Internet DRAFT - draft-vgovindan-mpls-extended-bfd-disc-tlv
draft-vgovindan-mpls-extended-bfd-disc-tlv
Internet Engineering Task Force V. Govindan
Internet-Draft N. Akiya
Intended status: Standards Track Cisco Systems
Expires: January 5, 2015 July 4, 2014
Label Switched Path (LSP) Ping
Extended Bidirectional Forwarding Detection (BFD) Discriminator TLV
draft-vgovindan-mpls-extended-bfd-disc-tlv-00
Abstract
This document defines an extended Bidirectional Forwarding Detection
(BFD) discriminator TLV for the Multiprotocol Label Switching (MPLS)
Label Switched Path (LSP) Ping mechanism, to allow bootstrapping of
multiple BFD sessions for a given FEC.
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 RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on January 5, 2015.
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Background . . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Procedures for BFD session establishment and removal using
the Extended BFD TLV . . . . . . . . . . . . . . . . . . . . 3
3.1. Procedures for establishing BFD sessions . . . . . . . . 3
3.2. Procedures for removing BFD sessions . . . . . . . . . . 3
4. Extended BFD Discriminator TLV . . . . . . . . . . . . . . . 4
5. Mutually Exclusive: BFD TLVs . . . . . . . . . . . . . . . . 5
6. Backwards Compatibility . . . . . . . . . . . . . . . . . . . 5
7. Encapsulation . . . . . . . . . . . . . . . . . . . . . . . . 5
8. Security Considerations . . . . . . . . . . . . . . . . . . . 5
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
9.1. Extended BFD Discriminator TLV . . . . . . . . . . . . . 6
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
11. Contributing Authors . . . . . . . . . . . . . . . . . . . . 6
12. Normative References . . . . . . . . . . . . . . . . . . . . 6
Appendix A. Alternate format for the BFD Extended TLV . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Background
Bidirectional Forwarding Detection (BFD) [RFC5880] for Multiprotocol
Label Switching (MPLS) Label Switched Paths (LSPs), [RFC5884],
describes a mechanism to use BFD to monitor the connectivity in-band
on the LSPs. The BFD session on the LSP egress is bootstrapped using
the LSP Ping mechanism, defined in [RFC4379], carrying the BFD
Discriminator TLV that describes the BFD discriminator of the BFD
session on the LSP ingress.
The BFD Discriminator TLV and defined procedures around this TLV only
allow one BFD session to be bootstrapped per <MPLS Forwarding
Equivalent Class (FEC), LSP> There are scenarios where an LSP ingress
may desire to run multiple BFD sessions to monitor the connectivity
on an LSP. To achieve the bootstrapping of multiple BFD sessions per
FEC, a new TLV and procedures are required. Two scenarios where this
is useful are described below:
o Entropy labels help achieve load balancing of traffic belonging to
the same <MPLS FEC, LSP>. It may be beneficial to track the
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individual paths of the multi-path network using separate BFD
sessions for each non-congruent path.
o It may be useful to establish multiple BFD sessions for the same
<MPLS FEC, LSP> to achieve BFD session redundancy, i.e. protection
against false positives due to equipment or soft failures inside
boxes.
2. Overview
An LSR ingress wanting to bootstrap one or more BFD sessions on an
LSP is to include the Extended BFD Discriminator TLV, described in
Section 4, in the MPLS echo request message for the FEC. The
Extended BFD Discriminator TLV is capable of carrying multiple BFD
discriminators, and each BFD discriminator is accompanied with an an
instance identifier. The LSR egress, upon reception of this MPLS
echo request, is to create requested number of BFD sessions for the
specified FEC. Each BFD session object created on the LSR ingress
and the LSR egress MUST be annotated with corresponding instance
identifier. BFD session procedures are to follow those described in
[RFC5884].
3. Procedures for BFD session establishment and removal using the
Extended BFD TLV
3.1. Procedures for establishing BFD sessions
There are at least two options possible here:
1. BFD session establishment MUST follow the procedure specified in
[RFC5884].
2. The base procedure for BFD session establishment MUST be the same
as that of [RFC5884]. This procedure can be enhanced by
specifying additional Operation type field and Operation status
field in the proposed Extended BFD Discriminator TLV. See
Appendix A for a description of Operation types and Operation
status codes.
3.2. Procedures for removing BFD sessions
[RFC5884] does not specify an explicit procedure for deleting BFD
sessions. A few options are possible here:
1. Specify an explicit delete procedure for the BFD session using
Operation types field and Operation status field through the
Extended BFD TLV. See Appendix A for a description of Operation
types and Operation status codes.
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2. Specify a timer based deletion procedure: A new purge timer field
can be introduced within the proposed Extended BFD Discriminator
TLV. The ingress specifies the value for the purge timer field.
Once the BFD session transitions from up to down state, the
egress is to delete the session after the value specified in the
purge timer field. Ed Note: This approach is an open topic for
discussion.
3. No new procedure to delete a BFD session is introduced.
Assumption by the egress is that BFD sessions can be deleted if
corresponding FEC is deleted from the system or sometime after
BFD sessions go down.
Regardless of the option chosen to proceed, all BFD sessions
established with the FEC MUST be removed automatically if the FEC is
removed.
4. Extended BFD Discriminator TLV
The Extended BFD Discriminator object is a new TLV that MAY be
included in the MPLS echo request message. An MPLS echo request MUST
NOT include more than one Extended BFD Discriminator object. The
Extended BFD Discriminator object describes one or more BFD
discriminators along with each having an instance identifier. An
MPLS echo reply MAY include the Extended BFD Discriminator object,
but MUST NOT include more than one Extended BFD Discriminator object.
Extended BFD Discriminator TLV Type is TBD1. Length is 8 or
multiples of 8. Length of (8 x N) implies that there are N entries
in the Value field of the Extended BFD Discriminator TLV. Each entry
in the Value field of the Extended BFD Discriminator TLV has
following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Instance Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFD Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Extended BFD Discriminator TLV
Reserved - This field MUST be set to zero on transmit, and ignored
on receipt.
Instance Identifier - An instance identifier of the BFD session.
The instance identifier is a value allocated by the LSP ingress
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for corresponding BFD Discriminator, and MUST be unique within the
FEC on the LSP ingress node. The instance identifier MUST NOT
change for the lifetime of the BFD session.
BFD Discriminator - The BFD discriminator allocated for this BFD
session by the LSP ingress.
See Appendix A for a discussion on an alternate format for the TLV.
5. Mutually Exclusive: BFD TLVs
The BFD Discriminator TLV and the Extended BFD Discriminator TLV are
mutually exclusive. An MPLS echo request/reply message MUST NOT
include both the BFD Discriminator TLV and the Extended BFD
Discriminator TLV. Reception of an MPLS echo request with both the
BFD Discriminator TLV and the Extended BFD Discriminator TLV is to
result in the Return Code being set to Malformed echo request
received (1).
6. Backwards Compatibility
If an LSP ingress wishes to bootstrap multiple BFD sessions with the
Extended BFD Discriminator TLV when an LSP already has a BFD session
bootstrapped with the BFD Discriminator TLV, following procedures are
RECOMMENDED.
The LSP ingress is to send an MPLS echo request carrying the Extended
BFD Discriminator TLV with the same BFD discriminator of the existing
BFD session (one bootstrapped previously with the BFD Discriminator
TLV), giving it an instance identifier. Once the transition of the
existing BFD session is completed, then the LSP ingress can generate
further MPLS echo request messages with the Extended BFD
Discriminator TLV to bootstrap more BFD sessions.
7. Encapsulation
The encapsulation of BFD packets are the same as specified by
[RFC5884]
8. Security Considerations
This document defines a mechanism to bootstrap multiple BFD sessions
per FEC. BFD sessions, naturally, use system and network resources.
More BFD sessions means more resources will be used. It is highly
important to ensure only minimum number of BFD sessions are
provisioned per FEC, and bootstrapped BFD sessions are properly
deleted when no longer required. Additionally security measures
described in [RFC4379] and [RFC5884] are to be followed.
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9. IANA Considerations
9.1. Extended BFD Discriminator TLV
The IANA is requested to assign new value TBD1 for Extended BFD
Discriminator TLV from the "Multiprotocol Label Switching
Architecture (MPLS) Label Switched Paths (LSPs) Ping Parameters -
TLVs" registry.
Value Meaning Reference
----- ------- ---------
TBD1 Extended BFD Discriminator TLV this document
10. Acknowledgements
TBD
11. Contributing Authors
Girija Rao
Cisco Systems
Email: giraghav@cisco.com
Mallik Mudigonda
Cisco Systems
Email: mmudigon@cisco.com
12. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4379] Kompella, K. and G. Swallow, "Detecting Multi-Protocol
Label Switched (MPLS) Data Plane Failures", RFC 4379,
February 2006.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, June 2010.
[RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
"Bidirectional Forwarding Detection (BFD) for MPLS Label
Switched Paths (LSPs)", RFC 5884, June 2010.
Appendix A. Alternate format for the BFD Extended TLV
The BFD Extended TLV can be used to carry the Operation Type and the
Operation Status (Op Status) bits that are defined below:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Operation Type| Op Status | Instance Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFD Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Alternate format of the Extended
BFD Discriminator TLV
Ed Note: The definitions of Operation Type and Operation Status
fields are subject to discussion. Additional codes can be defined
if this approach is pursued.
Operation Type - Operation to be performed on the corresponding
BFD Discriminator. Valid values are:
1 - Create: This value MAY be used in the MPLS echo request,
but MUST NOT be used in the MPLS echo reply. The operation
type 1 indicates that receiver (i.e. LSP egress) is to ensure
that BFD session for this FEC, with corresponding BFD
Discriminator in "your discriminator" field, exists or is
created.
2 - Delete: This value MAY be used in the MPLS echo request,
but MUST NOT be used in the MPLS echo reply. The operation
type 2 indicates that receiver (i.e. LSP egress) is to ensure
that BFD session for this FEC, with corresponding BFD
Discriminator in "your discriminator" field, does not exist or
is deleted.
3 - CreateAck: This value MUST NOT be used in the MPLS echo
request, but MAY be used in the MPLS echo reply. The operation
type 3 indicates that receiver (i.e. LSP egress) is
acknowledging received Create(1) request.
4 - DeleteAck: This value MUST NOT be used in the MPLS echo
request, but MAY be used in the MPLS echo reply. The operation
type 4 indicates that receiver (i.e. LSP egress) is
acknowledging received Delete(2) request.
Op Status
0 - The operation succeeded.
1 - Not enough Resources.
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BFD Discriminator - When the Extended BFD Discriminator TLV is
carried in the MPLS echo request, this field describes the BFD
discriminator allocated for this BFD session by the LSP ingress.
When the Extended BFD Discriminator TLV is carried in the MPLS
echo reply, this field describes the BFD discriminator allocated
for this BFD session by the LSP egress.
The Extended BFD Discriminator TLV in an MPLS echo request MUST have
either Create(1) or Delete(2) operation type. The Extended BFD
Discriminator TLV in an MPLS echo reply MUST have either CreateAck(3)
or DeleteACK(4) operation type.
Authors' Addresses
Vengada Prasad Govindan
Cisco Systems
Email: venggovi@cisco.com
Nobo Akiya
Cisco Systems
Email: nobo@cisco.com
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