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 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 November 26, 2020. 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 Bush Expires November 26, 2020 [Page 1] Internet-Draft Trade-offs in BGP Peer Discovery May 2020 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. Bush Expires November 26, 2020 [Page 2] Internet-Draft Trade-offs in BGP Peer Discovery May 2020 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. Bush Expires November 26, 2020 [Page 3] Internet-Draft Trade-offs in BGP Peer Discovery May 2020 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. Bush Expires November 26, 2020 [Page 4] Internet-Draft Trade-offs in BGP Peer Discovery May 2020 o AS number, o IP address, IPv4 or IPv6, and o BGP Authentication. 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. Rendezvous approaches may appeal to deployments which favor a central control framework. Bush Expires November 26, 2020 [Page 5] Internet-Draft Trade-offs in BGP Peer Discovery May 2020 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-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. [RFC6830] Farinacci, D., Fuller, V., Meyer, D., and D. Lewis, "The Locator/ID Separation Protocol (LISP)", RFC 6830, DOI 10.17487/RFC6830, January 2013, . Appendix A. Acknowledgements The authors wish to thank . Bush Expires November 26, 2020 [Page 6] Internet-Draft Trade-offs in BGP Peer Discovery May 2020 Author's Address Randy Bush Arrcus, Inc. & Internet Initiative Japan 5147 Crystal Springs Bainbridge Island, Washington 98110 US Email: randy@psg.com Bush Expires November 26, 2020 [Page 7]