PIM Working Group G. Mirsky
Internet-Draft ZTE Corp.
Updates: 7761 (if approved) J. Xiaoli
Intended status: Standards Track ZTE Corporation
Expires: December 19, 2019 June 17, 2019
Bidirectional Forwarding Detection (BFD) for Multi-point Networks and
Protocol Independent Multicast - Sparse Mode (PIM-SM) Use Case
draft-ietf-pim-bfd-p2mp-use-case-01
Abstract
This document discusses the use of Bidirectional Forwarding Detection
(BFD) for multi-point networks to provide nodes that participate in
Protocol Independent Multicast - Sparse Mode (PIM-SM) with the sub-
second convergence. Optional extension to PIM-SM Hello, as specified
in RFC 7761, to bootstrap point-to-multipoint BFD session. also
defined in this document.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on December 19, 2019.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3
1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
3. Applicability of p2mp BFD . . . . . . . . . . . . . . . . . . 3
3.1. Multipoint BFD Encapsulation . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
Faster convergence in the control plane, in general, is beneficial
and allows minimizing periods of traffic blackholing, transient
routing loops, and other scenarios that may negatively affect service
data flow. That equally applies to unicast and multicast routing
protocols.
[RFC7761] is the current specification of the Protocol Independent
Multicast - Sparse Mode (PIM-SM) for IPv4 and IPv6 networks.
Confirming implementation of PIM-SM elects a Designated Router (DR)
on each PIM-SM interface. When a group of PIM-SM nodes is connected
to shared-media segment, e.g., Ethernet, the one elected as DR is to
act on behalf of directly connected hosts in the context of the PIM-
SM protocol. Failure of the DR impacts the quality of the multicast
services it provides to directly connected hosts because the default
failure detection interval for PIM-SM routers is 105 seconds.
Introduction of Backup DR (BDR), proposed in
[I-D.ietf-pim-dr-improvement], improves convergence time in the PIM-
SM over shared-media segment but still depends on long failure
detection interval.
Bidirectional Forwarding Detection (BFD) [RFC5880] had been
originally defined to detect failure of point-to-point (p2p) paths -
single-hop [RFC5881], multihop [RFC5883]. [RFC8562] extends the BFD
base specification [RFC5880] for multipoint and multicast networks,
which precisely characterizes deployment scenarios for PIM-SM over
LAN segment. This document demonstrates how point-to-multipoint
(p2mp) BFD can enable faster detection of PIM-SM router failure and
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thus minimize multicast service disruption. The document also
defines the extension to PIM-SM [RFC7761] and
[I-D.ietf-pim-dr-improvement] to bootstrap a PIM-SM router to join in
p2mp BFD session over shared-media link.
1.1. Conventions used in this document
1.1.1. Terminology
BFD: Bidirectional Forwarding Detection
BDR: Backup Designated Router
DR: Designated Router
p2mp: Pont-to-Multipoint
PIM-SM: Protocol Independent Multicast - Sparse Mode
1.1.2. Requirements Language
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
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Problem Statement
[RFC7761] does not provide a method for fast, e.g., sub-second,
failure detection of a neighbor PIM-SM router. BFD already has many
implementations based on HW that are capable of supporting multiple
sub-second sessions concurrently.
3. Applicability of p2mp BFD
[RFC8562] may provide an efficient and scalable solution for the
fast-converging environment that demonstrates the head-tails
relationship. Each such group presents itself as p2mp BFD session
with its head being the root and other routers being tails of the
p2mp BFD session. Figure 1 displays the new optional BFD
Discriminator TLV to bootstrap tail of the p2mp BFD session.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OptionType | OptionLength |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| My Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: BFD Discriminator TLV to Bootstrap P2MP BFD session
where new fields are interpreted as:
OptionType is a value (TBA1) assigned by IANA Section 4 that
identifies the TLV as BFD Discriminator TLV;
OptionLength value is always 4
My Discriminator - My Discriminator value allocated by the root of
the p2mp BFD session.
If PIM-SM routers that support this specification are configured to
use p2mp BFD for faster convergence, then the router to be monitored,
referred to as 'head', MUST create BFD session of type
MultipointHead, as defined in [RFC8562]. If the head doesn't support
[I-D.ietf-pim-dr-improvement], then it MUST include BFD TLV in its
PIM-Hello message. If the head uses extensions defined in
[I-D.ietf-pim-dr-improvement], then DR MUST include BFD TLV in its
Hello message after the DR Address TLV. For a BDR it is RECOMMENDED
to include BFD TLV in its Hello message. If BDR includes BFD TLV,
then it MUST be after the BDR Address TLV. Then the head MUST begin
periodic transmission of BFD control packets. Source IP address of
the BFD control packet MUST be the same as the source IP address of
the PIM-Hello with BFD TLV messages being transmitted by the head.
The values of My Discriminator in the BFD control packet and My
Discriminator field of the BFD TLV in PIM-Hello, transmitted by the
head MUST be the same. When a PIM-SM router is configured to monitor
the head by using p2p BFD, referred to through this document as
'tail', receives PIM-Hello packet with BFD TLV it MAY create p2mp BFD
session of type MultipointTail, as defined in [RFC8562].
Because p2mp BFD doesn't use the three-way handshake and the head
transmits BFD control packets with the value of Your Discriminator
field set to zero, [RFC8562] modified how a BFD system demultiplexes
received BFD control packet. The tail demultiplexes p2mp BFD test
session based on head's source IP address, the My Discriminator value
it learned from BFD Discriminator TLV and the identity of the
multipoint path that the BFD control packet was received from. The
Detection Time for p2mp BFD sessions is defined differently from the
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definition provided in [RFC5880]. The Detection Time for each
MultipointTail session is calculated as the product of the last
received values of Desired Min TX Interval and Detect Mult. A tail
declares the BFD session down after the Detection Timer expires. If
the tail has detected MultipointHead failure, it MUST remove the
neighbor. If the failed head node was PIM-SM DR or BDR, the tail MAY
start DR Election process as specified in Section 4.3.2 [RFC7761] or
Section 4.1 [I-D.ietf-pim-dr-improvement] respectively.
If the head ceased to include BFD TLV in its PIM-Hello message, tails
MUST close the corresponding MultipointTail BFD session. Thus the
tail stops using BFD to monitor the head and reverts to the
procedures defined in [RFC7761] and [I-D.ietf-pim-dr-improvement].
3.1. Multipoint BFD Encapsulation
The MultipointHead of p2mp BFD session when transmitting BFD control
packet:
MUST set TTL value to 1;
SHOULD use group address ALL-PIM-ROUTERS ('224.0.0.13' for IPv4
and 'ff02::d' for IPv6) as destination IP address
MAY use network broadcast address for IPv4 or link-local all nodes
multicast group for IPv6 as the destination IP address;
MUST set destination UDP port value to 3784 when transmitting BFD
control packets, as defined in [RFC8562].
4. IANA Considerations
IANA is requested to allocate a new OptionType value from PIM Hello
Options registry according to:
+-------------+----------------+-------------------+---------------+
| Value Name | Length Number | Name Protocol | Reference |
+-------------+----------------+-------------------+---------------+
| TBA | 4 | BFD Discriminator | This document |
+-------------+----------------+-------------------+---------------+
Table 1: BFD Discriminator option type
5. Security Considerations
Security considerations discussed in [RFC7761], [RFC5880], and
[RFC8562], and [I-D.ietf-pim-dr-improvement] apply to this document.
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An implementation that supports this specification SHOULD use a
mechanism to control the maximum number of BFD sessions that can be
active at the same time.
6. Acknowledgments
Authors cannot say enough to express their appreciation of comments
and suggestions we received from Stig Venaas.
7. Normative References
[I-D.ietf-pim-dr-improvement]
Zhang, Z., hu, f., Xu, B., and m. mishra, "PIM DR
Improvement", draft-ietf-pim-dr-improvement-07 (work in
progress), January 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>.
[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
DOI 10.17487/RFC5881, June 2010,
<https://www.rfc-editor.org/info/rfc5881>.
[RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883,
June 2010, <https://www.rfc-editor.org/info/rfc5883>.
[RFC7761] Fenner, B., Handley, M., Holbrook, H., Kouvelas, I.,
Parekh, R., Zhang, Z., and L. Zheng, "Protocol Independent
Multicast - Sparse Mode (PIM-SM): Protocol Specification
(Revised)", STD 83, RFC 7761, DOI 10.17487/RFC7761, March
2016, <https://www.rfc-editor.org/info/rfc7761>.
[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>.
[RFC8562] Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
Ed., "Bidirectional Forwarding Detection (BFD) for
Multipoint Networks", RFC 8562, DOI 10.17487/RFC8562,
April 2019, <https://www.rfc-editor.org/info/rfc8562>.
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Authors' Addresses
Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
Ji Xiaoli
ZTE Corporation
No.50 Software Avenue, Yuhuatai District
Nanjing
China
Email: ji.xiaoli@zte.com.cn
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