draft-ietf-bfd-intervals-00.txt   draft-ietf-bfd-intervals-01.txt 
Internet Engineering Task Force N. Akiya Internet Engineering Task Force N. Akiya
Internet-Draft M. Binderberger Internet-Draft M. Binderberger
Intended status: Informational Cisco Systems Intended status: Informational Cisco Systems
Expires: September 11, 2014 G. Mirsky Expires: December 13, 2014 G. Mirsky
Ericsson Ericsson
March 10, 2014 June 11, 2014
Common Interval Support in BFD Common Interval Support in BFD
draft-ietf-bfd-intervals-00 draft-ietf-bfd-intervals-01
Abstract Abstract
Some BFD implementations may be restricted to only support several Some BFD implementations may be restricted to only support several
interval values. When such BFD implementations speak to each other, interval values. When such BFD implementations speak to each other,
there is a possibility of two sides not being able to find a common there is a possibility of two sides not being able to find a common
interval value to run BFD sessions. interval value to run BFD sessions.
This document defines a small set of interval values for BFD that we This document defines a small set of interval values for BFD that we
call "Common intervals", and recommends implementations to support call "Common intervals", and recommends implementations to support
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 11, 2014. This Internet-Draft will expire on December 13, 2014.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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2. The problem with few supported intervals . . . . . . . . . . . 3 2. The problem with few supported intervals . . . . . . . . . . . 3
3. Well-defined, common intervals . . . . . . . . . . . . . . . . 4 3. Well-defined, common intervals . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative References . . . . . . . . . . . . . . . . . . . 5 7.1. Normative References . . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . . 5 7.2. Informative References . . . . . . . . . . . . . . . . . . 5
Appendix A. Why some intervals are in the common set . . . . . . . 5 Appendix A. Why some intervals are in the common set . . . . . . . 5
Appendix B. Timer adjustment with non-identical interval sets . . 6 Appendix B. Timer adjustment with non-identical interval sets . . 6
Appendix C. Open/upcoming topics . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
The standard [RFC5880] describes how to calculate the transmission The standard [RFC5880] describes how to calculate the transmission
interval and the detection time. It does not make any statement interval and the detection time. It does not make any statement
though how so solve a situation where one BFD speaker cannot support though how to solve a situation where one BFD speaker cannot support
the calculated value. In practice this may not been a problem as the calculated value. In practice this may not been a problem as
long as software-implemented timers have been used and as long as the long as software-implemented timers have been used and as long as the
granularity of such timers was small compared to the interval values granularity of such timers was small compared to the interval values
being supported, i.e. as long as the error in the timer interval was being supported, i.e. as long as the error in the timer interval was
small compared to 25 percent jitter. small compared to 25 percent jitter.
In the meantime requests exist for very fast interval values, down to In the meantime requests exist for very fast interval values, down to
3.3msec for MPLS-TP. At the same time the requested scale for the 3.3msec for MPLS-TP. At the same time the requested scale for the
number of BFD sessions in increasing. Both requirements have driven number of BFD sessions in increasing. Both requirements have driven
vendors to use Network Processors (NP), FPGAs or other hardware-based vendors to use Network Processors (NP), FPGAs or other hardware-based
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agree on a interval to run any BFD sessions. agree on a interval to run any BFD sessions.
3. Well-defined, common intervals 3. Well-defined, common intervals
The problem can be reduced by defining interval values that are The problem can be reduced by defining interval values that are
supported by all implementations. Then the adjustment mechanism supported by all implementations. Then the adjustment mechanism
could find a commonly supported interval without deviating too much could find a commonly supported interval without deviating too much
from the original request. from the original request.
In technical terms the requirement is as follows: a BFD In technical terms the requirement is as follows: a BFD
implementation MUST support all values in the set of Common interval implementation SHOULD support all values in the set of Common
values which are equal to or larger than the fastest, i.e. lowest, interval values which are equal to or larger than the fastest, i.e.
interval the particular BFD implementation supports. lowest, interval the particular BFD implementation supports.
The proposed set of Common interval values is: 3.3msec, 10msec, The proposed set of Common interval values is: 3.3msec, 10msec,
20msec, 50msec, 100msec and 1sec. 20msec, 50msec, 100msec and 1sec.
In addition support for 10sec interval together with multiplier In addition support for 10sec interval together with multiplier
values up to 255 is recommended to support graceful restart. values up to 255 is recommended to support graceful restart.
The adjustment is always towards larger, i.e. slower, interval values The adjustment is always towards larger, i.e. slower, interval values
when the initial interval proposed by the peer is not supported. when the initial interval proposed by the peer is not supported.
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(A) DesiredTx: 1sec, MinimumRx: 1sec, P-bit (A) DesiredTx: 1sec, MinimumRx: 1sec, P-bit
Tx: 200msec , Detect: 3 * 1sec Tx: 200msec , Detect: 3 * 1sec
Router B would adjust its timers based on the received Final Router B would adjust its timers based on the received Final
(B) Tx: 300msec , Detect: 3 * 1sec (B) Tx: 300msec , Detect: 3 * 1sec
and would then reply to the Poll sequence from router A: and would then reply to the Poll sequence from router A:
(B) DesiredTx: 1sec, MinimumRx: 1sec, F-bit (B) DesiredTx: 300msec, MinimumRx: 300msec, F-bit
Tx: 1sec , Detect: 3 * 1sec Tx: 1sec , Detect: 3 * 1sec
which finally makes router A adjusting its timers: which finally makes router A adjusting its timers:
(A) Tx: 1sec , Detect: 3 * 1sec (A) Tx: 1sec , Detect: 3 * 1sec
In other words router A and B go through multiple poll sequences In other words router A and B go through multiple poll sequences
until they reach a commonly supported interval value. Reaching such until they reach a commonly supported interval value. Reaching such
a value is guaranteed by this draft. a value is guaranteed by this draft.
Appendix C. Open/upcoming topics
As part of the ongoing BFD workgroup effort the following topics may
require more discussion and investigation:
Alignment of BFD intervals with [G.8013_Y.1731] intervals. Some
contradicting requirements. Ethernet OAM intervals do not fit
intervals of existing BFD implementations while adding more intervals
to the common set would complicate hardware implementations.
Larger interval values. To simplify hardware implementation a
question would be if we want to make all the intervals above 1sec
part of the common interval set.
Jitter. For the very fast interval of 3.3msec, do we want jitter.
Question comes up from hardware teams.
Do we need more of the adjustment examples? E.g. if A is configured
for 50msec again, what happens? Or when BFD session goes Down->Up
with A configured 200msec and B 50msec?
Authors' Addresses Authors' Addresses
Nobo Akiya Nobo Akiya
Cisco Systems Cisco Systems
Email: nobo@cisco.com Email: nobo@cisco.com
Marc Binderberger Marc Binderberger
Cisco Systems Cisco Systems
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