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Versions: (draft-mirsky-pim-bfd-p2mp-use-case)
00 01 02 03 04 05
PIM Working Group G. Mirsky
Internet-Draft ZTE Corp.
Intended status: Standards Track J. Xiaoli
Expires: June 3, 2021 ZTE Corporation
November 30, 2020
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-05
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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 3, 2021.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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include Simplified BSD License text as described in Section 4.e of
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3
1.1.1. Acronyms . . . . . . . . . . . . . . . . . . . . . . 3
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4
3. Applicability of p2mp BFD . . . . . . . . . . . . . . . . . . 4
3.1. Using P2MP BFD in PIM DR/BDR Monitoring . . . . . . . . . 4
3.2. P2MP BFD in PIM DR Load Balancing . . . . . . . . . . . . 5
3.3. Multipoint BFD Encapsulation . . . . . . . . . . . . . . 6
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
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]. In some PIM-SM
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deployments, a p2p BFD can be used to detect a failure and enable
faster conversion. [RFC8562] extends the BFD base specification
[RFC5880] for multipoint and multicast networks, which precisely
characterizes deployment scenarios for PIM-SM over a LAN segment.
Among specific characteristics of p2mp BFD that are particularly
benefit PIM-SM over a LAN segment is a faster transition to the Up
state of the p2mp BFD session due to avoidance of the three-way
handshake required in p2p BFD [RFC5880]. Also, because the router
that transmits BFD Control messages uses the BFD Demand mode
[RFC5880] it maintains less BFD state comparing to the Asynchronous
mode. This document demonstrates how point-to-multipoint (p2mp) BFD
can enable faster detection of PIM-SM router failure and 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. Acronyms
BFD: Bidirectional Forwarding Detection
BDR: Backup Designated Router
DR: Designated Router
DRLB: Designated Router Load Balancing
DRLB-Cap: DRLB Capability Hello Option
DRLB-List: DRLB List Hello Option
GDR: Group Designated Router
p2mp: Point-to-Multipoint
p2p: Point-to-Point
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.
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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 PIM Hello Option to bootstrap tail of the p2mp BFD
session.
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 PIM Hello Option
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.
3.1. Using P2MP BFD in PIM DR/BDR Monitoring
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 a BFD session of type
MultipointHead, as defined in [RFC8562]. Note that any PIM-SM router
that supports this specification, regardless of its role in PIM-SM,
MAY become a head of a p2mp BFD session. If the head doesn't support
[I-D.ietf-pim-dr-improvement], but, for example, uses procedures
defined in [I-D.mankamana-pim-bdr], then it MUST include BFD TLV in
its PIM-Hello message. If the head uses extensions defined in
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[I-D.ietf-pim-dr-improvement], then DR MUST include BFD TLV in its
Hello message. The DR Address TLV also MUST be included in the Hello
message. For a BDR, it is RECOMMENDED to include BFD TLV in its
Hello message. If BDR includes BFD TLV, then the BDR Address TLV
also MUST be present in the Hello message. As mentioned earlier, any
non-DR and non-BDR MAY include BFD TLV in its Hello message. Then
the head MUST begin periodic transmission of BFD Control packets.
The 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. My Discriminator's field value 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 p2mp BFD, referred
to through this document as 'tail', receives PIM-Hello packet with
BFD TLV, the tail MAY create a 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
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].
3.2. P2MP BFD in PIM DR Load Balancing
[RFC8775] defined the modification, Designated Router Load Balancing
(DRLB), to the PIM-SM protocol that allows for distribution of PIM-SM
DR responsibilities on a multi-access network segment. [RFC8775]
introduced the new PIM Hello options - Load Balancing Capability
(DRLB-Cap) and DR Load Balancing List (DRLB-List). PIM router that
includes DRLB-Cap Hello Option MAY include BFD Discriminator PIM
Hello Option (Figure 1). That router MUST create a BFD session and
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set itself as MultipointHead [RFC8562]. The router MUST set
bfd.SessionState in the MultipointHead session to Down. If a PIM
router that includes BFD Discriminator Option in its Hello finds its
address in DRLB-List PIM Hello Option as Group Designated Router
(GDR) Candidate for the first time, the router MUST set
bfd.SessionState to Up and start periodically transmit BFD Control
messages. If the PIM router that was GDR Candidate doesn't find its
address in the most recent DRLB-List Option, the router MUST set
bfd.SessionState to Down and cease transmitting BFD Control messages.
For each GDR Candidate that includes BFD Discriminator Option in its
PIM Hello, PIM DR creates a MultipointTail session [RFC8562]. PIM DR
demultiplexes BFD sessions based on the value in My Discriminator
field and the source IP address. If PIM DR detects a failure of one
of the sessions, it MUST remove that router from the GDR Candidate
list and immediately transmit a new DRLB-List Option.
3.3. 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
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5. Security Considerations
Security considerations discussed in [RFC7761], [RFC5880], and
[RFC8562], and [I-D.ietf-pim-dr-improvement] apply to this document.
PIM-SM link-local messages can be authenticated using various
mechanisms, as described in Section 6.3 [RFC7761]. Authentication of
BFD Control messages defined in Section 6.7 [RFC5880]. Each protocol
MAY use authentication of its messages independently of the mode used
by the other protocol.
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. References
7.1. Normative References
[I-D.ietf-pim-dr-improvement]
Zhang, Z., hu, f., Xu, B., and M. Mishra, "Protocol
Independent Multicast - Sparse Mode (PIM-SM) Designated
Router (DR) Improvement", draft-ietf-pim-dr-improvement-10
(work in progress), September 2020.
[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>.
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[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>.
[RFC8775] Cai, Y., Ou, H., Vallepalli, S., Mishra, M., Venaas, S.,
and A. Green, "PIM Designated Router Load Balancing",
RFC 8775, DOI 10.17487/RFC8775, April 2020,
<https://www.rfc-editor.org/info/rfc8775>.
7.2. Informative References
[I-D.mankamana-pim-bdr]
Mishra, M., Goh, J., and G. Mishra, "PIM Backup Designated
Router Procedure", draft-mankamana-pim-bdr-04 (work in
progress), April 2020.
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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