LISP Working Group                                    A. Rodriguez-Natal
Internet-Draft                                                V. Ermagan                                             Cisco Systems
Intended status: Experimental                                   J. Leong                                 V. Ermagan
Expires: May 7, September 12, 2019                                       Google
                                                                J. Leong
                                                                F. Maino
                                                           Cisco Systems
                                                    A. Cabellos-Aparicio
                                       Technical University of Catalonia
                                                               S. Barkai
                                                        Fermi Serverless
                                                            D. Farinacci
                                                            M. Boucadair
                                                            C. Jacquenet
                                                                S. Secci
                                                        November 3, 2018
                                                          March 11, 2019

                Publish/Subscribe Functionality for LISP


   This document specifies an extension to the use of Map-Request to
   enable Publish/Subscribe (PubSub) operation for LISP.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   3.  Definition of Terms . . . . . . . . . . . . . . . . . . . . .   3
   4.  Deployment Assumptions  . . . . . . . . . . . . . . . . . . .   4
   5.   3
   4.  Map-Request PubSub Additions  . . . . . . . . . . . . . . . .   4
   5.  Mapping Request Subscribe Procedures  . . . . . . . . . . . .   6
   6.  Mapping Notification Publish Procedures . . . . . . . . . . .   8
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   11.   9
   10. Normative References  . . . . . . . . . . . . . . . . . . . .  10
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   The Locator/ID Separation Protocol (LISP) [I-D.ietf-lisp-rfc6833bis]
   splits current IP addresses in two different namespaces, Endpoint
   Identifiers (EIDs) and Routing Locators (RLOCs).  LISP uses a map-
   and-encap approach that relies on (1) a Mapping System (basically a
   distributed database) that stores and disseminates EID-RLOC mappings
   and on (2) LISP tunnel routers (xTRs) that encapsulate and
   decapsulate data packets based on the content of those mappings.

   Ingress Tunnel Routers (ITRs) / Re-encapsulating Tunnel Routers
   (RTRs) / Proxy Ingress Tunnel Routers (PITRs) pull EID-to-RLOC
   mapping information from the Mapping System by means of an explicit
   request message.  [I-D.ietf-lisp-rfc6833bis] indicates how Egress
   Tunnel Routers (ETRs) can tell ITRs/RTRs/PITRs about mapping changes.
   This document presents a Publish/Subscribe (PubSub) extension in
   which the Mapping System can notify ITRs/RTRs/PITRs about mapping
   changes.  When this mechanism is used, mapping changes can be
   notified faster and can be managed in the Mapping System versus the
   LISP sites.

   In general, when an ITR/RTR/PITR wants to be notified for mapping
   changes for a given EID-prefix, the following steps occur:

   (1)  The ITR/RTR/PITR sends a Map-Request for that EID-prefix.

   (2)  The ITR/RTR/PITR sets the Notification-Requested bit (N-bit) on
        the Map-Request and includes its xTR-ID and Site-ID.

   (3)  The Map-Request is forwarded to one of the Map-Servers that the
        EID-prefix is registered to.

   (4)  The Map-Server creates subscription state for the ITR/RTR/PITR
        on the EID-prefix.

   (5)  The Map-Server sends a Map-Notify to the ITR/RTR/PITR to
        acknowledge the successful subscription.

   (6)  When there is an RLOC-set change for the EID-prefix, the Map-
        Server sends a Map-Notify message to each ITR/RTR/PITR in the
        subscription list.

   (7)  Each ITR/RTR/PITR sends a Map-Notify-Ack to acknowledge the
        received Map-Notify.

   This operation is repeated for all EID-prefixes for which ITR/RTR/
   PITR want to be notified.  The ITR/RTR/PITR can set the N-bit for
   several EID-prefixes within a single Map-Request.

2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].

3.  Definition of Terms

      LISP xTR-ID: A 128-bit field that is used as a unique identifier
      for an xTR.  The xTR-ID is especially useful for identifying
      multiple xTRs serving the same site/EID-prefix.  A value of all
      zeros indicate the xTR-ID is unspecified.

      LISP Site-ID: A 64-bit field that is used as a unique identifier
      of a group of xTRs belonging to the same site.  A value of 0
      indicate the Site-ID is unspecified.

4.  Deployment Assumptions

   The specification described in this document makes the following
   deployment assumptions:

   (1)  A unique 128-bit xTR-ID (plus a 64-bit Site-ID) identifier is
        assigned to each xTR.

   (2)  Map-Servers are configured in proxy-reply mode, i.e., they are
        solicited to generate and send Map-Reply messages for the
        mappings they are serving.

   (3)  There can be either a soft-state or hard-state security
        association between the xTRs and the Map-Servers.

   The distribution of xTR-IDs (and Site-IDs) as well as the management
   of security associations are out of the scope of this document and
   are for further study (see Section 8).

5. 7).

4.  Map-Request PubSub Additions

   Figure 1 shows the format of the updated Map-Request to support the
   PubSub functionality.

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       |Type=1 |A|M|P|S|p|s|R|I|   Reserved  |  Rsvd   |L|D|   IRC   | Record Count  |
       |                         Nonce . . .                           |
       |                         . . . Nonce                           |
       |         Source-EID-AFI        |   Source EID Address  ...     |
       |         ITR-RLOC-AFI 1        |    ITR-RLOC Address 1  ...    |
       |                              ...                              |
       |         ITR-RLOC-AFI n        |    ITR-RLOC Address n  ...    |
     / |N|   Reserved  | EID mask-len  |        EID-Prefix-AFI         |
   Rec +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     \ |                       EID-Prefix  ...                         |
       |                   Map-Reply Record  ...                       |
       |                                                               |
       +                                                               +
       |                                                               |
       +                            xTR-ID                             +
       |                                                               |
       +                                                               +
       |                                                               |
       |                                                               |
       +                           Site-ID                             +
       |                                                               |

       Figure 1: Map-Request with I-bit, N-bit, xTR-ID, and Site-ID

   The following is added to the Map-Request message defined in
   Section 5.2 of [I-D.ietf-lisp-rfc6833bis]:

      xTR-ID bit (I-bit): The I-bit of a Map-Request message is set to 1
      to indicate that a 128 bit xTR-ID and a 64 bit Site-ID fields are
      present at the end of the Map-Request message.  If an xTR is
      configured with an xTR-ID or Site-ID, it MUST set the I-bit to 1
      and include its xTR-ID and Site-ID in the Map-Request messages it
      generates.  If either the xTR-ID or Site-ID is not configured, an
      unspecified value is encoded for whichever ID that is not

      Notification-Requested bit (N-bit): The N-bit of an EID-record is
      set to 1 to specify that the xTR wants to be notified of updates
      for that mapping record.

      xTR-ID field: xTR-ID is a 128 bit field at the end of the Map-
      Request message, starting after the final Record in the message
      (or the Map-Reply Record, if present).  The xTR-ID is used to
      uniquely identify the sender of a Map-Request message, especially
      in the case where a site has more than one xTR.  A value of all
      zeros indicate that an xTR-ID is not specified, though encoded in
      the message.  This is useful in the case where a Site-ID is
      specified, but no  The xTR-ID
      is configured. defined in [I-D.ietf-lisp-rfc6833bis]

      Site-ID field: Site-ID is a 64 bit field at the end of the Map-
      Request message, following the xTR-ID.  Site-ID is used by the
      Map-Server receiving the Map-Request message to identify which
      xTRs belong to the same site.  A value of 0 indicates that a Site-
      ID  The Site-ID is not specified, though encoded defined in the message.


5.  Mapping Request Subscribe Procedures

   The xTR subscribes for RLOC-set changes for a given EID-prefix by
   sending a Map-Request to the Mapping System with the N-bit set on the
   EID-Record.  The xTR builds a Map-Request according to
   [I-D.ietf-lisp-rfc6833bis] but also does the following:

   (1)  The xTR MUST set the I-bit to 1 and append its xTR-ID and Site-
        ID to the Map-Request.  The xTR-ID uniquely identifies the xTR.

   (2)  The xTR MUST set the N-bit to 1 for each EID-Record to which the
        xTR wants to subscribe.

   The Map-Request is forwarded to the appropriate Map-Server through
   the Mapping System.  This document does not assume that a Map-Server
   is pre-assigned to handle the subscription state for a given xTR.
   The Map-Server that receives the Map-Request will be the Map-Server
   responsible to notify that specific xTR about future mapping changes
   for the subscribed mapping records.

   Upon receipt of the Map-Request, the Map-Server processes it as
   described in [I-D.ietf-lisp-rfc6833bis].  Furthermore, upon
   processing, for each EID-Record that has the N-bit set to 1, the Map-
   Server proceeds adding the xTR-ID contained in the Map-Request to the
   list of xTR that have requested to be subscribed to that mapping

   If the xTR-ID is added to the list, the Map-Server MUST send a Map-
   Notify message back to the xTR to acknowledge the successful
   subscription.  The Map-Server MUST follow the specification in
   Section 6.1.7 of [I-D.ietf-lisp-rfc6833bis] to build the Map-Notify
   with the following considerations:

   (1)  The Map-Server MUST use the nonce from the Map-Request as the
        nonce for the Map-Notify.

   (2)  The Map-Server MUST use its security association with the xTR
        (see Section 4) 3) to compute the authentication data of the Map-

   (3)  The Map-Server MUST send the Map-Notify to one of the ITR-RLOCs
        received in the Map-Request.

   When the xTR receives a Map-Notify with a nonce that matches one in
   the list of outstanding Map-Request messages sent with an N-bit set,
   it knows that the Map-Notify is to acknowledge a successful
   subscription.  The xTR processes this Map-Notify as described in
   [I-D.ietf-lisp-rfc6833bis] with the following considerations.  The
   xTR MUST use its security association with the Map-Server (see
   Section 4) 3) to validate the authentication data on the Map-Notify.
   The xTR MUST use the Map-Notify to populate its map-cache with the
   returned EID-prefix and RLOC-set.

   The subscription of an xTR-ID to the list of subscribers for the EID-
   Record may fail for a number of reasons.  For example, because of
   local configuration policies (such as white/black lists of
   subscribers), or because the Map-Server has exhausted the resources
   to dedicate to the subscription of that EID-Record (e.g., the number
   of subscribers excess the capacity of the Map-Server).

   If the subscription fails, the Map-Server MUST send a Map-Reply to
   the originator of the Map-Request, as described in
   [I-D.ietf-lisp-rfc6833bis].  This is also the case when the Map-
   Server does not support PubSub operation.  The xTR processes the Map-
   Reply as specified in [I-D.ietf-lisp-rfc6833bis].

   If an xTR-ID is successfully added to the list of subscribers for an
   EID-Record, the Map-Server MUST extract the nonce and ITR-RLOCs
   present in the Map-Request, and store the association between the
   xTR-ID, ITR-RLOCs and nonce.  Any already present state regarding
   ITR-RLOCs and/or nonce for the same xTR-ID MUST be overwritten.

   If the Map-Request only has one ITR-RLOC with AFI = 0 (i.e., Unknown
   Address), the Map-Server MUST remove the subscription state for that
   xTR-ID.  In this case, the Map-Server MUST send the Map-Notify to the
   source RLOC of the Map-Request.  When the TTL for the EID-record
   expires, the EID-prefix is removed from the Map-Server's subscription
   cache.  On EID-Record removal, the Map-Server notifies the
   subscribers via a Map-Notify with TTL equal 0.


6.  Mapping Notification Publish Procedures

   The publish procedure is implemented via Map-Notify messages that the
   Map-Server sends to xTRs.  The xTRs acknowledge the reception of Map-
   Notifies via sending Map-Notify-Ack messages back to the Map-Server.
   The complete mechanism works as follows.

   When a mapping stored in a Map-Server is updated (e.g., via a Map-
   Register from an ETR), the Map-Server MUST notify the subscribers of
   that mapping via sending Map-Notify messages with the most updated
   mapping information.  The Map-Notify message sent to each of the
   subscribers as a result of an update event MUST follow the exact
   encoding and logic defined in [I-D.ietf-lisp-rfc6833bis] for Map-
   Notify, except for the following:

   (1)  The Map-Notify MUST be sent to one of the ITR-RLOCs associated
        with the xTR-ID of the subscriber.

   (2)  For this version of the specification, the nonce in the Map-
        Notify sent as publication is set as follows.  If the
        subscription state at the Map-Server was created by a received
        Map-Request with the N-bit set, the nonce in the Map-Notify sent
        as publication MUST be the one used in the Map-Request that
        created the subscription state.  If the subscription state was
        created by explicit configuration at the Map-Server, the nonce
        in the Map-Notify sent as publication MUST be randomly generated
        by the Map-Server.

   (3)  The Map-Server MUST use its security association with the xTR to
        compute the authentication data of the Map-Notify.

   When the xTR receives a Map-Notify with a nonce sent previously in a
   Map-Request, or with a nonce not present in any list of previously
   sent nonces but with an EID not local to the xTR, the xTR knows that
   the Map-Notify has been received to update an entry on its map-cache.
   Processing of unsolicited Map-Notify messages MUST be explicitly
   enabled via configuration at the xTR.

   The xTR processes the received Map-Notify as specified in
   [I-D.ietf-lisp-rfc6833bis], with the following considerations.  The
   xTR MUST use its security association with the Map-Server (see
   Section 4) 3) to validate the authentication data on the Map-Notify.
   The xTR MUST use the mapping information carried in the Map-Notify to
   update its internal map-cache.  The xTR MUST acknowledge the Map-
   Notify by sending back a Map-Notify-Ack (specified in

   [I-D.ietf-lisp-rfc6833bis]), with the nonce from the Map-Notify, to
   the Map-Server.  If after a configurable timeout, the Map-Server has
   not received back the Map-Notify-Ack, it can try to send the Map-
   Notify to a different ITR-RLOC for that xTR-ID.


7.  Security Considerations

   Generic security considerations related to LISP control messages are
   discussed in [I-D.ietf-lisp-rfc6833bis].

   In the particular case of PubSub, cache poisoning via malicious Map-
   Notify messages is avoided by the use of nonce and the security
   association between the ITRs and the Map-Servers.  Nevertheless, the
   way to provide a security association between the ITRs and the Map-
   Servers must be evaluated according to the size of the deployment.
   For small deployments, it is possible to have a shared key (or set of
   keys) between the ITRs and the Map-Servers.  For larger and Internet-
   scale deployments, scalability is a concern and further study is
   needed.  Such evaluation is one of the goals of this experimental

   Misbehaving nodes may send massive subscription requests which may
   lead to exhaust the resources of Map-Servers.  Furthermore,
   frequently changing the state of a subscription may also be
   considered as an attack vector.  To mitigate such issues, xTRs SHOULD
   rate-limit Map-Requests and Map-Servers SHOULD rate-limit Map-
   Notifies.  Rate-limiting Map-Requests is discussed in
   [I-D.ietf-lisp-rfc6833bis] and the same guidelines apply here.  To
   rate-limit Map-Notifies, a Map-Server MUST NOT send more than one
   Map-Notify per second to a particular xTR-ID.  This parameter MUST be
   configurable.  Note that when the Map-Notify rate-limit threshold is
   met for a particular xTR-ID, the Map-Server will silently discard
   additional subscription requests from that xTR-ID.  Similarly, for
   pending mapping updates that need to be notified to that xTR-ID, the
   Map-Server will combine them into a single Map-Notify (with multiple
   EID-records) which it will send when the rate-limit mechanism allows
   it to transmit again Map-Notifies to that xTR-ID.


8.  Acknowledgments

   This work is partly funded by the ANR LISP-Lab project #ANR-
   13-INFR-009 (


9.  IANA Considerations

   This document is requesting bit allocations in the Map-Request
   message from the "LISP Control Plane Header Bits" registry introduced
   in [I-D.ietf-lisp-rfc6833bis].  In particular, this document requests
   allocating the following two bits from the sub-registry "Map-Request
   Header Bits".  The position of these two bits in the Map-Request
   message can be found in Figure 1.

   | Spec     | IANA Name     | Bit         | Description              |
   | Name     |               | Position    |                          |
   | I        | map-request-I | 11          | xTR-ID Bit               |
   | N        | map-request-N | ... + 0     | Notification-Requested   |
   |          |               |             | Bit                      |

    Table 1: Additions to the LISP Map-Request Header Bits Sub-Registry


10.  Normative References

              Fuller, V., Farinacci, D., and A. Cabellos-Aparicio,
              "Locator/ID Separation Protocol (LISP) Control-Plane",
              draft-ietf-lisp-rfc6833bis-24 (work in progress), October
              2018. February

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

Authors' Addresses

   Alberto Rodriguez-Natal
   Cisco Systems
   170 Tasman Drive
   San Jose, CA


   Vina Ermagan
   Cisco Systems
   170 Tasman Drive
   San Jose, CA

   Johnson Leong
   Cisco Systems
   170 Tasman Drive
   San Jose, CA


   Fabio Maino
   Cisco Systems
   170 Tasman Drive
   San Jose, CA


   Albert Cabellos-Aparicio
   Technical University of Catalonia


   Sharon Barkai
   Fermi Serverless


   Dino Farinacci
   San Jose, CA


   Mohamed Boucadair
   Rennes  35000

   Christian Jacquenet
   Rennes  35000


   Stefano Secci