[Docs] [txt|pdf|xml|html] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02 03 04 05 06

NFVRG                                                P. Aranda Gutierrez
Internet-Draft                                                      UC3M
Intended status: Informational                                  D. Lopez
Expires: January 16, 2019                                     Telefonica
                                                              S. Salsano
                                          Univ. of Rome Tor Vergata/CNIT
                                                             E. Batanero
                                                           July 15, 2018


                 High-level VNF Descriptors using NEMO
                  draft-aranda-nfvrg-recursive-vnf-06

Abstract

   Current efforts in the scope of Network Function Virtualisation(NFV)
   propose YAML-based descriptors for Virtual Network Functions (VNFs)
   and for their composition in Network Services (NS) These descriptors
   are human-readable but hardly understandable by humans.  On the other
   hand, there has been an effort proposed to the IETF to define a
   human-readable (and understandable) representation for networks,
   known as NEMO.  In this draft, we propose a simple extension to NEMO
   to accommodate VNF Descriptors (VNFDs) in a similar manner as inline
   assembly is integrated in higher-level programming languages.

   This approach enables the creation of recursive VNF forwarding graphs
   in Service Descriptors, practically making them recursive.  An
   implementation generating VNF Descriptors (VNFDs) for OpenMANO and
   OSM is available.

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/.

   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 January 16, 2019.





Aranda Gutierrez, et al.Expires January 16, 2019                [Page 1]


Internet-Draft         High-level VNFDs with NEMO              July 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
   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology and abbreviations . . . . . . . . . . . . . . . .   3
   3.  Prior art . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Virtual network function descriptors  . . . . . . . . . .   3
       3.1.1.  OpenMANO VNFDs  . . . . . . . . . . . . . . . . . . .   4
       3.1.2.  ETSI MANO VNFDs . . . . . . . . . . . . . . . . . . .   5
     3.2.  NEMO  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
   4.  Additional requirements on NEMO . . . . . . . . . . . . . . .   9
     4.1.  Referencing VNFDs in a NodeModel  . . . . . . . . . . . .   9
     4.2.  Referencing the network interfaces of a VNF in a
           NodeModel . . . . . . . . . . . . . . . . . . . . . . . .   9
     4.3.  An example  . . . . . . . . . . . . . . . . . . . . . . .   9
   5.  Implementation  . . . . . . . . . . . . . . . . . . . . . . .  10
   6.  Operational Experience  . . . . . . . . . . . . . . . . . . .  11
   7.  Future work . . . . . . . . . . . . . . . . . . . . . . . . .  13
   8.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . .  13
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  13
   11. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .  13
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     12.2.  Informative References . . . . . . . . . . . . . . . . .  14
     12.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   Currently, there is a lot of on-going activity to deploy NFV in the
   network.  From the point of view of the orchestration, Virtual
   Network Functions are blocks that are deployed in the infrastructure
   as independent units.  Following the reference architectural model



Aranda Gutierrez, et al.Expires January 16, 2019                [Page 2]


Internet-Draft         High-level VNFDs with NEMO              July 2018


   proposed in [ETSI-NFV-MANO], VNFs provide for one layer of components
   (VNF components(VNFCs)) below, i.e. a set of VNFCs accessible to a
   VNF provider can be composed into VNFs.  However, there is no simple
   way to use existing VNFs as components in VNFs with a higher degree
   of complexity.  In addition, Network Service Descriptors (NSD) and
   VNF Descriptors (VNFDs) specified in [ETSI-NFV-MANO] and used in
   different open source MANO frameworks are YAML-based files, which
   despite being human readable, are not easy to understand.

   On the other hand, there has been recently an attempt to work on a
   modelling language for networks or Network Modelling (NEMO) language.
   This language is human-readable and provides constructs that support
   recursiveness.  In this draft, we propose an addition to NEMO to make
   it interact with VNFDs supported by a NFV MANO framework.  This
   integration creates a new language for VNFDs that is recursive,
   allowing VNFs to be created based on the definitions of existing
   VNFs.

   This draft uses two example formats to show how low level descriptors
   can be imported into NEMO.  The first one is the format used in the
   OpenMANO [1]  framework.  The second one follows strictly the
   specifications provided by ETSI NFV ISG in [ETSI-NFV-MANO].
   Conceptually, other descriptor formats like TOSCA can also be used at
   this level.

2.  Terminology and abbreviations

   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.  Prior art

3.1.  Virtual network function descriptors

   Virtual network function descriptors (VNFDs) are used in the
   Management and orchestration (MANO) framework of the ETSI NFV to
   achieve the optimal deployment of virtual network functions (VNFs).
   The Virtual Infrastructure Manager (VIM) uses this information to
   place the functions optimally.  VNFDs include information of the
   components of a specific VNF and their interconnection to implement
   the VNF, in the form of a forwarding graph.  In addition to the
   forwarding graph, the VNFD includes information regarding the
   interfaces of the VNF.  These are then used to connect the VNF to
   either physical or logical interfaces once it is deployed.

   There are different MANO frameworks available.  For this draft, we
   will first concentrate on the example of OpenMANO [2], which uses a



Aranda Gutierrez, et al.Expires January 16, 2019                [Page 3]


Internet-Draft         High-level VNFDs with NEMO              July 2018


   YAML [3] representation similar to the one specified in
   [ETSI-NFV-MANO].  Then we will provide an example using the exact
   format specified in [ETSI-NFV-MANO].

3.1.1.  OpenMANO VNFDs

   Taking the example from the (public) OpenMANO github repository, we
   can easily identify the virtual interfaces of the sample VNFs in
   their descriptors:










































Aranda Gutierrez, et al.Expires January 16, 2019                [Page 4]


Internet-Draft         High-level VNFDs with NEMO              July 2018


          +----------------------------+
          |                            |
    mgt0  |     +---------------+      |   ge0
          |     |               |      |
       ---+-----+  Template VM  +------+------
          |     |               |      |
          |     +---+--------+--+      |
          |         |        |         |
          +---------+--------+---------+
                    |        |
                  xe0       xe1

   vnf:
       name: TEMPLATE
       description: This is a template to help in the creation of
       # class: parent      # Optional. Used to organize VNFs
       external-connections:
       -   name:              mgmt0
           type:              mgmt
           VNFC:              TEMPLATE-VM
           local_iface_name:  mgmt0
           description:       Management interface
       -   name:              xe0
           type:              data
           VNFC:              TEMPLATE-VM
           local_iface_name:  xe0
           description:       Data interface 1
       -   name:              xe1
           type:              data
           VNFC:              TEMPLATE-VM
           local_iface_name:  xe1
           description:       Data interface 2
       -   name:              ge0
           type:              bridge
           VNFC:              TEMPLATE-VM
           local_iface_name:  ge0
           description:       Bridge interface

       Figure 1: Sample VNF and descriptor (source: OpenMANO github)

3.1.2.  ETSI MANO VNFDs

   In this example we consider the VNF represented in Figure 6.4 of
   [ETSI-NFV-MANO].  Its internal diagram, including a VNF component, is
   represented in Figure Figure 2.  A YAML representation of the VNF
   Descriptor is reported in Figure Figure 3.  The topology of the
   interconnection of VNFs is expressed by using the abstraction of
   Virtual Links, which interconnect Connection Points of the VNFs.  The



Aranda Gutierrez, et al.Expires January 16, 2019                [Page 5]


Internet-Draft         High-level VNFDs with NEMO              July 2018


   Virtual Links are described by Virtual Link Descriptors (VLD) files.
   An example YAML representation of the Virtual Link VL1 in the example
   VNF is reported in Figure Figure 3.  In order to understand the
   topology, a (potentially large) set of VNFD and VLD files needs to be
   analysed.  For a human programmer of the service, this representation
   is not friendly to write and very hard to read/understand/debug.

   +----------------------------+
   |            VNF1            |
   +----------------------------+
   |                            |
   |       +-------------+      |
   |       |   VNFC11    |      |
   |       +-------------+      |
   |       |             |      |
   |       |   +----+    |      |
   |       |   |CP14|    |      |
   |       |   +-+--+    |      |
   |       |     |       |      |
   |       +-------------+      |
   |             |              |
   |          +--+----+         |
   |     +----+  VL11 +---+     |
   |     |    +--+----+   |     |
   |     |       |        |     |
   |   +-+--+  +-+--+  +--+-+    |
   |   |CP11|  |CP12|  |CP13|    |
   |   +-+--+  +-+--+  +--+-+    |
   |     |       |        |     |
   +----------------------------+
         |       |        |
    +----+--+ +--+----+ +-+-----+
    |  VL1  | |  VL2  | |  VL3  |
    +-------+ +-------+ +-------+

                           Figure 2: VNF example















Aranda Gutierrez, et al.Expires January 16, 2019                [Page 6]


Internet-Draft         High-level VNFDs with NEMO              July 2018


   #######################################
   # VNF Descriptor of a VNF called vnf1
   #######################################
   id: vnf1
   description_version: '0.1'
   vendor: netgroup
   version: '0.1'
   connection_point:
   - id: cp11
     type: ''
     virtual_link_reference: vl11
   - id: cp12
     type: ''
     virtual_link_reference: vl11
   - id: cp13
     type: ''
     virtual_link_reference: vl11
   vdu:
   - id: vdu11
     computation_requirement: ''
     virtual_memory_resource_element: ''
     virtual_network_bandwidth_resource: ''
     vnfc:
     - id: vnfc11
       connection_point:
       - id: cp14
         type: NIC
         virtual_link_reference: vl11
   virtual_link:
   - id: vl11
     connection_points_references:
     - cp11
     - cp12
     - cp13
     - cp14
     connectivity_type: ' E-Line'
     root_requirement: ''

           Figure 3: ETSI MANO compliant VNF descriptor example












Aranda Gutierrez, et al.Expires January 16, 2019                [Page 7]


Internet-Draft         High-level VNFDs with NEMO              July 2018


   ############################################
   # Virtual Link Descriptor of a VL called vl1
   ############################################
   id: vl1
   descriptor_version: '0.1'
   test_access: none
   vendor: netgroup
   connection:
   - cp01
   - cp11
   connectivity_type: E-LAN
   number_of_endpoints: 2
   root_requirement: ''


       Figure 4: ETSI MANO compliant Virtual Link descriptor example

3.2.  NEMO

   The Network Modeling (NEMO) language is described in
   [I-D.xia-sdnrg-nemo-language].  It provides a simple way of
   describing network scenarios.  The language is based on a two-stage
   process.  In the first stage, models for nodes, links and other
   entities are defined.  In the second stage, the defined models are
   instantiated.  The NEMO language also allows for behavioural
   descriptions.  A variant of the NEMO language is used in the
   OpenDaylight NEMO northbound API [4].

   NEMO allows to define NodeModels, which are then instantiated in the
   infrastructure.  NodeModels are recursive and can be build with basic
   node types or with previously defined NodeModels.  An example for a
   script defining a NodeModel is shown below:


   CREATE NodeModel dmz
     Property string: location-fw, string: location-n2,
       string: ipprefix, string: gatewayip, string: srcip,
       string: subnodes-n2;
     Node fw1
       Type fw
       Property location: location-fw,
         operating-mode: layer3;
   ...

                  Figure 5: Creating a NodeModel in NEMO






Aranda Gutierrez, et al.Expires January 16, 2019                [Page 8]


Internet-Draft         High-level VNFDs with NEMO              July 2018


4.  Additional requirements on NEMO

   In order to integrate VNFDs into NEMO, we need to take into account
   two specifics of VNFDs, which cannot be expressed in the current
   language model.  Firstly, we need a way to reference the file which
   holds the VNFD provided by the VNF developer.  This will normally be
   a universal resource identifier (URI).  Additionally, we need to make
   the NEMO model aware of the virtual network interfaces.

4.1.  Referencing VNFDs in a NodeModel

   As explained in the introduction, in order integrate VNFDs into the
   NEMO language in the easiest way we need to reference the VNFD as a
   Universal Resource Identifier (URI) as defined in RFC 3986 [RFC3986].
   To this avail, we define a new element in the NodeModel to import the
   VNFD:

   CREATE NodeModel <node_model_name> VNFD <vnfd_uri>;

4.2.  Referencing the network interfaces of a VNF in a NodeModel

   As shown in Figure 1, VNFDs include an exhaustive list of interfaces,
   including the interfaces to the management network.  However, since
   these interfaces may not be significant for specific network
   scenarios and since interface names in the VNFD may not be adequate
   in NEMO, we propose to define a new entity, namely the
   ConnectionPoint, which is included in the node model .

   CREATE NodeModel <node_model_name>;
     ConnectionPoint <cp_name> at VNFD:<iface_from_vnfd>;

4.3.  An example

   Once these two elements are included in the NEMO language, it is
   possibly to recursively define NodeModel elements that use VNFDs in
   the lowest level of recursion.  Firstly, we create NodeModels from
   VNFDs:

   CREATE NodeModel sample_vnf VNFD https://github.com/nfvlabs
   /openmano.git/openmano/vnfs/examples/dataplaneVNF1.yaml;
       ConnectionPoint data_inside at VNFD:ge0;
       ConnectionPoint data_outside at VNFD:ge1;

          Import from a sample VNFD from the OpenMANO repository

   Then we can reuse these NodeModels recursively to create complex
   NodeModels:




Aranda Gutierrez, et al.Expires January 16, 2019                [Page 9]


Internet-Draft         High-level VNFDs with NEMO              July 2018


   CREATE NodeModel complex_vnf;
       Node input_vnf Type sample_vnf;
       Node output_vnf Type shaper_vnf;
       ConnectionPoint input;
       ConnectionPoint output;
       Connection icon Type p2p Endnodes input, input_vnf:data_inside;
       Connection ocon Type p2p Endnodes output, output_vnf:wan;
       Connection intn Type p2p \
           Endnodes input_vnf:data_outside, output_vnf:lan;


                        Create a composed NodeModel

   This NodeModel definition creates a composed model linking the
   sample_vnf created from the VNFD with a hypothetical shaper_vnf
   defined elsewhere.  This definition can be represented graphically as
   follows:


       +--------------------------------------------------------+
       |       complex_vnf                                      |
       |      +--------------+           +--------------+       |
    input     |              |           |              |     output
       +------+  sample_vnf  +-----------+  shaper_vnf  +-------+
       |      |              |           |              |       |
       |      +--------------+           +--------------+       |
       |  data_inside   data_outside   lan           wan        |
       +--------------------------------------------------------+


                                 Figure 6

   In ETSI NFV, a network service is described by one or more VNFs that
   are connected through one or more network VNFFGs.  This is no more
   than what is defined in the composed NodeModel shown if Figure 6.  By
   using NEMO, we provide a simple way to define VNF forwarding graphs
   (VNF-FGs) in network service descriptors in a recursive way.

5.  Implementation

   There is a proof of concept implementation of the concepts described
   in this draft is available at github [5].  This proof of concept is
   implemented as an OpenDayLight (ODL) [6] plugin and includes two
   output stages to generate VNFDs for OpenMANO and OSM.  In its current
   implementation, the ODL plugin depends on an outdated NEMO project.






Aranda Gutierrez, et al.Expires January 16, 2019               [Page 10]


Internet-Draft         High-level VNFDs with NEMO              July 2018


   This implementation is currently being updated to OpenDaylight Oxygen
   (the latest version at the time of writing), as a first step towards
   an ODL-independent implementation.

6.  Operational Experience

   We have used NEMO descriptors in the context of the MAMI Project [7],
   to describe a measurement network service based on three virtual
   network function components:

   1.  A Trafic [8] traffic generator and sink based on iperf3.

   2.  A tshark [9]-based packet capture

   3.  An InfluxDB [10]-based time series database to store measurements

   The Network Service Descriptor must always include two instances of
   the trafic-based VNFC, while the tshak VNFC and the influxdb VNFC are
   optional (more information is provided at the trafic VNFC creation
   description page [11].)

   The process of creating the different node models is incremental.  We
   start by importing the node models:


   CREATE NodeModel trafic VNFD https://<repo_url>/trafic.yaml;
       ConnectionPoint mgmt at VNFD:eth0;
       ConnectionPoint gen at VNFD:eth1;

   CREATE NodeModel tshark VNFD https://<repo_url>/tshark.yaml;
       ConnectionPoint mgmt at VNFD:eth0;
       ConnectionPoint probe at VNFD:eth1;

   CREATE NodeModel influxdb VNFD https://<repo_url>/influxdb.yaml;
       ConnectionPoint mgmt at VNFD:eth0;


                         Figure 7: Creating VNFCs

   Then, we create the kernel NSD, based on the trafic VNFCs only:











Aranda Gutierrez, et al.Expires January 16, 2019               [Page 11]


Internet-Draft         High-level VNFDs with NEMO              July 2018


   CREATE NodeModel trafic_kernel;
       Node iperf-servers Type trafic;
       Node iperf-clients Type trafic;
       ConnectionPoint client;
       ConnectionPoint server;
       ConnectionPoint mgmt;
       Connection icon Type p2p Endnodes client, iperfs-clients:gen;
       Connection ocon Type p2p Endnodes server, iperfs-servers:gen;
       Connection mgmt Type Lan \
           Endnodes mgmt, iperfs-servers:mgmt, iperfs-clients:mgmt;


              Figure 8: Kernel NSD based on the trafic VNFCs

   Adding the influxdb VNFC to create an autonomous measurement NSD that
   includes local storage for the measurement results is accomplished
   with the following NEMO script:


   CREATE NodeModel
       Node iperf-servers Type trafic_kernel;
       Node database Type influxdb;
       ConnectionPoint client;
       ConnectionPoint server;
       ConnectionPoint mgmt;
       Connection icon Type p2p Endnodes client, trafic_kernel:client;
       Connection ocon Type p2p Endnodes server, trafic_kernel:server;
       Connection mgmt Type Lan \
           Endnodes mgmt, trafic_kernel:mgmt, influxdb:mgmt;


                         Figure 9: Adding influxdb

   NEMO has shown a fundamental advantage when compared to YAML or JSON-
   based descriptors: since it is human-understandable, the development
   and debugging times of moderate to complex network service
   descriptors have been shortened considerably and the learning curve
   is much shallower compared with the original formats.

   NEMO allows to identify requirements both for itself and MANO
   developers more quickly.  An example is the connection of the
   wireshark-based traffic sniffing VNFC.  The current connection types
   (LAN or p2p ) do not consider port mirroring, a functionality
   provided by the TAPaaS plugin in Openstack.  This requirement will be
   fed back to the different MANO communities (OSM, etc.) as a user
   requirement.





Aranda Gutierrez, et al.Expires January 16, 2019               [Page 12]


Internet-Draft         High-level VNFDs with NEMO              July 2018


7.  Future work

   Future work includes extensions to the language to separate control
   and data plane connections explicitly and new types of connectivity
   models, including a model that provides the TAP as a Service [12]
   (TAPaaS) functionality available for OpenStack.

8.  Conclusion

   With the strategy defined in this document, we are able to link a
   low-level VNF description into a high-level description language for
   networks like NEMO.  Effectively, we are introducing recursiveness in
   VNFDs, allowing complex service descriptors to be built by reusing
   previously tested descriptors graphs as building blocks.

   Although we have used the OpenMANO and OSM descriptor formats in this
   document and for the reference implementation, other descriptors and
   concepts (i.e. as those used by TOSCA [13]) can also be used as the
   lowest level in this extension to the NEMO language.

9.  IANA Considerations

   This draft includes no request to IANA.

10.  Security Considerations

   The VNFD construct as IMPORT allows referencing external resources.
   Developers using it in NEMO scripts are advised to verify the source
   of those external resources, and whenever possible, rely on sources
   with a verifiable identity through cryptographic methods.

11.  Acknowledgement

   The work presented in this paper is partially funded by the European
   Union's Horizon 2020 research and innovation programme under grant
   agreement No 688421.

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.






Aranda Gutierrez, et al.Expires January 16, 2019               [Page 13]


Internet-Draft         High-level VNFDs with NEMO              July 2018


   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, DOI 10.17487/RFC3986, January 2005,
              <https://www.rfc-editor.org/info/rfc3986>.

   [ETSI-NFV-MANO]
              ETSI, "Network Functions Virtualisation (NFV); Management
              and Orchestration", ETSI GS NFV-MAN 001 V1.1.1 (2014-12),
              December 2014.

12.2.  Informative References

   [I-D.xia-sdnrg-nemo-language]
              Xia, Y., Jiang, S., Zhou, T., Hares, S., and Y. Zhang,
              "NEMO (NEtwork MOdeling) Language", draft-xia-sdnrg-nemo-
              language-04 (work in progress), April 2016.

12.3.  URIs

   [1] https://github.com/nfvlabs/openmano

   [2] https://github.com/nfvlabs/openmano

   [3] yaml.org

   [4] https://wiki.opendaylight.org/view/NEMO:Main

   [5] https://github.com/telefonicaid/vibnemo

   [6] http://www.opendaylight.org

   [7] https://mami-project.eu

   [8] https://github.com/mami-project/trafic/

   [9] https://www.wireshark.org

   [10] https://www.influxdata.com

   [11] https://github.com/mami-project/trafic/blob/master/README-VM.md

   [12] https://docs.openstack.org/developer/dragonflow/specs/
        tap_as_a_service.html

   [13] http://docs.oasis-open.org/tosca/tosca-nfv/v1.0/tosca-nfv-
        v1.0.html





Aranda Gutierrez, et al.Expires January 16, 2019               [Page 14]


Internet-Draft         High-level VNFDs with NEMO              July 2018


Authors' Addresses

   Pedro A. Aranda Gutierrez
   Universidad Carlos III Madrid
   Leganes  28911
   Spain

   Email: paranda@it.uc3m.es


   Diego R. Lopez
   Telefonica I+D
   Zurbaran, 12
   Madrid  28010
   Spain

   Email: diego.r.lopez@telefonica.com


   Stefano Salsano
   Univ. of Rome Tor Vergata/CNIT
   Via del Politecnico, 1
   Rome  00133
   Italy

   Email: stefano.salsano@uniroma2.it


   Elena Batanero

   Email: elena.batanero.18@gmail.com




















Aranda Gutierrez, et al.Expires January 16, 2019               [Page 15]


Html markup produced by rfcmarkup 1.129d, available from https://tools.ietf.org/tools/rfcmarkup/