Internet DRAFT - draft-merciaz-idr-bgp-bfd-strict-mode
draft-merciaz-idr-bgp-bfd-strict-mode
IDR WorkGroup M. Zheng
Internet-Draft A. Lindem
Intended status: Standards Track Cisco Systems
Expires: January 8, 2020 J. Haas
Juniper Networks, Inc.
July 7, 2019
BGP BFD Strict-Mode
draft-merciaz-idr-bgp-bfd-strict-mode-02
Abstract
This document specifies extensions to RFC4271 BGP-4 that enable a BGP
speaker to negotiate additional Bidirectional Forwarding Detection
(BFD) extensions using a BGP 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.
Status of This Memo
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to this document. Code Components extracted from this document must
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. BFD Capability . . . . . . . . . . . . . . . . . . . . . . . 3
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Manageability Considerations . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 5
9. Normative References . . . . . . . . . . . . . . . . . . . . 6
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 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
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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. 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 have BFD strict-mode enabled, then BGP
session establishment will be prevented until a BFD session is
established between the peering addresses. A BGP speaker with BFD
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strict-mode enabled MUST advertise the BFD capability with "S" bit
set.
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 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, 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 have BFD strict-mode enabled, the BGP finite state machine
does not transition to the Established state from OpenSent or
OpenConfirm state [RFC4271] until the BFD session is in the Up state
(see below for AdminDown state). This means that a KEEPALIVE message
is not sent nor is the KeepaliveTimer set.
If the BFD session does not transition to the Up state, and the
HoldTimer has been negotiated to a non-zero value, the BGP FSM will
close the session appropriately. If the HoldTimer has been
negotiated to a zero value, the session should be closed after a time
of X. This time X is referred as "BGP BFD Hold time". The proposed
default BGP BFD Hold time value is 30 seconds. The BGP BFD Hold time
value is configurable.
If BFD session is in the AdminDown state, then the BGP finite state
machine will proceed normally without input from BFD. This means
that BFD session "AdminDown" state WILL NOT prevent the BGP state
transition to Established state from OpenConfirm.
Once the BFD session has transitioned to the Up state, the BGP FSM
may proceed to transition to the Established state from the OpenSent
or OpenConfirm state appropriately. I.e. a KEEPALIVE message is
sent, and the KeepaliveTimer is started.
If either BGP peer has not advertised the BFD Capability with strict-
mode enabled, then a BFD session WILL NOT be required for the BGP
session to reach Established state. This does not preclude usage of
BFD after BGP session establishment [RFC5882].
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5. Manageability Considerations
Auto-configuration is possible for the enabling BGP BFD restrict-
mode. However, the configuration automation is out of the scope of
this document.
A BGP NOTIFICATION message subcode indicating BFD Hold timer
expiration may be required for network management. (To be discussed
in the next revision of this document.)
6. Security Considerations
The mechanism defined in this document interacts with the BGP finite
state machine when so configured. The security considerations of BFD
thus become considerations for BGP-4 [RFC4271] so used. The use of
the BFD Authentication mechanism defined in [RFC5880] is thus
RECOMMENDED when used to protect BGP-4 [RFC4271].
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, Mohammed Mirza, Bruno Decraene, and Carlos Pignataro.
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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>.
[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>.
[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
301 Midenhall Way
GARY, NC 27513
UNITED STATES
Email: acee@cisco.com
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Jeffrey Haas
Juniper Networks, Inc.
1133 Innovation Way
SUNNYVALE, CALIFORNIA 94089
UNITED STATES
Email: jhaas@juniper.net
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