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draft-bgp-discovery-layers/draft-ymbk-bgp-discovery-layers.txt
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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
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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.
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.
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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,
<https://www.rfc-editor.org/info/rfc6830>.
Appendix A. Acknowledgements
The authors wish to thank .
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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]
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