Re: [Bgp-autoconf] Move forward with bgp autoconf requirements and design principle

[Randy Bush <[e-mail]>]

so, a small attempt to move forward again

git be found at https://git.rg.net/randy/draft-bgp-discovery-layers

randy



Network Working Group                                            R. Bush
Internet-Draft                  Arrcus, Inc. & Internet Initiative Japan
Updates: 6811 (if approved)                                 May 25, 2020
Intended status: Informational
Expires: November 26, 2020


                    Trade-offs in BGP Peer Discovery
                   draft-ymbk-bgp-discovery-layers-00

Abstract

   This draft is an exploration of the alternatives and trade-offs in
   BGP peer discovery at various layers in the stack.  It is based on
   discussions in the IDR WG BGP Discovery Design Team.  The current
   target environment is the datacenter; while keeping an eye not to
   preclude WAN deployment.  This document is not intended to become an
   RFC.

Status of This Memo

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

1.  Introduction

   This draft is an exploration of the alternatives and trade-offs in
   BGP peer discovery at various layers in the stack.  It is based on
   discussions in the IDR WG BGP Discovery Design Team.  The current
   target environment is the datacenter; while keeping an eye not to
   preclude WAN deployment.  This document is not intended to become an
   RFC.

2.  Background

   Previous design team discussions converged on a number of aspects of
   the problem.

2.1.  BGP is the Underlay

   The assumed environment has BGP used as the underlay routing protocol
   in data center.

2.2.  Some Requirements

   Some requirements have been agreed by the design team as follows:

   o  Support IPv4 and IPv6 address families, but do not assume both are
      available.
   o  Support discovery of the peering addresses for the BGP session
      endpoints.
   o  Support using either a device's external interface or one of its
      loopback addresses for the BGP session endpoint.
   o  Support discovery of the peers' ASs.
   o  Agree on any BGP session authentication and parameters.
   o  Enable Layer 3 link liveness detection, such as BFD.

2.3.  Simplicity

   The goal is to provide the minimal set of configuration parameters
   needed by BGP OPEN to successfully start a BGP peering.  The goal is
   specifically not to replace or conflict with data exchanged during
   BGP OPEN.  Multiple sources of truth are a recipe for complexity and
   hence painful errors.

   Simplicity is key.  Features not absolutely needed will not be
   included in the design.





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3.  Assumptions

   BGP OPEN will do the heavy lifting.

   BGP discovery should not do anything that could be done by BGP OPEN.
   Two sources of the same data are a recipe for errors.

   BGP peering will be selective; every BGP speaker may not want to peer
   with every other speaker.

   Before BGP OPEN, there is discovery and there is choosing peers.

   After discovery, it would be nice if another exchange was not needed
   before BGP OPEN.

4.  Needs of Discovery

   In discovery, an aspiring BGP speaker needs to discover:

   o  The set of possible peers,
   o  To start, discovery does not know the potential peers' layer three
      IP addresses.
   o  Each one's attributes, a deployment defined set, e.g.: leaf,
      spine, ice cream flavor, ...  These attributes are arbitrary and
      operator dependent.  No assumptions should be made, code points
      assigned,, etc.
   o  Each one's layer three peering address(es), and
   o  Other attributes required for BGP OPEN to succeed, e.g.
      authentication data.

5.  Operator Configuration

   Operator configuration should be able to decide at lest the
   following:

   o  Select or otherwise filter which peers to actually try to BGP
      OPEN,
   o  What parameters to use, e.g.:

      *  IP addressing: IPv4, IPv6, Loopback, or Direct
      *  Any special forwarding or routing needed for reaching the
         prospective peer, e.g., loopback,
      *  AS numbering, and
      *  BGP Authentication Options.







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6.  Success Criteria

   What are the criteria for success and failure of the design
   decisions, and how do we measure them?

7.  Discovery at Layer Two

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

   There are two available candidates for peer discovery at Layer-2,
   Link Layer Discovery Protocol, LLDP, and Layer 3 Discovery Protocol,
   L3DL [I-D.ietf-lsvr-l3dl].

7.1.  Link Layer Discovery Protocol (LLDP)

   LLDP is a widely deployed protocol with implementations for most
   devices.  Unfortunately it does not currently reveal Layer-3 IP
   addresses.  There is an early LLDPv2 development to extend it in
   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
   transport BGP Config Sub-TLVs signaling

   o  AFI,
   o  IP address (IPv4 or IPv6),
   o  Local ASs,
   o  Local BGP Identifier (AKA, BGP Router ID),
   o  Session Group-ID,
   o  BGP [Authentication] Session Capabilities, and
   o  Local Address (Next Hop).

   Which of these are really necessary could be discussed.

7.2.  Layer-3 Discovery Protocol (L3DL)

   L3DL [I-D.ietf-lsvr-l3dl] is an ongoing development in the IETF LSVR
   Working Group with the goals 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 using
   BGP-SPF and similar protocols.

   L3DL Upper Layer Protocol Configuration, [I-D.ymbk-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.



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

   L3DL and L3DL-ULPC have well-specified security mechanisms, see
   [I-D.ymbk-lsvr-l3dl-signing].

   This is similar but not quite the sane as the needs of this IDR
   Design Team.  E.g., L3DL is designed to meet more complex needs.
   L3DL's predecessor, LSOE, [I-D.ymbk-lsvr-lsoe], was simpler and might
   be a better candidate for adaptation.  A week's work could customize
   the design for the IDR Design Team's needs.  But ...

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

8.  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.

   The principal problem would appear to be discovery at Layer-3,
   because one neither knows whether to use IPv4 or IPv6.  This is
   exacerbated by the possibility of a potential peer not being on the
   local subnet, and hence broadcast and similar techniques may not be
   applicable.

   If one can assume point-to-point links , then discovery might try
   IPv6 link-local or even IPv4 link-local.  Or maybe a link broadcast
   protocol.

   For switched or bridged multi-point which is at least on the same
   subnet, VLAN, etc., broadcasts might be a viable approach.

   There will be difficulty if one or both peers wish to use a loopback
   for peering.

9.  Discovery at Layer Seven

   Peer discovery at Layer-7 requires application layer rendezvous
   mechanisms analogous to those used by LISP, [RFC6830] or the Bitcoin
   Protocol.

   If the infrastructure is at all complex, e.g. multi-segment or worse,
   then it will need prior routing/forwarding knowledge in order to
   reach the rendezvous.  In a BGP centric deployment this could pose a
   chicken and egg problem.



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   Rendezvous approaches may appeal to deployments which favor a central
   control framework.

   On the other hand, those who favor distributed protocols will have
   the classic worries about fragility, redundancy, reliability, etc.

10.  Security Considerations

   None yet, but there will be many.

11.  Acknowledgments

   The IDR BGP Discovery Design Team.

12.  IANA Considerations

   None

13.  Normative References

   [I-D.acee-idr-lldp-peer-discovery]
              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-06 (work in
              progress), November 2019.

   [I-D.ietf-lsvr-l3dl]
              Bush, R., Austein, R., and K. Patel, "Layer 3 Discovery
              and Liveness", draft-ietf-lsvr-l3dl-04 (work in progress),
              May 2020.

   [I-D.ymbk-lsvr-l3dl-signing]
              Bush, R. and R. Austein, "Layer 3 Discovery and Liveness
              Signing", draft-ymbk-lsvr-l3dl-signing-01 (work in
              progress), May 2020.

   [I-D.ymbk-lsvr-l3dl-ulpc]
              Bush, R. and K. Patel, "L3DL Upper Layer Protocol
              Configuration", draft-ymbk-lsvr-l3dl-ulpc-03 (work in
              progress), May 2020.

   [I-D.ymbk-lsvr-lsoe]
              Bush, R., Austein, R., and K. Patel, "Link State Over
              Ethernet", draft-ymbk-lsvr-lsoe-03 (work in progress),
              November 2018.






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   [RFC6830]  Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The
              Locator/ID Separation Protocol (LISP)", RFC 6830,
              DOI 10.17487/RFC6830, January 2013,
              <https://www.rfc-editor.org/info/rfc6830>.

Appendix A.  Acknowledgements

   The authors wish to thank .

Author's Address

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

   Email: [e-mail]

































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