Routing Working Group A. Mishra
Internet-Draft Ciena Corporation
Intended status: Standards Track S. Pallagatti
Expires: January 1, 2015 Juniper Networks
M. Jethanandani
Ciena Corporation
M. Chen
Huawei
A. Saxena
Ciena Corporation
June 30, 2014
BFD Stability
draft-ashesh-bfd-stability-00.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, of delays in
frame transmitter and receiver engines, and of inter-frame delays
that might explain issues with a BFD session.
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.
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 1, 2015.
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Internet-Draft BFD Stability June 2014
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. BFD Null-Authentication TLV . . . . . . . . . . . . . . . . . 3
3. Theory of Operations . . . . . . . . . . . . . . . . . . . . 4
3.1. Frame Loss . . . . . . . . . . . . . . . . . . . . . . . 4
3.2. Inter-Frame Gap . . . . . . . . . . . . . . . . . . . . . 5
3.3. Frame Transmission Delay . . . . . . . . . . . . . . . . 5
4. IANA Requirements . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Consideration . . . . . . . . . . . . . . . . . . . 6
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The Bidirectional Forwarding Detection (BFD) 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 (the Detection Time as described in RFC 5880)
is set to the smallest feasible value. In certain cases, this
Detection Time is comparable to the inter-frame delays caused by
random network events such as frame drops or frame processing
(transmitter or receiver) delays.
This document proposes a mechanism to measure such transient effects
to detect instability in in the receive direction of the data path
from the session peer in addition to the datapath fault detection
mechanisms of BFD. Such a mechanism presents significant value with
the ability to measure the stability of BFD sessions and provides
data to the operators.
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In addition to stability measurement, the information exchanged
between BFD peers can be used for rudimentary, but low-overhead,
authentication.
2. BFD Null-Authentication TLV
The functionality proposed for BFD stability measurement is achieved
by appending the Null-Authentication TLV to the BFD control frame.
The Null-Authentication TLV (called 0-Auth in this document) extends
the existing BFD Authentication TLV structure by adding a new Auth-
Type of . This TLV carries the Sequence Number for
frame loss measurement, and Sender Timestamps for delay measurements.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Auth Type | Auth Len | Auth Key ID | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Timestamp 1 (IFG only) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Timestamp 2 (IFG+TD only) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Auth Type: The Authentication Type, which in this case is (Null Authentication).
Auth Len: The length of the Authentication Section, in bytes. For
Loss Measurement only, the length is set to 4. For Loss and Inter-
Frame Gap measurements, the length is set to 8. For Loss, Inter-
Frame Gap and Transmission Delay on sender node, the length is set to
12.
Auth Key ID: The Authentication Key ID in use for this packet. This
MUST be set to zero on transmit, and ignored on receipt.
Reserved: This byte MUST be set to zero on transmit, and ignored on
receipt.
Sequence Number: This indicates the sequence number for this packet
and MUST be present in every 0-Auth TLV. This value is incremented
by 1 for every frame transmitted while the session state is UP. A
value of 0 indicates a request by sender to reset the sequence number
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correlation logic at the receiver. The first frame transmitted by
the sender MAY set this field to 0.
Inter-Frame Gap (IFG) Mode:
Sender Timestamp 1 (IFG-ST): This is the Inter-Frame Gap Sender
Timestamp (IFG-ST) and is added at the last possible instance on
the sender (preferably on the PHY). The difference between two
such timestamps on consecutive frames is the Inter-Frame gap.
Inter-Frame Gap and Transmission Delay (IFG & TD) Mode:
Sender Timestamp 1 (TD-ST): This is the Transmission Delay Sender
Timestamp (TD-ST) and is added at the first possible instance on
the sender in the frame transmission engine. The difference
between TD-ST and the IFG-ST that follows the TD-ST is the Sender
Transmission Delay.
Sender Timestamp 2 (IFG-ST): This is the Inter-Frame Gap Sender
Timestamp (IFG-ST) and is added at the last possible instance on
the sender (preferably on the PHY). The difference between two
such timestamps on consecutive frames is the Inter-Frame gap.
3. Theory of Operations
This mechanism allows operator to read three measures of stability of
BFD: Frame Loss, Inter-Frame Gap and Transmission Delay. The
Receiver Delay (interval between receipt of a frame on the PHY and
the completion of processing in the receiver engine) can be measured
using timestamps similar to the Sender Timestamps on the receiver
node.
+---------+ +---------+
| Sender |===================...=================| Receiver|
+---------+ +---------+
| | | |
TD-ST | | RD-RT
IFG-ST IFG-RT
3.1. Frame Loss
This measurement counts the number of BFD control frames missed at
the receiver due to a transient change in the network such as
congestion. Frame-loss is detected by comparing the Sequence Number
field in the 0-Auth TLV 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.
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The first BFD Loss-Delay 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.
3.2. Inter-Frame Gap
This measurement is the difference between the IFG-ST on any two
consecutive BFD CC frames that carry the 0-Auth TLV (IFG or IFG&TD
mode only) for a session. This is a key metric to determine
transient changes in stability of BFD transmission engine or to
determine the systems capability of handling the existing load. A
significant deviation of IFG from the negotiated transmission
interval on the local node indicates potential instabilities in the
BFD transmission engine. Based on the IFG measurements, the operator
MAY take action to configure the system to maintain normal operation
of the node.
Similar IFG measurements on the receiver can be made using timestamps
(IFG-RT). In conjunction with IFG-ST measurements, these can
indicate delays caused by data-path. While a constant delay may not
be indicator of instability, large transient delays can decrease the
BFD session stability significantly.
3.3. Frame Transmission Delay
This measurement (TD) is the interval between the timestamp (TD-ST)
when the frame transmission timer expires, triggering the BFD control
frame generation, and the timestamp (IFG-TD) when the frame reaches
the last level in the frame processing logic on the transmitter where
the frame can be manipulated. Large variations in the TD
measurements over time are indicative of non-deterministic
transmission behavior of the BFD engine and can be a pre-cursor to
BFD engine instability.
Similar measurements for Receiver Delay (RD) can be made using IFG-RT
and RD-RT timestamps, and indicate similar instabilities on the BFD
receiver engine.
4. IANA Requirements
IANA is requested to assign new Auth-Type for the Null-Authentication
TLV for BFD Stability Measurement. The following number is
suggested.
Value Meaning
6 Null-Authentication TLV
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5. Security Consideration
Since this method uses an authentication TLV to achive the
functionality, usage of this TLV will prevent the use of other
authentication TLVs.
6. Acknowledgements
Nobo Akiya, Jeffery Haas, Peng Fan, Dileep Singh, Basil Saji, Sagar
Soni and Mallik Mudigonda also conributed to this document.
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, June 2010.
Authors' Addresses
Ashesh Mishra
Ciena Corporation
3939 North 1st Street
San Jose, CA 95134
USA
Email: mishra.ashesh@gmail.com
Santosh Pallagatti
Juniper Networks
Juniper Networks, Exora Business Park
Bangalore, Karnataka 560103
India
Phone: +
Email: santoshpk@juniper.net
Mahesh Jethanandani
Ciena Corporation
3939 North 1st Street
San Jose, CA 95134
USA
Email: mjethanandani@gmail.com
URI: www.ciena.com
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Mach Chen
Huawei
Email: mach.chen@huawei.com
Ankur Saxena
Ciena Corporation
3939 North 1st Street
San Jose, CA 95134
USA
Email: ankurpsaxena@gmail.com
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