Internet DRAFT - draft-mirsky-pim-bfd-p2mp-use-case
draft-mirsky-pim-bfd-p2mp-use-case
PIM Working Group G. Mirsky
Internet-Draft ZTE Corp.
Updates: 7761 (if approved) J. Xiaoli
Intended status: Standards Track ZTE Corporation
Expires: December 29, 2018 June 27, 2018
Bidirectional Forwarding Detection (BFD) for Multi-point Networks and
Protocol Independent Multicast - Sparse Mode (PIM-SM) Use Case
draft-mirsky-pim-bfd-p2mp-use-case-02
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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This Internet-Draft will expire on December 29, 2018.
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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 . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
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 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]. [I-D.ietf-bfd-multipoint]
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
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PIM-SM router ailure and thus minimize multicast service disruption.
The document also defines the extension to PIM-SM [RFC7761] 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 to support multiple sub-
second session concurrently.
3. Applicability of p2mp BFD
[I-D.ietf-bfd-multipoint] may provide the efficient and scalable
solution for the fast-converging environment that has head-tails
relationships. 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 BFD Discriminator TLV
[RFC7761] 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 MultipointHead, as
defined in [I-D.ietf-bfd-multipoint]. The head MUST include BFD TLV
in its PIM-Hello message and periodically transmit 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 configured to monitor the head, referred to as 'tail', via
p2mp BFD receives PIM-Hello packet with BFD TLV it MAY create p2mp
BFD session as MultipointTail, as defined in
[I-D.ietf-bfd-multipoint], and demultiplex p2mp BFD test session
based on head's source IP address the My Discriminator value it
learned from BFD Discriminator TLV. If the head ceased to include
BFD TLV in its PIM-Hello message, tails MUST close the corresponding
MultipointTail BFD session. If the tail detects 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 in Section 4.1
[I-D.ietf-pim-dr-improvement] respectively.
3.1. Multipoint BFD Encapsulation
The MultipointHead of p2mp BFD session when transmitting BFD control
packet:
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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 [I-D.ietf-bfd-multipoint].
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
[I-D.ietf-bfd-multipoint], apply to this document.
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-bfd-multipoint]
Katz, D., Ward, D., Networks, J., and G. Mirsky, "BFD for
Multipoint Networks", draft-ietf-bfd-multipoint-18 (work
in progress), June 2018.
[I-D.ietf-pim-dr-improvement]
Zhang, Z., hu, f., Xu, B., and m. mishra, "PIM DR
Improvement", draft-ietf-pim-dr-improvement-04 (work in
progress), December 2017.
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[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>.
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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