BFD Stability
draft-ietf-bfd-stability-06

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 packet loss.

Status of This Memo

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Use Cases
• 4. BFD Null-Authentication Type
• 5. Theory of Operation
• 5.1. Loss Measurement
• 6. IANA Considerations
• 7. Security Consideration
• 8. Contributors
• 9. Acknowledgements
• 10. Normative References
• Authors' Addresses

1. Introduction

The Bidirectional Forwarding Detection ( BFD) protocol operates by transmitting and receiving BFD control packets, generally at high frequency, over the datapath being monitored. In order to prevent significant data loss due to a datapath failure, BFD session detection time as defined in BFD is set to the smallest feasible value.

This document proposes a mechanism to detect lost packet 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 any BFD extension to measure data traffic loss or delay on a link or tunnel and the scope is limited to BFD packets.

2. Terminology

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 and RFC 8174.

The reader is expected to be familiar with the BFD, Optimizing BFD Authentication and BFD Secure Sequence Numbers.

3. Use Cases

Bidirectional Forwarding Detection as defined in BFD cannot detect any BFD packet loss if loss does not last for detection time. This document proposes a method to detect a dropped packet on the receiver. For example, if the receiver receives BFD control packet k at time t but receives packet k+3 at time t+10ms, and never receives packet k+1 and/or k+2, then it has experienced a drop.

This proposal enables BFD implementation 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, an 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.

4. BFD Null-Authentication Type

The functionality proposed for BFD stability measurement is achieved by appending the Null-Authentication type (as defined in Optimizing BFD Authentication ) to the BFD control packets that do not have authentication enabled.

5. Theory of Operation

This mechanism allows operators to measure the loss of BFD control packets.

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 packets MUST include NULL-Auth TLV.

5.1. Loss Measurement

Loss measurement counts the number of BFD control packets 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 control packets. The Sequence Number in each successive control packet generated on a BFD session by the transmitter is incremented by one.

The first BFD NULL-Auth type processed by the receiver that has a non-zero sequence number is used for bootstrapping the logic. When using secure sequence numbers, if the expected values are pre-calculated, the value must be matched to detect lost packets as defined in BFD secure sequence numbers.

6. IANA Considerations

This document has no actions for IANA.

7. Security Consideration

Other than concerns raised in BFD, Optimizing BFD Authentication and BFD Secure Sequence Numbers. There are no new concerns with this proposal.

8. Contributors

Manav Bhatia

9. 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.

10. Normative References

Authors' Addresses