BFD Stability
draft-ashesh-bfd-stability-05.txt

Abstract

This document describes extensions to the Bidirectional Forwarding Detection (BFD) protocol to measure BFD stability. Specifically, it describes a mechanism for detection of BFD frame loss.

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 July 30, 2017.

Copyright Notice

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Table of Contents

• 1. Introduction
• 2. Use Cases
• 3. BFD Null-Authentication TLV
• 4. Theory of Operations
• 4.1. Loss Measurement
• 5. IANA Requirements
• 6. Security Consideration
• 7. Contributors
• 8. Acknowledgements
• 9. Normative References
• Authors' Addresses

1. Introduction

The Bidirectional Forwarding Detection (BFD) [RFC5880] protocol operates by transmitting and receiving control frames, generally at high frequency, over the datapath being monitored. In order to prevent significant data loss due to a datapath failure, the tolerance for lost or delayed frames in the Detection Time, as defined in BFD [RFC5880] is set to the smallest feasible value.

This document proposes a mechanism to detect lost frames in a BFD session in addition to the datapath fault detection mechanisms of BFD. Such a mechanism presents significant value to measure the stability of BFD sessions and provides data to the operators for the cause of a BFD failure.

This document does not propose BFD extension to measure data traffic loss or delay on a link or tunnel and the scope is limited to BFD frames.

2. Use Cases

Legacy BFD cannot detect any BFD frame loss if loss does not last for dead interval. This draft proposes a method to detect a dropped frame on the receiver. For example, if the receiver receives BFD CC frame k at time t but receives frame k+3 at time t+10ms, and never receives frame k+1 and/or k+2, then it has experienced a drop.

This proposal enables BFD engine to generate diagnostic information on the health of each BFD session that could be used to preempt a failure on a link that BFD was monitoring by allowing time for a corrective action to be taken.

In a faulty datapath scenario, operator can use BFD health information to trigger delay and loss measurement OAM protocol (Connectivity Fault Management (CFM) or Loss Measurement (LM)-Delay Measurement (DM)) to further isolate the issue.

3. BFD Null-Authentication TLV

The functionality proposed for BFD stability measurement is achieved by appending the Null-Authentication TLV (as defined in Optimizing BFD Authentication [I-D.ietf-bfd-optimizing-authentication] ) to the BFD control frame that do not have authentication enabled.

4. Theory of Operations

This mechanism allows operator to measure the loss of BFD CC frames.

When using MD5 or SHA authentication, BFD uses authentication TLV that carries the Sequence Number. However, if non-meticulous authentication is being used, or no authentication is in use, then the non-authenticated BFD frames MUST include NULL-Auth TLV.

4.1. Loss Measurement

Loss measurement counts the number of BFD control frames missed at the receiver during any Detection Time period. The loss is detected by comparing the Sequence Number field in the Auth TLV (NULL or otherwise) in successive BFD CC frames. The Sequence Number in each successive control frame generated on a BFD session by the transmitter is incremented by one.

The first BFD NULL-Auth TLV processed by the receiver that has a non-zero sequence number is used for bootstrapping the logic. Each successive frame after this is expected to have a Sequence Number that is one greater than the Sequence Number in the previous frame. When the Sequence Number wraps around it should start from 1 instead of 0.

5. IANA Requirements

N/A

6. Security Consideration

Other than concerns raised in BFD [RFC5880] there are no new concerns with this proposal.

7. Contributors

Manav Bhatia

8. Acknowledgements

Authors would like to thank Nobo Akiya, Jeffery Haas, Peng Fan, Dileep Singh, Basil Saji, Sagar Soni and Mallik Mudigonda who also contributed to this document.

9. Normative References

Authors' Addresses