PCE Working Group C. Li
Internet-Draft Huawei Technologies
Intended status: Standards Track M. Negi
Expires: January 4, 2021 RtBrick Inc
M. Koldychev
Cisco Systems, Inc.
P. Kaladharan
RtBrick Inc
Y. Zhu
China Telecom
July 3, 2020
PCEP Extensions for Segment Routing leveraging the IPv6 data plane
draft-ietf-pce-segment-routing-ipv6-06
Abstract
The Source Packet Routing in Networking (SPRING) architecture
describes how Segment Routing (SR) can be used to steer packets
through an IPv6 or MPLS network using the source routing paradigm.
SR enables any head-end node to select any path without relying on a
hop-by-hop signaling technique (e.g., LDP or RSVP-TE).
It depends only on "segments" that are advertised by Link- State
IGPs. A Segment Routed Path can be derived from a variety of
mechanisms, including an IGP Shortest Path Tree (SPT), explicit
configuration, or a Path Computation Element (PCE).
Since SR can be applied to both MPLS and IPv6 forwarding plane, a PCE
should be able to compute SR-Path for both MPLS and IPv6 forwarding
plane. This document describes the extensions required for SR
support for IPv6 data plane in Path Computation Element communication
Protocol (PCEP). The PCEP extension and mechanism to support SR-MPLS
is described in RFC 8664. This document extends it to support SRv6
(SR over IPv6).
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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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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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 January 4, 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
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview of PCEP Operation in SRv6 Networks . . . . . . . . . 5
3.1. Operation Overview . . . . . . . . . . . . . . . . . . . 6
3.2. SRv6-Specific PCEP Message Extensions . . . . . . . . . . 6
4. Object Formats . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. The OPEN Object . . . . . . . . . . . . . . . . . . . . . 7
4.1.1. The SRv6 PCE Capability sub-TLV . . . . . . . . . . . 7
4.2. The RP/SRP Object . . . . . . . . . . . . . . . . . . . . 8
4.3. ERO . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.3.1. SRv6-ERO Subobject . . . . . . . . . . . . . . . . . 9
4.4. RRO . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.4.1. SRv6-RRO Subobject . . . . . . . . . . . . . . . . . 11
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 12
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5.1. Exchanging the SRv6 Capability . . . . . . . . . . . . . 12
5.2. ERO Processing . . . . . . . . . . . . . . . . . . . . . 13
5.2.1. SRv6 ERO Validation . . . . . . . . . . . . . . . . . 13
5.2.2. Interpreting the SRv6-ERO . . . . . . . . . . . . . . 14
5.3. RRO Processing . . . . . . . . . . . . . . . . . . . . . 14
6. Security Considerations . . . . . . . . . . . . . . . . . . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7.1. PCEP ERO and RRO subobjects . . . . . . . . . . . . . . . 15
7.2. New SRv6-ERO Flag Registry . . . . . . . . . . . . . . . 15
7.3. PATH-SETUP-TYPE-CAPABILITY Sub-TLV Type Indicators . . . 16
7.4. SRv6 PCE Capability Flags . . . . . . . . . . . . . . . . 16
7.5. New Path Setup Type . . . . . . . . . . . . . . . . . . . 17
7.6. ERROR Objects . . . . . . . . . . . . . . . . . . . . . . 17
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Contributor . . . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
As per [RFC8402], with Segment Routing (SR), a node steers a packet
through an ordered list of instructions, called segments. A segment
can represent any instruction, topological or service-based. A
segment can have a semantic local to an SR node or global within an
SR domain. SR allows to enforce a flow through any path and service
chain while maintaining per-flow state only at the ingress node of
the SR domain. Segments can be derived from different components:
IGP, BGP, Services, Contexts, Locater, etc. The list of segment
forming the path is called the Segment List and is encoded in the
packet header. Segment Routing can be applied to the IPv6
architecture with the Segment Routing Header (SRH) [RFC8754]. A
segment is encoded as an IPv6 address. An ordered list of segments
is encoded as an ordered list of IPv6 addresses in the routing
header. The active segment is indicated by the Destination Address
of the packet. Upon completion of a segment, a pointer in the new
routing header is incremented and indicates the next segment.
Segment Routing use cases are described in [RFC7855] and [RFC8354].
Segment Routing protocol extensions are defined in [RFC8667], and
[RFC8666].
As per [RFC8754], an SRv6 Segment is a 128-bit value. "SRv6 SID" or
simply "SID" are often used as a shorter reference for "SRv6
Segment". Further details are in an illustration provided in
[I-D.ietf-spring-srv6-network-programming].
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The SR architecture can be applied to the MPLS forwarding plane
without any change, in which case an SR path corresponds to an MPLS
Label Switching Path (LSP). The SR is applied to IPV6 forwarding
plane using SRH. A SR path can be derived from an IGP Shortest Path
Tree (SPT), but SR-TE paths may not follow IGP SPT. Such paths may
be chosen by a suitable network planning tool, or a PCE and
provisioned on the ingress node.
[RFC5440] describes Path Computation Element communication Protocol
(PCEP) for communication between a Path Computation Client (PCC) and
a Path Computation Element (PCE) or between a pair of PCEs. A PCE or
a PCC operating as a PCE (in hierarchical PCE environment) computes
paths for MPLS Traffic Engineering LSPs (MPLS-TE LSPs) based on
various constraints and optimization criteria. [RFC8231] specifies
extensions to PCEP that allow a stateful PCE to compute and recommend
network paths in compliance with [RFC4657] and defines objects and
TLVs for MPLS-TE LSPs. Stateful PCEP extensions provide
synchronization of LSP state between a PCC and a PCE or between a
pair of PCEs, delegation of LSP control, reporting of LSP state from
a PCC to a PCE, controlling the setup and path routing of an LSP from
a PCE to a PCC. Stateful PCEP extensions are intended for an
operational model in which LSPs are configured on the PCC, and
control over them is delegated to the PCE.
A mechanism to dynamically initiate LSPs on a PCC based on the
requests from a stateful PCE or a controller using stateful PCE is
specified in [RFC8281]. As per [RFC8664], it is possible to use a
stateful PCE for computing one or more SR-TE paths taking into
account various constraints and objective functions. Once a path is
chosen, the stateful PCE can initiate an SR-TE path on a PCC using
PCEP extensions specified in [RFC8281] using the SR specific PCEP
extensions specified in [RFC8664]. [RFC8664] specifies PCEP
extensions for supporting a SR-TE LSP for MPLS data plane. This
document extends [RFC8664] to support SR for IPv6 data plane.
Additionally, using procedures described in this document, a PCC can
request an SRv6 path from either stateful or a stateless PCE. This
specification relies on the PATH-SETUP-TYPE TLV and procedures
specified in [RFC8408].
This specification provides a mechanism for a network controller
(acting as a PCE) to instantiate candidate paths for an SR Policy
onto a head-end node (acting as a PCC) using PCEP. For more
information on the SR Policy Architecture, see
[I-D.ietf-spring-segment-routing-policy].
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2. Terminology
This document uses the following terms defined in [RFC5440]: PCC,
PCE, PCEP Peer.
This document uses the following terms defined in [RFC8051]: Stateful
PCE, Delegation.
The message formats in this document are specified using Routing
Backus-Naur Format (RBNF) encoding as specified in [RFC5511].
NAI: Node or Adjacency Identifier.
PCC: Path Computation Client.
PCE: Path Computation Element.
PCEP: Path Computation Element Protocol.
SR: Segment Routing.
SID: Segment Identifier.
SRv6: Segment Routing for IPv6 forwarding plane.
SRH: IPv6 Segment Routing Header.
SR Path: IPv6 Segment List (List of IPv6 SIDs representing a path in
IPv6 SR domain)
Further, note that the term LSP used in the PCEP specifications,
would be equivalent to a SRv6 Path (represented as a list of SRv6
segments) in the context of supporting SRv6 in PCEP.
3. Overview of PCEP Operation in SRv6 Networks
Basic operations for PCEP speakers is as per [RFC8664]. SRv6 Paths
computed by a PCE can be represented as an ordered list of SRv6
segments of 128-bit value. "SRv6 SID" or simply "SID" are often used
as a shorter reference for "SRv6 Segment" in this document.
[RFC8664] defined a new Explicit Route Object (ERO) subobject denoted
by "SR-ERO subobject" capable of carrying a SID as well as the
identity of the node/adjacency represented by the SID. SR-capable
PCEP speakers should be able to generate and/or process such ERO
subobject. An ERO containing SR-ERO subobjects can be included in
the PCEP Path Computation Reply (PCRep) message defined in [RFC5440],
the PCEP LSP Initiate Request message (PCInitiate) defined in
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[RFC8281], as well as in the PCEP LSP Update Request (PCUpd) and PCEP
LSP State Report (PCRpt) messages defined in defined in [RFC8231].
This document define new subobjects "SRv6-ERO" and "SRv6-RRO" in ERO
and RRO respectively to carry SRv6 SID (IPv6 Address). SRv6-capable
PCEP speakers MUST be able to generate and/or process this.
When a PCEP session between a PCC and a PCE is established, both PCEP
speakers exchange their capabilities to indicate their ability to
support SRv6 specific functionality.
In summary, this document:
o Defines a new PCEP capability for SRv6.
o Defines a new subobject SRv6-ERO in ERO.
o Defines a new subobject SRv6-RRO in RRO.
o Defines a new path setup type carried in the PATH-SETUP-TYPE TLV
and the PATH-SETUP-TYPE-CAPABILITY TLV.
3.1. Operation Overview
In SR networks, an ingress node of an SR path appends all outgoing
packets with an SR header consisting of a list of SIDs (IPv6 Prefix
in case of SRv6). The header has all necessary information to guide
the packets from the ingress node to the egress node of the path, and
hence there is no need for any signaling protocol.
For IPv6 in control plane with MPLS data-plane, mechanism remains
same as [RFC8664]
This document describes extensions to SR path for IPv6 data plane.
SRv6 Path (i.e. ERO) consists of an ordered set of SRv6 SIDs(see
details in Figure 2).
A PCC or PCE indicates its ability to support SRv6 during the PCEP
session Initialization Phase via a new SRv6-PCE-CAPABILITY sub-TLV
(see details in Section 4.1.1).
3.2. SRv6-Specific PCEP Message Extensions
As defined in [RFC5440], a PCEP message consists of a common header
followed by a variable length body made up of mandatory and/or
optional objects. This document does not require any changes in the
format of PCReq and PCRep messages specified in [RFC5440], PCInitiate
message specified in [RFC8281], and PCRpt and PCUpd messages
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specified in [RFC8231]. However, PCEP messages pertaining to SRv6
MUST include PATH-SETUP-TYPE TLV in the RP or SRP object to clearly
identify that SRv6 is intended.
4. Object Formats
4.1. The OPEN Object
4.1.1. The SRv6 PCE Capability sub-TLV
This document defines a new Path Setup Type (PST) [RFC8408] for SRv6,
as follows:
o PST = TBD2: Path is setup using SRv6.
A PCEP speaker MUST indicate its support of the function described in
this document by sending a PATH-SETUP-TYPE-CAPABILITY TLV in the OPEN
object with this new PST included in the PST list.
This document also defines the SRv6-PCE-CAPABILITY sub-TLV. PCEP
speakers use this sub-TLV to exchange information about their SRv6
capability. If a PCEP speaker includes PST=TBD2 in the PST List of
the PATH-SETUP-TYPE-CAPABILITY TLV then it MUST also include the
SRv6-PCE-CAPABILITY sub-TLV inside the PATH-SETUP-TYPE-CAPABILITY
TLV.
The format of the SRv6-PCE-CAPABILITY sub-TLV is shown in the
following figure:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=TBD1 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |N|X|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value | MSD-Type | MSD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ... //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SRv6-PCE-CAPABILITY sub-TLV format
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The code point for the TLV type (TBD1) is to be defined by IANA. The
TLV length is variable.
The value comprises of -
Reserved: 2 octet, this field MUST be set to 0 on transmission,
and ignored on receipt.
Flags: 2 octet, two bits are currently assigned in this document.
N bit: A PCC sets this flag bit to 1 to indicate that it is
capable of resolving a Node or Adjacency Identifier (NAI) to a
SRv6-SID.
X bit: A PCC sets this bit to 1 to indicate that it does not
impose any limit on MSD (irrespective of the MSD-Type).
Unassigned bits MUST be set to 0 and ignored on receipt.
A pair of (MSD-Type, MSD-Value): Where MSD-Type (1 octet) is as
per the IGP MSD Type registry created by [RFC8491] and populated
with SRv6 MSD types as per [I-D.ietf-lsr-isis-srv6-extensions];
MSD-Value (1 octet) is as per [RFC8491].
This sub-TLV format is compliant with the PCEP TLV format defined in
[RFC5440]. That is, the sub-TLV is composed of 2 octets for the
type, 2 octets specifying the length, and a Value field. The Type
field when set to TBD1 identifies the SRv6-PCE-CAPABILITY sub-TLV and
the presence of the sub-TLV indicates the support for the SRv6 paths
in PCEP. The Length field defines the length of the value portion in
octets. The TLV is padded to 4-octet alignment, and padding is not
included in the Length field. The number of (MSD-Type,MSD-Value)
pairs can be determined from the Length field of the TLV.
4.2. The RP/SRP Object
In order to indicate the SRv6 path, RP or SRP object MUST include the
PATH-SETUP-TYPE TLV specified in [RFC8408]. This document defines a
new Path Setup Type (PST=TBD2) for SRv6.
The LSP-IDENTIFIERS TLV MAY be present for the above PST type.
4.3. ERO
In order to support SRv6, new subobject "SRv6-ERO" is defined in ERO.
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4.3.1. SRv6-ERO Subobject
An SRv6-ERO subobject is formatted as shown in the following figure.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type=TBD3 | Length | NT | Flags |F|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Endpoint Behavior |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SRv6 SID (optional) |
| (128-bit) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// NAI (variable, optional) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SRv6-ERO Subobject Format
The fields in the SRv6-ERO Subobject are as follows:
The 'L' Flag: Indicates whether the subobject represents a loose-hop
(see [RFC3209]). If this flag is set to zero, a PCC MUST NOT
overwrite the SID value present in the SRv6-ERO subobject.
Otherwise, a PCC MAY expand or replace one or more SID values in the
received SRv6-ERO based on its local policy.
Type: indicates the content of the subobject, i.e. when the field is
set to TBD3, the suboject is a SRv6-ERO subobject representing a SRv6
SID.
Length: Contains the total length of the subobject in octets. The
Length MUST be at least 24, and MUST be a multiple of 4. An SRv6-ERO
subobject MUST contain at least one of a SRv6-SID or an NAI. The S
and F bit in the Flags field indicates whether the SRv6-SID or NAI
fields are absent.
NAI Type (NT): Indicates the type and format of the NAI contained in
the object body, if any is present. If the F bit is set to zero (see
below) then the NT field has no meaning and MUST be ignored by the
receiver. This document reuses NT types defined in [RFC8664]:
If NT value is 0, the NAI MUST NOT be included.
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When NT value is 2, the NAI is as per the 'IPv6 Node ID' format
defined in [RFC8664], which specifies an IPv6 address. This is
used to identify the owner of the SRv6 Identifier. This is
optional, as the LOC (the locater portion) of the SRv6 SID serves
a similar purpose (when present).
When NT value is 4, the NAI is as per the 'IPv6 Adjacency' format
defined in [RFC8664], which specify a pair of IPv6 addresses.
This is used to identify the IPv6 Adjacency and used with the SRv6
Adj-SID.
When NT value is 6, the NAI is as per the 'link-local IPv6
addresses' format defined in [RFC8664], which specify a pair of
(global IPv6 address, interface ID) tuples. It is used to
identify the IPv6 Adjacency and used with the SRv6 Adj-SID.
SR-MPLS specific NT types are not valid in SRv6-ERO.
Flags: Used to carry additional information pertaining to the
SRv6-SID. This document defines the following flag bits. The other
bits MUST be set to zero by the sender and MUST be ignored by the
receiver.
o S: When this bit is set to 1, the SRv6-SID value in the subobject
body is absent. In this case, the PCC is responsible for choosing
the SRv6-SID value, e.g., by looking up in the SR-DB using the NAI
which, in this case, MUST be present in the subobject. If the S
bit is set to 1 then F bit MUST be set to zero.
o F: When this bit is set to 1, the NAI value in the subobject body
is absent. The F bit MUST be set to 1 if NT=0, and otherwise MUST
be set to zero. The S and F bits MUST NOT both be set to 1.
Reserved: MUST be set to zero while sending and ignored on receipt.
Endpoint Behavior: A 16 bit field representing the behavior
associated with the SRv6 SIDs. This information is optional and
plays no role in the fields in SRH imposed on the packet. It could
be used for maintainability and diagnostic purpose. If behavior is
not known, 0 is used. The list of Endpoint behavior are defined in
[I-D.ietf-spring-srv6-network-programming].
SRv6 SID: SRv6 Identifier is the 128 bit IPv6 addresses representing
the SRv6 segment.
NAI: The NAI associated with the SRv6-SID. The NAI's format depends
on the value in the NT field, and is described in [RFC8664].
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At least one of the SRv6-SID or the NAI MUST be included in the
SRv6-ERO subobject, and both MAY be included.
4.4. RRO
In order to support SRv6, new subobject "SRv6-RRO" is defined in RRO.
4.4.1. SRv6-RRO Subobject
A PCC reports an SRv6 path to a PCE by sending a PCRpt message, per
[RFC8231]. The RRO on this message represents the SID list that was
applied by the PCC, that is, the actual path taken. The procedures
of [RFC8664] with respect to the RRO apply equally to this
specification without change.
An RRO contains one or more subobjects called "SRv6-RRO subobjects"
whose format is shown 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=TBD4 | Length | NT | Flags |F|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Endpoint Behavior |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SRv6 SID |
| (128-bit) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// NAI (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: SRv6-RRO Subobject Format
The format of the SRv6-RRO subobject is the same as that of the
SRv6-ERO subobject, but without the L flag.
Ordering of SRv6-RRO subobjects by PCC in PCRpt message remains as
per [RFC8664].
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5. Procedures
5.1. Exchanging the SRv6 Capability
A PCC indicates that it is capable of supporting the head-end
functions for SRv6 by including the SRv6-PCE-CAPABILITY sub-TLV in
the Open message that it sends to a PCE. A PCE indicates that it is
capable of computing SRv6 paths by including the SRv6-PCE-CAPABILITY
sub-TLV in the Open message that it sends to a PCC.
If a PCEP speaker receives a PATH-SETUP-TYPE-CAPABILITY TLV with a
PST list containing PST=TBD2, but the SRv6-PCE-CAPABILITY sub-TLV is
absent, then the PCEP speaker MUST send a PCErr message with Error-
Type 10 (Reception of an invalid object) and Error-Value TBD5 (to be
assigned by IANA) (Missing PCE-SRv6-CAPABILITY sub-TLV) and MUST then
close the PCEP session. If a PCEP speaker receives a PATH-SETUP-
TYPE-CAPABILITY TLV with a SRv6-PCE-CAPABILITY sub-TLV, but the PST
list does not contain PST=TBD2, then the PCEP speaker MUST ignore the
SRv6-PCE-CAPABILITY sub-TLV.
The number of SRv6 SIDs that can be imposed on a packet depends on
the PCC's IPv6 data plane's capability. If a PCC sets the X flag to
1 then the MSD is not used and MUST NOT be included. If a PCE
receives an SRv6-PCE-CAPABILITY sub-TLV with the X flag set to 1 then
it MUST ignore any MSD-Type, MSD-Value fields and MUST assume that
the sender can impose any length of SRH. If a PCC sets the X flag to
zero, then it sets the SRv6 MSD-Type, MSD-Value fields that it can
impose on a packet. If a PCE receives an SRv6-PCE-CAPABILITY sub-TLV
with the X flag and SRv6 MSD-Type, MSD-Value fields both set to zero
then it is considered as an error and the PCE MUST respond with a
PCErr message (Error-Type=1 "PCEP session establishment failure" and
Error-Value=1 "reception of an invalid Open message or a non Open
message."). In case the MSD-Type in SRv6-PCE-CAPABILITY sub-TLV
received by the PCE does not correspond to one of the SRv6 MSD types,
the PCE MUST respond with a PCErr message (Error-Type=1 "PCEP session
establishment failure" and Error-Value=1 "reception of an invalid
Open message or a non Open message.").
Note that the MSD-Type, MSD-Value exchanged via the SRv6-PCE-
CAPABILITY sub-TLV indicates the SRv6 SID imposition limit for the
PCC node. However, if a PCE learns these via different means, e.g
routing protocols, as specified in:
[I-D.li-ospf-ospfv3-srv6-extensions];
[I-D.ietf-lsr-isis-srv6-extensions]; [I-D.ietf-idr-bgpls-srv6-ext],
then it ignores the values in the SRv6-PCE-CAPABILITY sub-TLV.
Furthermore, whenever a PCE learns the other advanced SRv6 MSD via
different means, it MUST use that value regardless of the values
exchanged in the SRv6-PCE-CAPABILITY sub-TLV.
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Once an SRv6-capable PCEP session is established with a non-zero SRv6
MSD value, the corresponding PCE MUST NOT send SRv6 paths with a
number of SIDs exceeding that SRv6 MSD value (based on the SRv6 MSD
Type). If a PCC needs to modify the SRv6 MSD value, it MUST close
the PCEP session and re-establish it with the new value. If a PCEP
session is established with a non-zero SRv6 MSD value, and the PCC
receives an SRv6 path containing more SIDs than specified in the SRv6
MSD value (based on the SRv6 MSD type), the PCC MUST send a PCErr
message with Error-Type 10 (Reception of an invalid object) and
Error-Value 3 (Unsupported number of Segment ERO subobjects). If a
PCEP session is established with an SRv6 MSD value of zero, then the
PCC MAY specify an SRv6 MSD for each path computation request that it
sends to the PCE, by including a "maximum SID depth" metric object on
the request similar to [RFC8664].
The N flag, X flag and (MSD-Type,MSD-Value) pair inside the SRv6-PCE-
CAPABILITY sub-TLV are meaningful only in the Open message sent from
a PCC to a PCE. As such, a PCE MUST set the flags to zero and not
include any (MSD-Type,MSD-Value) pair in the SRv6-PCE-CAPABILITY sub-
TLV in an outbound message to a PCC. Similarly, a PCC MUST ignore
N,X flag and any (MSD-Type,MSD-Value) pair received from a PCE. If a
PCE receives multiple SRv6-PCE-CAPABILITY sub-TLVs in an Open
message, it processes only the first sub-TLV received.
5.2. ERO Processing
The ERO processing remains as per [RFC5440] and [RFC8664].
5.2.1. SRv6 ERO Validation
If a PCC does not support the SRv6 PCE Capability and thus cannot
recognize the SRv6-ERO or SRv6-RRO subobjects, it will respond
according to the rules for a malformed object per [RFC5440].
On receiving an SRv6-ERO, a PCC MUST validate that the Length field,
the S bit, the F bit and the NT field are consistent, as follows.
o If NT=0, the F bit MUST be 1, the S bit MUST be zero and the
Length MUST be 24.
o If NT=2, the F bit MUST be zero. If the S bit is 1, the Length
MUST be 24, otherwise the Length MUST be 40.
o If NT=4, the F bit MUST be zero. If the S bit is 1, the Length
MUST be 40, otherwise the Length MUST be 56.
o If NT=6, the F bit MUST be zero. If the S bit is 1, the Length
MUST be 48, otherwise the Length MUST be 64.
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o NT types (1,3, and 5) are not valid for SRv6.
If a PCC finds that the NT field, Length field, S bit and F bit are
not consistent, it MUST consider the entire ERO invalid and MUST send
a PCErr message with Error-Type = 10 ("Reception of an invalid
object") and Error-Value = 11 ("Malformed object").
If a PCEP speaker that does not recognize the NT value received in
SRv6-ERO subobject, it would behave as per [RFC8664].
In case a PCEP speaker receives the SRv6-ERO subobject, when the PST
is not set to TBD2 or SRv6-PCE-CAPABILITY sub-TLV was not exchanged,
it MUST send a PCErr message with Error-Type = 19 ("Invalid
Operation") and Error-Value = TBD5 ("Attempted SRv6 when the
capability was not advertised").
If a PCC receives a list of SRv6 segments, and the number of SRv6
segments exceeds the SRv6 MSD that the PCC can impose on the packet
(SRH), it MUST send a PCErr message with Error-Type = 10 ("Reception
of an invalid object") and Error-Value = TBD ("Unsupported number of
Segment ERO subobjects") as per [RFC8664].
When a PCEP speaker detects that all subobjects of ERO are not of
type TBD3, and if it does not handle such ERO, it MUST send a PCErr
message with Error-Type = 10 ("Reception of an invalid object") and
Error-Value = TBD ("Non-identical ERO subobjects")as per [RFC8664].
5.2.2. Interpreting the SRv6-ERO
The SRv6-ERO contains a sequence of subobjects. According to
[I-D.ietf-spring-segment-routing-policy], each SRv6-ERO subobject in
the sequence identifies a segment that the traffic will be directed
to, in the order given. That is, the first subobject identifies the
first segment the traffic will be directed to, the second SRv6-ERO
subobject represents the second segment, and so on.
The PCC interprets the SRv6-ERO by converting it to an SRv6 SRH plus
a next hop. The PCC sends packets along the segment routed path by
prepending the SRH onto the packets and sending the resulting,
modified packet to the next hop.
5.3. RRO Processing
The syntax checking rules that apply to the SRv6-RRO subobject are
identical to those of the SRv6-ERO subobject, except as noted below.
If a PCEP speaker receives an SRv6-RRO subobject in which both SRv6
SID and NAI are absent, it MUST consider the entire RRO invalid and
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send a PCErr message with Error-Type = 10 ("Reception of an invalid
object") and Error-Value = TBD6 ("Both SID and NAI are absent in
SRv6-RRO subobject").
If a PCE detects that the subobjects of an RRO are a mixture of
SRv6-RRO subobjects and subobjects of other types, then it MUST send
a PCErr message with Error-Type = 10 ("Reception of an invalid
object") and Error-Value = TBD7 ("RRO mixes SRv6-RRO subobjects with
other subobject types").
6. Security Considerations
The security considerations described in [RFC5440], [RFC8231] and
[RFC8281], [RFC8664], are applicable to this specification. No
additional security measure is required.
7. IANA Considerations
7.1. PCEP ERO and RRO subobjects
This document defines a new subobject type for the PCEP explicit
route object (ERO), and a new subobject type for the PCEP record
route object (RRO). The code points for subobject types of these
objects is maintained in the RSVP parameters registry, under the
EXPLICIT_ROUTE and ROUTE_RECORD objects. IANA is requested to
allocate code-points in the RSVP Parameters registry for each of the
new subobject types defined in this document.
Object Subobject Subobject Type
--------------------- -------------------------- ------------------
EXPLICIT_ROUTE SRv6-ERO (PCEP-specific) TBD3
ROUTE_RECORD SRv6-RRO (PCEP-specific) TBD4
7.2. New SRv6-ERO Flag Registry
IANA is requested to create a new sub-registry, named "SRv6-ERO Flag
Field", within the "Path Computation Element Protocol (PCEP) Numbers"
registry to manage the Flag field of the SRv6-ERO subobject. New
values are to be assigned by Standards Action [RFC8126]. Each bit
should be tracked with the following qualities:
o Bit number (counting from bit 0 as the most significant bit)
o Capability description
o Defining RFC
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The following values are defined in this document:
Bit Description Reference
----- ------------------ --------------
0-9 Unassigned
10 NAI is absent (F) This document
11 SID is absent (S) This document
7.3. PATH-SETUP-TYPE-CAPABILITY Sub-TLV Type Indicators
IANA maintains a sub-registry, named "PATH-SETUP-TYPE-CAPABILITY Sub-
TLV Type Indicators", within the "Path Computation Element Protocol
(PCEP) Numbers" registry to manage the type indicator space for sub-
TLVs of the PATH-SETUP-TYPE-CAPABILITY TLV. IANA is requested to
make the following assignment:
Value Meaning Reference
----- ------- ---------
TBD1 SRv6-PCE-CAPABILITY This Document
7.4. SRv6 PCE Capability Flags
IANA is requested to create a new sub-registry, named "SRv6
Capability Flag Field", within the "Path Computation Element Protocol
(PCEP) Numbers" registry to manage the Flag field of the SRv6-PCE-
CAPABILITY sub-TLV. New values are to be assigned by Standards
Action [RFC8126]. Each bit should be tracked with the following
qualities:
o Bit number (counting from bit 0 as the most significant bit)
o Capability description
o Defining RFC
The following values are defined in this document:
Bit Description Reference
0-13 Unassigned
14 Node or Adjacency This document
Identifier (NAI) is
supported (N)
15 Unlimited Maximum SID This document
Depth (X)
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7.5. New Path Setup Type
[RFC8408] created a sub-registry within the "Path Computation Element
Protocol (PCEP) Numbers" registry called "PCEP Path Setup Types".
IANA is requested to allocate a new code point within this registry,
as follows:
Value Description Reference
----- ----------- ---------
TBD2 Traffic engineering path is This Document
setup using SRv6.
7.6. ERROR Objects
IANA is requested to allocate code-points in the PCEP-ERROR Object
Error Types and Values registry for the following new error-values:
Error-Type Meaning
---------- -------
10 Reception of an invalid object
Error-value = TBD5 (Missing
PCE-SRv6-CAPABILITY sub-TLV)
Error-value = TBD6 (Both SID and NAI are absent
in SRv6-RRO subobject)
Error-value = TBD7 (RRO mixes SRv6-RRO subobjects
with other subobject types)
19 Invalid Operation
Error-value = TBD5 (Attempted SRv6 when the
capability was not advertised)
8. Acknowledgements
The authors would like to thank Jeff Tentsura, Adrian Farrel, Aijun
Wang and Khasanov Boris for valuable suggestions.
9. References
9.1. 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>.
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[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC5511] Farrel, A., "Routing Backus-Naur Form (RBNF): A Syntax
Used to Form Encoding Rules in Various Routing Protocol
Specifications", RFC 5511, DOI 10.17487/RFC5511, April
2009, <https://www.rfc-editor.org/info/rfc5511>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[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>.
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>.
[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>.
[RFC8408] Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J.
Hardwick, "Conveying Path Setup Type in PCE Communication
Protocol (PCEP) Messages", RFC 8408, DOI 10.17487/RFC8408,
July 2018, <https://www.rfc-editor.org/info/rfc8408>.
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[RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
DOI 10.17487/RFC8491, November 2018,
<https://www.rfc-editor.org/info/rfc8491>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
[I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extension to Support Segment Routing over
IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-08
(work in progress), April 2020.
[I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
Matsushima, S., and Z. Li, "SRv6 Network Programming",
draft-ietf-spring-srv6-network-programming-16 (work in
progress), June 2020.
9.2. Informative References
[RFC4657] Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol Generic
Requirements", RFC 4657, DOI 10.17487/RFC4657, September
2006, <https://www.rfc-editor.org/info/rfc4657>.
[RFC7855] Previdi, S., Ed., Filsfils, C., Ed., Decraene, B.,
Litkowski, S., Horneffer, M., and R. Shakir, "Source
Packet Routing in Networking (SPRING) Problem Statement
and Requirements", RFC 7855, DOI 10.17487/RFC7855, May
2016, <https://www.rfc-editor.org/info/rfc7855>.
[RFC8051] Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
Stateful Path Computation Element (PCE)", RFC 8051,
DOI 10.17487/RFC8051, January 2017,
<https://www.rfc-editor.org/info/rfc8051>.
[RFC8354] Brzozowski, J., Leddy, J., Filsfils, C., Maglione, R.,
Ed., and M. Townsley, "Use Cases for IPv6 Source Packet
Routing in Networking (SPRING)", RFC 8354,
DOI 10.17487/RFC8354, March 2018,
<https://www.rfc-editor.org/info/rfc8354>.
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[RFC8666] Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions
for Segment Routing", RFC 8666, DOI 10.17487/RFC8666,
December 2019, <https://www.rfc-editor.org/info/rfc8666>.
[RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
Extensions for Segment Routing", RFC 8667,
DOI 10.17487/RFC8667, December 2019,
<https://www.rfc-editor.org/info/rfc8667>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-07 (work in progress),
May 2020.
[I-D.li-ospf-ospfv3-srv6-extensions]
Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak,
"OSPFv3 Extensions for SRv6", draft-li-ospf-
ospfv3-srv6-extensions-07 (work in progress), November
2019.
[I-D.ietf-idr-bgpls-srv6-ext]
Dawra, G., Filsfils, C., Talaulikar, K., Chen, M.,
daniel.bernier@bell.ca, d., and B. Decraene, "BGP Link
State Extensions for SRv6", draft-ietf-idr-bgpls-
srv6-ext-02 (work in progress), January 2020.
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Appendix A. Contributor
The following persons contributed to this document:
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
EMail: dhruv.ietf@gmail.com
Huang Wumin
Huawei Technologies
Huawei Building, No. 156 Beiqing Rd.
Beijing 100095
China
Email: huangwumin@huawei.com
Shuping Peng
Huawei Technologies
Huawei Building, No. 156 Beiqing Rd.
Beijing 100095
China
Email: pengshuping@huawei.com
Authors' Addresses
Cheng Li(Editor)
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
EMail: c.l@huawei.com
Mahendra Singh Negi
RtBrick Inc
Bangalore, Karnataka
India
EMail: mahend.ietf@gmail.com
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Mike Koldychev
Cisco Systems, Inc.
Canada
EMail: mkoldych@cisco.com
Prejeeth Kaladharan
RtBrick Inc
Bangalore, Karnataka
India
EMail: prejeeth@rtbrick.com
Yongqing Zhu
China Telecom
109 West Zhongshan Ave, Tianhe District
Bangalore, Guangzhou
P.R. China
EMail: zhuyq8@chinatelecom.cn
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