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Protocol Assisted Protocol (PAP)
draft-li-rtgwg-protocol-assisted-protocol-03

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This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors Zhenbin Li , Shuanglong Chen , Yunan Gu
Last updated 2020-11-02 (Latest revision 2020-03-06)
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draft-li-rtgwg-protocol-assisted-protocol-03
Network Working Group                                              Z. Li
Internet-Draft                                                   S. Chen
Intended status: Standards Track                                   Y. Gu
Expires: May 6, 2021                                              Huawei
                                                       November 02, 2020

                    Protocol Assisted Protocol (PAP)
              draft-li-rtgwg-protocol-assisted-protocol-03

Abstract

   For routing protocol troubleshooting, different approaches exibit
   merits w.r.t. different situations.  They can be generally divided
   into two categories, the distributive way and the centralized way.  A
   very commonly used distributive approach is to log in possiblly all
   related devices one by one to check massive data via CLI.  Such
   approach provides very detailed device information, however it
   requires operators with high NOC (Network Operation Center)
   experience and suffers from low troubleshooting efficiency and high
   cost.  The centralized approach is realized by collecting data from
   devices via approaches, like the streaming Telemetry or BMP(BGP
   Monitoring Protocol) RFC7854 [RFC7854], for the centralized server to
   analyze all gathered data.  Such approach allows a comprehensive view
   fo the whole network and facilitates automated troubleshooting, but
   is limited by the data collection boundary set by different
   management domains, as well as high network bandwidth and CPU
   computation costs.

   This document proposes a semi-distributive and semi-centralized
   approach for fast routing protocol troubleshooting, localizing the
   target device and possibly the root cause, more precisely.  It
   defines a new protocol, called the PAP (Protocol assisted Protocol),
   for devices to exchange protocol related information between each
   other in both active and on-demand manners.  It allow devices to
   request specific information from other devices and receive replies
   to the requested data.  It also allows actively transmission of
   information without request to inform other devices to better react
   w.r.t. network issues.

Requirements Language

   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 RFC 2119 [RFC2119].

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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 May 6, 2021.

Copyright Notice

   Copyright (c) 2020 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  PAP Usage Use cases . . . . . . . . . . . . . . . . . . .   5
       1.2.1.  Use Case 1: BGP Route Oscillation . . . . . . . . . .   5
       1.2.2.  Use Case 2: RSVP-TE Set Up Failure  . . . . . . . . .   6
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.  PAP Overview  . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.1.  PAP Encapsulation . . . . . . . . . . . . . . . . . . . .   7
     3.2.  PAP Speaker and PAP Agent . . . . . . . . . . . . . . . .   7
     3.3.  PAP Event . . . . . . . . . . . . . . . . . . . . . . . .   7
     3.4.  Summary of Operation  . . . . . . . . . . . . . . . . . .   8
       3.4.1.  PAP Capability Negotiation Process  . . . . . . . . .   8
       3.4.2.  PAP Request and Reply Process . . . . . . . . . . . .   8
       3.4.3.  PAP Notification Process  . . . . . . . . . . . . . .   9

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   4.  PAP Message Format  . . . . . . . . . . . . . . . . . . . . .   9
     4.1.  Common Header . . . . . . . . . . . . . . . . . . . . . .   9
       4.1.1.  Capability Negotiation Message  . . . . . . . . . . .  10
     4.2.  Request Message . . . . . . . . . . . . . . . . . . . . .  11
     4.3.  Reply Message . . . . . . . . . . . . . . . . . . . . . .  12
     4.4.  Notification Message  . . . . . . . . . . . . . . . . . .  13
     4.5.  ACK Message . . . . . . . . . . . . . . . . . . . . . . .  14
   5.  PAP Operations  . . . . . . . . . . . . . . . . . . . . . . .  14
     5.1.  Capability Negotiation Process  . . . . . . . . . . . . .  14
       5.1.1.  PAP Peering Relation Establish Process  . . . . . . .  14
       5.1.2.  PAP Capability Enabling Notification Process  . . . .  15
       5.1.3.  PAP Capability Disabling Notification Process . . . .  16
     5.2.  PAP Request and Reply Process . . . . . . . . . . . . . .  16
     5.3.  PAP Notification Process  . . . . . . . . . . . . . . . .  18
   6.  PAP Error Handling  . . . . . . . . . . . . . . . . . . . . .  18
   7.  Discussion  . . . . . . . . . . . . . . . . . . . . . . . . .  19
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  20
   9.  IANA  . . . . . . . . . . . . . . . . . . . . . . . . . . . .  20
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  20
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  20
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   A healthy control plane, providing network connectivity, is the
   foundation of a well-functioning network.  There have been rich
   routing and signaling protocols designed and used for IP networks,
   such as IGP (ISIS,OSPF), BGP, LDP, RSVP-TE and so on.  The health
   issues of these protocols, such as neighbor/peer disconnect/set up
   failure, LSP set up failure, route flapping and so on, have been
   devoted with ongoing efforts for diagnosing and remediation.

1.1.  Motivation

   The distributive protocol troubleshooting approach is typically
   realized through manual per-device check.  It's both time- and labor-
   consuming, and requires NOC experience of the operators.  Amongst
   all, localizing the target device is usually the most diffcult and
   time-consuming part.  For example, in the case of route loop,
   operators first log in a random deivce that reports TTL alarms, and
   then check the looped route in the Forwarding Information Base (FIB)
   and/or the Routing Information Base (RIB).  It requires device by
   device check, as well as manul data correlation, to pin point to the
   exact responsible device, since the information retrival and analysis
   of such distributive way is fragmented.  In addition, the low
   efficiency and manul troubleshooting activities may further impact
   new network services and/or enlarge affected areas.

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   The centralized network OAM, by collecting network-wide data from
   devices, enables automatic routing protocol troubleshooting.  Date
   collection protocols, such as SNMP (Simple Network Management
   Protocol) [RFC1157], NETCONF (Network Configuration Protocol)
   [RFC6241], and (BMP) [RFC7854], can provide various information
   retrival, such as network states, routing data, configurations and so
   on.  Such centrazlized way relies on the existence of a centralized
   server/controller, which is not supported by some legacy networks.
   What's more, even with the existence of a centralized server/
   controller, it can only collect the data within its own management
   domain, while the cross-domain data are not available due to
   independent managment of different ISPs.  Thus, the lack of such
   information may lead to troubleshooting failure.  In addition,
   centralized approaches may suffer from high network bandwidth and CPU
   computation consumptions.

   Another way of protocol troubleshooting is utilzing the protocol
   itself to convey diagnosing information.  For example, some reason
   codes are carried in the Path-Err/ResvErr messages of RSVP-TE, so
   that to other nodes may know the why the tunnel fails to be set up.
   Such approaches is semi-distributive and semi-centralized.  It does
   not rely on the deployment of a centralized server, but still gets
   partial global view of the network.  However, there still requires
   non-trivial augementation works to existing routing protocols in
   order to support troubleshooting.  This then raises the question that
   whether such non-routing data is suitable to be carried in these
   routing protocols.  The extra encapsulation, parsing and analyzing
   work for the non-routing data would further slow down the network
   convergence.  Thus, it's better to separate the routing and non-
   routing data transmission as well as data parsing.  In addition,
   coexisting with legacy devices may cause interop issues.  Thus,
   relying on augumenting existing routing protocols without network-
   wide upgrading may not only fail to provide the truobleshooting
   benefit, but further affect the operation of the existing routing
   system.  What's more, the failure of routing protocol instance would
   lead to the failure of diagnosing itself.  All in all, it's
   reasonable to separate the protocol diagnosing data
   generation/encapsulation/transmission/parsing from the protocol
   itself.

   This document proposes a new protocol, called the PAP (Protocol
   assisted Protocol), for devices to exchange protocol related
   information between each other.  It allows both active and on-demand
   data exchange.  Considering that massiveness of protocol/routing
   related data, the intuitive of designing PAP is not to exchange the
   comprehensive protocol/routing status between devices, but to provide
   very specific information required for fast troubleshooting.  The

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   benefits of such a semi-distributive and semi-centralized approach
   are summarized as follows:

   1.  It facilitates automatic troubleshooting without requiring manul
       device by device check.

   2.  It allows individual device to have a more global view by
       requesting data from other devices.

   3.  It does not rely on the deployement of a centralized server/
       controller.

   4.  It passes the dtata collection boundary set by different
       management domains by cross-domain data exchange between devices.

   5.  It relieves the bandwidth pressure of network-wide data
       collection, and the processing pressure of the centralized
       server.

   6.  It does not affect the running of existing routing protocols.

1.2.  PAP Usage Use cases

   PAP allows both data request/reply and data notification between
   devices.  PAP speakers use the exchanged PAP data to help fast
   localize the network issues.

1.2.1.  Use Case 1: BGP Route Oscillation

   A BGP route oscillation can be caused by various reasons, and usually
   leaves network-wide impact.  In order to find the root cause and take
   remediation actions, the first step is to localize the oscillation
   source.  In this case, a BGP speaker can send a PAP Request Message
   to the next hop device of the oscillating route asking " Are you the
   oscillation source?".  If the BGP speaker is the oscillation source,
   possiblly knows by running a device diagnosing system, replies with a
   PAP Reply Message saying that "I'm the oscillation source!" to the
   device who sends the PAP Request Message.  If the BGP speaker is not
   the oscillation source, it further asks the same question with a PAP
   Request Message to its next hop device of the oscillating route.
   This request and reply process continues util the request has reached
   the oscillation source.  The source device then sends a PAP Reply
   Message to tell its upstream device along the PAP request path that "
   I am the oscillation source!", and then "xx is the oscillation
   source!" information is further sent back hop by hop to the device
   who originates the request.

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1.2.2.  Use Case 2: RSVP-TE Set Up Failure

   The MPLS label switch path set up, either using RSVP-TE or LDP, may
   fail due to various reasons.  Typical troubleshooting procedures are
   to log in the device, and then check if the failure lies on the
   configuration, or path computation error, or link failure.
   Sometimes, it requires the check of multiple devices along the
   tunnel.  Certain reason codes can be carried in the Path-Err/ResvErr
   messages of RSVP-TE, while other data are currently not supported to
   be transmitted to the path ingress/egress node, such as the
   authentication failure.  Using PAP, the device, which is reponsible
   for the tunnel set up failure, can send the PAP Notification Message
   to the Ingress device, and possibly with some reason codes so that
   the ingress device can not only localize the target device but also
   the root cause.

2.  Terminology

   IGP: Interior Gateway Protocol

   IS-IS: Intermediate System to Intermediate System

   OSPF: Open Shortest Path First

   BGP: Boarder Gateway Protocol

   BGP-LS: Boarder Gateway Protocol-Link State

   MPLS: Multi-Protocol Label Switching

   RSVP-TE: Resource Reservation Protocol-Traffic Engineering

   LDP: Label Distribution Protocol

   BMP: BGP Monitoring Protocol

   LSP: Link State Packet

   IPFIX: Internet Protocol Flow Information Export

   PAP: Protocol assisted Protocol

   UDP: User Datagram Protocol

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3.  PAP Overview

3.1.  PAP Encapsulation

   PAP uses UDP as its transport protocol, which is connectionless.  The
   reason that UDP is selected over TCP is because PAP is intended for
   on-demand communications.  The PAP packet is defined as follows.
   This document requires the assignment of a User Port registry for the
   UDP Destination Port.

 +-------------+-------------+-------------+-------------+-------------+
 | ETH. Header |  IP Header  | UDP Header  |  PAP Header | PAP Payload |
 +-------------+-------------+-------------+-------------+-------------+

                   Figure 1. Encapsulation in UDP

3.2.  PAP Speaker and PAP Agent

   This document uses PAP speakers to refer to routing devices that
   communicate with each other using PAP.  PAP speakers SHOULD be
   implemented with a supporting module (or multiple modules) to
   receive, parse, analyze, generate, and send PAP messages.  For
   example, a BGP diagnosing module used for BGP related PAP message
   handling functions as a PAP agent.  A PAP Agent is the union of
   multiple such modules regarding different protocols, or one module
   for all protocols.  Such supporting module is called PAP Agent in
   this document.  PAP Agent, standalone, SHOULD be able to provide
   protocol troubleshooting capability with local information.  Enabling
   PAP exchange capability, PAP agent gains information from remote PAP
   speakers to improve diagnosing accuracy . The primary function of PAP
   is to provide a unfied tunnel for protocol diagnosing information
   exchange without augumenting each specific protocol.

3.3.  PAP Event

   A PAP Event is referred to as the a troubleshooting instance running
   within a PAP Agent.  A PAP Agent may instantiate one or multiple PAP
   Events for each protocol at the same time depending on the configured
   troubleshooting triggering condition.  For example, an PAP Event is
   intiated automatically when device CPU is over high, or manually with
   related command line input from a device operator.  Once a PAP Event
   is generated, corresponding PAP processes are to be called on demand.
   Notice, the initiation of PAP Capability Negotiation does not require
   the existance of a PAP Event.

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3.4.  Summary of Operation

   The communications between two PAP speakders should follow three
   major processes, i.e., the Capability Negotiation Process, the
   Request and Reply Process, and the Notification Process.  This
   document defines 5 PAP Message types, i.e., Negotiation Message,
   Request Message, Reply Message, Notification Message, and ACK
   Message, which are used in the above PAP processes.

3.4.1.  PAP Capability Negotiation Process

   The purpose of the Capability Negotiation process is to inform two
   PAP speakers of each other's PAP capabilties.  The PAP capability
   indicates, for which specific protocol(s), that PAP supports its/
   their diagnosing information exchange.  The process can be further
   divided into three procudures: 1) PAP Peering Relations Establish
   process, 2) PAP Capability Enabling Notification Process, 3) PAP
   Capability Disabling Notification Process.  The Capability
   Negotiation Process is realized by the exchange of PAP Capability
   Negotiation Message, which is defined in Section 4.

   Although PAP is connectionless, a successful PAP Peering Relations
   Establish Process is required to be successfully performed before any
   other PAP process.  This process can be initiated by either the local
   or remote PAP speaker through sending out a PAP Capability
   Negotiation Message.  The Negotiation Message may or may not require
   an ACK Message, as indicated in the Negotiation Message.  A
   successful Peering is established if both PAP speakers have correctly
   received the other speaker's Capability Negotiation Message.  After a
   successful negotiation, two PAP speakers can exchange any PAP Message
   on-demand.  The PAP Capability Enabling Notification Process is used
   to inform the PAP peer its newly supported capability, which can be
   intiated by the PAP speaker at any moment after a PAP Peering is
   established with the respective PAP Peer.  The PAP Capability
   Disabling Notification Process is used to inform the PAP peer its
   newly unsupported capability, which can be intiated by the PAP
   speaker at any moment after a PAP Peering is established with the
   respective PAP Peer.

3.4.2.  PAP Request and Reply Process

   The purpose of the PAP Request and Reply Process is to acquire
   information needed by a PAP speaker from other PAP speakers for a
   specific PAP Event.  The Request and Reply Messages can be customized
   for different events.  The process is triggered by the instantiation
   of a PAP Event, and starts with sending a Request Message to a target
   PAP peer.  The target PAP peer is selected by the PAP agent regarding
   the current PAP Event, which is out of the scope of this document.

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   The remote PAP speaker, after receiving the Request Message, sends
   out a Reply Message to the request sender.  ACK is required or not as
   indicated in the Message Flag.

   One Request Message received at the local PAP speaker from a PAP peer
   may further results in a new Request Message generation regarding a
   third PAP speaker, if the local PAP speaker does not have the right
   Reply to this PAP peer.  This local PAP speaker does not send Reply
   Message to the requesting PAP peer until it receives a new Reply
   Message from this third PAP speaker.  So the whole process In order
   to avoid Request/Reply loops, a Residua Hop value is used to limit
   the Request/Reply rounds.

3.4.3.  PAP Notification Process

   The Notification Process is used by a PAP speaker voluntarily to
   notify other PAP speakers of certain information regarding a PAP
   Event.  The process is triggered by the instantiation of a PAP Event,
   and starts with sending a Notification Message to one or multiple
   target PAP peer(s).  The target PAP peer(s) is/are selected by the
   PAP agent regarding the current PAP Event, which is out of the scope
   of this document.  The Notification Message may or may not require an
   ACK Message, as indicated in the Notification Message.

4.  PAP Message Format

4.1.  Common Header

   The common header is encapsulated in all PAP messages.  It is defined
   as follows.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +---------------+----------------+------------------------------+
     |V|  Flag       |   Msg. Type    |            Length            |
     +---------------+----------------+------------------------------+
     +                    Peer Address (16 bytes)                    +
     ~                                                               ~
     +--------------------------------+------------------------------+
     |        Msg. Sequence           |
     +--------------------------------+

                    Figure 2. PAP Common Header

   o  Flag (1 byte): The V flag indicates that the source IP address is
      an IPv6 address.  For IPv4 address, this is set to 0.

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   o  Message Type (1 byte): This indicates the PAP message type.The
      following types are defined, and listed as follows.

      *  Type = TBD1: Capability Negotiation Message.  It is used for
         two devices to inform each other of the capabilties they
         support and no longer support.

      *  Type = TBD2: Request Message.

      *  Type = TBD3: Reply Message.

      *  Type = TBD4: Notification Message.

      *  Type = TBD5: ACK Message.  It is used to confirm to the local
         device that the remote device has received a previous sent PAP
         message, which can be either a Negotiation Message, a Request
         Message, a Reply Message or an Notification Message.

   o  Length (2 bytes): Length of the message in bytes, including the
      Common Header and the following Message.

   o  Souece IP Address (16 bytes): It indicates the IP address who
      initiates the PAP message.  It is 4 bytes long if an IPv4 address
      is carried in this field (with the 12 most significant bytes zero-
      filled) and 16 bytes long if an IPv6 address is carried in this
      field.

   o  Message Sequence (2 bytes): It indicates the sequence number of
      each PAP message.

4.1.1.  Capability Negotiation Message

   The Negotiation Message is used in the PAP Capability Negotiation
   Process.  It is defined as follows.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +--------------------------------+------------------------------+
     |     Version   |A|E|   Flag     |
     +--------------------------------+------------------------------+
     |                        Protocol Capacity                      |
     +---------------------------------------------------------------+

                    Figure 3. PAP Negotiation Message

   o  Version (1 byte): It indicates the PAP version.  The current
      version is 0.

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   o  Flags (1 bytes): Two flag bits are currently defined.

      *  The A bit is used to indicate if an ACK Message from the remote
         PAP speaker is required for each Negotiation Message sent.  If
         an ACK is required, then the A bit SHOULD be set to "1", and
         "0" otherwise.

      *  The E bit is used to indicate the enabling/disabling of the
         capabilities that carried in the Protocol Capability field.  If
         the local device wants to inform the remote device of enabling
         one or more capabilities, the E bit SHOULD be set to "1".  If
         the local device wants to inform the remote device of disabling
         one or more capabilities, the E bit SHOULD be set to "0".

   o  Protocol Capability (4 bytes): It is 4-byte bitmap that indicates
      the capability of inforamtion exchange regarding various
      protocols.  Each bit represents one protocol.  The following
      protocol capability is defined (from the rightmost bit).

      *  Bit 0: ISIS

      *  Bit 1: OSPF

      *  Bit 2: BGP

      *  Bit 3: LDP

4.2.  Request Message

   The Request Message is used for the local device to request specific
   data regarding one specific protocol or application from the remote
   device.  It MUST be sent after a successful Capability Negotiation
   Process (described in Section 5.1), and the requested protocol/
   application MUST be supported by both the local and remote devices,
   as indicated in the Negotiation Messages exchanged between the local
   and remote devices.  It is defined as follows.

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      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +---------------+----------------+------------------------------+
     |A|    Flag     |   Prot. Capb.  |          Event ID            |
     +--------------------------------+------------------------------+
     |  Res. Hop     |
     +---------------+-----------------------------------------------+
     +                          Request Data                         +
     ~                                                               ~
     +---------------------------------------------------------------+

                       Figure 4. PAP Request Message

   o  Flags (1 byte): It is currently reserved.  The A bit is used to
      indicate if an ACK Message from the remote PAP speaker is required
      for each Request Message sent.  If an ACK is required, then the A
      bit SHOULD be set to "1", and "0" otherwise.

   o  Capability (1 byte): It represents the bit index of the protocol,
      which the Request Message is requesting data for.

   o  Event ID (2 bytes): It indicates the event number that this
      Request message is regarding.

   o  Residua hop (1 byte): it indicates the residua Request hops of the
      current PAP Event.  It is reduced by 1 at each PAP speaker when
      generating a further PAP Request to a third PAP speaker.

   o  Request Data (Variable): Specifies information of the data that
      the local device is requesting.  The specific format remains to be
      determined per each protocol, as well as each use case.

4.3.  Reply Message

   The Reply Message is used to carry the information that the local
   device requests from the remote device through the Request Message.
   It is defined as follows.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +---------------+----------------+------------------------------+
     |A|    Flag     |   Prot. Capb.  |          Event ID            |
     +---------------+----------------+------------------------------+
     +                           Reply Data                          +
     ~                                                               ~
     +---------------------------------------------------------------+

                       Figure 5. PAP Reply Message

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   o  Flags (1 byte): It is currently reserved.  The A bit is used to
      indicate if an ACK Message from the remote PAP speaker is required
      for each Reply Message sent.  If an ACK is required, then the A
      bit SHOULD be set to "1", and "0" otherwise.

   o  Capability (1 byte): It represents the bit index of the protocol,
      which the Reply Message is replying data for.

   o  Event ID (2 bytes): It indicates the event number that this Reply
      message is regarding.

   o  Reply Data (Variable): Specifies information of the data that the
      local device is replying.  The specific format remains to be
      determined per each protocol, as well as each use case.

4.4.  Notification Message

   The Notification Message is used to carry the information that the
   local device sends to the remote device.

      0                   1                   2                   3
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +---------------+----------------+------------------------------+
     |A|    Flag     |   Prot. Capb.  |          Event ID            |
     +---------------+----------------+------------------------------+
     +                     Notification Data                         +
     ~                                                               ~
     +---------------------------------------------------------------+

                    Figure 6. PAP Notification Message

   o  Flags (1 byte): It is currently reserved.  The A bit is used to
      indicate if an ACK Message from the remote PAP speaker is required
      for each Notification Message sent.  If an ACK is required, then
      the A bit SHOULD be set to "1", and "0" otherwise.

   o  Capability (1 byte): It represents the bit index of the protocol,
      which the Notification Message is notifying for.

   o  Event ID (2 bytes): It indicates the event number that this
      Notification Message is regarding.

   o  Notification Data (Variable): Specifies information of the data
      that the local device is notifying.  The specific format remains
      to be determined per each protocol, as well as each use case.

   o

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4.5.  ACK Message

   The ACK Message is used to confirm that the remote device has
   received a PAP Message with the A bit set to "1".  The ACK Message
   includes only the PAP Common Header.  The Msg. Sequence MUST be set
   to the sequence number carried in the received PAP message, which
   requires this ACK.

5.  PAP Operations

   The PAP operations include the following 3 major processes, the
   Capability Negotiation Process, the Data Request and Reply Process,
   and the Data Notification Process.

5.1.  Capability Negotiation Process

5.1.1.  PAP Peering Relation Establish Process

   A successful PAP Peering relation MUST be Established between two PAP
   speakers before any other PAP process.

   As the first step, a Capability Negotiation Message can be initiated
   at any time by a PAP speaker,as long as the target PAP peer is IP
   reachable.  It usually companies the establishment of neighboring/
   peering relation between two routing devices.  The "A" bit in the
   Negotiation Message MUST be set as 1 during the PAP Peering Establish
   Process, meaning ACK required.  The "E" in the Negotiation Message
   MUST be set to 1 during this process, meaning the capabilities
   indicated in the Protocol Capability field are enabled by default.
   The Protocol Capability field SHOULD indicate all the protocol
   capabilities that are supported by the local PAP Agent and currently
   enabled.  After the first Negotiation Message is sent, the local
   device SHUOLD wait for the ACK Message from the remote device for a
   certain time period before taking further actions, and if no ACK
   Message is received within this time frame, the local device SHOULD
   resend the Negotiation Message to the remote device.  The waiting
   period can be configured locally.  This send and wait process CAN be
   repeated for at most 3 times before receiving a ACK Message from the
   remote device.  If after 3 times of resending the Negotiation
   Message, still no ACK received, then this peering establishment is
   treated as unsuccessful.

   The next step for the local PAP speaker is to wait for the
   Negotiation Message from the remote PAP speaker.  If no Negotiation
   Message is received from the remote PAP speaker within a time frame
   after its own Negotiation Message is sent , the local PAP speaker CAN
   resend the Negotiation Message.  This time frame is also configured
   locally.  This send and wait process CAN be repeated for at most 3

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   times before receiving a Negotiation Message from the remote PAP
   speaker.  If after 3 times of resending the Negotiation Message,
   still no Negotiation Message received, then this negotiation is
   treated as unsuccessful.  If a Negotiation Message is received and
   parsed correctly, an ACK MUST be sent to the remote PAP speaker.

   Once an ACK Message and a Negotiation Message are received from the
   remote PAP speaker and correctly parsed, a PAP Peering relation is
   considered as successfully established.  The local PAP speaker
   maintains locally the protocol capabilities of the remote PAP
   speaker, and uses them during other PAP processes.

5.1.2.  PAP Capability Enabling Notification Process

   Once the PAP Peering relation is set up between two PAP speakers,
   they become PAP peers.  Thereafter, any PAP speaker supports a new
   protocol capability, it SHOULD call the Capability Enabling
   Notification Process to inform all its PAP peers.

   When the local PAP speaker initates a PAP Capability Enabling
   Notification Process: The "A" bit in the Negotiation Message MUST be
   set as 1 during the PAP Capability Enabling Notification Process,
   meaning ACK required.  The "E" in the Negotiation Message MUST be set
   to 1 during this process, meaning the capabilities indicated in the
   Protocol Capability field are enabled.  The Protocol Capability field
   SHOULD indicate all the protocol capabilities that are supported by
   the local PAP Agent and currently enabled.  After the Negotiation
   Message is sent, the local PAP speaker SHUOLD wait for the ACK
   Message from the PAP peer for a certain time period before taking
   further actions, and if no ACK Message is received within this time
   frame, the local device SHOULD resend the Negotiation Message to the
   remote device.  The waiting period can be configured locally.  This
   send and wait process CAN be repeated for at most 3 times before
   receiving a ACK Message from the remote device.  If after 3 times of
   resending the Negotiation Message, still no ACK received, then this
   Capability Enabling Notification Process is treated as unsuccessful.
   This process MAY be intiated at another time thereafter.  If a ACK is
   received, the Capability Enabling Notification Process is considered
   successful.

   When a PAP peer initates a PAP Capability Enabling Notification
   Process: The local PAP speaker, after receiving the PAP Negotiation
   Message and correctly parsing it, sends out an ACK.  This Capability
   Enabling Notification Process is considered successful.  The local
   PAP speaker updates the capability status maintained accordingly.

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5.1.3.  PAP Capability Disabling Notification Process

   Whenever a PAP speaker disables a PAP capability, it SHOULD initiate
   a PAP Capability Disabling Notification Process to inform all its PAP
   peers.

   When the local PAP speaker initates a PAP Capability Disabling
   Notification Process: The "A" bit in the Negotiation Message MUST be
   set as 1 during the PAP Capability Disabling Notification Process,
   meaning ACK required.  The "E" in the Negotiation Message MUST be set
   to 0 during this process, meaning the capabilities indicated in the
   Protocol Capability field are disabled.  The Protocol Capability
   field SHOULD indicate all the protocol capability that is disabled.
   After the Negotiation Message is sent, the local PAP speaker SHUOLD
   wait for the ACK Message from the PAP peer for a certain time period
   before taking further actions, and if no ACK Message is received
   within this time frame, the local device SHOULD resend the
   Negotiation Message to the remote device.  The waiting period can be
   configured locally.  This send and wait process CAN be repeated for
   at most 3 times before receiving a ACK Message from the remote
   device.  If after 3 times of resending the Negotiation Message, still
   no ACK received, then this Capability Disabling Notification Process
   is treated as unsuccessful.  This process MAY be intiated at another
   time thereafter.

   When a PAP peer initates a PAP Capability Disabling Notification
   Process: The local PAP speaker, after receiving the PAP Negotiation
   Message and correctly parsing it, sends out an ACK.  This Capability
   Disabling Notification Process is considered successful.  The local
   PAP speaker updates the capability status maintained accordingly.

5.2.  PAP Request and Reply Process

   When a local PAP Event triggers a PAP Request and Reply Process, the
   local PAP speaker initates a Request Message, and send to a target
   PAP peer as indicated by PAP Agent per this PAP Event.  This local
   PAP speaker is called the Request and Reply Process Starter.  It sets
   the Residua Hop as the maximum number of Request/Reply rounds (e.g.,
   10) it will wait in order to receive the final Reply.  The Event ID
   and the Request are set by the local PAP Agent.  The A bit of the
   Request Message MUST be set to "1" (i.e., ACK is required).  The
   local device waits for the ACK Message from the remote device for a
   certain time period before taking further actions, and if no ACK
   Message is received within this time frame, the local device SHOULD
   resend the Request Message to the remote device.  The waiting period
   can be configured locally.  This send and wait process CAN be
   repeated for at most 3 times before receiving a ACK Message from the
   remote device.  If after 3 times of resending the Request Message,

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   still no ACK received, then this Request and Reply Process is treated
   as unsuccessful.  If ACK received, the local device waits for the
   Reply Message.  If no Reply Message is received from the remote
   device within a time frame, the local device can resend the Request
   Message.  This send and wait process CAN be repeated for at most 3
   times before receiving a Reply Message from the remote device.  If
   after 3 times of resending the Request Message, still no Reply
   Message received, then this Request and Reply Process is treated as
   unsuccessful.  The waiting period can be configured locally, and
   SHOULD take into consideration of the Residua Hop value.  If the
   Request and Reply Process Starter receives the Reply Message within
   the time frame, and the Event ID is matched to the local PAP Event,
   the PAP Request and Reply Process is considered as successful.

   When a local PAP speaker receives a Request Message from its PAP peer
   (i.e., it is not the Pequest and Reply Process Starter), it sends
   back an ACK Message.  With the received Request Message, a new PAP
   event it instantiated at the local PAP Agent.  The PAP event triggers
   the troubleshooting analysis of the received Request Message, and
   then generate the Reply Message if the Reply condition is met, or
   generate a new Request Message when the Reply condition is not met.
   The Reply condition and the troubleshooting analysis of the PAP Agent
   is out of the scope of this document.

   If the Reply condition is met, the local PAP speaker is called the
   Request and Reply Process Terminator.  It generates the Reply Message
   and send the message back to the requesting PAP peer.  The Event ID
   is set to be the same as the Event ID of the received Request
   Message.  The Reply Data is set by the local PAP Agent per this
   generated event.  The A bit of the Reply Message MUST be set to "1"
   (i.e., ACK is required).  The local device waits for the ACK Message
   from the remote device for a certain time period before taking
   further actions, and if no ACK Message is received within this time
   frame, the local device SHOULD resend the Reply Message to the remote
   device.  The waiting period can be configured locally.  This send and
   wait process CAN be repeated for at most 3 times before receiving a
   ACK Message from the remote device.  If after 3 times of resending
   the Request Message, still no ACK received, then this Request and
   Reply Process is treated as unsuccessful.

   If the Reply condition is not met, the local PAP speaker is called
   the Request and Reply Process mid-handler.  It generates a new
   Request Message and send the message to a third PAP speaker per
   indicated by the local PAP Agent per this generated event.  In the
   new generated Request Message, the Residua Hop value by MUST be
   reduced by 1.  The A bit of the Request Message MUST be set to "1"
   (i.e., ACK is required).  The local device waits for the ACK Message
   from the remote device for a certain time period before taking

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   further actions, and if no ACK Message is received within this time
   frame, the local device SHOULD resend the Request Message to the
   remote device.  The waiting period can be configured locally.  This
   send and wait process CAN be repeated for at most 3 times before
   receiving a ACK Message from the remote device.  If after 3 times of
   resending the Request Message, still no ACK received, then this
   Request and Reply Process is treated as unsuccessful.  If ACK
   received, the local device waits for the Reply Message.  If no Reply
   Message is received from the remote device within a time frame, the
   local device can resend the Request Message.  This send and wait
   process CAN be repeated for at most 3 times before receiving a Reply
   Message from the remote device.  If after 3 times of resending the
   Request Message, still no Reply Message received, then this Request
   and Reply Process is treated as unsuccessful.  The waiting period can
   be configured locally, and SHOULD take into consideration of the
   Residua Hop value.  If the local device receives the Reply Message
   within the time frame, it generates a new Reply Message and sends
   back to it requesting PAP peer.  The Event ID of the new Reply
   Message is set to be the same as the Event ID of the received Request
   Message.

5.3.  PAP Notification Process

   When a local PAP Event triggers a PAP Notification Process, the local
   PAP speaker initates a Notification Message.  The target PAP peer(s)
   is/are selected by the PAP agent regarding the current PAP Event,
   which is out of the scope of this document.  The Notification Message
   may or may not require an ACK Message, as indicated in the
   Notification Message.  If the A bit is set to 1 (meaning ACK
   required), the local device waits for the ACK Message from the remote
   device for a certain time period before taking further actions, and
   if no ACK Message is received within this time frame, the local
   device SHOULD resend the Notification Message to the remote device.
   The waiting period can be configured locally.  This send and wait
   process CAN be repeated for at most 3 times before receiving a ACK
   Message from the remote device.  If after 3 times of resending the
   Request Message, still no ACK received, then this Request and Reply
   Process is treated as unsuccessful.  The waiting period can be
   configured locally.  If ACK is received within the time frame, the
   Notification Process is considered to be successful.  If the A bit is
   set to 0 (meaning no ACK required), after sending the Notification
   Message, the Notification Process is considered successful.

6.  PAP Error Handling

   When any PAP process is unsuccessful, information is recorded or not
   by local PAP Agent.  No further action is taken.

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7.  Discussion

   In addition to the preceding message definition and process
   description, the security and reliability requirements of the PAP
   need to be considered.  There are two possible options to implement
   PAP.

   - Option 1: PAP is developed independently as a new protocol.

   - Option 2: PAP reuses the existing protocol Generic Autonomic
   Signaling Protocol(GRASP) [I-D.ietf-anima-grasp] .

   Option1:

   1.  Definition of the Message Format and Interaction Process: It can
   be defined independently in the PAP.

   2.  Reliability: The transmission mode of PAP is based on UDP mainly
   considering that the collected information is the auxiliary
   information to help locate the protocol fault, and the information
   loss has no impact on the service.  In addition, if TCP mode is
   adopted, the resource consumption of the device may be large,
   especially when there area large number of neighbors.  If it is
   considered that PAP must ensure reliability, it can done in the
   application layer, such as adding the sequence number to the message.

   3.  Security: MD5 authentication can be introduced for PAP security.

   Option2:

   ANIMA GRASP is a signaling protocol used for dynamic peer discovery,
   status synchronization, and parameter negotiation between AS nodes or
   AS service agents.  GRASP specifies that unicast packets must be
   transmitted based on TCP, and multicast packets (Discovery and Flood)
   must be transmitted based on UDP.

   1.  Message format and interaction process: PAP can reuse the defined
   messages and procedures of the GRASP.  Messages defined in the PAP
   include Capability Negotiation Message, Request Message, Reply
   Message, and Negotiation Message.  These message types are also
   defined in GRASP.

   2.  Reliability: TCP mode of GRASP can be used to ensure reliability
   for PAP.  But there may be challenge for the equipment resources.

   3.  Security: Autonomic Control Plane(ACP)
   [I-D.ietf-anima-autonomic-control-plane] can be reused.

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8.  Security Considerations

   TBD

9.  IANA

   TBD

10.  Contributors

   We thank Jiaqing Zhang (Huawei), Tao Du (Huawei) and Lei Li (Huawei)
   for their contributions.

11.  Acknowledgments

12.  References

   [I-D.brockners-inband-oam-requirements]
              Brockners, F., Bhandari, S., Dara, S., Pignataro, C.,
              Gredler, H., Leddy, J., Youell, S., Mozes, D., Mizrahi,
              T., Lapukhov, P., and r. remy@barefootnetworks.com,
              "Requirements for In-situ OAM", draft-brockners-inband-
              oam-requirements-03 (work in progress), March 2017.

   [I-D.ietf-anima-autonomic-control-plane]
              Eckert, T., Behringer, M., and S. Bjarnason, "An Autonomic
              Control Plane (ACP)", draft-ietf-anima-autonomic-control-
              plane-30 (work in progress), October 2020.

   [I-D.ietf-anima-grasp]
              Bormann, C., Carpenter, B., and B. Liu, "A Generic
              Autonomic Signaling Protocol (GRASP)", draft-ietf-anima-
              grasp-15 (work in progress), July 2017.

   [I-D.ietf-netconf-yang-push]
              Clemm, A. and E. Voit, "Subscription to YANG Datastores",
              draft-ietf-netconf-yang-push-25 (work in progress), May
              2019.

   [I-D.song-ntf]
              Song, H., Zhou, T., Li, Z., Fioccola, G., Li, Z.,
              Martinez-Julia, P., Ciavaglia, L., and A. Wang, "Toward a
              Network Telemetry Framework", draft-song-ntf-02 (work in
              progress), July 2018.

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   [RFC1157]  Case, J., Fedor, M., Schoffstall, M., and J. Davin,
              "Simple Network Management Protocol (SNMP)", RFC 1157,
              DOI 10.17487/RFC1157, May 1990,
              <https://www.rfc-editor.org/info/rfc1157>.

   [RFC1191]  Mogul, J. and S. Deering, "Path MTU discovery", RFC 1191,
              DOI 10.17487/RFC1191, November 1990,
              <https://www.rfc-editor.org/info/rfc1191>.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, DOI 10.17487/RFC1195,
              December 1990, <https://www.rfc-editor.org/info/rfc1195>.

   [RFC1213]  McCloghrie, K. and M. Rose, "Management Information Base
              for Network Management of TCP/IP-based internets: MIB-II",
              STD 17, RFC 1213, DOI 10.17487/RFC1213, March 1991,
              <https://www.rfc-editor.org/info/rfc1213>.

   [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>.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
              <https://www.rfc-editor.org/info/rfc3209>.

   [RFC3988]  Black, B. and K. Kompella, "Maximum Transmission Unit
              Signalling Extensions for the Label Distribution
              Protocol", RFC 3988, DOI 10.17487/RFC3988, January 2005,
              <https://www.rfc-editor.org/info/rfc3988>.

   [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>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <https://www.rfc-editor.org/info/rfc7752>.

   [RFC7854]  Scudder, J., Ed., Fernando, R., and S. Stuart, "BGP
              Monitoring Protocol (BMP)", RFC 7854,
              DOI 10.17487/RFC7854, June 2016,
              <https://www.rfc-editor.org/info/rfc7854>.

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Authors' Addresses

   Zhenbin Li
   Huawei
   156 Beiqing Rd
   Beijing
   China

   Email: lizhenbin@huawei.com

   Shuanglong Chen
   Huawei
   156 Beiqing Road
   Beijing,100095
   P.R. China

   Email: chenshuanglong@huawei.com

   Yunan Gu
   Huawei
   156 Beiqing Rd
   Beijing
   China

   Email: guyunan@huawei.com

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