ignored by
   xTRs that do not support the mechanism.

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on January 13, 2011.




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Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   described in the BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  3
   3.  EID-to-RLOC Map-Version number . . . . . . . . . . . . . . . .  4
     3.1.  The special Map-Version 0  . . . . . . . . . . . . . . . .  4
   4.  Dealing with Map-Version numbers . . . . . . . . . . . . . . .  5
     4.1.  Handling Destination Map-Version Number  . . . . . . . . .  5
     4.2.  Handling Source Map-Version Number . . . . . . . . . . . .  6
   5.  LISP header and Map-Version numbers  . . . . . . . . . . . . .  7
   6.  Map Record and Map-Version . . . . . . . . . . . . . . . . . .  9
   7.  Benefits and case studies for Map-Versioning . . . . . . . . . 10
     7.1.  Synchronization of different xTRs  . . . . . . . . . . . . 10
     7.2.  Map-Versioning and unidirectional traffic  . . . . . . . . 11
     7.3.  Map-Versioning and interworking  . . . . . . . . . . . . . 11
     7.4.  Graceful RLOC shutdown/withdraw  . . . . . . . . . . . . . 12
     7.5.  Map-Version for lightweight LISP implementation  . . . . . 12
   8.  Incremental deployment and implementation status . . . . . . . 13
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 13
     9.1.  Map-Versioning against traffic disruption  . . . . . . . . 13
     9.2.  Map-Versioning against reachability information DoS  . . . 14
   10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 14
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     11.1. Normative References . . . . . . . . . . . . . . . . . . . 14
     11.2. Informative References . . . . . . . . . . . . . . . . . . 15
   Appendix A.  Map-Version wrap-around . . . . . . . . . . . . . . . 15
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 16








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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 encapsulation.  The mechanism is
   totally transparent to xTRs not supporting such a functionality.  It
   is not meant to replace any existing LISP mechanism, but rather to
   complete them providing new functionalities.  The basic mechanism is
   to associate Map-Version numbers to each LISP 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 mappings used to select the RLOCs in the
   outer header (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-Versions, 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 that sent it is using the
   latest mapping for the destination EID.  If it is not the case the
   eTR can send to the ITR a Map-Request containing the updated mapping
   or invoking 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 xTR receiving such a packet
   to know if it has in its cache the latest mapping for the source EID
   (in case of bidirectional traffic).  If it is not the case a Map-
   Request can be send.


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].




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3.  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 in a per-mapping fashion,
   meaning that different mappings will have assigned a different
   version number, which is also updated independently.  An update in
   the version number (i.e., a newer version) consist 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 than the current Map-Version number and
   the other half is smaller 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 three cases may
   happen:

   V1 = V2 :  This is the exact match case.
   V1 < V2 :  True if and only if V1 < V2 < (V1 + 2**(N-1)).
   V1 > V2 :  True if and only if V1 > V2 > (V1 - 2**(N-1)).

   Using 12 bits, as defined in this document, and assuming a Map-
   Version value of 69, Map-Versions in [70; 69 + 2047] are greater and
   versions in [69 + 2048; (69 + 4095) mod 4096] are smaller.

   The initial Map-Version number of a new mapping can be randomly
   generated.  However, it MUST NOT be zero (0) because it has a special
   meaning (see section Section 3.1).

3.1.  The special Map-Version 0

   The value 0 (zero) is not a valid Map-Version Number.  The only valid
   use of Map-Version number equal to 0 is in the Map Records.  Map
   Records that have Map-Version number equal 0 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 never contain Map-Version number (i.e., V bit MUST
   always be 0).  In other words, Map-Version number equal to 0 signal
   to the requester of the mapping that the Map-Versioning is not
   supported, or even if supported it must not be used for that specific
   EID-Prefix.  Any value different from zero means that Map-Versionig
   is supported and can be used.

   For LISP encapsulated packets with the V-bit set, if the Source Map-
   Version is 0, it means that the version number must be ignored and no
   checks (described in Section 4) need to be performed.

   The fact that the 0 value has a special meaning for the Map-Version



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   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, the next valid value).


4.  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 an ISP
   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
   ISP updates the mapping with a new Map-Version number.

   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  A first one from the EID-to-RLOC mapping in the EID-to-RLOC
      Database used to select the source RLOC, and called Source Map-
      Version Number.
   o  A second one from the EID-to-RLOC mapping in the EID-to-RLOC Cache
      used to select the destination RLOC, and called Destination Map-
      Version Number.
   By embedding both Source Map-Version Number and Destination Map-
   Version Number an ETR can perform the following checks:
   1.  The ITR has an up-to-date mapping in its cache for the
       destination EID and is performing encapsulation correctly.
   2.  In case of bedirectional traffic, the mapping in the local xTR
       cache for the source EID is up-to-date.
   If one or both of the above conditions do not hold, the xTR can send
   a Map-Request either to make the ITR aware that a new mapping is
   available (see Section 4.1) or to updated local mapping in the cache
   (see section Section 4.2).

4.1.  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 LISP 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 is
   done, where the following cases can arise:
   o  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.



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   o  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, this means that
      someone is not behaving correctly w.r.t. the specifications, thus
      the packets carries a not valid version number and can be silently
      dropped.
   o  The packets arrive with an 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.  Further
      actions are needed.  The ITR sending the packet must 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 SMR bit or it will piggy-back
      the newer mapping.  These are not new mechanisms; how to SMR or
      piggy-back mappings in Map-Request messages is already described
      in [I-D.ietf-lisp], while their security is discussed in
      [I-D.saucez-lisp-security].  These Map-Request message should be
      rate limited (rate limitation policies are also described in
      [I-D.ietf-lisp]).  The gain introduced by Map-Version Numbers is
      that after a certain number of retries, if the Destination Map-
      Version Number in the packets is not updated, packet can be
      silently dropped because either the ITR is refusing to use the
      mapping for which the ETR is authoritative or it might be some
      form of attack.  Note that the rule can be even more restrictive.
      If the mapping has been the same for a period of time as long as
      the TTL (defined in LISP [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.  Indeed, if the new mapping with the updated version
      number has been stable for at least the same time as the TTL of
      the older mapping, all the entries in the caches of ITRs must have
      expired.  If packets with old Map-Version number are still
      received, the reason is that either someone has not respected the
      TTL, or it is a form of spoof/attack.  In both cases this is not
      valid behavior w.r.t. the specifications and the packet can be
      silently dropped.

4.2.  Handling Source Map-Version Number

   When an xTR receives a packet, the Source Map-Version Number relates
   to the mapping for the source EID for which the ITR is authoritative.
   If the xTR has an entry in its LISP Cache a check is performed and
   the following cases can arise:
   o  The packet arrives with the same Source Map-Version number stored
      in the LISP Cache.  This is the correct regular case.  The xTR has
      in its cache an up-to-date copy of the mapping.  No further
      actions are needed.



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   o  The packet arrives with a Source Map-Version number greater (i.e.,
      newer) than the one stored in the local LISP Cache.  This means
      that xTR has in its cache a mapping that is stale and needs to be
      updated.  The packet is considered valid but further actions are
      needed.  In particular a Map-Request must 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.
   o  The packet arrives with a Source Map-Version number smaller (i.e.,
      older) than the one stored in the local LISP Cache.  Such a case
      is not valid w.r.t. the specifications.  Indeed, if the mapping is
      already present in the LISP 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 LISP Cache is the correct
      one, hence the packet is not valid and can be silently dropped.

   Otherwise, if the xTR does not have an entry in its cache (e.g.
   unidirectional traffic) the Source Map-Version can be safely ignored.


5.  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.  When the V-bit is set the low-order 24-bits of the
   first longword (which usually contains the nonce) are used transport
   both source and destination Map-Versions.  In particular the first 12
   bits are used for Source Map-Version and the second 12 bits for the
   Destination Map-Version.

   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, IPv6-in-IPv6).  The
   authoritative document for LISP packet format is [I-D.ietf-lisp], the
   following example is proposed only for explanation purposes.













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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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /|Version|  IHL  |Type of Service|          Total Length         |
     / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    /  |         Identification        |Flags|      Fragment Offset    |
   /   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   OH  |  Time to Live | Protocol = 17 |         Header Checksum       |
   \   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    \  |                    Source Routing Locator                     |
     \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      \|                 Destination Routing Locator                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |       Source Port = xxxx      |       Dest Port = 4341        |
   UDP +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |           UDP Length          |        UDP Checksum           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     / |N|L|E|V|I|flags|  Source Map-Version   |Destination Map-Version|
   LISP+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                 Instance ID/Locator Status Bits               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      /|Version|  IHL  |Type of Service|          Total Length         |
     / +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    /  |         Identification        |Flags|      Fragment Offset    |
   /   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   IH  |  Time to Live |    Protocol   |         Header Checksum       |
   \   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    \  |                           Source EID                          |
     \ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      \|                         Destination EID                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   V: this is the Map-Version bit as defined in [I-D.ietf-lisp].  When
      this bit is set to 1 the low-order 24-bits of the first longword
      of the LISP header contain Map-Version numbers.
   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.  Note that the mapping used for such a selection
      is determined by the Source EID through a search in the LISP
      Database of the ITR.
   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.  Note that the mapping used for such a
      selection is determined by the Destination EID, used as lookup key
      in the LISP Cache of the ITR.

   Not all of the LISP encapsulated packets need to carry version
   numbers.  When Map-Version number are carried the V bit must be set



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   to 1.  All legal combination of the flags, when the V-bit is set to 1
   are described in [I-D.ietf-lisp].  As a recall and in summary, Map-
   Version cannot be used with the Echo-Nonce feature (E = 1) and the
   Nonce feature (N = 1), since they use the same bitfield.


6.  Map Record and Map-Version

   To accommodate the proposed mechanism, the Map Records that are
   transported on Map-Request/Map-Reply 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 [I-D.ietf-lisp] and reported here as example.


        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-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 3.1 this field can be zero (0),
      meaning that no Map-Version is associated to the mapping, hence
      LISP encapsulated packet must not contain Map-Version in the LISP
      specific header.

   Note that this packet format works perfectly with xTRs that do not
   support Map-Versioning, since they can simply ignore those bits.
   Furthermore, existing and future mapping distribution protocol (e.g.,
   ALT [I-D.ietf-lisp-alt]) are able to carry version numbers without
   needing any modification.  The same applies to the LISP Map Server
   ([I-D.ietf-lisp-ms]) which will still work without any change since
   reserved bits are simply ignored.





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7.  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 9.

7.1.  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.

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


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

                                 Figure 1

   Obviously in the case of Map-Versioning both xTRs of domain A must
   use the same value otherwise the xTR of domain B will start to send
   Map-Requests.

   The same problem can, however, arise without Map-Versioning.  For
   instance if the two xTRs of domain A send different Loc Status Bits.
   In this case either the traffic is disrupted, if the xTR B trusts the
   Locator Status Bits, or it xTR B 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.



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   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 6.

7.2.  Map-Versioning and unidirectional traffic

   When using Map-Versioning the LISP specific header carries two Map-
   Version numbers, for both source and destination mapping.  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.

    +-----------------+            +-----------------+
    | 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 4, ignoring
   the Source Map-Version number.

7.3.  Map-Versioning and interworking

   Map-Versioning works in the context of interworking between LISP and
   IPv4 and IPv6 ([I-D.ietf-lisp-interworking]) in the following way.

   The case of proxy-ITR encapsulating packet for LISP sites is
   basically the same as the unidirectional traffic case presented in
   the previous section.  The same rules can be applied.  The only
   difference that arises is the fact that a proxy-ITR does not have any
   mapping, since it just encapsulate packets arriving from non-LISP
   site, thus it has no Source Map-Version.  In this case, the proxy-ITR
   will just put the special value 0 (zero) as Source Map-Version
   number, while the receiving ETR will ignore the field.






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7.4.  Graceful 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, because all sites have
   updated the mapping, it can be shut down safely.

7.5.  Map-Version for lightweight LISP implementation

   The use of Map-Versioning can help in simplifying the 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 disruptionless.  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 disruptionless.

   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.  This eases implementation.

   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 proposed in the present section is just a case study
   and MUST NOT be considered as specification for a lightweight LISP
   implementation.







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8.  Incremental deployment and implementation status

   Map-Versioning can be incrementally deployed without any negative
   impact on existing LISP xTRs.  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].


9.  Security Considerations

   Map-Versioning does not introduces any new security issue concerning
   both the data-plane and the control-plane.  On the contrary, as
   described in the following, if Map-Versioning is 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.

   A thorough security analysis of LISP is documented in
   [I-D.saucez-lisp-security].

9.1.  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 4, 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.  Note also
   that in the case of Map-Versioning the attacker should "guess" a
   valid version number that triggers a Map-Request, as described in
   Section 4, otherwise the packet is simply dropped.

   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



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   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 9.2).

9.2.  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.


10.  Acknowledgements

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

   This work has been partially supported by the INFSO-ICT-216372
   TRILOGY Project (www.trilogy-project.org).


11.  References

11.1.  Normative References

   [I-D.ietf-lisp]
              Farinacci, D., Fuller, V., Meyer, D., and D. Lewis,
              "Locator/ID Separation Protocol (LISP)",
              draft-ietf-lisp-07 (work in progress), April 2010.

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



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11.2.  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-04
              (work in progress), April 2010.

   [I-D.ietf-lisp-interworking]
              Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
              "Interworking LISP with IPv4 and IPv6",
              draft-ietf-lisp-interworking-00 (work in progress),
              May 2009.

   [I-D.ietf-lisp-ms]
              Fuller, V. and D. Farinacci, "LISP Map Server",
              draft-ietf-lisp-ms-05 (work in progress), April 2010.

   [I-D.saucez-lisp-security]
              Saucez, D., Iannone, L., and O. Bonaventure, "Notes on
              LISP Security Threats and Requirements",
              draft-saucez-lisp-security-00 (work in progress),
              October 2009.


Appendix A.  Map-Version wrap-around

   The present section proposes an estimation of the wrap-around time
   for proposed 12 bits size for the Map-Version Number.  Using a
   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]).  Using a granularity of
   minutes leads 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 happens considering
   different sizes of the Map-Version Number and different time



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   granularity.

   +---------------+--------------------------------------------+
   |Version Number |           Time before wrap around          |
   |  Size (bits)  +--------------------------------------------+
   |               |Granularity: Minutes | Granularity: Seconds |
   +------------------------------------------------------------+
   |          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 3: Estimation of time before wrap-around


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


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

   Email: olivier.bonaventure@uclouvain.be




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