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.

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/.

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This Internet-Draft will expire on January 5, 2015.

Copyright Notice

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Table of Contents

• 1. Background
• 2. Overview
• 3. Procedures for BFD session establishment and removal using the Extended BFD TLV
• 3.1. Procedures for establishing BFD sessions
• 3.2. Procedures for removing BFD sessions
• 4. Extended BFD Discriminator TLV
• 5. Mutually Exclusive: BFD TLVs
• 6. Backwards Compatibility
• 7. Encapsulation
• 8. Security Considerations
• 9. IANA Considerations
• 9.1. Extended BFD Discriminator TLV
• 10. Acknowledgements
• 11. Contributing Authors
• 12. Normative References
• Appendix A. Alternate format for the BFD Extended TLV
• Authors' Addresses

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:

• Entropy labels help achieve load balancing of traffic belonging to the same <MPLS FEC, LSP>. It may be beneficial to track the individual paths of the multi-path network using separate BFD sessions for each non-congruent path.
• 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.
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 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

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.

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

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:

   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.

• 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