SPRING Working Group G. Mirsky
Internet-Draft ZTE Corp.
Intended status: Standards Track May 8, 2017
Expires: November 9, 2017
Bidirectional Forwarding Detection (BFD) in Segment Routing Networks
Using MPLS Dataplane
draft-mirsky-spring-bfd-00
Abstract
Segment Routing architecture leverages the paradigm of source
routing. It can be realized in the Multiprotocol Label Switching
(MPLS) network without any change to the data plane. A segment is
encoded as an MPLS label and an ordered list of segments is encoded
as a stack of labels. Bidirectional Forwarding Detection (BFD) is
expected to monitor any kind of paths between systems. This document
defines how to use Label Switched Path Ping to bootstrap and control
path in reverse direction of a BFD session on the Segment Routing
network over MPLS dataplane.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 2
1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 2
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3
2. Bootstrapping BFD session over Segment Routed tunnel . . . . 3
3. Use BFD Reverse Path TLV over Segment Routed MPLS tunnel . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
[RFC5880], [RFC5881], and [RFC5883] established the Bidirectional
Forwarding Detection (BFD) protocol for IP networks. [RFC5884] and
[RFC7726] set rules of using BFD Asynchronous mode over Multiprotocol
Label Switching (MPLS) Label Switched Path (LSP). These latter
standards implicitly assume that the egress BFD peer, which is the
egress Label Edge Router (LER), will use the shortest path route
regardless of the path the ingress LER uses to send BFD control
packets towards it.
This document defines use of LSP Ping for Segment Routing networks
over MPLS dataplane [I-D.ietf-mpls-spring-lsp-ping] to bootstrap and
control path of a BFD session from the egress to ingress LER.
1.1. Conventions used in this document
1.1.1. Terminology
BFD: Bidirectional Forwarding Detection
FEC: Forwarding Equivalence Class
MPLS: Multiprotocol Label Switching
LSP: Label Switching Path
LER: Label Edge Router
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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
[RFC2119].
2. Bootstrapping BFD session over Segment Routed tunnel
As discussed in [I-D.ietf-mpls-spring-lsp-ping] introduction of
Segment Routing network domains with an MPLS data plane adds three
new sub-TLVs that MAY be used with Target Forwarding Equivalence
Class (FEC) TLV. Section 6.1 addresses use of the new sub-TLVs in
Target FEC TLV in LSP ping and LSP traceroute. For the case of LSP
ping the [I-D.ietf-mpls-spring-lsp-ping] states that:
Initiator MUST include FEC(s) corresponding to the destination
segment.
Initiator, i.e. ingress LSR, MAY include FECs corresponding to
some or all of segments imposed in the label stack by the ingress
LSR to communicate the segments traversed.
It has been noted in [RFC5884] that a BFD session monitors for
defects particular <MPLS LSP, FEC> tuple. [RFC7726] clarified how to
establish and operate mutiple BFD sessions for the same <MPLS LSP,
FEC> tuple. Because only ingress edge router is aware of the SR-
based explicit route egress edge router can associate the LSP ping
with BFD Discriminator TLV with only one of the FECs it advertised
for the particular segment. Thus this document defines that: When
LSP ping is used to bootstrap a BFD session this document updates the
statement and defines that:
When LSP Ping is used to bootstrap a BFD session it MUST include
only one FEC corresponding to the destination segment and SHOULD
NOT include FECs corresponding to some or all of other segments
imposed by the ingress LSR.
Operationally such restriction would not cause any problem or
uncertainty as LSP ping with FECs corresponding to some or all
segments or traceroute that validate the segment route MAY precede
the LSP ping that bootstraps the BFD session.
Encapsulation of a BFD Control packet in Segment Routing network with
MPLS dataplane MUST follow Section 7 [RFC5884] when IP/UDP header
used and MUST follow Section 3.4 [RFC6428] without IP/UDP header
being used.
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3. Use BFD Reverse Path TLV over Segment Routed MPLS tunnel
When a BFD session is used to monitor a source routed unidirectional
path there may be a need to direct egress BFD peer to use specific
path for the reverse direction of the BFD session by using the BFD
Reverse Path TLV [I-D.ietf-mpls-bfd-directed]. For the case of MPLS
dataplane, Segment Routing Architecture
[I-D.ietf-spring-segment-routing] explains that "a segment is encoded
as an MPLS label. An ordered list of segments is encoded as a stack
of labels." Following on that this document defines Segment Routing
with MPLS dataplane sub-TLV that MAY be used with the BFD Reverse
Path TLV [I-D.ietf-mpls-bfd-directed]. The format of the sub-TLV is
presented in Figure 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SegRouting MPLS sub-TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Entry 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Entry 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Entry N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Segment Routing MPLS Tunnel sub-TLV
The Segment Routing Tunnel sub-TLV Type is two octets in length, and
has a value of TBD (to be assigned by IANA as requested in
Section 4).
The egress LSR MUST use the Value field as label stack for BFD
control packets for the BFD session identified by the source IP
address of the MPLS LSP Ping packet and the value in the BFD
Discriminator TLV. Label Entries MUST be in network order.
Exactly one Segment Routing Tunnel sub-TLV MUST be included in the
Reverse Path TLV. If more than one Segment Routing Tunnel sub-TLV is
present in the Reverse Path TLV, then, in order to avoid ambiguity of
which of TLVs to use, the egress BFD peer MUST send Echo Reply with
the received Reverse Path TLVs and set the Return Code to "Too Many
TLVs Detected" [I-D.ietf-mpls-bfd-directed]
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The Segment Routing Tunnel sub-TLV MAY be used in Reply Path TLV
defined in [RFC7110]
4. IANA Considerations
The IANA is requested to assign new sub-TLV type from "Multiprotocol
Label Switching Architecture (MPLS) Label Switched Paths (LSPs) Ping
Parameters - TLVs" registry, "Sub-TLVs for TLV Types 1, 16, and 21"
sub-registry.
+---------+-------------------------------------+---------------+
| Value | Description | Reference |
+---------+-------------------------------------+---------------+
| X (TBD) | Segment Routing MPLS Tunnel sub-TLV | This document |
+---------+-------------------------------------+---------------+
Table 1: New Segment Routing Tunnel sub-TLV
5. Security Considerations
Security considerations discussed in [RFC5880], [RFC5884], [RFC7726],
and [RFC8029] apply to this document.
6. Acknowledgements
TBD
7. Normative References
[I-D.ietf-mpls-bfd-directed]
Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen,
"Bidirectional Forwarding Detection (BFD) Directed Return
Path", draft-ietf-mpls-bfd-directed-06 (work in progress),
April 2017.
[I-D.ietf-mpls-spring-lsp-ping]
Kumar, N., Swallow, G., Pignataro, C., Akiya, N., Kini,
S., Gredler, H., and M. Chen, "Label Switched Path (LSP)
Ping/Trace for Segment Routing Networks Using MPLS
Dataplane", draft-ietf-mpls-spring-lsp-ping-02 (work in
progress), December 2016.
[I-D.ietf-spring-segment-routing]
Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
and R. Shakir, "Segment Routing Architecture", draft-ietf-
spring-segment-routing-11 (work in progress), February
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,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<http://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,
<http://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, <http://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, <http://www.rfc-editor.org/info/rfc5884>.
[RFC6428] Allan, D., Ed., Swallow, G., Ed., and J. Drake, Ed.,
"Proactive Connectivity Verification, Continuity Check,
and Remote Defect Indication for the MPLS Transport
Profile", RFC 6428, DOI 10.17487/RFC6428, November 2011,
<http://www.rfc-editor.org/info/rfc6428>.
[RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord,
"Return Path Specified Label Switched Path (LSP) Ping",
RFC 7110, DOI 10.17487/RFC7110, January 2014,
<http://www.rfc-editor.org/info/rfc7110>.
[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,
<http://www.rfc-editor.org/info/rfc7726>.
[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,
<http://www.rfc-editor.org/info/rfc8029>.
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Author's Address
Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
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