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rfc:rfc6834

Internet Engineering Task Force (IETF) L. Iannone Request for Comments: 6834 Telecom ParisTech Category: Experimental D. Saucez ISSN: 2070-1721 INRIA Sophia Antipolis

                                                        O. Bonaventure
                                      Universite catholique de Louvain
                                                          January 2013
        Locator/ID Separation Protocol (LISP) Map-Versioning

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 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 the
 mechanism.

Status of This Memo

 This document is not an Internet Standards Track specification; it is
 published for examination, experimental implementation, and
 evaluation.
 This document defines an Experimental Protocol for the Internet
 community.  This document is a product of the Internet Engineering
 Task Force (IETF).  It represents the consensus of the IETF
 community.  It has received public review and has been approved for
 publication by the Internet Engineering Steering Group (IESG).  Not
 all documents approved by the IESG are a candidate for any level of
 Internet Standard; see Section 2 of RFC 5741.
 Information about the current status of this document, any errata,
 and how to provide feedback on it may be obtained at
 http://www.rfc-editor.org/info/rfc6834.

Iannone, et al. Experimental [Page 1] RFC 6834 LISP Map-Versioning January 2013

Copyright Notice

 Copyright (c) 2013 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
 (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 ............................10
 7. Map Record and Map-Version .....................................11
 8. Benefits and Case Studies for Map-Versioning ...................12
    8.1. Map-Versioning and Unidirectional Traffic .................12
    8.2. Map-Versioning and Interworking ...........................12
         8.2.1. Map-Versioning and Proxy-ITRs ......................13
         8.2.2. Map-Versioning and LISP-NAT ........................13
         8.2.3. Map-Versioning and Proxy-ETRs ......................14
    8.3. RLOC Shutdown/Withdraw ....................................14
    8.4. Map-Version for Lightweight LISP Implementation ...........15
 9. Incremental Deployment and Implementation Status ...............15
 10. Security Considerations .......................................16
    10.1. Map-Versioning against Traffic Disruption ................16
    10.2. Map-Versioning against Reachability Information DoS ......17
 11. Open Issues and Considerations ................................17
    11.1. Lack of Synchronization among ETRs .......................17
 12. Acknowledgments ...............................................19
 13. References ....................................................19
    13.1. Normative References .....................................19
    13.2. Informative References ...................................19
 Appendix A. Estimation of Time before Map-Version Wrap-Around .....21

Iannone, et al. Experimental [Page 2] RFC 6834 LISP Map-Versioning January 2013

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
 [RFC6830]) context to perform packet encapsulation.  The mechanism is
 totally transparent to xTRs (Ingress and Egress Tunnel Routers) not
 supporting such functionality.  It is not meant to replace any
 existing LISP mechanisms but rather to extend them by providing new
 functionalities.  If for any unforeseen reason a normative conflict
 between this document and the LISP main specifications is found, the
 latter ([RFC6830]) has precedence over this 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 (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 has
 the latest version number that any ETR at the destination EID site
 has provided 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 [RFC6830]).  In this way, the ITR can update its EID-to-RLOC
 Cache.  On the other hand, it enables an ETR receiving such a packet

Iannone, et al. Experimental [Page 3] RFC 6834 LISP Map-Versioning January 2013

 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.
 Issues and concerns about the deployment of LISP for Internet traffic
 are discussed in [RFC6830].  Section 11 provides additional issues
 and concerns raised by this document.  In particular, Section 11.1
 provides details about the ETRs' synchronization issue in the context
 of Map-Versioning.

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 [RFC6830].  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.  Appendix A contains a rough estimation of the
 wrap-around time for the Map-Version number.

Iannone, et al. Experimental [Page 4] RFC 6834 LISP Map-Versioning January 2013

 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
 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

Iannone, et al. Experimental [Page 5] RFC 6834 LISP Map-Versioning January 2013

 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,
 which are part of the Map-Request, Map-Reply, and Map-Register
 messages (defined in [RFC6830]).  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.  In principle, this is orthogonal to whether or
 not Map-Versioning is used.  The synchronization problem and its
 implication on the traffic are out of the scope of this document (see
 Section 11).

Iannone, et al. Experimental [Page 6] RFC 6834 LISP Map-Versioning January 2013

 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.
 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

Iannone, et al. Experimental [Page 7] RFC 6834 LISP Map-Versioning January 2013

     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
     its EID-to-RLOC Cache containing stale information.  The ETR MAY
     choose to normally process the encapsulated datagram according to
     [RFC6830]; 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
     [RFC6830], while their security is discussed in [LISP-THREATS].
     These Map-Request messages should be rate-limited
     (rate-limitation policies are also described in [RFC6830]).  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 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.  Another case might be that the
     control plane is experiencing transient failures, so the
     Map-Requests cannot reach that ITR.  By continually sending
     Map-Requests at a 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 Time to Live
 (TTL) (defined in [RFC6830]) 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 [RFC6830].  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.

Iannone, et al. Experimental [Page 8] RFC 6834 LISP Map-Versioning January 2013

 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.

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 [RFC6830], 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.

Iannone, et al. Experimental [Page 9] RFC 6834 LISP Map-Versioning January 2013

 If the ETR does not have an entry in the EID-to-RLOC Cache for the
 source EID (e.g., in the 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 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 [RFC6830] Section 5.3.  When
 the V-bit is set, the low-order 24 bits of the first longword are
 used to transport both the source and 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 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.  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.
 This document only 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 [RFC6830].  Not all of the LISP-encapsulated packets need to carry

Iannone, et al. Experimental [Page 10] RFC 6834 LISP Map-Versioning January 2013

 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 [RFC6830].

7. 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-Prefix-AFI' field in the Record that describes a
 mapping are used.  This is defined in Section 6.1.4 of [RFC6830] and
 reported here as an 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-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.

Iannone, et al. Experimental [Page 11] RFC 6834 LISP Map-Versioning January 2013

8. 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.

8.1. 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.
           +-----------------+            +-----------------+
           | 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.

8.2. 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.

Iannone, et al. Experimental [Page 12] RFC 6834 LISP Map-Versioning January 2013

8.2.1. 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 8.1;
 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
 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.  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 [RFC6830] and [RFC6832].

8.2.2. 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.

Iannone, et al. Experimental [Page 13] RFC 6834 LISP Map-Versioning January 2013

8.2.3. 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.  If this is the case, the mapping for LISP
 Domain A on the PETR can be updated using one of the mechanisms
 defined in [RFC6830] and [RFC6832].

8.3. 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 [RFC6830]), but without actually
 turning it off.
 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.
 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.

Iannone, et al. Experimental [Page 14] RFC 6834 LISP Map-Versioning January 2013

8.4. Map-Version for Lightweight LISP Implementation

 The use of Map-Versioning can help in developing a lightweight
 implementation of LISP.  However, this comes with the price of not
 supporting the Locator-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
 Locator-Status-Bits (see Section 6.5 of [RFC6830]).  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 Section 6.5 of
 [RFC6830].  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.
 Further, Map-Versioning can be used as a substitute for the "clock
 sweep" operation described in Section 6.6.1 of [RFC6830].  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 this section is just an example and
 MUST NOT be considered as specifications for a lightweight LISP
 implementation.  If the IETF decides to undertake such 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 Map-Version numbers carried in the
 LISP header.  Further, there is no need of any specific mechanism to
 discover whether or not an xTR supports Map-Versioning.  This
 information is already included in the Map Record.
 Map-Versioning is currently implemented in OpenLISP [OPENLISP].

Iannone, et al. Experimental [Page 15] RFC 6834 LISP Map-Versioning January 2013

 Note that the reference document for LISP implementations and
 interoperability tests remains [RFC6830].

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 [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 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
 [RFC6830] in order to avoid DoS attacks.
 Note that a similar level of security can be obtained with
 Locator-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).

Iannone, et al. Experimental [Page 16] RFC 6834 LISP Map-Versioning January 2013

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 [RFC6830].  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
 LISP header of packets sent by attackers.  This is independent of
 Map-Versioning and is the same for Locator-Status-Bits.

11. Open Issues and Considerations

 There are a number of implications of the use of Map-Versioning that
 are not yet completely explored.  Among these are:
 o  Performance of the convergence time when an EID-to-RLOC mapping
    changes, i.e., how much time is needed to update mappings in the
    EID-to-RLOC Cache of the ITRs currently sending traffic to ETRs
    for the EID whose mapping has been changed.
 o  Support for ETR synchronization.  The implications that a
    temporary lack of synchronization may have on the traffic are yet
    to be fully explored.  Details on how to maintain synchronization
    are presented in Section 6.6 of [RFC6830].  Section 11.1 discusses
    the issue in further detail with respect to the Map-Versioning
    mechanism.
 The authors expect that experimentation will help assess the
 performance and limitations of the Map-Versioning mechanism.  Issues
 and concerns about the deployment of LISP for Internet traffic are
 discussed in [RFC6830].

11.1. Lack of Synchronization among ETRs

 Even without Map-Versioning, LISP ([RFC6830]) 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.

Iannone, et al. Experimental [Page 17] RFC 6834 LISP Map-Versioning January 2013

 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
 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.

Iannone, et al. Experimental [Page 18] RFC 6834 LISP Map-Versioning January 2013

 So far, LISP does not provide any specific synchronization mechanism
 but assumes that synchronization is provided by configuring the
 different xTRs consistently (see Section 6.6 in [RFC6830]).  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.

12. Acknowledgments

 The authors would like to thank Alia Atlas, Jesper Skriver, Pierre
 Francois, Noel Chiappa, and Dino Farinacci for their comments and
 review.
 This work has been partially supported by the INFSO-ICT-216372
 TRILOGY Project (http://www.trilogy-project.org).

13. References

13.1. Normative References

 [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
            Requirement Levels", BCP 14, RFC 2119, March 1997.
 [RFC6830]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
            Locator/ID Separation Protocol (LISP)", RFC 6830,
            January 2013.
 [RFC6832]  Lewis, D., Meyer, D., Farinacci, D., and V. Fuller,
            "Interworking between Locator/ID Separation Protocol
            (LISP) and Non-LISP Sites", RFC 6832, January 2013.

13.2. Informative References

 [LISP-THREATS]
            Saucez, D., Iannone, L., and O. Bonaventure, "LISP Threats
            Analysis", Work in Progress, October 2012.
 [OPENLISP] Iannone, L., Saucez, D., and O. Bonaventure, "Implementing
            the Locator/ID Separation Protocol: Design and
            experience", Computer Networks Vol. 55, Number 4,
            Pages 948-958, March 2011.

Iannone, et al. Experimental [Page 19] RFC 6834 LISP Map-Versioning January 2013

Appendix A. Estimation of Time before Map-Version Wrap-Around

 This section proposes an estimation of the wrap-around time for the
 12-bit size of 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 ([RFC6830]).
 Alternatively, a granularity of minutes can also be used, as for the
 TTL of the Map-Reply ([RFC6830]).  In this case, the worst-case
 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, Figure 5 below provides a rough estimation
 of the time before wrap-around in the worst-case scenario,
 considering different sizes (length in bits) of the Map-Version
 number and different time granularities.
 Since even in the case of a high mapping change rate (1 per second)
 the wrap-around time using 12 bits is far larger than any reasonable
 Round-Trip Time (RTT), there is no risk of race conditions.
    +---------------+--------------------------------------------+
    |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

Iannone, et al. Experimental [Page 20] RFC 6834 LISP Map-Versioning January 2013

Authors' Addresses

 Luigi Iannone
 Telecom ParisTech
 EMail: luigi.iannone@telecom-paristech.fr
 Damien Saucez
 INRIA Sophia Antipolis
 2004 route des Lucioles - BP 93
 Sophia Antipolis
 France
 EMail: damien.saucez@inria.fr
 Olivier Bonaventure
 Universite catholique de Louvain
 Place St. Barbe 2
 Louvain-la-Neuve
 Belgium
 EMail: olivier.bonaventure@uclouvain.be

Iannone, et al. Experimental [Page 21]

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