MPLS Working Group G. Mirsky
Internet-Draft ZTE Corp.
Intended status: Standards Track G. Mishra
Expires: April 21, 2021 Verizon Inc.
October 18, 2020
BFD for Multipoint Networks over Point-to-Multi-Point MPLS LSP
draft-mirsky-mpls-p2mp-bfd-11
Abstract
This document describes procedures for using Bidirectional Forwarding
Detection (BFD) for multipoint networks to detect data plane failures
in Multiprotocol Label Switching (MPLS) point-to-multipoint (p2mp)
Label Switched Paths (LSPs) using active tails with unsolicited
notifications mode. It also describes the applicability of LSP Ping,
as in-band, and the control plane, as out-band, solutions to
bootstrap a BFD session in this environment.
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 April 21, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 2
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. Multipoint BFD Encapsulation . . . . . . . . . . . . . . . . 3
3.1. IP Encapsulation of Multipoint BFD . . . . . . . . . . . 3
3.2. Non-IP Encapsulation of Multipoint BFD . . . . . . . . . 4
4. Bootstrapping Multipoint BFD . . . . . . . . . . . . . . . . 4
4.1. LSP Ping . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Operation of Multipoint BFD with Active Tail over P2MP
MPLS LSP . . . . . . . . . . . . . . . . . . . . . . . . 5
4.3. Control Plane . . . . . . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
[RFC8562] defines a method of using Bidirectional Detection (BFD)
[RFC5880] to monitor and detect unicast failures between the sender
(head) and one or more receivers (tails) in multipoint or multicast
networks. [RFC8562] added two BFD session types - MultipointHead and
MultipointTail. Throughout this document, MultipointHead and
MultipointTail refer to the value bfd.SessionType is set on a BFD
system. This document describes procedures for using such a mode of
BFD protocol to detect data plane failures in Multiprotocol Label
Switching (MPLS) point-to-multipoint (p2mp) Label Switched Paths
(LSPs). The document also describes the applicability of out-band
solutions to bootstrap a BFD session in this environment.
2. Conventions used in this document
2.1. Terminology
MPLS: Multiprotocol Label Switching
LSP: Label Switched Path
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BFD: Bidirectional Forwarding Detection
p2mp: Point-to-Multipoint
FEC: Forwarding Equivalence Class
G-ACh: Generic Associated Channel
ACH: Associated Channel Header
GAL: G-ACh Label
2.2. 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.
3. Multipoint BFD Encapsulation
[RFC8562] uses BFD in the Demand mode from the very start of a point-
to-multipoint (p2mp) BFD session. Because the head doesn't receive
any BFD Control packet from a tail, the head of the p2mp BFD session
transmits all BFD Control packets with the value of Your
Discriminator field set to zero. As a result, a tail cannot
demultiplex BFD sessions using Your Discriminator, as defined in
[RFC5880]. [RFC8562] requires that to demultiplex BFD sessions, the
tail uses the source IP address, My Discriminator, and the identity
of the multipoint tree from which the BFD Control packet was
received. The p2mp MPLS LSP label MAY provide the identification of
the multipoint tree in case of an inclusive p-tree or upstream
assigned label in case of aggregate p-tree. If the BFD Control
packet is encapsulated in IP/UDP, then the source IP address MUST be
used to demultiplex the received BFD Control packet as described in
Section 3.1. The non-IP encapsulation case is described in
Section 3.2.
3.1. IP Encapsulation of Multipoint BFD
[RFC8562] defines IP/UDP encapsulation for multipoint BFD over p2mp
MPLS LSP:
UDP destination port MUST be set to 3784;
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destination IP address MUST be set to the loopback address
127.0.0.1/32 for IPv4, or the loopback address ::1/128 for IPv6
[RFC4291].
This specification further clarifies that:
if multiple alternative paths for the given p2mp LSP Forwarding
Equivalence Class (FEC) exist, the MultipointHead SHOULD use
Entropy Label [RFC6790] used for LSP Ping [RFC8029] to exercise
that particular alternative path;
or the MultipointHead MAY use the UDP port number as discovered by
LSP Ping traceroute [RFC8029] as the source UDP port number to
possibly exercise that particular alternate path.
3.2. Non-IP Encapsulation of Multipoint BFD
In some environments, the overhead of extra IP/UDP encapsulations may
be considered as overburden, thus making the use of more compact
G-ACh encapsulation attractive. Also, the validation of the IP/UDP
encapsulation of BFD Control packet of p2mp BFD session may fail
because of a problem not related to neither MPLS label stack nor to
BFD. Avoiding unnecessary encapsulation of p2mp BFD over MPLS LSP
improves the accuracy of the correlation of the detected failure and
defect in MPLS LSP. Non-IP encapsulation for multipoint BFD over
p2mp MPLS LSP MUST use Generic Associated Channel (G-ACh) Label (GAL)
(see [RFC5586]) at the bottom of the label stack followed by
Associated Channel Header (ACH). If BFD Control, PW-ACH
encapsulation (without IP/UDP Headers) channel to be used in ACH, an
implementation would not be able to verify the identity of the
MultipointHead and, as a result, will not properly demultiplex BFD
packets. Hence, a new channel type value is needed. The Channel
Type field in ACH MUST be set to TBA1 value Section 6. To provide
the identity of the MultipointHead for the particular multipoint BFD
session, a Source Address TLV [RFC7212] MUST immediately follow a BFD
Control message.
4. Bootstrapping Multipoint BFD
4.1. LSP Ping
LSP Ping is the part of the on-demand OAM toolset to detect and
localize defects in the data plane and verify the control plane
against the data plane by ensuring that the LSP is mapped to the same
FEC, at the egress, as the ingress.
LSP Ping, as defined in [RFC6425], MAY be used to bootstrap
MultipointTail. If the LSP Ping used, it MUST include the Target FEC
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TLV and the BFD Discriminator TLV defined in [RFC5884]. The Target
FEC TLV MUST use sub-TLVs defined in Section 3.1 [RFC6425]. It is
RECOMMENDED setting the value of Reply Mode field to "Do not reply"
[RFC8029] for the LSP Ping to bootstrap MultipointTail of the p2mp
BFD session. Indeed, because BFD over a multipoint network is using
BFD Demand mode, the LSP echo reply from a tail has no useful
information to convey to the head, unlike in the case of the BFD over
a p2p MPLS LSP [RFC5884]. A MultipointTail that receives the LSP
Ping that includes the BFD Discriminator TLV:
o MUST validate the LSP Ping;
o MUST associate the received BFD Discriminator value with the p2mp
LSP;
o MUST create a p2mp BFD session and set bfd.SessionType =
MultipointTail as described in [RFC8562];
o MUST use the source IP address of LSP Ping, the value of BFD
Discriminator from the BFD Discriminator TLV, and the identity of
the p2mp LSP to properly demultiplex BFD sessions.
Besides bootstrapping a BFD session over a p2mp LSP, LSP Ping SHOULD
be used to verify the control plane against the data plane
periodically by checking that the p2mp LSP is mapped to the same FEC
at the MultipointHead and all active MultipointTails. The rate of
generation of these LSP Ping Echo request messages SHOULD be
significantly less than the rate of generation of the BFD Control
packets because LSP Ping requires more processing to validate the
consistency between the data plane and the control plane. An
implementation MAY provide configuration options to control the rate
of generation of the periodic LSP Ping Echo request messages.
4.2. Operation of Multipoint BFD with Active Tail over P2MP MPLS LSP
[RFC8562] defined how the BFD Demand mode can be used in multipoint
networks. When applied in MPLS, procedures specified in [RFC8562]
allow an egress LSR to detect a failure of the part of the MPLS p2mp
LSP from the ingress LSR. The ingress LSR is not aware of the state
of the p2mp LSP. [RFC8563], using mechanisms defined in [RFC8562],
defined an "active tail" behavior. An active tail might notify the
head of the detected failure and responds to a poll sequence
initiated by the head. The first method, referred to as Head
Notification without Polling, is mentioned in Section 5.2.1
[RFC8563], is the simplest of all described in [RFC8563]. The use of
this method in BFD over MPLS p2mp LSP is discussed in this document.
Analysis of other methods of a head learning of the state of an MPLS
p2mp LSP is outside the scope of this document.
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As specified in [RFC8563] for the active tail mode, BFD variables
MUST be as follows:
On an ingress LSR:
o bfd.SessionType is MultipointHead;
o bfd.RequiredMinRxInterval is set to nonzero allowing egress LSRs
to send BFD Control packets.
On an egress LSR:
o bfd.SessionType is MultipointTail;
o bfd.SilentTail is set to zero.
In Section 5.2.1 [RFC8563] is noted that "the tail sends unsolicited
BFD packets in response to the detection of a multipoint path
failure" but without the specifics on the information in the packet
and frequency of transmissions. This document defines the procedure
of the active tail with unsolicited notifications for p2mp MPLS LSP
as specified below.
Upon detecting the failure of the p2mp MPLS LSP, an egress LSR sends
BFD Control packet with the following settings:
o the Poll (P) bit is set;
o the Status (Sta) field set to Down value;
o the Diagnostic (Diag) field set to Control Detection Time Expired
value;
o the value of the Your Discriminator field is set to the value the
egress LSR has been using to demultiplex that BFD multipoint
session;
o BFD Control packet is encapsulated in IP/UDP with the destination
IP address of the ingress LSR and the UDP destination port number
set to 4784 per [RFC5883]
o these BFD Control packets are transmitted at the rate of one per
second until either it receives the valid for this BFD session
control packet with the Final (F) bit set from the ingress LSR or
the defect condition clears.
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To improve the likelihood of notifying the ingress LSR of the failure
of the p2mp MPLS LSP, the egress LSR SHOULD transmit three BFD
Control packets defined above in short succession.
An ingress LSR that has received the BFD Control packet, as described
above, sends the unicast IP/UDP encapsulated BFD Control packet with
the Final (F) bit set to the egress LSR.
4.3. Control Plane
BGP-BFD Attribute [I-D.ietf-bess-mvpn-fast-failover] MAY be used to
bootstrap multipoint BFD session on a tail.
5. Security Considerations
This document does not introduce new security aspects but inherits
all security considerations from [RFC5880], [RFC5884], [RFC7726],
[RFC8562], [RFC8029], and [RFC6425].
Also, BFD for p2mp MPLS LSP MUST follow the requirements listed in
section 4.1 [RFC4687] to avoid congestion in the control plane or the
data plane caused by the rate of generating BFD Control packets. An
operator SHOULD consider the amount of extra traffic generated by
p2mp BFD when selecting the interval at which the MultipointHead will
transmit BFD Control packets. Also, the operator MAY consider the
size of the packet the MultipointHead transmits periodically as using
IP/UDP encapsulation adds up to 28 octets, which is more than 50% of
BFD Control packet length, comparing to G-ACh encapsulation.
6. IANA Considerations
IANA is requested to allocate value (TBA1) from its MPLS Generalized
Associated Channel (G-ACh) Types registry.
+-------+------------------------+---------------+
| Value | Description | Reference |
+-------+------------------------+---------------+
| TBA1 | Multipoint BFD Session | This document |
+-------+------------------------+---------------+
Table 1: Multipoint BFD Session G-ACh Type
7. Acknowledgements
The author sincerely appreciates the comments received from Andrew
Malis and thought stimulating questions from Carlos Pignataro.
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8. References
8.1. Normative References
[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>.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<https://www.rfc-editor.org/info/rfc5586>.
[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>.
[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>.
[RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
"Bidirectional Forwarding Detection (BFD) for MPLS Label
Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884,
June 2010, <https://www.rfc-editor.org/info/rfc5884>.
[RFC6425] Saxena, S., Ed., Swallow, G., Ali, Z., Farrel, A.,
Yasukawa, S., and T. Nadeau, "Detecting Data-Plane
Failures in Point-to-Multipoint MPLS - Extensions to LSP
Ping", RFC 6425, DOI 10.17487/RFC6425, November 2011,
<https://www.rfc-editor.org/info/rfc6425>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[RFC7212] Frost, D., Bryant, S., and M. Bocci, "MPLS Generic
Associated Channel (G-ACh) Advertisement Protocol",
RFC 7212, DOI 10.17487/RFC7212, June 2014,
<https://www.rfc-editor.org/info/rfc7212>.
[RFC7726] Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S.
Aldrin, "Clarifying Procedures for Establishing BFD
Sessions for MPLS Label Switched Paths (LSPs)", RFC 7726,
DOI 10.17487/RFC7726, January 2016,
<https://www.rfc-editor.org/info/rfc7726>.
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[RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
Switched (MPLS) Data-Plane Failures", RFC 8029,
DOI 10.17487/RFC8029, March 2017,
<https://www.rfc-editor.org/info/rfc8029>.
[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>.
[RFC8563] Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
Ed., "Bidirectional Forwarding Detection (BFD) Multipoint
Active Tails", RFC 8563, DOI 10.17487/RFC8563, April 2019,
<https://www.rfc-editor.org/info/rfc8563>.
8.2. Informative References
[I-D.ietf-bess-mvpn-fast-failover]
Morin, T., Kebler, R., and G. Mirsky, "Multicast VPN Fast
Upstream Failover", draft-ietf-bess-mvpn-fast-failover-11
(work in progress), October 2020.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing
Architecture", RFC 4291, DOI 10.17487/RFC4291, February
2006, <https://www.rfc-editor.org/info/rfc4291>.
[RFC4687] Yasukawa, S., Farrel, A., King, D., and T. Nadeau,
"Operations and Management (OAM) Requirements for Point-
to-Multipoint MPLS Networks", RFC 4687,
DOI 10.17487/RFC4687, September 2006,
<https://www.rfc-editor.org/info/rfc4687>.
Authors' Addresses
Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
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Gyan Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com
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