Segment Routing Generic TLV for MPLS Label Switched Path (LSP) Ping/ Traceroute
draft-nainar-mpls-spring-lsp-ping-sr-generic-sid-05
Network Work group N. Nainar, Ed.
Internet-Draft C. Pignataro, Ed.
Intended status: Standards Track Z. Ali
Expires: November 19, 2021 C. Filsfils
Cisco
T. Saad
Juniper
May 18, 2021
Segment Routing Generic TLV for MPLS Label Switched Path (LSP) Ping/
Traceroute
draft-nainar-mpls-spring-lsp-ping-sr-generic-sid-05
Abstract
RFC8402 introduces Segment Routing architecture that leverages source
routing and tunneling paradigms and can be directly applied to the
Multi Protocol Label Switching (MPLS) data plane. A node steers a
packet through a controlled set of instructions called segments, by
prepending the packet with Segment Routing header. SR architecture
defines different types of segments with different forwarding
semantics associated. SR can be applied to the MPLS directly and to
IPv6 dataplane using a new routing header.
RFC8287 defines the extensions to MPLS LSP Ping and Traceroute for
Segment Routing IGP-Prefix and IGP-Adjacency Segment Identifier
(SIDs) with an MPLS data plane. Various SIDs are proposed as part of
SR architecture with different associated instructions that raises a
need to come up with new Target FEC Stack Sub-TLV for each such SIDs.
This document defines a new Target FEC Stack Sub-TLV that is used to
validate the instruction associated with any SID.
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 November 19, 2021.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Challenges with Existing Mechanism . . . . . . . . . . . 3
2. Requirements notation . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Target FEC Stack sub-TLV for Segment Routing SID . . . . . . 4
4.1. Segment Routing Generic Label . . . . . . . . . . . . . . 4
4.2. FEC for Path validation . . . . . . . . . . . . . . . . . 4
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. SID to Interface Mapping . . . . . . . . . . . . . . . . 5
5.2. Initiator behavior . . . . . . . . . . . . . . . . . . . 6
5.2.1. SRGL in Target FEC Stack TLV . . . . . . . . . . . . 6
5.3. Responder behavior . . . . . . . . . . . . . . . . . . . 7
5.4. PHP flag behavior . . . . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
6.1. New Target FEC Stack Sub-TLVs . . . . . . . . . . . . . . 8
6.2. Security Considerations . . . . . . . . . . . . . . . . . 8
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 8
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
[RFC8402] introduces and describes a Segment Routing architecture
that leverages the source routing and tunneling paradigms. A node
steers a packet through a controlled set of instructions called
segments, by prepending the packet with Segment Routing header. A
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detailed definition of the Segment Routing architecture is available
in [RFC8402]
As described in [RFC8402] and [I-D.ietf-spring-segment-routing-mpls],
the Segment Routing architecture can be directly applied to an MPLS
data plane, the Segment identifier (Segment ID) will be of 20-bits
size and the Segment Routing header is the label stack.
1.1. Challenges with Existing Mechanism
[RFC8287] defines the mechanism to perform LSP Ping and Traceroute
for Segment Routing with MPLS data plane. [RFC8287] defines the
Target FEC Stack Sub-TLVs for IGP-Prefix Segment ID and IGP-Adjacency
Segment ID.
There are various other Segment IDs proposed by different documents
that are applicable for SR architecture.
[I-D.ietf-idr-bgp-prefix-sid] defines BGP Prefix Segment ID,
[I-D.ietf-idr-bgpls-segment-routing-epe] defines BGP Peering Segment
ID such as Peer Node SID, Peer Adj SID and Peer Set SID.
[I-D.sivabalan-pce-binding-label-sid] defines Path Binding Segment
ID. As SR evolves for different usecases, we may see more types of
SIDs defined in the future. This raises a need to propose new Target
FEC Stack Sub-TLV for each such Segment ID that may need specific or
network wide software upgrade to support such new Target FEC Stack
Sub-TLVs.
So instead of proposing different Target FEC Stack Sub-TLV for each
SID, this document attempt to propose a SR Generic Label Sub-TLV for
Target FEC Stack TLV with the procedure to validate the associated
instruction.
This document describes the new Target FEC Stack Sub-TLV that carries
the SID and the procedure to use LSP Ping and Traceroute using the
new sub-tlv to support path validation and fault isolation for any SR
Segment IDs. This document neither deprecates any existing Target
FEC Stack Sub-TLVs nor precludes defining new Sub-TLVs in the future.
2. Requirements notation
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 RFC
2119 [RFC2119] RFC 8174 [RFC8174] when and only when, they appear in
all capitals, as shown here.
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3. Terminology
This document uses the terminologies defined in [RFC8402], [RFC8029],
readers are expected to be familiar with it.
4. Target FEC Stack sub-TLV for Segment Routing SID
Following the procedure defined in [RFC8029], below defined Target
FEC Stack Sub-TLV will be included for each labels in the stack. The
below Sub-TLV is defined for Target FEC Stack TLV (Type 1), the
Reverse-Path Target FEC Stack TLV (Type 16), and the Reply Path TLV
(Type 21).
sub-Type Value Field
-------- ---------------
TBD1 Segment Routing Generic Label (SRGL)
4.1. Segment Routing Generic Label
The format of the Sub-TLV is as specified below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SR SID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
SR SID
Carries 20 bits of Segment ID that is used for validating the
instruction.
4.2. FEC for Path validation
In SR architecture, any SID is associated with topology or service
instruction. While the topology instruction steers the packet over
best path or specific path, the service instruction instructs the
type of service to be applied on the packet.
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R3-------R6 L1
/ \ +-------+
/ \ | L2 |
R1----R2 R7------R8
\ /
\ /
R4-------R5
Figure 1: Segment Routing network
The Node Segment IDs for Rx for Algo 0 is 16000x. (Ex: For R1, it is 160001)
The Node Segment IDs for Rx for Algo 128 is 16128x. (Ex: For R1, it is 161281)
9178 --> Adjacency Segment ID from R7 to R8 over link L1.
9278 --> Adjacency Segment ID from R7 to R8 over link L2.
9378 --> Parallel Adjacency Segment ID from R7 to R8 over Link L1 or L2.
9187 --> Adjacency Segment ID from R8 to R7 over link L1.
9287 --> Adjacency Segment ID from R8 to R7 over link L2.
9387 --> Parallel Adjacency Segment ID from R8 to R7 over Link L1 or L2.
The instruction associated with any SID can be validated by verifying
if the segment is terminated on the correct node and optionally
received over the correct incoming interface. In Figure 1, inorder
to validate the SID 9178, R1 can use {(SID=9178)} as FEC in Target
FEC Stack Sub-TLV.
5. Procedures
This section describes the procedure to validate SR Generic Label
Sub-TLV.
5.1. SID to Interface Mapping
Any End point MAY maintain a SID to Interface mapping table that
maintains the below:
o All the local Prefix/Node SID with any SR enabled interface as
incoming interface.
o All the Adj-SIDs assigned by directly connected neighbor nodes
with the relevant interface incoming interface.
In Figure 1, R8 maintains 160008 and 161288 with Incoming interface
as any SR enabled interface. Similarly, R8 maintains 9178 with Link
L1 as incoming interface, 9278 with Link L2 as incoming interface and
9378 with Link L1 or L2 as incoming interface.
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How this mapping is populated and maintained is a local
implementation matter. It can be populated based on the IGP database
or can be based on a query to Path Computation Element (PCE)
controller. The mapping can be persistent or on-demand triggered by
receiving LSP Ping Request.
5.2. Initiator behavior
This section defines the Target FEC Stack TLV construction mechanism
by an initiator when using SR Generic Label Sub-TLV.
Ping
Initiator MUST include FEC(s) corresponding to the destination
segment.
Initiator MAY include FECs corresponding to some or all of
segments imposed in the label stack by the initiator to
communicate the segments traversed.
Traceroute
Initiator MUST initially include FECs corresponding to all of
segments imposed in the label stack.
When a received echo reply contains FEC Stack Change TLV with
one or more of original segment(s) being popped, initiator MAY
remove corresponding FEC(s) from Target FEC Stack TLV in the
next (TTL+1) traceroute request as defined in section 4.6 of
[RFC8029].
When a received echo reply does not contain FEC Stack Change
TLV, initiator MUST NOT attempt to remove FEC(s) from Target
FEC Stack TLV in the next (TTL+1) traceroute request.
5.2.1. SRGL in Target FEC Stack TLV
When the last segment ID in the label stack is IGP Prefix SID, Adj-
SID, Binding SID, BGP Prefix SID or BGP Peering SID, set the SR SID
field to the Segment ID value advertised by the LSP End Point. When
the SID is advertised as index, the Segment ID value MUST be derived
based on the index and the SRGB advertised by the LSP End Point.
How the above values are derived is a local implementation matter.
It can be manually defined using CLI knob while triggering the LSP
Ping Request or can use other mechanisms like querying the local
database.
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5.3. Responder behavior
Step 4a defined in Section 7.4 of [RFC8287] is updated as below:
If the Label-stack-depth is 0 and Target FEC Stack Sub-TLV at FEC-
stack-depth is TBD1 (SRGL) {
* Set the Best-return-code to 10 when the responding node is not
the LSP End Point for SR SID.
* Set the Best-return-code to 35, if Interface-I does not match
the SID to Interface mapping for the received SR SID.
* set FEC-Status to 1, and return.
}
If the Label-stack-depth is greater than 0 and Target FEC Stack
Sub-TLV at FEC-stack-depth is TBD1 (SRGL), {
* If the Label at Label-stack-depth is Imp-null {
+ Set the Best-return-code to 10 when the responding node is
not the LSP End Point for the SR SID.
+ Set the Best-return-code to 35, if Interface-I does not
match the SID to Interface mapping for the received SR SID.
+ set FEC-Status to 1, and return.
}
* Else:
+ Set the Best-return-code to 10 when the index derived from
the label at Label-stack-depth is not advertised by LSP End
Point.
+ set FEC-Status to 1, and return.
}
5.4. PHP flag behavior
Section 7.2 of [RFC8287] explains the behavior for FEC stack change
for Adjacency Segment ID. The same procedure is applicable for BGP
Peering SID as well.
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6. IANA Considerations
6.1. New Target FEC Stack Sub-TLVs
IANA is requested to assign three new Sub-TLVs from "Sub-TLVs for TLV
Types 1, 16 and 21" sub-registry from the "Multi-Protocol Label
Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
[IANA-MPLS-LSP-PING] registry.
Sub-Type Sub-TLV Name Reference
-------- ----------------- ------------
TBD1 Segment Routing Generic Label Section 4.1 of this document
6.2. Security Considerations
This document defines additional MPLS LSP Ping Sub-TLVs and follows
the mechanisms defined in [RFC8029]. All the security considerations
defined in [RFC8029] will be applicable for this document, and in
addition, they do not impose any additional security challenges to be
considered.
7. Acknowledgement
TBD
8. Contributors
Danial Johari, Cisco Systems
9. References
9.1. Normative References
[I-D.ietf-idr-bgp-prefix-sid]
Previdi, S., Filsfils, C., Lindem, A., Sreekantiah, A.,
and H. Gredler, "Segment Routing Prefix Segment Identifier
Extensions for BGP", draft-ietf-idr-bgp-prefix-sid-27
(work in progress), June 2018.
[I-D.ietf-idr-bgpls-segment-routing-epe]
Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray,
S., and J. Dong, "BGP-LS extensions for Segment Routing
BGP Egress Peer Engineering", draft-ietf-idr-bgpls-
segment-routing-epe-19 (work in progress), May 2019.
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[I-D.sivabalan-pce-binding-label-sid]
Sivabalan, S., Filsfils, C., Tantsura, J., Hardwick, J.,
Previdi, S., and C. Li, "Carrying Binding Label/Segment-ID
in PCE-based Networks.", draft-sivabalan-pce-binding-
label-sid-07 (work in progress), July 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>.
[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>.
[RFC8287] Kumar, N., Ed., Pignataro, C., Ed., Swallow, G., Akiya,
N., Kini, S., and M. Chen, "Label Switched Path (LSP)
Ping/Traceroute for Segment Routing (SR) IGP-Prefix and
IGP-Adjacency Segment Identifiers (SIDs) with MPLS Data
Planes", RFC 8287, DOI 10.17487/RFC8287, December 2017,
<https://www.rfc-editor.org/info/rfc8287>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
9.2. Informative References
[I-D.ietf-spring-segment-routing-mpls]
Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
Litkowski, S., and R. Shakir, "Segment Routing with the
MPLS Data Plane", draft-ietf-spring-segment-routing-
mpls-22 (work in progress), May 2019.
[IANA-MPLS-LSP-PING]
IANA, "Multi-Protocol Label Switching (MPLS) Label
Switched Paths (LSPs) Ping Parameters",
<http://www.iana.org/assignments/mpls-lsp-ping-parameters/
mpls-lsp-ping-parameters.xhtml>.
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Authors' Addresses
Nagendra Kumar Nainar (editor)
Cisco Systems, Inc.
7200-12 Kit Creek Road
Research Triangle Park, NC 27709-4987
US
Email: naikumar@cisco.com
Carlos Pignataro (editor)
Cisco Systems, Inc.
7200-11 Kit Creek Road
Research Triangle Park, NC 27709-4987
US
Email: cpignata@cisco.com
Zafar Ali
Cisco Systems, Inc.
Email: zali@cisco.com
Clarence Filsfils
Cisco Systems, Inc.
Email: cfilsfil@cisco.com
Tarek Saad
Juniper Networks
Email: tsaad@juniper.net
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