PCE S. Sivabalan
Internet-Draft C. Filsfils
Intended status: Standards Track Cisco Systems, Inc.
Expires: May 24, 2018 J. Tantsura
Individual
W. Henderickx
Nokia
J. Hardwick
Metaswitch Networks
November 20, 2017
PCEP Extensions for Segment Routing
draft-ietf-pce-segment-routing-11
Abstract
Segment Routing (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 Interior Gateway Protocols (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). This document specifies extensions to the Path
Computation Element Protocol (PCEP) that allow a stateful PCE to
compute and initiate Traffic Engineering (TE) paths, as well as a PCC
to request a path subject to certain constraint(s) and optimization
criteria in SR networks.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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 http://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
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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 May 24, 2018.
Copyright Notice
Copyright (c) 2017 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
(http://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 . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview of PCEP Operation in SR Networks . . . . . . . . . . 5
4. SR-Specific PCEP Message Extensions . . . . . . . . . . . . . 6
5. Object Formats . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. The OPEN Object . . . . . . . . . . . . . . . . . . . . . 7
5.1.1. The SR PCE Capability sub-TLV . . . . . . . . . . . . 7
5.1.2. Exchanging the SR PCE Capability . . . . . . . . . . 8
5.2. The RP/SRP Object . . . . . . . . . . . . . . . . . . . . 9
5.3. ERO Object . . . . . . . . . . . . . . . . . . . . . . . 9
5.3.1. SR-ERO Subobject . . . . . . . . . . . . . . . . . . 10
5.3.2. NAI Associated with SID . . . . . . . . . . . . . . . 12
5.3.3. ERO Processing . . . . . . . . . . . . . . . . . . . 13
5.4. RRO Object . . . . . . . . . . . . . . . . . . . . . . . 14
5.4.1. RRO Processing . . . . . . . . . . . . . . . . . . . 14
5.5. METRIC Object . . . . . . . . . . . . . . . . . . . . . . 15
6. Backward Compatibility . . . . . . . . . . . . . . . . . . . 15
7. Management Considerations . . . . . . . . . . . . . . . . . . 16
7.1. Policy . . . . . . . . . . . . . . . . . . . . . . . . . 16
7.2. The PCEP Data Model . . . . . . . . . . . . . . . . . . . 16
8. Security Considerations . . . . . . . . . . . . . . . . . . . 16
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
9.1. PCEP Objects . . . . . . . . . . . . . . . . . . . . . . 16
9.2. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 17
9.3. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 18
9.4. New Path Setup Type . . . . . . . . . . . . . . . . . . . 18
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9.5. New Metric Type . . . . . . . . . . . . . . . . . . . . . 18
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 18
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
12.1. Normative References . . . . . . . . . . . . . . . . . . 19
12.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
SR technology leverages the source routing and tunneling paradigms.
A source node can choose a path without relying on hop-by-hop
signaling protocols such as LDP or RSVP-TE. Each path is specified
as a set of "segments" advertised by link-state routing protocols
(IS-IS or OSPF). [I-D.ietf-spring-segment-routing] provides an
introduction to SR architecture. The corresponding IS-IS and OSPF
extensions are specified in
[I-D.ietf-isis-segment-routing-extensions] and
[I-D.ietf-ospf-segment-routing-extensions], respectively. SR
architecture defines a "segment" as a piece of information advertised
by a link-state routing protocols, e.g. an IGP prefix or an IGP
adjacency. Several types of segments are defined. A Node segment
represents an ECMP-aware shortest-path computed by IGP to a specific
node, and is always global within SR/IGP domain. An Adjacency
Segment represents a unidirectional adjacency. An Adjacency Segment
is local to the node which advertises it. Both Node segments and
Adjacency segments can be used for SR Traffic Engineering (SR-TE).
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). This document is relevant to the MPLS
forwarding plane only. In this document, "Node-SID" and "Adjacency-
SID" denote Node Segment Identifier and Adjacency Segment Identifier
respectively.
A Segment Routed path (SR path) can be derived from an IGP Shortest
Path Tree (SPT). SR-TE paths may not follow an IGP SPT. Such paths
may be chosen by a suitable network planning tool and provisioned on
the ingress node of the SR-TE path.
[RFC5440] describes the Path Computation Element 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
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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 [I-D.ietf-pce-pce-initiated-lsp]. This mechanism is
useful in Software Defined Networking (SDN) applications, such as on-
demand engineering, or bandwidth calendaring.
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
[I-D.ietf-pce-pce-initiated-lsp] using the SR specific PCEP
extensions specified in this document. Additionally, using
procedures described in this document, a PCC can request an SR path
from either stateful or a stateless PCE. This specification relies
on the procedures specified in [I-D.ietf-pce-lsp-setup-type].
2. Terminology
The following terminologies are used in this document:
ERO: Explicit Route Object
IGP: Interior Gateway Protocol
IS-IS: Intermediate System to Intermediate System
LSR: Label Switching Router
MSD: Maximum SID Depth
NAI: Node or Adjacency Identifier
OSPF: Open Shortest Path First
PCC: Path Computation Client
PCE: Path Computation Element
PCEP: Path Computation Element Protocol
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RRO: Record Route Object
SID: Segment Identifier
SR: Segment Routing
SR-TE: Segment Routed Traffic Engineering
TED: Traffic Engineering Database
3. Overview of PCEP Operation in SR Networks
In SR networks, an ingress node of an SR path appends all outgoing
packets with an SR header consisting of a list of SIDs (or MPLS
labels in the context of this document). 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.
In a PCEP session, LSP information is carried in the Explicit Route
Object (ERO), which consists of a sequence of subobjects. Various
types of ERO subobjects have been specified in [RFC3209], [RFC3473],
and [RFC3477]. In SR networks, an ingress node of an SR path appends
all outgoing packets with an SR header consisting of a list of SIDs
(or MPLS labels in the context of this document). SR-TE LSPs
computed by a PCE can be represented in one of the following forms:
o An ordered set of IP address(es) representing network nodes/links:
In this case, the PCC needs to convert the IP address(es) into the
corresponding MPLS labels by consulting its Traffic Engineering
Database (TED).
o An ordered set of SID(s).
o An ordered set of both MPLS label(s) and IP address(es): In this
case, the PCC needs to convert the IP address(es) into the
corresponding SID(s) by consulting its TED.
This document defines a new 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
[I-D.ietf-pce-pce-initiated-lsp], as well as in the PCEP LSP Update
Request (PCUpd) and PCEP LSP State Report (PCRpt) messages defined in
[RFC8231].
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When a PCEP session between a PCC and a PCE is established, both PCEP
speakers exchange their capabilites to indicate their ability to
support SR-specific functionality.
An PCE can update an LSP that is initially established via RSVP-TE
signaling to use an SR-TE path, by sending a PCUpd to the PCC that
delegated the LSP to it ([RFC8231]). Similarly, an LSP initially
created with an SR-TE path can be updated to use RSVP-TE signaling,
if necessary. This capability is useful when a network is migrated
from RSVP-TE to SR-TE technology.
A PCC MAY include an RRO object containing the recorded LSP in PCReq
and PCRpt messages as specified in [RFC5440] and [RFC8231],
respectively. This document defines a new RRO subobject for SR
networks. The methods used by a PCC to record the SR-TE LSP are
outside the scope of this document.
In summary, this document:
o Defines a new ERO subobject, a new RRO subobject and new PCEP
error codes.
o Specifies how two PCEP speakers can establish a PCEP session that
can carry information about SR-TE paths.
o Specifies processing rules for the ERO subobject.
o Defines a new path setup type to be used in the PATH_SETUP_TYPE
and PATH_SETUP_TYPE_CAPABILITY TLVs
([I-D.ietf-pce-lsp-setup-type]).
o Defines a new sub-TLV for the PATH_SETUP_TYPE_CAPABILITY TLV.
The extensions specified in this document complement the existing
PCEP specifications to support SR-TE paths. As such, the PCEP
messages (e.g., Path Computation Request, Path Computation Reply,
Path Computation Report, Path Computation Update, Path Computation
Initiate, etc.,) MUST be formatted according to [RFC5440], [RFC8231],
[I-D.ietf-pce-pce-initiated-lsp], and any other applicable PCEP
specifications.
4. SR-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 the PCReq and PCRep messages specified in [RFC5440],
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PCInitiate message specified in [I-D.ietf-pce-pce-initiated-lsp], and
PCRpt and PCUpd messages specified in [RFC8231].
5. Object Formats
5.1. The OPEN Object
5.1.1. The SR PCE Capability sub-TLV
This document defines a new Path Setup Type (PST) for SR, as follows:
o PST = 1: Path is setup using Segment Routing Traffic Engineering.
A PCEP speaker SHOULD 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 SR-PCE-CAPABILITY sub-TLV. PCEP
speakers use this sub-TLV to exchange information about their SR
capability. If a PCEP speaker includes PST=1 in the PST List of the
PATH-SETUP-TYPE-CAPABILITY TLV then it MUST also include the SR-PCE-
CAPABILITY sub-TLV inside the PATH-SETUP-TYPE-CAPABILITY TLV.
The format of the SR-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=26 | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |L| MSD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SR-PCE-CAPABILITY sub-TLV format
The code point for the TLV type is 26. The TLV length is 4 octets.
The 32-bit value is formatted as follows. The "Maximum SID Depth" (1
octet) field (MSD) specifies the maximum number of SIDs (MPLS label
stack depth in the context of this document) that a PCC is capable of
imposing on a packet. The "Reserved" (2 octets) field is unused, and
MUST be set to zero on transmission and ignored on reception. The
"Flags" field is 1 octect long, and this document defines the
following flag:
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o L-flag: A PCC sets this flag to 1 to indicate that it does not
impose any limit on the MSD.
5.1.2. Exchanging the SR PCE Capability
A PCC indicates that it is capable of supporting the head-end
functions for SR-TE LSP by including the SR-PCE-CAPABILITY sub-TLV in
the Open message that it sends to a PCE. A PCE indicates that it is
capable of computing SR-TE paths by including the SR-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=1, but the SR-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 TBD1 (to be
assigned by IANA) (Missing PCE-SR-CAPABILITY sub-TLV) and MUST then
close the PCEP session. If a PCEP speaker receives a PATH-SETUP-
TYPE-CAPABILITY TLV with a SR-PCE-CAPABILITY sub-TLV, but the PST
list does not contain PST=1, then the PCEP speaker MUST ignore the
SR-PCE-CAPABILITY sub-TLV.
The number of SIDs that can be imposed on a packet depends on the
PCC's data plane's capability. If a PCC sets the L flag to 1 then
the MSD is not used and MUST be set to zero. If a PCE receives an
SR-PCE-CAPABILITY sub-TLV with the L flag set to 1 then it MUST
ignore the MSD field and MUST assume that the sender can impose a SID
stack of any depth. If a PCC sets the L flag to zero, then it sets
the MSD field to the maximum number of SIDs that it can impose on a
packet. If a PCE receives an SR-PCE-CAPABILITY sub-TLV with the L
flag and MSD both set to zero then it MUST assume that the PCC is not
capable of imposing a SID stack of any depth and hence is not SR-TE
capable, unless it learns a non-zero MSD for the PCC through some
other means.
Note that the MSD value exchanged via the SR-PCE-CAPABILITY sub-TLV
indicates the SID/label imposition limit for the PCC node. However,
if a PCE learns the MSD value of a PCC node via different means, e.g
routing protocols, as specified in:
[I-D.ietf-isis-segment-routing-msd];
[I-D.ietf-ospf-segment-routing-msd];
[I-D.ietf-idr-bgp-ls-segment-routing-msd], then it ignores the MSD
value in the SR-PCE-CAPABILITY sub-TLV. Furthermore, whenever a PCE
learns the MSD for a link via different means, it MUST use that value
for that link regardless of the MSD value exchanged in the SR-PCE-
CAPABILITY sub-TLV.
Once an SR-capable PCEP session is established with a non-zero MSD
value, the corresponding PCE MUST NOT send SR-TE paths with a number
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of SIDs exceeding that MSD value. If a PCC needs to modify the MSD
value, it MUST close the PCEP session and re-establish it with the
new MSD value. If a PCEP session is established with a non-zero MSD
value, and the PCC receives an SR-TE path containing more SIDs than
specified in the MSD value, 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 MSD value of zero, then the PCC MAY specify an
MSD for each path computation request that it sends to the PCE, by
including a "maximum SID depth" metric object on the request, as
defined in Section 5.5.
The L flag and MSD value inside the SR-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 L flag and MSD value to zero in an outbound
message to a PCC. Similarly, a PCC MUST ignore any MSD value
received from a PCE. If a PCE receives multiple SR-PCE-CAPABILITY
sub-TLVs in an Open message, it processes only the first sub-TLV
received.
5.2. The RP/SRP Object
In order to setup an SR-TE LSP using SR, RP or SRP object MUST
include PATH-SETUP-TYPE TLV, specified in
[I-D.ietf-pce-lsp-setup-type], with the PST set to 1 (path setup
using SR-TE).
The LSP-IDENTIFIERS TLV MAY be present for the above PST type.
5.3. ERO Object
An SR-TE path consists of one or more SID(s) where each SID MAY be
associated with the identifier that represents the node or adjacency
corresponding to the SID. This identifier is referred to as the
'Node or Adjacency Identifier' (NAI). As described later, a NAI can
be represented in various formats (e.g., IPv4 address, IPv6 address,
etc). Furthermore, a NAI is used for troubleshooting purposes and,
if necessary, to derive SID value as described below.
The ERO object specified in [RFC5440] is used to carry SR-TE path
information. In order to carry SID and/or NAI, this document defines
a new ERO subobject referred to as "SR-ERO subobject" whose format is
specified in the following section. An ERO object carrying an SR-TE
path consists of one or more ERO subobject(s), and MUST carry only
SR-ERO subobject(s). Note that an SR-ERO subobject does not need to
have both SID and NAI. However, at least one of them MUST be
present.
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When building the MPLS label stack from ERO, a PCC MUST assume that
SR-ERO subobjects are organized as a last-in-first-out stack. The
first subobject relative to the beginning of ERO contains the
information about the topmost label. The last subobject contains
information about the bottommost label.
5.3.1. SR-ERO Subobject
An SR-ERO subobject consists of a 32-bit header followed by the SID
and the NAI associated with the SID. The SID is a 32-bit number.
The size of the NAI depends on its respective type, as described in
the following sections.
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 | Length | ST | Flags |F|S|C|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// NAI (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SR-ERO Subobject format
The fields in the SR-ERO Subobject are as follows:
The 'L' Flag indicates whether the subobject represents a loose-hop
in the LSP [RFC3209]. If this flag is unset, a PCC MUST not
overwrite the SID value present in the SR-ERO subobject.
Otherwise, a PCC MAY expand or replace one or more SID value(s) in
the received SR-ERO based on its local policy.
Type is the type of the SR-ERO subobject. This document defines the
SR-ERO subobject type, and requests a new codepoint from IANA.
Length contains the total length of the subobject in octets,
including the L, Type and Length fields. Length MUST be at least
8, and MUST be a multiple of 4. As mentioned earlier, an SR-ERO
subobject MUST have at least SID or NAI. The length should take
into consideration SID or NAI only if they are not null. The
flags described below used to indicate whether SID or NAI field is
null.
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SID Type (ST) indicates the type of information associated with the
SID contained in the object body. When ST value is 0, SID MUST
NOT be null and NAI MUST be null. Other ST values are described
later in this document.
Flags is used to carry any additional information pertaining to SID.
Currently, the following flag bits are defined:
* M: When this bit is set, the SID value represents an MPLS label
stack entry as specified in [RFC5462] where only the label
value is specified by the PCE. Other fields (TC, S, and TTL)
fields MUST be considered invalid, and PCC MUST set these
fields according to its local policy and MPLS forwarding rules.
* C: When this bit as well as the M bit are set, then the SID
value represents an MPLS label stack entry as specified in
[RFC5462], where all the entry's fields (Label, TC, S, and TTL)
are specified by the PCE. However, a PCC MAY choose to
override TC, S, and TTL values according its local policy and
MPLS forwarding rules.
* S: When this bit is set, the SID value in the subobject body is
null. In this case, the PCC is responsible for choosing the
SID value, e.g., by looking up its TED using the NAI which, in
this case, MUST be present in the subobject.
* F: When this bit is set, the NAI value in the subobject body is
null.
SID is the Segment Identifier.
NAI contains the NAI associated with the SID. Depending on the
value of ST, the NAI can have different format as described in the
following section.
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5.3.2. NAI Associated with SID
This document defines the following NAIs:
'IPv4 Node ID' is specified as an IPv4 address. In this case, ST
value is 1, and the Length is 8 or 12 depending on either SID or
NAI or both are included in the subobject.
'IPv6 Node ID' is specified as an IPv6 address. In this case, ST
and Length are 2, and Length is 8, 20, or 24 depending on either
SID or NAI or both are included in the subobject.
'IPv4 Adjacency' is specified as a pair of IPv4 addresses. In this
case, ST value is 3. The Length is 8, 12, or 16 depending on
either SID or NAI or both are included in the subobject, and the
format of the NAI 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote IPv4 address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: NAI for IPv4 adjacency
'IPv6 Adjacency' is specified as a pair of IPv6 addresses. In this
case, ST valie is 4. The Length is 8, 36 or 40 depending on
whether SID or NAI or both included in the subobject,and the
format of the NAI 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local IPv6 address (16 bytes) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Remote IPv6 address (16 bytes) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: NAI for IPv6 adjacency
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'Unnumbered Adjacency with IPv4 NodeIDs' is specified as a pair of
Node ID / Interface ID tuples. In this case, ST value is 5. The
Length is 8, 20, or 24 depending on whether SID or NAI or both
included in the subobject, and the format of the NAI 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Node-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Node-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote Interface ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: NAI for Unnumbered adjacency with IPv4 Node IDs
5.3.3. ERO Processing
A PCEP speaker that does not recognize the SR-ERO subobject in PCRep,
PCInitiate, PCUpd or PCRpt messages MUST reject the entire PCEP
message and MUST send a PCErr message with Error-Type=3 ("Unknown
Object") and Error-Value=2 ("Unrecognized object Type") or Error-
Type=4 ("Not supported object") and Error-Value=2 ("Not supported
object Type"), defined in [RFC5440].
When the SID represents an MPLS label (i.e. the M bit is set), its
value (20 most significant bits) MUST be larger than 15, unless it is
special purpose label, such as an Entropy Label Indicator (ELI). If
a PCEP speaker receives an invalid value, it MUST send a PCErr
message with Error-Type = 10 ("Reception of an invalid object") and
Error Value = 2 ("Bad label value"). If both M and C bits of an SR-
ERO subobject are set, and if a PCEP speaker finds erroneous setting
in one or more of TC, S, and TTL fields, it MUST send a PCErr message
with Error-Type = 10 ("Reception of an invalid object") and Error-
Value = 4 ("Bad label format").
If a PCC receives a stack of SR-ERO subobjects, and the number of
stack exceeds the maximum number of SIDs that the PCC can impose on
the packet, it MAY send a PCErr message with Error-Type = 10
("Reception of an invalid object") and Error-Value = 3 ("Unsupported
number of Segment ERO subobjects").
When a PCEP speaker detects that all subobjects of ERO are not
identical, and if it does not handle such ERO, it MUST send a PCErr
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message with Error-Type = 10 ("Reception of an invalid object") and
Error-Value = 5 ("Non-identical ERO subobjects").
If a PCEP speaker receives an SR-ERO subobject in which both SID and
NAI are absent, it MUST consider the entire ERO object invalid and
send a PCErr message with Error-Type = 10 ("Reception of an invalid
object") and Error-Value = 6 ("Both SID and NAI are absent in ERO
subobject").
When a PCEP speaker receives an SR-ERO subobject in which ST is 0,
SID MUST be present and NAI MUST NOT be present(i.e., S-flag MUST be
0, F-flag MUST be 1, and the Length MUST be 8). Otherwise, it MUST
consider the entire ERO object invalid and send a PCErr message with
Error-Type = 10 ("Reception of an invalid object") and Error-Value =
11 ("Malformed object"). The PCEP speaker MAY include the malformed
SR-ERO object in the PCErr message as well.
5.4. RRO Object
A PCC can record SR-TE LSP and report the LSP to a PCE via RRO. An
RRO object contains one or more subobjects called "SR-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 | Length | ST | Flags |F|S|C|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// NAI (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: SR-RRO Subobject format
The format of SR-RRO subobject is the same as that of SR-ERO
subobject without L flag.
A PCC MUST assume that SR-RRO subobjects are organized such that the
first subobject relative to the beginning of RRO contains the
information about the topmost label, and the last subobject contains
information about the bottommost label of the SR-TE LSP.
5.4.1. RRO Processing
Processing rules of SR-RRO subobject are identical to those of SR-ERO
subobject.
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If a PCEP speaker receives an SR-RRO subobject in which both SID and
NAI are absent, it MUST consider the entire RRO object invalid and
send a PCErr message with Error-Type = 10 ("Reception of an invalid
object") and Error-Value = 7 ("Both SID and NAI are absent in RRO
subobject").
If a PCE detects that all subobjects of RRO are not identical, and if
it does not handle such RRO, it MUST send a PCErr message with Error-
Type = 10 ("Reception of an invalid object") and Error-Value = 10
("Non-identical RRO subobjects").
5.5. METRIC Object
If a PCEP session is established with an MSD value of zero, then the
PCC MAY specify the MSD for an individual path computation request
using the METRIC object defined in [RFC5440]. This document defines
a new type for the METRIC object to be used for this purpose as
follows:
o T = 11: Maximum SID Depth of the requested path.
The PCC sets the metric-value to the MSD for this path. The PCC MUST
set the B (bound) bit to 1 in the METRIC object, which specifies that
the SID depth for the computed path MUST NOT exceed the metric-value.
If a PCEP session is established with a non-zero MSD value, then the
PCC MUST NOT send an MSD METRIC object. If the PCE receives a path
computation request with an MSD METRIC object on a session with a
non-zero MSD value then it MUST consider the request invalid and send
a PCErr with Error-Type = 10 ("Reception of an invalid object") and
Error-Value 9 ("Default MSD is specified for the PCEP session").
6. Backward Compatibility
A PCEP speaker that does not support the SR PCEP capability cannot
recognize the SR-ERO or SR-RRO subobjects. As such, it MUST send a
PCEP error with Error-Type = 4 (Not supported object) and Error-Value
= 2 (Not supported object Type) as per [RFC5440].
Some implementations, which are compliant with an earlier version of
this specification, do not send the PATH-SETUP-TYPE-CAPABILITY TLV in
their OPEN objects. Instead, to indicate that they support SR, these
implementations include the SR-CAPABILITY-TLV as a top-level TLV in
the OPEN object. Unfortunately, some of these implementations made
it into the field before this document was published in its final
form. Therefore, if a PCEP speaker receives an OPEN object in which
the SR-CAPABILITY-TLV appears as a top-level TLV, then it MUST
interpret this as though the sender had sent a PATH-SETUP-TYPE-
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CAPABILITY TLV with a PST list of (0, 1) (that is, both RSVP-TE and
SR-TE PSTs are supported) and with the SR-CAPABILITY-TLV as a sub-
TLV. If a PCEP speaker receives an OPEN object in which both the SR-
CAPABILITY-TLV and PATH-SETUP-TYPE-CAPABILITY TLV appear as top-level
TLVs, then it MUST ignore the top-level SR-CAPABILITY-TLV and process
only the PATH-SETUP-TYPE-CAPABILITY TLV.
7. Management Considerations
7.1. Policy
PCEP implementation:
o Can enable SR PCEP capability either by default or via explicit
configuration.
o May generate PCEP error due to unsupported number of SR-ERO or SR-
RRO subobjects either by default or via explicit configuration.
7.2. The PCEP Data Model
A PCEP MIB module is defined in [RFC7420]n eeds be extended to cover
additional functionality provided by [RFC5440] and
[I-D.ietf-pce-pce-initiated-lsp]. Such extension will cover the new
functionality specified in this document.
8. Security Considerations
The security considerations described in [RFC5440] and
[I-D.ietf-pce-pce-initiated-lsp] are applicable to this
specification. No additional security measure is required.
9. IANA Considerations
9.1. PCEP Objects
This document defines a new sub-object type for the PCEP explicit
route object (ERO), and a new sub-object type for the PCEP record
route object (RRO). The code points for sub-object types of these
objects is maintained in the RSVP parameters registry, under the
EXPLICIT_ROUTE and ROUTE_RECORD objects. IANA is requested to
confirm the early allocation of the following code points in the RSVP
Parameters registry for each of the new sub-object types defined in
this document.
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Object Sub-Object Sub-Object Type
--------------------- -------------------------- ------------------
EXPLICIT_ROUTE SR-ERO (PCEP-specific) 36
ROUTE_RECORD SR-RRO (PCEP-specific) 36
9.2. PCEP-Error Object
IANA is requested to confirm the early allocation of the 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 = 2: Bad label value
Error-value = 3: Unsupported number
of Segment ERO
subobjects
Error-value = 4: Bad label format
Error-value = 5: Non-identical ERO
subobjects
Error-value = 6: Both SID and NAI
are absent in ERO
subobject
Error-value = 7: Both SID and NAI
are absent in RRO
subobject
Error-value = 9: Default MSD is
specified for the
PCEP session
Error-value = 10: Non-identical RRO
subobjects
Error-value = TBD1: Missing PCE-SR-
CAPABILITY sub-TLV
Note to IANA: this draft originally had an early allocation for
Error-value=11 (Malformed object) in the above list. However, we
have since moved the definition of that code point to draft-ietf-pce-
lsp-setup-type and we included an instruction in that draft for you
to update the reference in the indicated registry. Please ensure
that this has happened when you process the present draft.
Note to IANA: the final Error-value (Missing PCE-SR-CAPABILITY sub-
TLV) in the above list was defined after the early allocation took
place, and so does not currently have a code point assigned. Please
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assign a code point from the indicated registry and replace each
instance of "TBD1" in this document with the allocated code point.
9.3. PCEP TLV Type Indicators
IANA is requested to confirm the early allocation of the following
code point in the PCEP TLV Type Indicators registry.
Value Meaning Reference
------------------------- ---------------------------- --------------
26 SR-PCE-CAPABILITY This document
9.4. New Path Setup Type
[I-D.ietf-pce-lsp-setup-type] requests that IANA creates 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
------------------------- ---------------------------- --------------
1 Traffic engineering path is This document
setup using Segment Routing.
9.5. New Metric Type
IANA is requested to confirm the early allocation of the following
code point in the PCEP METRIC object T field registry:
Value Description Reference
------------------------- ---------------------------- --------------
11 Segment-ID (SID) Depth. This document
10. Contributors
The following people contributed to this document:
- Lakshmi Sharma
- Jan Medved
- Edward Crabbe
- Robert Raszuk
- Victor Lopez
11. Acknowledgements
We thank Ina Minei, George Swallow, Marek Zavodsky, Dhruv Dhody, Ing-
Wher Chen and Tomas Janciga for the valuable comments.
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12. References
12.1. Normative References
[I-D.ietf-idr-bgp-ls-segment-routing-msd]
Tantsura, J., Chunduri, U., Mirsky, G., and S. Sivabalan,
"Signaling Maximum SID Depth using Border Gateway Protocol
Link-State", draft-ietf-idr-bgp-ls-segment-routing-msd-01
(work in progress), October 2017.
[I-D.ietf-isis-segment-routing-extensions]
Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
Litkowski, S., Decraene, B., and j. jefftant@gmail.com,
"IS-IS Extensions for Segment Routing", draft-ietf-isis-
segment-routing-extensions-13 (work in progress), June
2017.
[I-D.ietf-isis-segment-routing-msd]
Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling MSD (Maximum SID Depth) using IS-IS", draft-
ietf-isis-segment-routing-msd-04 (work in progress), June
2017.
[I-D.ietf-ospf-segment-routing-extensions]
Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", draft-ietf-ospf-segment-
routing-extensions-21 (work in progress), October 2017.
[I-D.ietf-ospf-segment-routing-msd]
Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
"Signaling MSD (Maximum SID Depth) using OSPF", draft-
ietf-ospf-segment-routing-msd-05 (work in progress), June
2017.
[I-D.ietf-pce-lsp-setup-type]
Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J.
Hardwick, "Conveying path setup type in PCEP messages",
draft-ietf-pce-lsp-setup-type-05 (work in progress),
October 2017.
[I-D.ietf-pce-pce-initiated-lsp]
Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP
Extensions for PCE-initiated LSP Setup in a Stateful PCE
Model", draft-ietf-pce-pce-initiated-lsp-11 (work in
progress), October 2017.
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[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-12 (work in progress), June 2017.
[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>.
[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>.
[RFC5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, DOI 10.17487/RFC5462, February
2009, <https://www.rfc-editor.org/info/rfc5462>.
[RFC7420] Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
Hardwick, "Path Computation Element Communication Protocol
(PCEP) Management Information Base (MIB) Module",
RFC 7420, DOI 10.17487/RFC7420, December 2014,
<https://www.rfc-editor.org/info/rfc7420>.
[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>.
12.2. Informative References
[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>.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
DOI 10.17487/RFC3473, January 2003, <https://www.rfc-
editor.org/info/rfc3473>.
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[RFC3477] Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links
in Resource ReSerVation Protocol - Traffic Engineering
(RSVP-TE)", RFC 3477, DOI 10.17487/RFC3477, January 2003,
<https://www.rfc-editor.org/info/rfc3477>.
[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>.
Authors' Addresses
Siva Sivabalan
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario K2K 3E8
Canada
Email: msiva@cisco.com
Clarence Filsfils
Cisco Systems, Inc.
Pegasus Parc
De kleetlaan 6a, DIEGEM BRABANT 1831
BELGIUM
Email: cfilsfil@cisco.com
Jeff Tantsura
Individual
444 San Antonio Rd, 10A
Palo Alto, CA 94306
USA
Email: jefftant.ietf@gmail.com
Wim Henderickx
Nokia
Copernicuslaan 50
Antwerp 2018, CA 95134
BELGIUM
Email: wim.henderickx@alcatel-lucent.com
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Jon Hardwick
Metaswitch Networks
100 Church Street
Enfield, Middlesex
UK
Email: jonathan.hardwick@metaswitch.com
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