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Versions: 00                                                            
Network Working Group                                            R. Bush
Internet-Draft                  Arrcus, Inc. & Internet Initiative Japan
Intended status: Informational                                   J. Dong
Expires: September 9, 2021                           Huawei Technologies
                                                            J. Haas, Ed.
                                                        Juniper Networks
                                                          W. Kumari, Ed.
                                                           March 8, 2021

     Requirements and Considerations in BGP Peer Auto-Configuration


   This draft is an exploration of the requirements, the alternatives,
   and trade-offs in BGP peer auto-discovery at various layers in the
   stack.  It is based on discussions in the IDR Working Group BGP
   Autoconf Design Team.  The current target environment is the

   This document is not intended to become an RFC.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in BCP 14 [RFC2119]
   [RFC8174] when, and only when, they appear in all capitals, as shown

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 September 9, 2021.

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Copyright Notice

   Copyright (c) 2021 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
   2.  Design Team Determinations  . . . . . . . . . . . . . . . . .   3
     2.1.  Problem Scope . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Simplicity  . . . . . . . . . . . . . . . . . . . . . . .   3
     2.3.  BGP Auto-Discovery Protocol State Requirements  . . . . .   3
       2.3.1.  BGP Session Transport State . . . . . . . . . . . . .   4
       2.3.2.  BGP Session Protocol State  . . . . . . . . . . . . .   4
     2.4.  BGP Auto-Discovery Protocol Transport Requirements  . . .   5
     2.5.  Operator Configuration  . . . . . . . . . . . . . . . . .   5
   3.  Design Principle Considerations . . . . . . . . . . . . . . .   6
     3.1.  Transport Considerations  . . . . . . . . . . . . . . . .   6
     3.2.  Auto-Discovery Protocol Timing Considerations . . . . . .   6
     3.3.  Relationship with BGP . . . . . . . . . . . . . . . . . .   7
     3.4.  Session Selection Considerations  . . . . . . . . . . . .   7
     3.5.  Operational Trust Considerations  . . . . . . . . . . . .   7
     3.6.  Error Handling Considerations . . . . . . . . . . . . . .   9
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
     5.1.  BGP Transport Security Considerations . . . . . . . . . .  10
     5.2.  Auto-discovery Protocol Considerations  . . . . . . . . .  10
       5.2.1.  Potential Scopes of an Auto-discovery Protocol  . . .  10
       5.2.2.  Desired Security Properties of the Auto-discovery
               Protocols . . . . . . . . . . . . . . . . . . . . . .  11
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  11
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     7.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Appendix A.  Analysis of Candidate Approaches . . . . . . . . . .  14
     A.1.  BGP Peer Discovery at Layer Two . . . . . . . . . . . . .  14
       A.1.1.  LLDP based Approach . . . . . . . . . . . . . . . . .  14
       A.1.2.  L3DL based Approach . . . . . . . . . . . . . . . . .  15

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     A.2.  Link-Local Discovery  . . . . . . . . . . . . . . . . . .  15
     A.3.  BGP peer Discovery at Layer Three . . . . . . . . . . . .  16
       A.3.1.  New BGP Hello Message based Approach  . . . . . . . .  16
       A.3.2.  BGP OPEN Message based Approach . . . . . . . . . . .  17
       A.3.3.  Bootstrapping BGP via BGP . . . . . . . . . . . . . .  17
       A.3.4.  Bootstrapping BGP via OSPF  . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   This draft is an exploration of the requirements, the alternatives,
   and trade-offs in BGP peer auto-discovery at various layers in the
   stack.  It is based on discussions in the IDR Working Group BGP
   Autoconf Design Team.  The current target environment is the

2.  Design Team Determinations

2.1.  Problem Scope

   The current target environment is BGP as used for the underlay
   routing protocol in data center networks.  Other scenarios may be
   considered as part of the analysis for this work, but work on those
   environments will be deferred to other efforts.

2.2.  Simplicity

   The auto-discovery mechanism is designed to be simple.

   The goal is to select BGP Speakers where a BGP session may be
   successfully negotiated for a particular purpose.  The auto-discovery
   mechanism will not replace or conflict with data exchanged by the BGP
   FSM, including its OPEN message.

2.3.  BGP Auto-Discovery Protocol State Requirements

   Tersely, the required state that MUST be carried by the BGP Auto-
   Discovery Protocol for a discovered session include:

   BGP Session Transport State:

   o  IP addresses
   o  Transport security parameters
   o  GTSM [RFC5082] configuration, if any
   o  BFD [RFC5880] configuration, if any

   BGP Session Protocol State:

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   o  AS Numbers
   o  BGP Identifier
   o  Supported AFI/SAFIs
   o  Device Role

   Once this information has been learned, discovery has been completed.
   The BGP Speaker has the necessary information to determine if it
   wishes to open a BGP session with the discovered BGP Speaker.  It can
   then then initiate a BGP session with the discovered BGP Speaker.

2.3.1.  BGP Session Transport State

   o  Support for IPv4 and IPv6 address families, but do not assume that
      both are available.
   o  The ability to use directly attached interface addresses, or the
      device's Loopback address.  When using the Loopback address,
      potentially exchange additional information to bootstrap
      forwarding to that address.
   o  Discovery of BGP transport protocol end-points and essential
      properties such as IP addresses, transport security parameters,
      layer 3 liveness mechanisms such as BFD, and support for GTSM.
   o  Transport security parameters include protocol - such as plain
      TCP, TCP-AO [RFC5925], IPsec [RFC4301], TCP-MD5 [RFC2385] - and
      necessary configuration for that protocol.  Some example
      considerations for this are represented in YANG Data Model for Key
      Chains [RFC8177].

2.3.2.  BGP Session Protocol State

   o  Discovery of BGP peer session parameters relevant to peer
      selection such as Autonomous System (AS) Numbers, BGP Identifiers,
      supported address families/subsequent-address families (AFI/
      SAFIs), and device roles.  BGP Auto-Discovery Device Role Requirements

   As part of peer selection, it may be necessary to understand the role
   of the discovered session to determine whether or not the BGP Speaker
   desires to establish a peering session.

   In some cases, role may be a clear function of the device in a
   deployment.  An example of this is a discovered session for a BGP
   Clos fabric: The interface may for a leaf, the aggregation layer, or
   the spine layer.  Even then, the type of fabric, what pod it belongs
   to and the peer type may be relevant information.

   Some types of device roles may be subject to standardization, such as
   BGP Clos fabrics.  Flexibility to permit operators to use device

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   roles for their own auto-configuration peer selection purposes is a

   Peering sessions may need to advertise that they are capable to be
   used for multiple roles.  Thus, it is a requirement that the auto-
   discovery protocols permit advertising multiple roles in the same

2.4.  BGP Auto-Discovery Protocol Transport Requirements

   BGP Auto-Discovery Protocol State may be carried in multiple
   protocols operating in different transport layers.

   Implementations supporting more than one protocol for this state must
   have a mechanism for consistently selecting discovered BGP sessions.
   The BGP Identifier, which is carried by the BGP OPEN message, can
   help detect sessions to the same BGP Speaker carried in multiple

2.5.  Operator Configuration

   With BGP auto-discovery, some configuration of BGP is still needed.
   Operator configuration should be able to decide at least the

   o  Select or otherwise filter which peers to actually try to send BGP
      OPEN messages.

      *  Permit the matching of device role from the discovery protocol
         as part of peer selection.
   o  Decide the parameters to use.  For example:

      *  IP addressing: IPv4 or IPv6.
      *  Interface for peering: Loopback, or Direct.
      *  Any special forwarding or routing needed for reaching the
         prospective peer; for example, loopback.
      *  AS numbering.
      *  BGP Transport Security Parameters.
      *  BGP Policy that is appropriate for the type of discovered

   In addition to actually forming the BGP sessions, a common deployment
   model may also be the so called "validation" model.  In this model,
   the operator configures the BGP sessions manually, and uses the
   information collected/populated by the BGP Autoconf mechanism to
   validate that the sessions are correct.

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3.  Design Principle Considerations

   This section summarizes the considerations of possible criteria for
   the design of a BGP auto-discovery mechanism, which may need further
   discussion in a wider community than the design team; for example,
   the IDR Working Group.

3.1.  Transport Considerations

   The network layer of the discovery mechanism may impact the scoping
   of the deployment of the auto-discovery mechanism.

   o  Layer 2: For example, based on Ethernet.
   o  Layer 3: Which is generic for any link-layer protocol.

   Potentially leveraging existing protocols deployed in the data

   The length of messages supported by the protocol.

   How extensible the protocol is to carry future state for BGP auto-

3.2.  Auto-Discovery Protocol Timing Considerations

   Establishing a reasonable expectation for the timeliness of auto-
   configuration is desirable.  When a link is plugged-in, one shouldn't
   have to wait minutes for potential peers to be discovered and BGP
   session establishment attempted.  For protocols crafted explicitly
   for BGP auto-configuration, the time for discovery should be a
   reasonable amount of time; for example ten seconds or less.

   Since discovery mechanisms may become very chatty when utilized by a
   number of devices on shared networks, the protocol should not impose
   undue burden on the devices on that network to process the discovery
   messages.  New auto-discovery protcols MUST NOT transmit messages
   more than once a second.

   When an auto-discovery mechanism is used for a point-to-point link,
   or with the expectation of establishing a BGP session with a single
   BGP Speaker on that network, the auto-discovery protocol MAY quiesce
   once the discovered BGP session has become Established.

   In cases where the auto-discovery protocol is carried as state in
   another protocol, that protocol will have its own timeliness
   considerations.  The auto-discovery mechanism SHOULD NOT interfere
   with the timing of the existing protocol.

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3.3.  Relationship with BGP

   o  The auto-discovery mechanism should be independent from BGP
      session establishment.
   o  Not affect on BGP session establishment and routing exchange,
      other than the interactions for triggering the setup/removal of
      peer sessions based on the discovery mechanism.
   o  Potentially leveraging existing BGP protocol sessions for
      discovery of new BGP sessions.

3.4.  Session Selection Considerations

   Candidate BGP sessions to a given BGP Speaker may be discovered by
   one or more auto-discovery protocols.  Even for a single protocol,
   multiple transport session endpoints may be discovered for the same
   BGP Speaker.  These different sessions may be required for supporting
   different address families, such as IPv4/IPv6, depending on the BGP
   operational practices for that device.  Examples include a distinct
   and matching session for the IPv4/IPv6 address family, a unified
   session carrying IPv4 over IPv6 and vice-versa, etc.

   The BGP Identifier (router-id), a required protocol component of BGP,
   can serve to identify the same instance of the BGP Speaker.  This is
   a required element of the information to be carried in the auto-
   discovery protocol.

   When multiple mechanisms exist to discovery the same BGP speaker in
   an implementation, that implementation MUST document the process by
   which it chooses discovered peers.  Those implementations also MUST
   describe interactions with their protocol state machinery for each

3.5.  Operational Trust Considerations

   Different deployment models will have different trust models and
   requirements.  Some of this will be driven by the size, complexity
   and operational practices of the operator.  For example, some
   operators have very strict physical protection of the datacenter, and
   their deployment model assumes that anything which plugs into devices
   in the datacenter is, by definition, trusted.  Other operators take a
   very different approach, and assume the least possible amount of

   Much of this difference is also reflected in the operator's
   bootstrapping solution.  Some operators build individual
   configurations for each device, and manually provision the
   configuration into the non-volatile storage of the device before it
   is shipped.  Other operators use solutions similar to PXE Boot to

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   automatically load an operating system and configuration onto the
   device, based on a unique device identifier (such as management
   Ethernet MAC address).  Some operators pre-configure devices with
   identical base configurations containing some bootstrapping policy
   logic (e.g., "If you are a Model-X device, and interface 23 is
   connected to a device of type Y, then you must be at Stage-2 in a
   Clos fabric") and allow the device to use this policy information to
   infer its role and position.  A final set of datacenter operators,
   for example enterprises, would like to be able to simply unpack a new
   device, plug it in and have the device infer everything.  (It is
   unclear if this is a deployment model that we want to support.)

   Many datacenter operators already have a well-developed process for
   installing and bringing up a new datacenter network, complete with
   solutions to bootstrap and configure the network.  These operators
   will want to be able to use the BGP Autoconf mechanism to perform
   validation of the datacenter fabric, and ongoing "sanity-checking" to
   confirm that the datacenter is correctly cabled, and that the BGP
   sessions which have been configured from the database match what the
   autodiscovered sessions would have created.  Over time, if the BGP
   Autoconf solution proves to be successful, reliable, and scaleable,
   operators may begin using it as the primary source of record.

   Closely related to these considerations is the "scope" of the
   discovery process.  It is expected that many operators will wish to
   only perform discovery on "infrastructure" or "fabric" interfaces,
   and not interfaces which face customers.

   It is not clear that the solution that chosen will be able to meet
   all of the trust and deployment models, and we will need to
   prioritize which set(s) of deployment scenarios are the most
   important for the Working Group to solve.

   Trust/Operational deployment driven requirements.  The solution

   o  Allow operators to determine which classes of interfaces the
      discovery protocol operates on (e.g: "Interfaces numbered 1-17" or
      "Only 100GE interfaces").  This is likely an implementation
   o  Allow operation in a "validation" or "verification" only mode,
      where the Autoconf solution populates a database or model showing
      what sessions it would bring up if allowed.
   o  Ideally allow for different levels of "granularity" in pre-
      configuration.  For example, if the protocol is capable of
      autoconfiguring everything, it should also support filtering or
      limiting the session according to configured policy.  (Likely an
      implementation detail.)

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   o  Support preconfigured authentication systems.  This is an area
      where more discussion is needed!  The solution MUST also support a
      "no authentication" mode.  Negotiated keying solutions, such as
      IKE, may be desireable but not mandatory for the solution.
   o  Support Ethernet sub-interfaces such as VLANs.
   o  Support non-Ethernet interfaces.  This may include tunnels.

3.6.  Error Handling Considerations

   The purpose of the BGP auto-discovery protocol is to discover
   potential BGP sessions and provide enough information for a BGP
   Speaker to start a BGP session.  It is possible for the information
   present in the auto-discovery protocol to not match the session's
   information.  Such mis-matches will result in different classes of

   o  The BGP transport session may not connect.  This could be the
      result of mismatches in IP addresses, GTSM configuration, BGP
      transport security configuration, etc.  In these cases, a BGP
      Speaker attempts to establish a session and fails.
      Implementations SHOULD provide a way to clear such discovered
      sessions or exclude them from further connect attempts.
   o  The BGP transport session connects, but the parameters in the BGP
      OPEN message do not match those in the auto-discovery protocol.
      In this case, the implementation may wish to disconnect from the
      BGP session and exclude it from further connection attempts.  The
      implementation SHOULD raise a visible fault to the operator.  The
      implementation SHOULD provide a mechanism to permit further
      attempts to connect to the discovered session.
   o  The operator may choose to leverage the auto-discovery mode for
      validation purposes only.  The implementation should provide
      access to the operator for discovered BGP sessions from the auto-
      discovery protocol; for example via the user-interface.  The
      implementation SHOULD permit a manually configured BGP session to
      conflict with information present in the auto-discovery protocol,
      but SHOULD raise an alarm with the operator that this has been

4.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an

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5.  Security Considerations

   There are two primary components to be secured in environments
   utilizing BGP auto-discovery: The BGP transport layer discovered via
   the protocol, and the auto-discovery protocol itself.

5.1.  BGP Transport Security Considerations

   The purpose of the auto-discovery protocol is to ease the setup of
   BGP sessions for various applications, including data-center fabrics.
   However, care must be taken to not permit sessions to be setup
   outside of trusted environments.  It is RECOMMENDED that sessions
   advertised using BGP auto-discovery be protected at the transport
   layer using mechanisms such as TCP-AO, IPsec, or the deprecated TCP-

   It is thus a requirement that the auto-discovery protocol carry
   sufficient information to determine what transport security is to be
   used when establishing a BGP session.

   All Security Considerations from [RFC4272], BGP Security
   Vulnerabilities Analysis, continue to apply.

5.2.  Auto-discovery Protocol Considerations

   As noted in previous sections, BGP auto-discovery be scoped to
   different portions of the network dependent on the network layar at
   which it is deployed.  The information present in the auto-discovery
   protocol is considered sensitive, since it identifies resources
   running the BGP protocol.  Care should be exercised in avoiding
   inadvertent disclosure of BGP sessions that are configured to permit
   auto-configuration even when BGP session transport security is in
   use.  The auto-discovery protocol sets the context for such
   inadvertent disclosure.

5.2.1.  Potential Scopes of an Auto-discovery Protocol

   A Layer 2 unicast protocol targets a known device, potentially
   discovered through other means.  The targeted device receives the
   message.  Depending on the Layer 2 environment, other devices on the
   same link may may be able to observe the protocol messages.  Point to
   point links may also fall into this category.

   A Layer 2 multicast protocol targets a group of devices on that Layer
   2 multicast domain.  A set of devices in that domain receives the
   message.  Such messages may cross a number of devices in the domain.
   An example of this includes a set of Ethernet switches.

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   A Layer 3 unicast protocol inherits the properties of the Layer 2
   protocol, and is intended to address a specific address - typically
   one device.  Layer 3 unicast protocols may leverage GTSM for their

   A Layer 3 multicast protocol addresses a group of devices in a given
   multicast domain.  Such domains may be scoped, such as a single
   link's "All-Routers" group or perhaps all devices subscribed to a
   specific multicast group in a network.  In many cases, a Layer 3
   multicast protocol inherits the properties of the Layer 2 multicast
   protocol.  Link-local scoped multicast protocols may be able to
   leverage GTSM.

   A Layer 7 protocol is scoped per the mechanism in the underlying
   protocol.  IGPs such as OSPF and IS-IS provide an "internal" scoping.
   BGP, depending on the deployment of the underlying address family,
   may vary from a targeted advertisement, to Internet-wide.

   Each of these scopes provide different opportunities for inadvertent
   disclosure.  The auto-discovery protocol will need to address how the
   desired security properties interact with the protocol scope.

5.2.2.  Desired Security Properties of the Auto-discovery Protocols

   Data Integrity is a required property.  The data that is transmitted
   by a speaker of the auto-configuration protocol should be able to
   pass among its speakers properly.

   Peer Entity authentication is a required property for Layer 2 and
   Layer 3 implementations.  In a Layer 7 protocol, that protocol may
   provide the necessary authentication.

   Confidentiality is an optional property.  There is a tension between
   the desire to provide for a simple auto-configuration protocol that
   is easy to diagnose and debug with inadvertent disclosure.

   The auto-configuration protocol must be resistant to Denial of
   Service, and to causing Denial of Service to discovered BGP session

6.  Acknowledgments

   The IDR BGP Auto-Conf Design Team.

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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,

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

7.2.  Informative References

              Lindem, A., Patel, K., Zandi, S., Haas, J., and X. Xu,
              "BGP Logical Link Discovery Protocol (LLDP) Peer
              Discovery", draft-acee-idr-lldp-peer-discovery-08 (work in
              progress), December 2020.

              Lindem, A., Patel, K., Zandi, S., and R. Raszuk, "OSPF
              Extensions for Advertising/Signaling BGP Route Reflector
              Information", draft-acee-ospf-bgp-rr-01 (work in
              progress), September 2017.

              Bush, R., Austein, R., and K. Patel, "Layer 3 Discovery
              and Liveness", draft-ietf-lsvr-l3dl-07 (work in progress),
              January 2021.

              Bush, R. and R. Austein, "Layer 3 Discovery and Liveness
              Signing", draft-ietf-lsvr-l3dl-signing-01 (work in
              progress), January 2021.

              Bush, R. and K. Patel, "L3DL Upper Layer Protocol
              Configuration", draft-ietf-lsvr-l3dl-ulpc-01 (work in
              progress), January 2021.

              Bush, R., Austein, R., and K. Patel, "Link State Over
              Ethernet", draft-ietf-lsvr-lsoe-01 (work in progress),
              February 2019.

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              Raszuk, R., Mitchell, J., Kumari, W., Patel, K., and J.
              Scudder, "BGP Auto Discovery", draft-raszuk-idr-bgp-auto-
              discovery-06 (work in progress), December 2019.

              Raszuk, R., "BGP Automated Session Setup", draft-raszuk-
              idr-bgp-auto-session-setup-01 (work in progress), December

              Xu, X., Talaulikar, K., Bi, K., Tantsura, J., and N.
              Triantafillis, "BGP Neighbor Discovery", draft-xu-idr-
              neighbor-autodiscovery-12 (work in progress), November

   [RFC0826]  Plummer, D., "An Ethernet Address Resolution Protocol: Or
              Converting Network Protocol Addresses to 48.bit Ethernet
              Address for Transmission on Ethernet Hardware", STD 37,
              RFC 826, DOI 10.17487/RFC0826, November 1982,

   [RFC2385]  Heffernan, A., "Protection of BGP Sessions via the TCP MD5
              Signature Option", RFC 2385, DOI 10.17487/RFC2385, August
              1998, <https://www.rfc-editor.org/info/rfc2385>.

   [RFC4272]  Murphy, S., "BGP Security Vulnerabilities Analysis",
              RFC 4272, DOI 10.17487/RFC4272, January 2006,

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <https://www.rfc-editor.org/info/rfc4301>.

   [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
              "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
              DOI 10.17487/RFC4861, September 2007,

   [RFC5082]  Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
              Pignataro, "The Generalized TTL Security Mechanism
              (GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,

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   [RFC5925]  Touch, J., Mankin, A., and R. Bonica, "The TCP
              Authentication Option", RFC 5925, DOI 10.17487/RFC5925,
              June 2010, <https://www.rfc-editor.org/info/rfc5925>.

   [RFC8177]  Lindem, A., Ed., Qu, Y., Yeung, D., Chen, I., and J.
              Zhang, "YANG Data Model for Key Chains", RFC 8177,
              DOI 10.17487/RFC8177, June 2017,

Appendix A.  Analysis of Candidate Approaches

   As part of the work on distilling the requirements for BGP auto-
   discovery, the Design Team reviewed several proposals for
   implementing auto-discovery.  The analysis of these proposals,
   including missing elements the Design Team decided were part of the
   requirements, follows.

A.1.  BGP Peer Discovery at Layer Two

   BGP Discovery at Layer-2 would entail finding potential peers on a
   LAN or on Point-to-Point links and discovering their Layer-3
   attributes, such as, IP addresses, etc.

   There are two available candidates for peer discovery at Layer-2, one
   is based on Link Layer Discovery Protocol (LLDP) and the other is
   based on Layer 3 Discovery Protocol, L3DL [I-D.ietf-lsvr-l3dl].

A.1.1.  LLDP based Approach

   LLDP is a widely deployed protocol with implementations in most
   devices in data centers.  Currently it only advertises the managment
   Layer-3 address, but could presumably be extended to include the per-
   interface addresses.

   LLDP has a limitation that all information must fit in a single PDU
   (it does not support fragmentation / a "session").  There is an early
   LLDPv2 development effort to extend this in the IEEE.

   [I-D.acee-idr-lldp-peer-discovery] describes how to use the LLDP IETF
   Organizationally Specific TLV to augment the LLDP TLV set to exchange
   BGP Config Sub-TLVs signaling:

   o  AFI
   o  IP address (IPv4 or IPv6)
   o  Local AS number
   o  Local BGP Identifier (AKA, BGP Router ID)
   o  Session Group-ID; i.e., the BGP Device Role
   o  BGP Session Capabilities

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   o  Key Chain
   o  Local Address (as BGP Next Hop).

A.1.2.  L3DL based Approach

   L3DL [I-D.ietf-lsvr-l3dl] is an ongoing development in the IETF LSVR
   Working Group with the goal of discovering IP Layer-3 attributes of
   links, such as neighbor IP addressing, logical link IP encapsulation
   abilities, and link liveness which may then be disseminated for the
   use of BGP-SPF and similar protocols.

   L3DL Upper Layer Protocol Configuration, [I-D.ietf-lsvr-l3dl-ulpc],
   details signaling the minimal set of parameters needed to start a BGP
   session with a discovered peer.  Details such as loopback peering are
   handled by attributes in the L3DL protocol itself.  The information
   which can be discovered by L3DL is:

   o  AS number
   o  Local IP address, IPv4 or IPv6, and
   o  BGP Authentication.

   L3DL and L3DL-ULPC have well-specified security mechanisms, see

   The functionality of L3DL-ULPC is similar but not quite the same as
   the needs of IDR Design Team.  For example, L3DL is designed to meet
   more complex needs.  L3DL's predecessor, LSOE [I-D.ietf-lsvr-lsoe],
   was simpler and might be a better candidate for adaptation.  If
   needed, the design of LSOE may be customized for the needs of BGP
   peer auto- disovery.

   Unlike LLDP, L3DL has only one implementation, and LSOE has only one
   open source implementation, and neither is significantly deployed.

A.2.  Link-Local Discovery

   Some existing BGP auto-configuration mechanisms leverage "point to
   point" addressing schemes to bootstrap BGP sessions.  One example
   utilizes an IP subnet numbered such that it may contain only two
   hosts - for IPv4, a /30 or /31 network; for IPv6 a /127 network.  An
   additional mechanism may leverage IPv4 ARP [RFC0826] or IPv6 Neighbor
   Discovery [RFC4861] to learn of hosts on a subnet.

   Such existing mechanisms do not provide an auto-discovery protocol
   with necessary parameters.  Rather, they simplify configuration by
   permitting BGP session configuration templates to be easily applied
   to interfaces without requiring addressing to be known a priori.

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A.3.  BGP peer Discovery at Layer Three

   Discovery at Layer-3 can assume IP addressability, though the IP
   addresses of potential peers are not known a priori and need to be
   discovered before further negotiation.  IP multicast may be a good
   choice to address the above concern.

   The possible problem would appear to discovery at Layer-3 is that one
   may not know whether to use IPv4 or IPv6.  This might be exacerbated
   by the possibility of a potential peer not being on the local subnet,
   and hence broadcast and similar techniques may not be applicable.
   While in data center network or networks in a single administrative
   domain, such issue could be easily solved.

   If one can assume that the BGP session is based on point-to-point
   link, then discovery might try IPv6 link-local or even IPv4 link-
   local.  A link broadcast or multicast protocol may also be used.  For
   switched or bridged multi-point which is at least on the same subnet,
   VLAN, etc., multicast or broadcasts might be a viable approach.

   There are four available candidates for BGP peer discovery at Layer-
   3: One is based on extending BGP with new Hello message for peer
   auto-discovery.  One is based on reusing BGP OPEN message format for
   peer auto-discovery.  One is based on bootstrapping BGP sessions via
   existing BGP sessions.  One is based upon bootstraping a BGP Route
   Reflector via the OSPF protocol.

A.3.1.  New BGP Hello Message based Approach

   [I-D.xu-idr-neighbor-autodiscovery] describes a BGP neighbor
   discovery mechanism which is based on a newly defined UDP based BGP
   Hello message.  The BGP Hello message is sent in multicast to
   discover the directly connected BGP peers.  According to the message
   header format and the TLVs carried in the message, the information
   which can be signaled is:

   o  AS number
   o  BGP Identifier
   o  Accepted ASN list
   o  Peering address (IPv4 or IPv6)
   o  Local prefix (for loopback)
   o  Link attributes
   o  Neighbor state
   o  BGP Authentication

   The mechanisms in this draft do not currently handle fragmentation.

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   The mechanism in this draft is perhaps unique among the other
   proposals in requiring bi-directional state.

A.3.2.  BGP OPEN Message based Approach

   [I-D.raszuk-idr-bgp-auto-session-setup] describes a BGP neighbor
   discovery mechanism by reusing BGP OPEN message format with newly
   defined UDP port.  The message is called BGP Session Explorer (BSE)
   packet and is sent in multicast.  Since the message format is the
   same as BGP OPEN, the information which can be signaled is:

   o  AS number
   o  BGP Identifier
   o  Peering address

   The mechanism is currently under-specified with respect to a number
   of similar properties described elsewhere.  A general implication is
   that those properties - and others providing for extensibility of the
   auto-discovery mechanism - would need to be added to the BGP OPEN
   message and deal with the related impacts on the BGP session's
   finite-state machine.

   BGP PDUs, including the OPEN message, may be up to 4k in size.  Since
   this mechanism leverages Layer 3 multicast, a PDU fragmentation
   mechanism may need to be described.

A.3.3.  Bootstrapping BGP via BGP

   [I-D.raszuk-idr-bgp-auto-discovery] describes a new BGP address
   family.  The NLRI carries a Group ID + BGP Identifier as the key.  A
   new BGP Path Attribute carries information about the sessions:

   o  AS Number
   o  AFI/SAFI
   o  BGP Identifier
   o  Peer Transport Address
   o  Flags to declare a session for information only, to force a reset
      of a session on parameter changes, etc.

   Since the BGP auto-discovery state is carried by BGP, it inherits the
   security implications of the underlying BGP session.

   PDU size considerations are identical to those of a BGP UPDATE

   Similarly, extensibility considerations would rely on either the new
   BGP Path Attribute, or one yet to be defined.

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A.3.4.  Bootstrapping BGP via OSPF

   [I-D.acee-ospf-bgp-rr] describes a mechanism to learn BGP Route
   Reflectors via OSPFv2/OSPFv3 LSAs.  Multiple types of scopes are
   defined for these LSAs to help constrain where they are advertised in
   an OSPF domain.

   The BGP Route Reflector TLV contains:

   o  Local AS Number
   o  IPv4 or IPv6 Address of the Route Reflector
   o  A list of AFI/SAFIs supported by the Route Reflector

   The BGP Route Reflector TLV may be advertised more than once,
   potentially to describe different IP transport endpoints.

   This mechanism does not provide for security properties of the BGP
   session or transport properties such as BFD or GTSM.

Authors' Addresses

   Randy Bush
   Arrcus, Inc. & Internet Initiative Japan
   5147 Crystal Springs
   Bainbridge Island, WA  98110

   Email: randy@psg.com

   Jie Dong
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Road
   Beijing  100095

   Email: jie.dong@huawei.com

   Jeffrey Haas (editor)
   Juniper Networks
   1133 Innovation Way
   Sunnyvale, CA  94089

   Email: jhaas@juniper.net

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   Warren Kumari (editor)
   1600 Amphitheatre Parkway
   Mountain View, CA  94043

   Email: warren@kumari.net

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