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.
Google
March 8, 2021
Requirements and Considerations in BGP Peer Auto-Configuration
draft-ietf-idr-bgp-autoconf-considerations-00
Abstract
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
datacenter.
This document is not intended to become an RFC.
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 BCP 14 [RFC2119]
[RFC8174] when, and only when, they appear in all capitals, as shown
here.
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
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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
datacenter.
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.
2.3.2.1. 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
requirement.
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
PDU.
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
protocols.
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
following:
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
session.
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
center.
The length of messages supported by the protocol.
How extensible the protocol is to carry future state for BGP auto-
configuration.
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
mechanism.
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
trust.
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
should:
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
detail.
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
problems:
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
done.
4. IANA Considerations
This document makes no request of IANA.
Note to RFC Editor: this section may be removed on publication as an
RFC.
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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-
MD5.
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
security.
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
end-points.
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,
<https://www.rfc-editor.org/info/rfc2119>.
[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
[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-08 (work in
progress), December 2020.
[I-D.acee-ospf-bgp-rr]
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.
[I-D.ietf-lsvr-l3dl]
Bush, R., Austein, R., and K. Patel, "Layer 3 Discovery
and Liveness", draft-ietf-lsvr-l3dl-07 (work in progress),
January 2021.
[I-D.ietf-lsvr-l3dl-signing]
Bush, R. and R. Austein, "Layer 3 Discovery and Liveness
Signing", draft-ietf-lsvr-l3dl-signing-01 (work in
progress), January 2021.
[I-D.ietf-lsvr-l3dl-ulpc]
Bush, R. and K. Patel, "L3DL Upper Layer Protocol
Configuration", draft-ietf-lsvr-l3dl-ulpc-01 (work in
progress), January 2021.
[I-D.ietf-lsvr-lsoe]
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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[I-D.raszuk-idr-bgp-auto-discovery]
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.
[I-D.raszuk-idr-bgp-auto-session-setup]
Raszuk, R., "BGP Automated Session Setup", draft-raszuk-
idr-bgp-auto-session-setup-01 (work in progress), December
2019.
[I-D.xu-idr-neighbor-autodiscovery]
Xu, X., Talaulikar, K., Bi, K., Tantsura, J., and N.
Triantafillis, "BGP Neighbor Discovery", draft-xu-idr-
neighbor-autodiscovery-12 (work in progress), November
2019.
[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,
<https://www.rfc-editor.org/info/rfc826>.
[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,
<https://www.rfc-editor.org/info/rfc4272>.
[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,
<https://www.rfc-editor.org/info/rfc4861>.
[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,
<https://www.rfc-editor.org/info/rfc5082>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
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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,
<https://www.rfc-editor.org/info/rfc8177>.
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
[I-D.ietf-lsvr-l3dl-signing].
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
message.
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
US
Email: randy@psg.com
Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Road
Beijing 100095
China
Email: jie.dong@huawei.com
Jeffrey Haas (editor)
Juniper Networks
1133 Innovation Way
Sunnyvale, CA 94089
US
Email: jhaas@juniper.net
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Warren Kumari (editor)
Google
1600 Amphitheatre Parkway
Mountain View, CA 94043
US
Email: warren@kumari.net
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