BFD Working Group X. Min
Internet-Draft ZTE Corp.
Intended status: Standards Track February 28, 2020
Expires: August 31, 2020
Bidirectional Forwarding Detection (BFD) Padding Alteration
draft-xiao-bfd-padding-alteration-00
Abstract
This document describes the procedures of the Bidirectional
Forwarding Detection (BFD) protocol to alter BFD padding, using BFD
in Asynchronous mode.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions Used in This Document . . . . . . . . . . . . 2
2. Turn On BFD Padding . . . . . . . . . . . . . . . . . . . . . 3
2.1. Switch From the Small BFD Packets . . . . . . . . . . . . 3
2.2. Switch From the Start of a BFD Session . . . . . . . . . 4
3. Increase BFD Padding . . . . . . . . . . . . . . . . . . . . 4
4. Decrease BFD Padding . . . . . . . . . . . . . . . . . . . . 4
5. Turn Off BFD Padding . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
9. Normative References . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
"BFD Encapsulated in Large Packets" [I-D.ietf-bfd-large-packets]
defines a new BFD variable bfd.PaddedPduSize, which can be configured
to the value the BFD transport protocol payload size is increased to,
and the contents of this additional payload MUST be zero. In other
words, the BFD protocol can be used to verify path MTU with BFD
padding.
Considering that there are implementations that do not support Large
BFD Packets, [I-D.ietf-bfd-large-packets] specifies that when an
implementation is incapable of processing Large BFD Packets, the BFD
state machine will behave as if it were not receiving Control
packets. The implementation would follow standard BFD procedures
with regards to not having received Control packets.
"Bidirectional Forwarding Detection (BFD)" [RFC5880] specifies the
Poll Sequence as an exchange of BFD Control packets that is used in
some circumstances to ensure that the remote system is aware of
parameter changes.
This document describes the procedures of the Bidirectional
Forwarding Detection (BFD) protocol to alter BFD padding, using BFD
in Asynchronous mode. The procedure defined in this document refers
to but differs from the Poll Sequence defined in Section 6.5 of
[RFC5880].
1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
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14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Turn On BFD Padding
There are two scenarios when turning on BFD padding. One is to turn
on BFD padding when the BFD session is Up and running with the Small
BFD Packets. Another one is to turn on BFD padding before the BFD
session is Up.
2.1. Switch From the Small BFD Packets
Consider a scenario when the BFD session is Up and running with the
Small BFD Packets, which don't include any padding. If the BFD
variable bfd.PaddedPduSize is set to a new non-zero value, i.e.,
switch from the Small BFD Packets to the Large BFD Packets whose size
equals to the provisioned new value, then the procedure described in
this section is applied, and the procedure is called Padding Poll
Sequence.
A Padding Poll Sequence consists of a system sending periodic Small
BFD Control packets and additional Padding Poll, namely Large BFD
Control packets with the Poll (P) bit set, which is used to notify
the BFD peer system, that it intends to switch from the current Small
BFD Packets, to the Large BFD Packets whose size equals to the
provisioned new value. When the BFD peer system receives a Padding
Poll, it immediately responds a BFD Control packet with the Final (F)
bit set, independent of any periodic BFD Control packets it is
sending. When the system sending the Padding Poll sequence receives
a replied packet with Final, the Padding Poll Sequence is considered
to be successfully terminated. Typically, the successfully
terminated sequence consists of a single packet in each direction,
but considering packet losses or relatively long packet latencies,
multiple Padding Poll packets may be sent before the sequence
successfully terminates, the maximum number of Padding Poll packets
and the interval between sequential Padding Poll packets are
implementation specific local matters. When the system sending the
Padding Poll sequence doesn't receive any replied packet with Final,
over the whole process of sending multiple Poll packets, the Padding
Poll Sequence is considered to be unsuccessfully terminated.
If a Padding Poll Sequence is successfully terminated, the system
requesting the Padding Poll Sequence would switch to the periodic
transmission of Large BFD Packets whose size equals to the
provisioned new value, with the Poll (P) bit clear.
If a Padding Poll Sequence is unsuccessfully terminated, the system
requesting the Padding Poll Sequence would report an error to its
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management, and continue the periodic transmission of Small BFD
Control packets with the Poll (P) bit clear.
2.2. Switch From the Start of a BFD Session
If the BFD variable bfd.PaddedPduSize is set to a non-zero value
indicating padding before the BFD session is Up, then the procedure
described in this section is applied.
At first the BFD session would be Up and running with the Small BFD
Packets which don't include any padding, following the BFD session
establishing procedures defined in [RFC5880], and then switch from
the Small BFD Packets to the Large BFD Packets, so that the Padding
Poll Sequence described in Section 2.1 is applied.
If BFD variable bfd.PaddedPduSize is set on both sides of the tested
path, then the Padding Poll Sequence would happen on both directions
separately.
3. Increase BFD Padding
While the BFD session is Up and running with the Large BFD Packets
which include padding, if the BFD variable bfd.PaddedPduSize is set
to a new value indicating larger padding, i.e., switch from the Large
BFD Packets to the Large BFD Packets whose size equals to the
provisioned new value, then the Padding Poll Sequence described in
Section 2.1 is applied. Specifically, Padding Poll would use Larger
BFD Packets with the Poll (P) bit set.
4. Decrease BFD Padding
While the BFD session is Up and running with the Large BFD Packets
which include padding, if the BFD variable bfd.PaddedPduSize is set
to a new value indicating smaller padding, i.e., switch from the
Larger BFD Packets to the Large BFD Packets whose size equals to the
provisioned new value, then the Poll Sequence described in
Section 6.5 of [RFC5880] is applied. Specifically, the Poll Sequence
MUST be performed by setting the Poll (P) bit on those scheduled
periodic transmissions, and additional packets MUST NOT be sent.
5. Turn Off BFD Padding
While the BFD session is Up and running with the Large BFD Packets
which include padding, if the BFD padding is turned off, i.e., switch
from the Large BFD Packets to the Small BFD Packets, then the Poll
Sequence described in Section 6.5 of [RFC5880] is also applied.
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6. Security Considerations
This document does not raise any additional security issues beyond
those of the specifications referred to in the list of normative
references.
7. IANA Considerations
This document has no IANA action requested.
8. Acknowledgements
TBA.
9. Normative References
[I-D.ietf-bfd-large-packets]
Haas, J. and A. Fu, "BFD Encapsulated in Large Packets",
draft-ietf-bfd-large-packets-02 (work in progress),
November 2019.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
Author's Address
Xiao Min
ZTE Corp.
Nanjing
China
Phone: +86 18061680168
Email: xiao.min2@zte.com.cn
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