LISP Working Group                                    A. Rodriguez-Natal
Internet-Draft                                             Cisco Systems
Intended status: Informational                      A. Cabellos-Aparicio
Expires: October 9, 2021               Technical University of Catalonia
                                                              V. Ermagan
                                                                F. Maino
                                                           Cisco Systems
                                                               S. Barkai
                                                              Nexar Inc.
                                                           April 7, 2021

                           MS-originated SMRs


   This document extends [I-D.ietf-lisp-rfc6833bis] to allow Map Servers
   to send SMR messages.

   This extension is intended to be used in some SDN deployments that
   use LISP as a southbound protocol with (P)ITRs that are compliant
   with [I-D.ietf-lisp-rfc6833bis].  In this use-case mapping updates do
   not come from ETRs, but rather from a centralized controller that
   pushes the updates directly to the Mapping System.  In such
   deployments, Map Servers will benefit from having a mechanism to
   inform directly (P)ITRs about updates in the mappings they are
   serving.  Although implementations of this extension exist, this
   extension is deprecated by [I-D.ietf-lisp-pubsub] and it is being
   documented for informational purposes.  Newer implementations should
   look into [I-D.ietf-lisp-pubsub] to support PubSub in LISP

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on October 9, 2021.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Map Server extension  . . . . . . . . . . . . . . . . . . . .   3
   3.  Interoperability with legacy (P)ITRs  . . . . . . . . . . . .   4
   4.  Deployment considerations . . . . . . . . . . . . . . . . . .   4
   5.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

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 in two entities, the Mapping System
   and the Tunnel Routers.  The Tunnel Routers are deployed at LISP
   sites edge points and perform encapsulation and decapsulation of LISP
   data packets.  The Mapping System is a distributed database that
   stores and disseminates EID-RLOC bindings across different Map-
   Servers.  LISP Tunnel Routers keep a cache of EID-RLOC mappings
   pulled from the Mapping System.

   There are several ways to keep this cache updated as described in
   [I-D.ietf-lisp-rfc6833bis].  Among them, the Solicit Map-Request
   (SMR) message allows to explicitly signal (P)ITRs to let them know

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   that some of their cached mappings may be outdated.  However, vanilla
   LISP as described in [I-D.ietf-lisp-rfc6833bis] only considers SMR
   messages to be sent by an ETR.  This document extends
   [I-D.ietf-lisp-rfc6833bis] to cover the case where SMRs can be sent
   also by a Map Server (MS).

   This document introduces changes in the MS specification allowing
   them to send SMR messages, however it does not require any
   modification in the (P)ITRs.  This document is backwards compatible
   and enables upgraded MSs to interoperate via SMRs with legacy (P)ITRs
   that only implement [I-D.ietf-lisp-rfc6833bis].

   This document offers a basic form of Publish/Subscribe (PubSub)
   compatible with legacy LISP devices.  The LISP WG is currently
   working on [I-D.ietf-lisp-pubsub] as the comprehensive mechanism to
   enable PubSub in LISP which deprecates this document.  Newer
   implementations should look into [I-D.ietf-lisp-pubsub] to support
   PubSub in LISP deployments.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Map Server extension

   This document enables MS to generate and send SMR messages towards
   (P)ITRs.  SMRs originated in a MS follow the same format described in
   [I-D.ietf-lisp-rfc6833bis].  Besides the fact that they are sent from
   a MS, there is no difference between an SMR originated in an ETR and
   one originated in a MS.

   A MS supporting the extension described in this document is supposed
   to keep track of the Map-Requests received for the mappings it is
   serving.  When receiving a Map-Request, the MS should extract the
   source EID and ITR-RLOCs from the message and keep them associated
   with the requested mapping.  The MS is expected to keep this state
   for a period equal to the TTL of the mapping.  When the mapping
   changes, the MS should build and send an SMR to the (P)ITR that
   requested the mapping using the stored EID and ITR-RLOCs, as
   described below.

   When a MS generates an SMR, it uses as source-EID the EID-prefix it
   wants the (P)ITR to send the SMR-invoked Map-Request for (i.e. the
   EID of the mapping that changed).  The EID included in the EID-record
   field is the one belonging to the (P)ITR the MS sends the SMR towards
   and that was extracted from the original Map-Request.  The

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   destination locator is one of the ITR-RLOCs associated with the EID
   of the (P)ITR that were received in the Map-Request.  As source
   locator for the SMR message, the MS uses one of its available
   locators.  This has implications in the processing of the SMR at the
   (P)ITR as described in Section 4

   As specified in [I-D.ietf-lisp-rfc6833bis] and noted in Section 7,
   SMRs MUST be rate-limited.  It must be noted as well that, as
   described in Section 3, a MS that sends an SMR may not necessarily
   receive the SMR-invoked Map-Request that the (P)ITR generates as
   response to the SMR.

3.  Interoperability with legacy (P)ITRs

   This document introduces no changes in the specification of (P)ITRs
   and thus it is backwards compatible with legacy equipment only
   compliant with [I-D.ietf-lisp-rfc6833bis].  However, since SMRs were
   designed to be sent by ETRs, and legacy (P)ITRs expect to receive
   SMRs only from ETRs, the implications of sending SMRs from a MS are
   discussed in this section.

   As indicated in Section 2, the MS generates the SMR message using one
   of its locators as source locator.  However, this locator will not be
   present in the Locator-Set cached for that EID-prefix at the (P)ITR.
   Following [I-D.ietf-lisp-rfc6833bis], upon receiving the SMR message,
   the (P)ITR will check if the source locator is in the Locator-Set
   cached for that EID-record.  Since it is not, the (P)ITR will send
   the SMR-invoked Map-Request always to the Mapping System and never to
   the source locator of the SMR message.  This means that a MS can not
   force an SMR-invoked Map-Request to be sent directly towards itself.
   However, it is possible that the Mapping System in use is
   instantiated (even partially) by the MS originator of the SMR.  In
   that case, it may be that the SMR-invoked Map Request will eventually
   reach the MS, either directly or after being internally forwarded
   through the Mapping System.

4.  Deployment considerations

   The extension defined in this document may be useful in scenarios
   where the MS wants to signal (P)ITRs about changes on mappings it is
   serving.  For instance, when the MS is keeping track of the (P)ITRs
   that are requesting its mappings and wants to inform them
   intermediately whenever a mapping is updated.

   SDN deployments that use LISP as a southbound protocol are
   particularly suitable to take advantage of this extension.  On the
   SDN scenario, mapping updates will unlikely come from ETRs, but
   rather from a centralized entity that pushes the updates directly to

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   the Mapping System.  In such deployments, Map Servers will benefit
   from having a mechanism to inform directly (P)ITRs about updates in
   the mappings they are serving.

   Due to scalability and security concerns, it is RECOMMENDED that this
   extension is only applied in intra-domain scenarios where all LISP
   devices are within a single administrative domain.

   To limit the impact of the extension and to ease its integration with
   the rest of LISP signaling and operation, it is RECOMMENDED that the
   MS only sends SMR messages for those mappings it is proxy-replying

5.  Acknowledgments

   The authors would like to thank Joel Halpern and Luigi Iannone for
   their guidance regarding this document.

6.  IANA Considerations

   This memo includes no request to IANA.

7.  Security Considerations

   As described in [I-D.ietf-lisp-rfc6833bis], the SMR messages and the
   SMR-invoked Map-Request MUST be rate-limited.  This does not change
   with the extension proposed in this document.

   The (P)ITRs receiving SMRs from the MS will send Map-Request messages
   to the Mapping System to retrieve authoritative mappings.  It is
   RECOMMENDED that the security mechanism described in
   [I-D.ietf-lisp-sec] and [RFC8111] are in place to secure the mapping
   retrieval and protect against unsolicited messages or hijacking

8.  References

8.1.  Normative References

              Farinacci, D., Maino, F., Fuller, V., and A. Cabellos-
              Aparicio, "Locator/ID Separation Protocol (LISP) Control-
              Plane", draft-ietf-lisp-rfc6833bis-30 (work in progress),
              November 2020.

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

   [RFC8111]  Fuller, V., Lewis, D., Ermagan, V., Jain, A., and A.
              Smirnov, "Locator/ID Separation Protocol Delegated
              Database Tree (LISP-DDT)", RFC 8111, DOI 10.17487/RFC8111,
              May 2017, <>.

8.2.  Informative References

              Rodriguez-Natal, A., Ermagan, V., Cabellos-Aparicio, A.,
              Barkai, S., and M. Boucadair, "Publish/Subscribe
              Functionality for LISP", draft-ietf-lisp-pubsub-07 (work
              in progress), January 2021.

              Maino, F., Ermagan, V., Cabellos-Aparicio, A., and D.
              Saucez, "LISP-Security (LISP-SEC)", draft-ietf-lisp-sec-22
              (work in progress), January 2021.

Authors' Addresses

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


   Albert Cabellos-Aparicio
   Technical University of Catalonia


   Vina Ermagan


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   Fabio Maino
   Cisco Systems
   170 Tasman Drive
   San Jose, CA


   Sharon Barkai
   Nexar Inc.


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