Internet DRAFT - draft-merciaz-ietf-idr-bgp-bfd-strict-mode
draft-merciaz-ietf-idr-bgp-bfd-strict-mode
IDR WorkGroup M. Zheng
Internet-Draft A. Lindem
Intended status: Standards Track Cisco Systems
Expires: September 12, 2019 March 11, 2019
BGP BFD Strict-Mode
draft-merciaz-ietf-idr-bgp-bfd-strict-mode-01
Abstract
This document specifies extensions to RFC4271 BGP-4 that enable a BGP
speaker to signal additional Bidirectional Forwarding Detection (BFD)
extensions using an optional parameter BFD capability. This BFD
capability enables a BGP speaker to prevent a BGP session from being
established until a BFD session is established. It is referred to as
BGP BFD "strict-mode". BGP BFD strict-mode will be supported when
both the local speaker and its remote peer are BFD strict-mode
capable, Otherwise, a BGP speaker and its peer should not require a
BFD session for BGP session establishment.
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 http://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 12, 2019.
Copyright Notice
Copyright (c) 2019 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
(http://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
Zheng & Lindem Expires September 12, 2019 [Page 1]
Internet-Draft BGP BFD Strict-Mode March 2019
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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. BGP BFD Capability . . . . . . . . . . . . . . . . . . . . . 3
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Backward Compatibility . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 4
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 5
9. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Bidirectional Forwarding Detection BFD [RFC5882] enables routers to
monitor data plane connectivity and to detect faults in the
bidirectional forwarding path between them. This capability is
leveraged by routing protocols such as BGP [RFC4271] to rapidly react
to topology changes in the face of path failures.
The BFD interaction with BGP is specified in Section 10.2 of
[RFC5882]. When BFD is enabled for a BGP neighbor, faults in the
bidirectional forwarding detected by BFD result in session
termination. It is possible in some failure scenarios for the
network to be in a state such that a BGP session may be established
but a BFD session cannot be established. In some other scenarios, it
may be possible to establish a BGP session, but a degraded or poor-
quality link may result in the corresponding BFD session going up and
down frequently.
To avoid situations which result in routing churn and to minimize the
impact of network interruptions, it will be beneficial to disallow
BGP to establish a neighbor session until BFD session is successfully
established and has stabilized. We refer to this mode of operation
as BGP BFD "strict-mode". However, always using strict-mode" would
preclude BGP operation in an environment where not all routers
support BFD strict-mode or have BFD enabled. This document defines
BGP "strict-mode" operation as preventing BGP session establishment
until both the local and remove speakers have a stable BFD session.
The document also specifies the BGP protocol extensions for BGP
capability [RFC5492] for announcing BFD parameters including a BGP
Zheng & Lindem Expires September 12, 2019 [Page 2]
Internet-Draft BGP BFD Strict-Mode March 2019
speaker's support for "strict-mode", i.e., requiring a BFD session
for BGP session establishment.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "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.
3. BGP BFD Capability
The BGP Capability [RFC5492] for BFD parameters will allow a BGP
speaker's BFD capabilities including its support for BFD strict-mode.
This capability is defined as follows:
Capability code: TBD
Capability length: 1 octet
Capability value: Consists of 1 octet BFD flags as follows:
+--------------------------------------------------+
| BFD Flags (8 bits) |
+--------------------------------------------------+
The use and meaning of the fields are as follows:
BFD Flags: This field contains bit flags relating to BFD.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|S| Reserved |
+-+-+-+-+-+-+-+-+
The most significant bit is defined as state of Strict-Mode ("Strict-
Mode", or "S") bit, which can be used by a BGP speaker to signal its
support for BFD Strict-mode. When set (value 1), this bit indicates
that the BGP speaker has the BFD "Strict-mode" enabled. If both
local BGP speaker and its peer are enabled with BFD strict-mode, then
BGP session establishment will be disallowed until a BFD session is
Zheng & Lindem Expires September 12, 2019 [Page 3]
Internet-Draft BGP BFD Strict-Mode March 2019
established. A BGP speaker with BFD strict-mode enabled MUST
advertise the BFD capability with "S" bit value 1.
The remaining bits are reserved and SHOULD be set to zero by the
sender and MUST be ignored by the receiver.
4. Operation
A BGP speaker that supports capabilities advertisement sends an OPEN
message to its BGP peer, the message MAY include an Optional
Parameter, called Capabilities. The parameter lists the capabilities
supported by the speaker. By following BGP capabilities
advertisement procedures defined in [RFC5492], BFD capability
advertisement for strict-mode is advertised to BGP peers.
A BGP speaker which supports capabilities advertisement and has BFD
strict-mode enabled MUST include the BGP BFD capability with the "S"
Bit set in the BGP capabilities it advertises.
A BGP speaker which supports BFD capability advertisement, examines
the list of capabilities present in the Capabilities BFD Parameter
that the speaker receives from its peer. If both the local and
remote BGP speakers BFD strict-mode enabled, then BGP session
establishment will be prevented until a BFD session is up. If either
peer has not advertised the BFD Capability with strict-mode enabled,
then a BFD session SHOULD NOT be required prior to BGP session
establishment. This does not preclude usage of BFD after BGP session
establishment [RFC5882].
A BGP speaker which does not support or recognize BFD capability
should ignore the BFD capability. If a BGP speaker advertising the
capability receives the Unsupported Capability NOTIFICATION message,
it MUST NOT be result in BGP session termination.
5. Backward Compatibility
The new BFD capability will introduce any backward compatibility if
the procedures defined in this document are followed. A BGP speaker
which does not support BFD capability MUST ignore this capability.
The Unsupported Capability NOTIFICATION message MUST NOT result in
session termination by the BGP speaker advertising the capability.
6. Security Considerations
This specification doesn't change the basic security model inherent
in [RFC4271]. To the extent [RFC4271] might be said to help defend
against denials of service by making the control plane more
resilient, this extension may modestly increase that resilience;
Zheng & Lindem Expires September 12, 2019 [Page 4]
Internet-Draft BGP BFD Strict-Mode March 2019
however, there are enough confounding and deployment-specific factors
that no general claims can be made.
7. IANA Considerations
This document defines a new BGP capability - BFD Capability. The
Capability Code for BFD Capability is TBD.
IANA is requested to establish a "BGP BFD Capability Flags" registry
within the "Border Gateway Protocol (BGP) Parameters" grouping. The
Registration Procedure should be Standards Action, the initial values
as follows:
+--------------+---------------+------------+---------------+
| Bit Position | Name | Short Name | Reference |
+--------------+---------------+------------+---------------+
| 0 | Strict-Mode | S | this document |
| 1-7 | Unassigned | | this document |
+--------------+---------------+------------+---------------+
8. Acknowledgement
The authors would like to acknowledge the review and inputs from
Shyam Sethuram and Mohammed Mirza.
9. 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>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006, <https://www.rfc-
editor.org/info/rfc4271>.
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <https://www.rfc-editor.org/info/rfc5492>.
Zheng & Lindem Expires September 12, 2019 [Page 5]
Internet-Draft BGP BFD Strict-Mode March 2019
[RFC5882] Katz, D. and D. Ward, "Generic Application of
Bidirectional Forwarding Detection (BFD)", RFC 5882,
DOI 10.17487/RFC5882, June 2010, <https://www.rfc-
editor.org/info/rfc5882>.
[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>.
Authors' Addresses
Mercia Zheng
Cisco Systems
821 Alder Drive,
MILPITAS, CALIFORNIA 95035
UNITED STATES
Email: merciaz@cisco.com
Acee Lindem
Cisco Systems
821 Alder Drive,
MILPITAS, CALIFORNIA 95035
UNITED STATES
Email: acee@cisco.com
Zheng & Lindem Expires September 12, 2019 [Page 6]
