draft-ietf-bfd-intervals-02.txt   draft-ietf-bfd-intervals-03.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: January 28, 2015 G. Mirsky Expires: February 17, 2015 G. Mirsky
Ericsson Ericsson
July 27, 2014 August 16, 2014
Common Interval Support in BFD Common Interval Support in BFD
draft-ietf-bfd-intervals-02 draft-ietf-bfd-intervals-03
Abstract Abstract
Some BFD implementations may be restricted to only support several BFD requires that messages are transmitted at regular intervals and
interval values. When such BFD implementations speak to each other, provides a way to negotiate the interval used by BFD peers. Some BFD
there is a possibility of two sides not being able to find a common implementations may be restricted to only support several interval
interval value to run BFD sessions. values. When such BFD implementations speak to each other, there is
a possibility of two sides not being able to find a common 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
the defined intervals. This solves the problem of finding an the defined intervals. This solves the problem of finding an
interval value that both BFD speakers can support while allowing a interval value that both BFD speakers can support while allowing a
simplified implementation as seen for hardware-based BFD. It does simplified implementation as seen for hardware-based BFD. It does
not restrict an implementation from supporting more intervals in not restrict an implementation from supporting more intervals in
addition to the Common intervals. addition to the Common intervals.
Requirements Language Requirements Language
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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 February 17, 2015.
This Internet-Draft will expire on January 28, 2015.
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
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. The problem with few supported intervals . . . . . . . . . . 3 2. The problem with few supported intervals . . . . . . . . . . 3
3. Well-defined, common intervals . . . . . . . . . . . . . . . 3 3. Well-defined, common intervals . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 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
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7 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 to 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 is 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
solutions to offload the periodic packet transmission and the timeout solutions to offload the periodic packet transmission and the timeout
detection in the receive direction. A potential problem with this detection in the receive direction. A potential problem with this
hardware-based BFD is the granularity of the interval timers. hardware-based BFD is the granularity of the interval timers.
Depending on the implementation only a few intervals may be Depending on the implementation only a few intervals may be
supported, which can cause interoperability problems. This document supported, which can cause interoperability problems. This document
proposes a set of interval values that should be supported by all proposes a set of interval values that should be supported by all
implementations. Details are laid out in the following sections. implementations. Details are laid out in the following sections.
2. The problem with few supported intervals 2. The problem with few supported intervals
Let's assume vendor "A" supports 10msec, 100msec and 1sec interval Let's assume vendor "A" supports 10msec, 100msec and 1sec interval
timers in hardware. Vendor "B" supports every value from 20msec timers in hardware. Vendor "B" supports every value from 20msec
onward, with a granularity of 1msec. For a BFD session "A" tries to onward, with a granularity of 1msec. For a BFD session "A" tries to
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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.
This document is not adding new requirements with respect to how This document is not adding new requirements with respect to the
exact a timer value must be implemented. Supporting an interval precision with which a timer value must be implemented. Supporting
value means to advertise this value in the DesiredMinTxInterval and/ an interval value means to advertise this value in the
or RequiredMinRxInterval field of the BFD packets and to provide DesiredMinTxInterval and/or RequiredMinRxInterval field of the BFD
timers that are reasonably close. [RFC5880] defines safety margins packets and to provide timers that are reasonably close. [RFC5880]
for the timers by defining a jitter range. defines safety margins for the timers by defining a jitter range.
How is the "Common interval set" used exactly? In the example above, How is the "Common interval set" used exactly? In the example above,
vendor "A" has a fastest interval of 10msec and thus would be vendor "A" has a fastest interval of 10msec and thus would be
required to support all intervals in the common set that are equal or required to support all intervals in the common set that are equal or
larger than 10msec, i.e. it would support 10msec, 20msec, 50msec, larger than 10msec, i.e. it would support 10msec, 20msec, 50msec,
100msec, 1sec. Vendor "B" has a fastest interval of 20msec and thus 100msec, 1sec. Vendor "B" has a fastest interval of 20msec and thus
would need to support 20msec, 50msec, 100msec and 1sec. As long as would need to support 20msec, 50msec, 100msec and 1sec. As long as
this requirement is met for the common set of values, then both this requirement is met for the common set of values, then both
vendor "A" and "B" are free to support additional values outside of vendor "A" and "B" are free to support additional values outside of
the common set. the common set.
4. IANA Considerations 4. IANA Considerations
No request to IANA. No request to IANA.
5. Security Considerations 5. Security Considerations
This document does not introduce any additional security issues. This document does not introduce any additional security concerns.
The security considerations described in the BFD documents, [RFC5880]
and others, apply to devices implementing the BFD protocol,
regardless of whether or not the common interval set is implemented.
6. Acknowledgements 6. Acknowledgements
We would like to thank Sylvain Masse and Anca Zamfir for bringing up We would like to thank Sylvain Masse and Anca Zamfir for bringing up
the discussion about the Poll sequence, and Jeffrey Haas helped the discussion about the Poll sequence, and Jeffrey Haas helped
finding the fine line between "exact" and "pedantic". finding the fine line between "exact" and "pedantic".
7. References 7. References
7.1. Normative References 7.1. Normative References
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