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Versions: 00 01

Network Working Group                                              C. Li
Internet-Draft                                                    C. Xie
Intended status: Informational                             China Telecom
Expires: December 30, 2018                                      R. Kumar
                                                               R. Lohiya
                                                        Juniper Networks
                                                             G. Fioccola
                                                          Telecom Italia
                                                                   W. Xu
                                                                  W. Liu
                                                     Huawei Technologies
                                                                   D. Ma
                                                                    ZDNS
                                                                   J. Bi
                                                     Tsinghua University
                                                           June 28, 2018


           Coordinated Address Space Management architecture
            draft-li-opsawg-address-pool-management-arch-01

Abstract

   IP addresses work as a basic element for providing broadband network
   services.  However, the increase in number, diversity and complexity
   of modern network devices and services creates unprecedented
   challenges for the currently prevailing approach of manual IP address
   management.  Manually maintaining IP addresses could always be sub-
   optimal for IP resource utilization.  Besides, it requires heavy
   human effort from network operators.  To achieve high utilization and
   flexible scheduling of IP network addresses, it is necessary to
   automate the address scheduling process.  This document describes an
   architecture for the IP address space management.  It includes
   architectural concepts and components used in the CASM (Coordinated
   Address Space Management), with a focus on those interfaces to be
   standardized in the IETF.

Status of This Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.





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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 30, 2018.

Copyright Notice

   Copyright (c) 2018 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
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
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   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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  CASM Reference architecture . . . . . . . . . . . . . . . . .   4
   4.  The overall procedure of CASM . . . . . . . . . . . . . . . .   7
   5.  CASM Interface and operation  . . . . . . . . . . . . . . . .   8
     5.1.  CASM App-facing Interface . . . . . . . . . . . . . . . .   8
       5.1.1.  Functional requirements . . . . . . . . . . . . . . .   8
       5.1.2.  Interface modeling requirements . . . . . . . . . . .   9
     5.2.  CASM device-facing Interface  . . . . . . . . . . . . . .   9
       5.2.1.  Functional requirements . . . . . . . . . . . . . . .  10
       5.2.2.  Interface modeling requirements/Initial Address Pool
               Configuration . . . . . . . . . . . . . . . . . . . .  10
       5.2.3.  Interface modeling requirements/Address Pool Status
               Report  . . . . . . . . . . . . . . . . . . . . . . .  12
       5.2.4.  Interface modeling requirements/Address Pool Status
               Query . . . . . . . . . . . . . . . . . . . . . . . .  13
       5.2.5.  Interface modeling requirements/Address Exhaustion  .  13
       5.2.6.  Interface modeling requirements / Address Pool
               Release . . . . . . . . . . . . . . . . . . . . . . .  14
   6.  Services SDN Management Use Cases . . . . . . . . . . . . . .  15
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  16
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  16



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     9.2.  Informative References  . . . . . . . . . . . . . . . . .  17
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   The address space management is an integral part of any network
   management solution.  However, the increase in number, diversity and
   complexity of modern network devices and services creates
   unprecedented challenges for the currently prevailing approach of
   manual IP address management.  Manually maintaining IP addresses
   could always be sub-optimal for IP resource utilization.  Besides, it
   requires heavy human effort from network operators.

   Another factor which drive this work is that tThe network
   architectures are rapidly changing with the migration toward private
   and public clouds.  At the same time, application architectures are
   also evolving with a shift toward micro-services and multi-tiered
   approach.

   There is a pressing need to define a new address management system
   which can meet these diverse set of requirements.  To achieve high
   utilization and flexible scheduling of IP network addresses, Such a
   system should be capable of automating the address scheduling
   process.  Such a system must be built with well-defined interfaces so
   users can easily migrate from one vendor to another without rewriting
   their network management systems.

   This document defines a reference architecture that should become the
   basis to develop a new address management system.  This system is
   called Coodinated Address Space Management (CSAM) system.

   A series of use cases are defined in "Use Case Draft".  For example,
   Broadband Network Gateway (BNG), which manages a routable IP address
   on behalf of each subscriber, should be configured with the IP
   address pools allocated to subscribers.  However, currently operators
   are facing with the address shortage problem, the remaining IPv4
   address pools are usually quite scattered, no more than /24 per
   address pool in many cases.  Therefore, it is complicated to manually
   configure the address pools on lots of Broadband Network Gateway
   (BNG) for operators.  For large scale Metro Area Network (MAN), the
   number of BNGs can be up to over one hundred.  Manual configuration
   on all the BNGs statically will not only greatly increase the
   workload, but also decrease the utilization efficiency of the address
   pools when the number of subscribers changes over time in the future.

   Above is one example of use case, there are other devices which may
   need to configure address pools as well.  In this document, we
   propose a general mechanism to manage the address pools coordinately,



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   which can be used in multiple use cases.  With this approach,
   operators do not need to configure the address pools one by one
   manually and it also helps to use the address pools more efficiently.

2.  Terminology

   The following terms are used in this document:

      CASM: Coordinated Address Space Management, a newly-defined
      general architecture which can automate IP address management for
      wide-variety of use cases

      IPAM: IP Address Management, a means of planning, tracking, and
      managing the Internet Protocol address space used in a network

      DA: A device agent within the device, which contacts with CASM
      Coordinator to manipulate address pool

      CASM Coordinator: A management system which has a database manage
      the overall address pools and allocate address pools to devices.

3.  CASM Reference architecture

   The figure below shows the reference architecture for CASM.  This
   figure covers the various possible scenarios that can exist in future
   network.

























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          +-------------+       +-------------+       +-------------+
          |     CASM    |       |     CASM    |       |     CASM    |
          |application 1|       |application j|       |application n|
          +------/------+       +------/------+       +------/------+
                 |                     |                     |
                 |                     |                     |
                 |                     |                     |
                 |                     |                     |
         +-------\---------------------\---------------------\-------+
         |    Coordinated Address Space Management System (CASM)     |
         |                       Coordinator                         |
         |    +-------------+  +-------------+  +-------------+      |
         |    |     Pool    |  |   Address   |  |   Address   |      |
         |    |  Management |  | Management  |  |  Database   |      |
         |    +-------------+  +-------------+  +-------------+      |
         |                                                           |
         +---.-------------------------.--------------------------.--+
             |                         |                          |
             |                         |                          |
             |                         |                          |
             |                         |                          |
             |                         |                          |
  +----------\--------+      +---------\---------+       +--------\----------+
  |                   |      |                   |       |                   |
  |  +-------------+  |      |  +-------------+  |       |  +-------------+  |
  |  |      DA     |  |      |  |     DA      |  |       |  |      DA     |  |
  |  +-------------+  |      |  +-------------+  |       |  +-------------+  |
  |                   |      |                   |       |                   |
  |  +-------------+  |      |  +-------------+  |       |  +-------------+  |
  |  |     CASM    |  |      |  |     CASM    |  |       |  |     CASM    |  |
  |  | Distributor |  |      |  | Distributor |  |       |  | Distributor |  |
  |  +-------------+  |      |  +-------------+  |       |  +-------------+  |
  |      Device 1     |      |      Device 2     |       |      Device m     |
  +-------------------+      +-------------------+       +-------------------+


                   Figure 1: CASM reference architecture

   Each component of CASM is introduced as below,

   1) CASM Application

   The CASM Application is a functional entity which usually has the
   requirements of centralized address management to realize its
   specific upper-layer functions.  In order to achieve this goal, it
   needs to manage, operate and maintain the CASM Coordinator.  For
   example, an operator or external user can manage the address pool in




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   the CASM Coordinator, as well as access log, address allocation
   records, etc.

   2) CASM Coordinator

   The CASM Coordinator is a coordinated address management coordinator
   for the CASM Application to maintain overall address pools,
   addresses, address properties, etc.  It maintains an address database
   including the overall address pools (OAP) and the address pool status
   (APS).  CASM Applications can maintain their remaining address pools
   in the OAP.  They can also reserve some address pools for special
   purposes.  The address pool status is to reflect the current usage of
   address pools for different devices.  The CASM Coordinator also has
   the capability to maintain the address pools to different devices
   dynamically.

   3) CASM Device

   A CASM Device is responsible for distributing or allocating addresses
   from local address pools received from the CASM Coordinator.  CASM
   has two components in devices.  The first one is Device Agent (DA),
   which resides in a CASM Device through which the device can contact
   with the CASM Coordinator.  On behalf of the device, the agent
   initiates the address pool allocation requests, passes the address
   pools to local instances, detect the availability of address pools or
   report the status of local address pool usage and update the address
   pool requests, etc.  For some devices, e.g.  IPv6 transition and VPN,
   additional routing modules are needed to update the routing table
   accordingly.

   The CASM Distributor is another component in a CASM device.  The DHCP
   server is a typical distributor that can assign IP addresses to
   client hosts, and the DHCP protocol is usually used for this task.
   The address assignment procedure between the CASM Distributor and the
   client host is out of the scope of this document.

   The device determines whether the usage status of the IP address pool
   resource within the device satisfies the condition.  When the IP
   address pool resource in the device is insufficient or excessive, the
   device will obtain IP address pool resource request, and sends the
   request to the CASM Coordinator.  The device receives a resource
   response with IP address pools allocated for it, then it use these
   address pools to assign IP addresses to end users.  Typical CASM
   Devices include BNGs, BRASes, CGNs, DHCP Servers, NATs, IPv6
   Transitions, DNS Servers, etc.

   The form of devices is diverse, it can be physical or virtual, and it
   can be box-integrated with a control plane and a user plane, or a



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   separated control plane remote from the box, where one or more
   devices share the centralized control plane.  In the latter case, the
   control plane will manage multiple user plane devices.  A number of
   devices that are subordinate to the control plane will jointly share
   the address pools to make address utilization much higher.

4.  The overall procedure of CASM

   1.  Operators configure remaining address pools centrally in the CASM
       Coordinator.  There are multiple address pools that can be
       configured.  The CASM Coordinator server then divides the address
       pools into addressing units (AUs) which would be allocated to
       device agents by default.

   2.  The agent will initiate an AddressPool request to the CASM
       Coordinator.  It can carry its desired size of address pool with
       the request, or just use a default value.  The address pool size
       in the request is only used as a hint.  The actual size of the
       address pool is totally determined by the CASM Coordinator.  It
       would also carry the DA's identification and the type of the
       address pool.

   3.  The CASM Coordinator looks up remaining address pools in its
       local database, and then allocates a set of address pools to the
       DA.  Each address pool has a lifetime.

   4.  The DA receives the AddressPool reply and uses it for its
       purpose.

   5.  If the lifetime of the address pool is going to expire, the DA
       should issue an AddressPoolRenew request to extend it, including
       IPv4, IPv6, port numbers, etc.

   6.  The AddressPoolReport module keeps monitoring and reports the
       usage of all current address pools for each transition mechanism.
       If it is running out of address pools, it can renew the
       AddressPoolRequest for a newly allocated one.  It can also
       release and recycle an existing address pool if that address pool
       has not been used for a specific and configurable time.

   7.  When the connection of the CASM Coordinator is lost or it needs
       the status information of certain applications, it may pre-
       actively query the DA for its status information.

   Currently, the CASM system focuses on the coordination of IP address
   resources.  This Solution should be extended to handle containers,
   VLAN assignments, etc.  These are subject for future work.




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5.  CASM Interface and operation

5.1.  CASM App-facing Interface

   The CASM architecture consists of three major distinct entities: CASM
   Application, CASM Coordinator and network device with a device Agent
   (DA).  In order to provide address space and pools resource that CASM
   Coordinator can centrally maintain, there is an interface between
   CASM Applications and CASM Coordinator.  The CASM Application can
   manage the address space and pool in the CASM Coordinator, and the
   get address allocation records, logs from CASM Coordinator.

5.1.1.  Functional requirements

   The CASM should support following functionality for it to be adopted
   for wide variety of use cases.

   1.  Address pools requirements

   A CASM system should allow ability to manage different kind of
   address pools.  The following pools should be considered for
   implementation; this is not mandatory or exhaustive by any means but
   given here as most commonly used in networks.  The CASM system should
   allow user-defined pools with any address objects.

   Unicast address pool:

   o  Private IPv4 addresses

   o  Public IPv4 addresses

   o  IPv6 addresses

   o  MAC Addresses

   Multicast address pool:

   o  IPv4 address

   o  IPv6 address

   2.  Pool management requirements

   There should be a rich set of functionality as defined in this
   section for operation of a given pool.

   Address management:




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   o  Address allocation either as single or block

   o  Address reservation

   o  Allocation logic such as mapping schemes or algorithm per pool

   o

   General management:

   o  Pool initializing, resizing, threshold markings for resource
      monitoring

   o  Pool attributes such as used to automatically create DNS record

   o  Pool priority for searching across different pools

   o  Pool fragmentation rules, such as how pool can be sub-divided

   o  Pool lease rules for allocation requests

5.1.2.  Interface modeling requirements

   There are three broad categories for CASM interface definition:

   Pool management interface: Interface to external user or applications
   such as SDN controller to manage addresses

   Log interface: Interface to access log and records such as DHCP, DNS,
   NAT Integration interface: Interface to address services such as
   DHCP, DNS, NAT

5.2.  CASM device-facing Interface

   In order to provide address pool manipulations between CASM
   Coordinator and device, the CASM architecture calls for well-defined
   protocols for interfacing between them.  Protocol such as radius can
   be used to compatible with legacy network equipment.  And in more
   modern network system, network device acts as NETCONF/RESTCONF server
   side, device like CASM Coordinator act as client side.  The network
   device sends address pool request message carrying the requested
   resource information to the CASM Coordinator, the CASM Coordinator
   send response message to the network device, where the response
   message includes address pool resource information allocated to the
   network device, and network device receives the response message and
   retrieve the allocated address pool resource information carried in
   the response message.




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5.2.1.  Functional requirements

   In order to build a complete address management system, it is
   important that CASM should be able to integrate with other address
   services.  This will provide a complete solution to network operators
   without requiring any manual or proprietary workflows.

   DHCP server:

   o  Interface to initialize address pools on DHCP server

   o  Notification interface whenever an address lease is modified

   o  Interface to access address lease records from DHCP server

   o  Ability to store lease records and play back to DHCP server on
      reboot

   DNS server:

   o  Interface to create DNS records on DNS server based on DHCP server
      events

   NAT device:

   o  Interface to initialize NAT pools

   o  Interface to access NAT records from NAT device

   o  Ability to store NAT records and play back to NAT device on reboot

5.2.2.  Interface modeling requirements/Initial Address Pool
        Configuration


















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          +--------------+                           +-----------------+
          |   Device     |                           |       CASM      |
          |   Agent      |                           |   Coordinator   |
          +------+-------+                           +--------+--------+
                 |                                            |
        +--------+-------+                                    |
        |1.DA start-up   |                                    |
        +---------+------+                                    |
                  |            2.Address Pool Request         |
                  |------------------------------------------>|
                  |                                           |
                  |                                  +--------+-------+
                  |                                  |  3. Check      |
                  |                                  |   address pool |
                  |                                  +--------+-------+
                  |          4.Address Pool Reply             |
                  |<------------------------------------------|
                  |                                           |


               Figure 2: Initial Address Pool Configuration

   As shown in Figure 2, the procedure is as follows:

   1.  The DA checks whether there is already address pool configured in
       the local site when it starts up.

   2.  The DA will initiate Address Pool request to the CASM
       Coordinator.  It can carry its desired size of address pool in
       the request, or just use a default value.  The address pool size
       in the DA's request is only used as a hint.  The actual size of
       the address pool is totally determined by CASM Coordinator.  It
       will also carry the DA's identification, the type of transition
       mechanism and the indication of port allocation support.

   3.  The CASM Coordinator determines the address pool allocated for
       the DA based on the parameters received.

   4.  The CASM Coordinator sends the Address Pool Reply to the DA.  It
       will also distribute the routing entry of the address pool
       automatically.  In particular, if the newly received address pool
       can be aggregated to an existing one, the routing should be
       aggregated accordingly.








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5.2.3.  Interface modeling requirements/Address Pool Status Report


        +--------------+                             +-----------------+
        |   Device     |                             |      CASM       |
        |   Agent      |                             |   Coordinator   |
        +------+-------+                             +--------+--------+
               |                                              |
      +--------+-------+                                      |
      |1.Monitor and   |                                      |
      |count the status|                                      |
      +--------+-------+                                      |
               |        2.Address Pool Status Report          |
               |--------------------------------------------->|
               |                                     +--------+-------+
               |                                     |  3. Record     |
               |                                     |   address pool |
               |                                     +--------+-------+
               |       4.Address Pool Report Confirm          |
               |<---------------------------------------------|
               |                                              |
               |                                              |



                   Figure 3: Address Pool Status Report

   Figure 3 illustrates the active address pool status report procedure:

   1.  The DA will monitor and count the usage status of the local
       address pool.  The DA counts the address usage status in one
       month, one week and one day, which includes the local address,
       address usage ratio (peak and average values), and the port usage
       ratio (peak and average values).

   2.  The DA reports the address pool usage status to the CASM
       Coordinator.  For example, it will report the address usage
       status in one day, which contains the IP address, NAT44, address
       list: 30.14.44.0/28, peak address value 14, average address usage
       ratio 90%, TCP port usage ratio 20%, UDP port usage ratio 30% and
       etc.

   3.  The CASM Coordinator records the status and compares with the
       existing address information to determine whether additional
       address pool is needed.

   4.  The CASM Coordinator will confirm the address pool status report
       request to the DA.  It will keep sending the address pool status



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       report request to the CASM Coordinator if no confirm message is
       received.

5.2.4.  Interface modeling requirements/Address Pool Status Query

   When the status of CASM Coordinator is lost or the CASM Coordinator
   needs the status information of the DAs, the CASM Coordinator may
   actively query the TD for the status information, as shown in step 1
   of Figure 4.  The following steps 2,3,4,5 are the same as the Address
   Pool Status Report procedure.


        +--------------+                             +-----------------+
        |   Device     |                             |      CASM       |
        |   Agent      |                             |   Coordinator   |
        +------+-------+                             +--------+--------+
               |                                              |
               |                                              |
               |         1.Address Pool Status Query          |
               |<---------------------------------------------|
               |                                              |
      +--------+-------+                                      |
      |2.Monitor and   |                                      |
      |count the status|                                      |
      +--------+-------+                                      |
               |        3.Address Pool Status Report          |
               |--------------------------------------------->|
               |                                     +--------+-------+
               |                                     |  4. Record     |
               |                                     |   address pool |
               |                                     +--------+-------+
               |       5.Address Pool Report Confirm          |
               |<---------------------------------------------|
               |                                              |
               |                                              |



                    Figure 4: Address Pool Status Query

5.2.5.  Interface modeling requirements/Address Exhaustion

   When the addresses used by the DA reaches a certain usage threshold,
   the DA will renew the address pool request to the CASM Coordinator
   for an additional address pool.  The procedure is the same as the
   initial address pool request.





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5.2.6.  Interface modeling requirements / Address Pool Release


        +--------------+                             +-----------------+
        |   Device     |                             |       CASM      |
        |   Agent      |                             |    Coordinator  |
        +------+-------+                             +--------+--------+
               |                                              |
      +--------+-------+                                      |
      |1.Address pools |                                      |
      |  not used for a|                                      |
      |   long time    |                                      |
      +--------+-------+                                      |
               |        2.Address Pool Release Request        |
               |--------------------------------------------->|
               |                                     +--------+-------+
               |                                     |3. Update       |
               |                                     |   address pool |
               |                                     |   database     |
               |                                     +--------+-------+
               |       4.Address Pool Release Notification    |
               |<---------------------------------------------|
      +--------+-------+                                      |
      |5. Reduce       |                                      |
      |  address pool  |                                      |
      +--------+-------+                                      |
               |         6.Address Pool Release Confirm       |
               |--------------------------------------------->|
               |                                              |
               |                                              |



                      Figure 5: Address Pool Release

   Figure 5 illustrates the address pool release procedure:

   1.  The counting module in the DA checks if the usage threshold of
       address pool reaches a certain condition;

   2.  The DA sends the address pool release request to the CASM
       Coordinator to ask the release of those addresses;

   3.  The CASM Coordinator updates the local address pool information
       to add the new addressed released;

   4.  The CASM Coordinator notifies the TD that the addresses have been
       release successfully;



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   5.  The DA will update the local address pool.  If no Address Pool
       Release Notification is received, the DA will repeat step 2;

   6.  Optionally, the DA confirms with the CASM Coordinator that the
       address pool has been released successfully.

6.  Services SDN Management Use Cases


                                  -------------
                                 |     CASM    |
                                 | Application |
                                  -------------
                                        :
                               ------------------
                              |     Provider     |
                              |   Orchestrator   |
                              |                  |
                              .------------------.
                             .          :         .
                            .           :          .
                 ------------     ------------     ------------
                |            |   |            |   |            |
                | Controller |   | Controller |   | Controller |
                |            |   |            |   |            |
                 ------------     ------------     ------------
                    :              .       .               :
                    :             .         .              :
                    :            .           .             :
                ---------     ---------   ---------     ---------
               | Network |   | Network | | Network |   | Network |
               | Element |   | Element | | Element |   | Element |
                ---------     ---------   ---------     ---------


                Figure 6: L3 and L2 Services Orchestration

   Network Operators need to manage addressing of undelay network
   elements in order to build end-to-end services and private or public
   clouds.  So address management of customer equipments, provider
   edges, but also of virtual machines, virtual functions and overlay
   networks is a very important task.  In general the SDN Orchestrators
   and other management systems must coordinate addressing schemes to
   ensure network operation.  There is need for one address management
   system that would meet the requirements of such a network deployment.
   The SDN Orchestrator manages IPv4, IPv6 addresses and also MAC
   addresses to assign to network interfaces in order to install end-to-
   end services, and this task can be achieved by the CASM coordination.



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   A typical use case is the application to the Service provisioning of
   L3VPN and L2VPN by the SDN orchestration level.  For example the
   architecture presented in [RFC8309] and, more in general in every SDN
   architecture, could be integrated with CASM.  It is important to
   mention also the possibility of Multi-Provider services, and in this
   case the two CASM coordinators of the two involved Providers should
   synchronize.  The following Figure shows how CASM Application can
   communicate with both the Network Operator Orchestrator and, in case
   of Multi-Provider Service, with another Network Operator Orchestrator
   too.

7.  Security Considerations

8.  Acknowledgements

   N/A.

9.  References

9.1.  Normative References

   [RFC2132]  Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
              Extensions", RFC 2132, DOI 10.17487/RFC2132, March 1997,
              <https://www.rfc-editor.org/info/rfc2132>.

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <https://www.rfc-editor.org/info/rfc3315>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.




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9.2.  Informative References

   [RFC6888]  Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,
              A., and H. Ashida, "Common Requirements for Carrier-Grade
              NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888,
              April 2013, <https://www.rfc-editor.org/info/rfc6888>.

Authors' Addresses

   Chen Li
   China Telecom
   No.118 Xizhimennei street, Xicheng District
   Beijing  100035
   P.R. China

   Email: lichen@ctbri.com.cn


   Chongfeng Xie
   China Telecom
   No.118 Xizhimennei street, Xicheng District
   Beijing  100035
   P.R. China

   Email: xiechf.bri@chinatelecom.cn


   Rakesh Kumar
   Juniper Networks
   1133 Innovation Way
   Sunnyvale  CA 94089
   US

   Email: rkkumar@juniper.net


   Anil Lohiya
   Juniper Networks
   1133 Innovation Way
   Sunnyvale  CA 94089
   US

   Email: alohiya@juniper.net








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   Giuseppe Fioccola
   Telecom Italia
   Via Reiss Romoli, 274
   Torino  10148
   Italy

   Email: giuseppe.fioccola@telecomitalia.it


   Weiping Xu
   Huawei Technologies
   Bantian, Longgang District
   shenzhen  518129
   P.R. China

   Email: xuweiping@huawei.com


   Will(Shucheng) Liu
   Huawei Technologies
   Bantian, Longgang District
   shenzhen  518129
   P.R. China

   Email: liushucheng@huawei.com


   Di Ma
   ZDNS
   4 South 4th St. Zhongguancun
   Beijing  100190
   P.R. China

   Email: madi@zdns.cn


   Jun Bi
   Tsinghua University
   3-212, FIT Building, Tsinghua University, Haidian District
   Beijing  100084
   P.R. China

   Email: junbi@tsinghua.edu.cn








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