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Versions: (draft-voit-netconf-restconf-notif) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 RFC 8650

NETCONF                                                          E. Voit
Internet-Draft                                               A. Tripathy
Intended status: Standards Track                       E. Nilsen-Nygaard
Expires: February 5, 2018                                  Cisco Systems
                                                                A. Clemm
                                                      A. Gonzalez Prieto
                                                              A. Bierman
                                                          August 4, 2017

          Restconf and HTTP Transport for Event Notifications


   This document defines Restconf, HTTP2, and HTTP1.1 bindings for the
   transport of Subscription requests and corresponding push updates.
   Being subscribed may be either publisher defined event streams or
   nodes/subtrees of YANG Datastores.

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 http://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 February 5, 2018.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of

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   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 . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Solution  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.1.  Dynamic YANG Subscription with RESTCONF control . . . . .   3
     3.2.  Subscription Multiplexing . . . . . . . . . . . . . . . .   6
   4.  Encoded Subscription and Notification Message Examples  . . .   7
     4.1.  Restconf Subscription and Events over HTTP1.1 . . . . . .   7
     4.2.  Event Notification over HTTP2 . . . . . . . . . . . . . .  12
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  13
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Appendix A.  End-to-End Deployment Guidance . . . . . . . . . . .  14
     A.1.  Call Home . . . . . . . . . . . . . . . . . . . . . . . .  14
     A.2.  TLS Heartbeat . . . . . . . . . . . . . . . . . . . . . .  15
   Appendix B.  RESTCONF over GRPC . . . . . . . . . . . . . . . . .  15
   Appendix C.  Changes between revisions  . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

1.  Introduction

   Mechanisms to support Event subscription and push are defined in
   [sn].  Enhancements to [sn] which enable YANG Datastore subscription
   and push are defined in [yang-push].  This document provides a
   transport specification for these protocols over Restconf and HTTP.
   Driving these requirements is [RFC7923].

   The streaming of notifications encapsulating the resulting
   information push can be done with either HTTP1.1 and HTTP2.  When
   using HTTP2 [RFC7540] benefits which can be realized include:

   o  Elimination of head-of-line blocking

   o  Weighting and proportional dequeuing of Events from different

   o  Explicit precedence in subscriptions so that events from one
      subscription must be sent before another dequeues

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2.  Terminology

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

   The following terms use the defintions from [sn]: configured
   subscription, dynamic subscription, event notification, publisher,
   receiver, subscriber, and subscription.

3.  Solution

   Subscribing to event streams is defined in [sn], YANG Datastore
   subscription is defined in [yang-push].  This section specifies
   transport mechanisms applicable to both.

3.1.  Dynamic YANG Subscription with RESTCONF control

   Dynamic Subscriptions for both [sn] and its [yang-push] augmentations
   are configured and managed via signaling messages transported over
   [RFC8040].  These interactions will be accomplished via a Restconf
   POST into RPCs located on the Publisher.  HTTP responses codes will
   indicate the results of the interaction with the Publisher.  An HTTP
   status code of 200 is the proper response to a successful <establish-
   subscription> RPC call.  The successful <establish-subscription> will
   result in a HTTP message with returned subscription URI on a
   logically separate mechanism than was used for the original Restconf
   POST.  This mechanism is via a parallel TCP connection in the case of
   HTTP 1.x, or in the case of HTTP2 via a separate HTTP stream within
   the HTTP connection.  When a being returned by the Publisher, failure
   will be indicated by error codes transported in payload.

   Once established, the resulting stream of notification messages are
   then delivered via SSE for HTTP1.1 and via HTTP Data for HTTP2.

3.1.1.  Call Flow for HTTP2

   Requests to [sn] or [yang-push] augmented RPCs are sent on one or
   more HTTP2 streams indicated by (a) in Figure 2.  Notification
   messages related to a single subscription are pushed on a unique
   logical channel (b).  In the case below, a newly established
   subscription has its associated messages pushed over HTTP2 stream

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   +------------+                                 +------------+
   | Subscriber |                                 | Publisher  |
   |HTTP2 Stream|                                 |HTTP2 Stream|
   |  (a)  (b)  |                                 |  (a)  (b)  |
   +------------+                                 +------------+
       | Restconf POST (RPC:establish-subscription)   |
       |                             HTTP 200 OK (URI)|
       |   (7)HTTP POST (URI)                             (7)
       |    |--------------------------------------------->|
       |    |                                   HTTP 200 OK|
       |    |<---------------------------------------------|
       |    |                       HTTP Data (event-notif)|
       |    |<---------------------------------------------|
       | Restconf POST (RPC:modify-subscription)      |    |
       |--------------------------------------------->|    |
       |    |                              HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    |             HTTP Data (subscription-modified)|
       |    |<---------------------------------------------|
       |    |                       HTTP Data (event-notif)|
       |    |<---------------------------------------------|
       | Restconf POST (RPC:delete-subscription)      |    |
       |--------------------------------------------->|    |
       |    |                              HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    |                  HTTP Headers (end of stream)|
       |   (/7)<-----------------------------------------(/7)

                       Figure 1: Dynamic with HTTP2

3.1.2.  Call flow for HTTP1.1

   Requests to [yang-push] RPCs are sent on the TCP connection indicated
   by (a).  Notification messages are pushed on a separate connection
   (b).  This connection (b) will be used for all notification messages
   across all subscriptions.

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   +--------------+                             +--------------+
   |  Subscriber  |                             |   Publisher  |
   |TCP connection|                             |TCP connection|
   |  (a)  (b)    |                             |    (a)  (b)  |
   +--------------+                             +--------------+
       | Restconf POST (RPC:establish-subscription)   |
       |                             HTTP 200 OK (URI)|
       |    |HTTP GET (URI)                                |
       |    |--------------------------------------------->|
       |    |                                   HTTP 200 OK|
       |    |<---------------------------------------------|
       |    |                             SSE (event-notif)|
       |    |<---------------------------------------------|
       | Restconf POST (RPC:modify-subscription)      |    |
       |--------------------------------------------->|    |
       |    |                              HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    |                   SSE (subscription-modified)|
       |    |<---------------------------------------------|
       |    |                             SSE (event-notif)|
       |    |<---------------------------------------------|
       | Restconf POST (RPC:delete-subscription)      |    |
       |--------------------------------------------->|    |
       |    |                              HTTP 200 OK|    |
       |<---------------------------------------------|    |
       |    |                                              |
       |    |

                      Figure 2: Dynamic with HTTP1.1

3.1.3.  Configured Subscription over HTTP2

   With a Configured Subscription, all information needed to establish a
   secure relationship with that Receiver is available on the Publisher.
   With this information, the Publisher will establish a secure
   transport connection with the Receiver and then begin pushing
   notification messages to the Receiver.  Since Restconf might not
   exist on the Receiver, it is not desirable to require that subscribed
   content be pushed with any dependency on Restconf.  Nor is there
   value which Restconf provides on top of HTTP.  Therefore in place of
   Restconf, a TLS secured HTTP2 Client connection must be established
   with an HTTP2 Server located on the Receiver.  Notification messages
   will then be sent as part of an extended HTTP POST to the Receiver.

   POST messages will be addressed to HTTP augmentation code on the
   Receiver capable of accepting and responding to state change

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   notifications and subscribed content notification messages.  The
   first POST message must be a subscription-started notification.
   Notifications which include any subscribed content must not be sent
   until the receipt of an HTTP 200 OK for this initial notification.
   The 200 OK will indicate that the Receiver is ready for the delivery
   of subscribed content.  At this point a Subscription must be
   allocated its own HTTP2 stream.  Figure 4 depicts this message flow.

   +------------+                                 +------------+
   |  Receiver  |                                 | Publisher  |
   |HTTP2 Stream|                                 |HTTP2 Stream|
   |  (a)  (b)  |                                 |  (a)  (b)  |
   +------------+                                 +------------+
       |    HTTP Post Headers, Data (sub-start, SubID)|
       | HTTP 200 OK                                  |
       |    |         HTTP Post Headers, Data (event-notif)|
       |    |<---------------------------------------------|
       |    |                       HTTP Data (event-notif)|
       |    |<---------------------------------------------|
       |    |                     HTTP Data (sub-terminate)|
       |    |<---------------------------------------------|
       |    |HTTP 200 OK                                   |
       |    |--------------------------------------------->|

                      Figure 3: Configured over HTTP2

   As the HTTP2 transport is available to the Receiver, the Publisher

   o  take any subscription-priority and copy it into the HTTP2 stream
      priority, and

   o  take a subscription-dependency if it has been provided and map the
      HTTP2 stream for the parent subscription into the HTTP2 stream

3.2.  Subscription Multiplexing

   It is possible that updates across subscriptions might be delivered
   in a different sequence than the encapsulated records were generated.
   Reasons for this might include (but are not limited to):

   o  generation of event records on different line cards

   o  replay of pushed information, and

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   o  temporary loss of transport connectivity, with update buffering
      and different dequeuing priorities per Subscription

   o  population, marshalling and bundling across independent
      Subscription Updates, and

   Therefore each notification message will include a timestamp to
   provide a Receiver with its best information indicating when a
   particular record was generated.  Use of this timestamp can give an
   indication of the state of objects at a Publisher.  This is
   especially important when state-entangled information is received
   across different subscriptions.  Note that use of notification
   message timestamps may not indicate a the exact time of occurrence.
   So when state-entangled updates have inconsistent object values and
   temporally close timestamps, a Receiver might consider performing a
   GET to validate the current state of a Publisher.

4.  Encoded Subscription and Notification Message Examples

4.1.  Restconf Subscription and Events over HTTP1.1

   Subscribers can dynamically learn whether a RESTCONF server supports
   various types of Event or Yang datastore subscription capabilities.
   This is done by issuing an HTTP request OPTIONS, HEAD, or GET on the
   stream.  Some examples building upon the Call flow for HTTP1.1 from
   Section 3.2.2 are:

   GET /restconf/data/ietf-restconf-monitoring:restconf-state/
            streams/stream=yang-push HTTP/1.1
   Host: example.com
   Accept: application/yang.data+xml

   If the server supports it, it may respond

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   HTTP/1.1 200 OK
   Content-Type: application/yang.api+xml
   <stream xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf-monitoring">
               <description>Yang push stream</description>

   If the server does not support any form of subscription, it may

   HTTP/1.1 404 Not Found
   Date: Mon, 25 Apr 2012 11:10:30 GMT
   Server: example-server

   Subscribers can determine the URL to receive updates by sending an
   HTTP GET as a request for the "location" leaf with the stream list
   entry.  The stream to use for may be selected from the Event Stream
   list provided in the capabilities exchange.  Note that different
   encodings are supporting using different Event Stream locations.  For
   example, the Subscriber might send the following request:

   GET /restconf/data/ietf-restconf-monitoring:restconf-state/
            streams/stream=yang-push/access=xml/location HTTP/1.1
   Host: example.com
   Accept: application/yang.data+xml

   The Publisher might send the following response:

   HTTP/1.1 200 OK
   Content-Type: application/yang.api+xml

   To subscribe and start receiving updates, the subscriber can then
   send an HTTP GET request for the URL returned by the Publisher in the
   request above.  The accept header must be "text/event-stream".  The

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   Publisher uses the Server Sent Events [W3C-20150203] transport
   strategy to push filtered events from the event stream.

   The Publisher MUST support individual parameters within the POST
   request body for all the parameters of a subscription.  The only
   exception is the encoding, which is embedded in the URI.  An example
   of this is:

   // subtree filter = /foo
   // periodic updates, every 5 seconds
   POST /restconf/operations/ietf-event-notifications:
        establish-subscription HTTP/1.1
         Host: example.com
         Content-Type: application/yang-data+json

           "ietf-event-notifications:input" : {
             "stream": "push-data"
             "period" : 5,
             "xpath-filter" : "/ex:foo[starts-with('bar'.'some']"

   Should the publisher not support the requested subscription, it may

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   HTTP/1.1 501 Not Implemented
   Date: Mon, 23 Apr 2012 17:11:00 GMT
   Server: example-server
   Content-Type: application/yang.errors+xml
       <errors xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
              <error-message>Xpath filters not supported</error-message>
                  <supported-subscription xmlns="urn:ietf:params:xml:ns:

   with an equivalent JSON encoding representation of:

   HTTP/1.1 501 Not Implemented
   Date: Mon, 23 Apr 2012 17:11:00 GMT
   Server: example-server
   Content-Type: application/yang.errors+json
           "ietf-restconf:errors": {
             "error": {
               "error-type": "protocol",
               "error-tag": "operation-not-supported",
               "error-message": "Xpath filters not supported."
               "error-info": {
                  "datastore-push:supported-subscription": {
                        "subtree-filter": [null]

   The following is an example of a pushed content for the Subscription
   above.  It contains a subtree with root foo that contains a leaf
   called bar:

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   XML encoding representation:
     <?xml version="1.0" encoding="UTF-8"?>
     <notification xmlns="urn:ietf:params:xml:ns:yang:ietf-restconf">
        <subscription-id xmlns="urn:ietf:params:xml:ns:restconf:
        <datastore-contents xmlns="urn:ietf:params:xml:ns:restconf:
           <foo xmlns="http://example.com/yang-push/1.0">

   Or with the equivalent YANG over JSON encoding representation as
   defined in [RFC7951]:

     "ietf-restconf:notification": {
       "datastore-push:subscription-id": "my-sub",
       "eventTime": "2015-03-09T19:14:56.233Z",
       "datastore-push:datastore-contents": {
         "example-mod:foo": { "bar": "some_string" }

   To modify a Subscription, the subscriber issues another POST request
   on the provided URI using the same subscription-id as in the original
   request.  For example, to modify the update period to 10 seconds, the
   subscriber may send:

   POST /restconf/operations/ietf-event-notifications:
         modify-subscription HTTP/1.1
         Host: example.com
         Content-Type: application/yang-data+json

           "ietf-event-notifications:input" : {
             "subscription-id": 100,
             "period" : 10

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   To delete a Subscription, the Subscriber issues a DELETE request on
   the provided URI using the same subscription-id as in the original

4.2.  Event Notification over HTTP2

   The basic encoding will look as below.  It will consists of a JSON
   representation wrapped in an HTTP2 header.

   HyperText Transfer Protocol 2
         Stream: HEADERS, Stream ID: 5
         Header: :method: POST
         Stream: HEADERS, Stream ID: 5

     "ietf-yangpush:notification": {
       "datastore-push:subscription-id": "my-sub",
       "eventTime": "2015-03-09T19:14:56.233Z",
       "datastore-push:datastore-contents": {
         "foo": { "bar": "some_string" }

5.  Security Considerations

   Subscriptions could be used to intentionally or accidentally overload
   the resources of a Publisher.  For this reason, it is important that
   the Publisher has the ability to prioritize the establishment and
   push of notification messages where there is the potential for
   resource exhaust.  In addition, a server needs to be able to suspend
   existing Subscriptions when needed.  When this occurs, the
   subscription status must be updated accordingly and the Receivers

   A Subscription could be used to attempt retrieve information for
   which a Receiver has no authorized access.  Therefore it is important
   that data pushed via a Subscription is authorized equivalently with
   regular data retrieval operations.  Data being pushed to a Receiver
   needs therefore to be filtered accordingly, just like if the data
   were being retrieved on-demand.  The Netconf Authorization Control
   Model [RFC6536] applies even though the transport is not NETCONF.

   One or more Publishers of Configured Subscriptions could be used to
   overwhelm a Receiver which doesn't even support Subscriptions.  There
   are two protections here.  First, notification messages for
   Configured Subscriptions MUST only be transmittable over encrypted
   transports.  Clients which do not want pushed content need only

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   terminate or refuse any transport sessions from the Publisher.
   Second, the HTTP transport augmentation on the Receiver must send an
   HTTP 200 OK to a subscription started notification before the
   Publisher starts streaming any subscribed content.

   One or more Publishers could overwhelm a Receiver which is unable to
   control or handle the volume of Event Notifications received.  In
   deployments where this might be a concern, HTTP2 transport such as
   HTTP2) should be selected.

6.  Acknowledgments

   We wish to acknowledge the helpful contributions, comments, and
   suggestions that were received from: Susan Hares, Tim Jenkins, Balazs
   Lengyel, Kent Watsen, Michael Scharf, and Guangying Zheng.

7.  References

7.1.  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,

   [RFC6520]  Seggelmann, R., Tuexen, M., and M. Williams, "Transport
              Layer Security (TLS) and Datagram Transport Layer Security
              (DTLS) Heartbeat Extension", RFC 6520,
              DOI 10.17487/RFC6520, February 2012,

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              DOI 10.17487/RFC6536, March 2012,

   [RFC7540]  Belshe, M., Peon, R., and M. Thomson, Ed., "Hypertext
              Transfer Protocol Version 2 (HTTP/2)", RFC 7540,
              DOI 10.17487/RFC7540, May 2015,

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,

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   [sn]       Voit, E., Clemm, A., Gonzalez Prieto, A., Prasad Tripathy,
              A., and E. Nilsen-Nygaard, "Subscribing to Event
              Notifications", February 2017,

7.2.  Informative References

   [GRPC]     "RPC framework that runs over HTTP2", August 2017,

   [RFC7923]  Voit, E., Clemm, A., and A. Gonzalez Prieto, "Requirements
              for Subscription to YANG Datastores", RFC 7923,
              DOI 10.17487/RFC7923, June 2016,

   [RFC7951]  Lhotka, L., "JSON Encoding of Data Modeled with YANG",
              RFC 7951, DOI 10.17487/RFC7951, August 2016,

   [RFC8071]  Watsen, K., "NETCONF Call Home and RESTCONF Call Home",
              RFC 8071, DOI 10.17487/RFC8071, February 2017,

              "Server-Sent Events, World Wide Web Consortium CR CR-
              eventsource-20121211", February 2015,

              Clemm, A., Voit, E., Gonzalez Prieto, A., Prasad Tripathy,
              A., Nilsen-Nygaard, E., Bierman, A., and B. Lengyel,
              "Subscribing to YANG datastore push updates", March 2017,

Appendix A.  End-to-End Deployment Guidance

   Several technologies are expected to be seen within a deployment to
   achieve security and ease-of-use requirements.  These are not
   necessary for an implementation of this specification, but will be
   useful to consider when considering the operational context.

A.1.  Call Home

   Implementations should include the ability to transparently
   incorporate 'call home' [RFC8071] so that secure TLS connections can
   originate from the desired device.

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A.2.  TLS Heartbeat

   HTTP sessions might not quickly allow a Subscriber to recognize when
   the communication path has been lost from the Publisher.  To
   recognize this, it is possible for a Receiver to establish a TLS
   heartbeat [RFC6520].  In the case where a TLS heartbeat is included,
   it should be sent just from Receiver to Publisher.  Loss of the
   heartbeat should result in any Subscription related TCP sessions
   between those endpoints being torn down.  The subscription can then
   attempt to re-establish.

Appendix B.  RESTCONF over GRPC

   An initial goal for this document was to support [GRPC] transport
   seamlessly without any mapping or extra layering.  However there is
   an incompatibility of RESTCONF and GRPC.  RESTCONF uses HTTP GET, and
   GRPC uses HTTP2's POST rather than GET.  As GET is used across
   RESTCONF for things like capabilities exchange, a seamless mapping
   depends on specification changes outside the scope of this document.
   If/when GRPC supports GET, or RESTCONF is updated to support POST,
   this should be revisited.  It is hoped that the resulting fix will be
   transparent to this document.

Appendix C.  Changes between revisions

   (To be removed by RFC editor prior to publication)

   v01 - v03

   o  Terminoology aligned with draft-voit-netconf-notification-

   o  Tweaks to wording/capitalization/format.

   v01 - v02

   o  Removed sections now redundant with [sn] and [yang-push] such as:
      mechanisms for subscription maintenance, terminology definitions,
      stream discovery.

   o  3rd party subscriptions are out-of-scope.

   o  SSE only used with Restconf and HTTP1.1 Dynamic Subscriptions

   o  Timeframes for event tagging are self-defined.

   o  Clean-up of wording, references to terminology, section numbers.

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   v00 - v01

   o  Removed the ability for more than one subscription to go to a
      single HTTP2 stream.

   o  Updated call flows.  Extensively.

   o  SSE only used with Restconf and HTTP1.1 Dynamic Subscriptions

   o  HTTP is not used to determine that a Receiver has gone silent and
      is not Receiving Event Notifications

   o  Many clean-ups of wording and terminology

Authors' Addresses

   Eric Voit
   Cisco Systems

   Email: evoit@cisco.com

   Ambika Prasad Tripathy
   Cisco Systems

   Email: ambtripa@cisco.com

   Einar Nilsen-Nygaard
   Cisco Systems

   Email: einarnn@cisco.com

   Alexander Clemm

   Email: ludwig@clemm.org

   Alberto Gonzalez Prieto

   Email: agonzalezpri@vmware.com

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   Andy Bierman

   Email: andy@yumaworks.com

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