Network Working Group S. Sivabalan
Internet-Draft J. Medved
Intended status: Standards Track C. Filsfils
Expires: September 22, 2016 Cisco Systems, Inc.
E. Crabbe
R. Raszuk
Mirantis Inc.
V. Lopez
Telefonica I+D
J. Tantsura
Ericsson
W. Henderickx
Alcatel Lucent
J. Hardwick
Metaswitch Networks
March 21, 2016
PCEP Extensions for Segment Routing
draft-ietf-pce-segment-routing-07.txt
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.
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Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on September 22, 2016.
Copyright Notice
Copyright (c) 2016 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview of PCEP Operation in SR Networks . . . . . . . . . . 5
4. SR-Specific PCEP Message Extensions . . . . . . . . . . . . . 7
5. Object Formats . . . . . . . . . . . . . . . . . . . . . . . 7
5.1. The OPEN Object . . . . . . . . . . . . . . . . . . . . . 7
5.1.1. The SR PCE Capability TLV . . . . . . . . . . . . . . 7
5.2. The RP/SRP Object . . . . . . . . . . . . . . . . . . . . 8
5.3. ERO Object . . . . . . . . . . . . . . . . . . . . . . . 8
5.3.1. SR-ERO Subobject . . . . . . . . . . . . . . . . . . 9
5.3.2. NAI Associated with SID . . . . . . . . . . . . . . . 11
5.3.3. ERO Processing . . . . . . . . . . . . . . . . . . . 12
5.4. RRO Object . . . . . . . . . . . . . . . . . . . . . . . 13
5.4.1. RRO Processing . . . . . . . . . . . . . . . . . . . 14
5.5. METRIC Object . . . . . . . . . . . . . . . . . . . . . . 14
6. Backward Compatibility . . . . . . . . . . . . . . . . . . . 15
7. Management Considerations . . . . . . . . . . . . . . . . . . 15
7.1. Policy . . . . . . . . . . . . . . . . . . . . . . . . . 15
7.2. The PCEP Data Model . . . . . . . . . . . . . . . . . . . 15
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8. Security Considerations . . . . . . . . . . . . . . . . . . . 15
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9.1. PCEP Objects . . . . . . . . . . . . . . . . . . . . . . 16
9.2. PCEP-Error Object . . . . . . . . . . . . . . . . . . . . 16
9.3. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 17
9.4. New Path Setup Type . . . . . . . . . . . . . . . . . . . 17
9.5. New Metric Type . . . . . . . . . . . . . . . . . . . . . 17
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 17
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
12.1. Normative References . . . . . . . . . . . . . . . . . . 18
12.2. Informative References . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
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.filsfils-rtgwg-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 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 only MPLS
forwarding plane, and assumes that a 32-bit Segment Identifier (SID)
represents an absolute value of MPLS label entry. 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 IGP SPT. Such paths may
be chosen by a suitable network planning tool and provisioned on the
source node of the SR-TE path.
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[RFC5440] describes Path Computation Element Protocol (PCEP) for
communication between a Path Computation Client (PCC) and a Path
Computation Element (PCE) or between one 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.
[I-D.ietf-pce-stateful-pce] 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 [I-D.ietf-pce-pce-initiated-lsp]. Such mechanism is
useful in Software Driven Networks (SDN) applications, such as 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 described 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 PATH-SETUP-TYPE TLV and 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
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OSPF: Open Shortest Path First
PCC: Path Computation Client
PCE: Path Computation Element
PCEP: Path Computation Element Protocol
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
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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
defined in [I-D.ietf-pce-stateful-pce].
When a PCEP session between a PCC and a PCE is established, both PCEP
speakers exchange information to indicate their ability to support
SR-specific functionality. Furthermore, an LSP initially established
via RSVP-TE signaling can be updated with SR-TE path. This
capability is useful when a network is migrated from RSVP-TE to SR-TE
technology. Similarly, an LSP initially created with SR-TE path can
updated to signal the LSP using RSVP-TE if necessary.
A PCC MAY include an RRO object containing the recorded LSP in PCReq
and PCRpt messages as specified in [RFC5440] and
[I-D.ietf-pce-stateful-pce] respectively. This document defines a
new RRO subobject for SR networks. Methods used by a PCC to record
SR-TE LSP are outside the scope of this document.
In summary, this document:
o Defines a new PCEP capability, new ERO subobject, new RRO
subobject, a new TLV, 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 of ERO subobject.
o Defines a new path setup type carried in the PATH-SETUP-TYPE TLV
for SR-TE LSP.
The extensions specified in this document complement the existing
PCEP specifications to support SR-TE path. 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],
[I-D.ietf-pce-stateful-pce], [I-D.ietf-pce-pce-initiated-lsp], and
any other applicable PCEP specifications.
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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 PCReq and PCRep messages specified in [RFC5440], PCInitiate
message specified in [I-D.ietf-pce-pce-initiated-lsp], and PCRpt and
PCUpd messages specified in [I-D.ietf-pce-stateful-pce]. However,
PCEP messages pertaining to SR-TE LSP MUST include PATH-SETUP-TYPE
TLV in the RP or SRP object to clearly identify that SR-TE LSP is
intended. In other words, a PCEP speaker MUST not infer whether or
not a PCEP message pertains to SR-TE LSP from any other object or
TLV.
5. Object Formats
5.1. The OPEN Object
This document defines a new optional TLV for use in the OPEN Object.
5.1.1. The SR PCE Capability TLV
The SR-PCE-CAPABILITY TLV is an optional TLV associated with the OPEN
Object to exchange SR capability of PCEP speakers. The format of the
SR-PCE-CAPABILITY 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=TBD | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags | MSD |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SR-PCE-CAPABILITY TLV format
The code point for the TLV type is to be defined by IANA. 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 that a PCC is
capable of imposing on a packet. The "Flags" (1 octet) and
"Reserved" (2 octets) fields are currently unused, and MUST be set to
zero on transmission and ignored on reception.
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5.1.1.1. Exchanging SR Capability
By including the SR-PCE-CAPABILITY TLV in the OPEN message destined
to a PCE, a PCC indicates that it is capable of supporting the head-
end functions for SR-TE LSP. By including the TLV in the OPEN
message destined to a PCC, a PCE indicates that it is capable of
computing SR-TE paths.
The number of SIDs that can be imposed on a packet depends on PCC's
data plane's capability. An MSD value of zero means that a PCC does
not impose any default limitation on the number of SIDs included in
any SR-TE path coming from PCE. Once an SR-capable PCEP session is
established with a non-zero MSD value, the corresponding PCE MUST NOT
send SR-TE paths with SIDs exceeding that MSD value. If a PCC needs
to modify the MSD value, the PCEP session MUST be closed and re-
established 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). 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.
The SR Capability TLV is meaningful only in the OPEN message sent
from a PCC to a PCE. As such, a PCE does not need to set MSD value
in outbound message to a PCC. Similarly, a PCC ignores any MSD value
received from a PCE. If a PCE receives multiple SR-PCE-CAPABILITY
TLVs in an OPEN message, it processes only the first TLV is
processed.
5.2. The RP/SRP Object
In order to setup an SR-TE LSP using SR, RP or SRP object MUST PATH-
SETUP-TYPE TLV specified in [I-D.ietf-pce-lsp-setup-type]. This
document defines a new Path Setup Type (PST) for SR as follows:
o PST = 1: Path is setup using Segment Routing Traffic Engineering
technique.
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,
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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. Note that an SR-ERO subobject does not need to
have both SID and NAI. However, at least one of them MUST be
present.
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.
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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.
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.
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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.
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:
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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 adjacenc y
'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
Editorial Note: We are yet to decide if another SID subobject is
required for unnumbered adjacency with 128 bit node ID.
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 a label ERO subobject with an invalid value,
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it MUST send a PCErr message with Error-Type = 10 ("Reception of an
invalid object") and Error Value = TBD ("Bad label value"). If both
M and C bits of an 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 = TBD ("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 = TBD
("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
message with Error-Type = 10 ("Reception of an invalid object") and
Error-Value = TBD ("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 = TBD ("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 =
TBD ("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:
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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.
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 = TBD ("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 = TBD
("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 = TBD (suggested value 11): Maximum SID Depth of the requested
path.
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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 TBD ("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].
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 [I-D.ietf-pce-pcep-mib] needs 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
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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
allocate code points in the RSVP Parameters registry for each of the
new sub-object types defined in this document, as follows:
Object Sub-Object Sub-Object Type
--------------------- -------------------------- ------------------
EXPLICIT_ROUTE SR-ERO (PCEP-specific) TBD (recommended 36)
ROUTE_RECORD SR-RRO (PCEP-specific) TBD (recommended 36)
9.2. PCEP-Error Object
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 = TBD (recommended 2): Bad label value
Error-value = TBD (recommended 3): Unsupported number
of Segment ERO
subobjects
Error-value = TBD (recommended 4): Bad label format
Error-value = TBD (recommended 5): Non-identical ERO
subobjects
Error-value = TBD (recommended 6): Both SID and NAI
are absent in ERO
subobject
Error-value = TBD (recommended 7): Both SID and NAI
are absent in RRO
subobject
Error-value = TBD (recommended 9): Default MSD is
specified for the
PCEP session
Error-value = TBD (recommended 10): Non-identical RRO
subobjects
Error-value = TBD (recommended 11): Malformed object
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9.3. PCEP TLV Type Indicators
IANA is requested to allocate a new code point in the PCEP TLV Type
Indicators registry, as follows:
Value Meaning Reference
------------------------- ---------------------------- --------------
TBD (recommended 26) SR-PCE-CAPABILITY This document
9.4. New Path Setup Type
[I-D.ietf-pce-lsp-setup-type] defines the PATH-SETUP-TYPE TLV and
requests that IANA creates a registry to manage the value of the
PATH_SETUP_TYPE TLV's PST field. IANA is requested to allocate a new
code point in the PCEP PATH_SETUP_TYPE TLV PST field registry, as
follows:
Value Description Reference
------------------------- ---------------------------- --------------
1 Traffic engineering path is This document
setup using Segment Routing
technique.
9.5. New Metric Type
IANA is requested to allocate a new code point in the PCEP METRIC
object T field registry, as follows:
Value Description Reference
------------------------- ---------------------------- --------------
TBD (recommended 11) Segment-ID (SID) Depth. This document
10. Contributors
The following people contributed to this document:
- Lakshmi Sharma
11. Acknowledgements
We like to thank Ina Minei, George Swallow, Marek Zavodsky and Tomas
Janciga for the valuable comments.
12. References
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12.1. Normative References
[I-D.filsfils-rtgwg-segment-routing]
Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,
Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,
"Segment Routing Architecture", draft-filsfils-rtgwg-
segment-routing-01 (work in progress), October 2013.
[I-D.ietf-isis-segment-routing-extensions]
Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
Litkowski, S., and J. Tantsura, "IS-IS Extensions for
Segment Routing", draft-ietf-isis-segment-routing-
extensions-00 (work in progress), April 2014.
[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-00 (work in progress), June 2014.
[I-D.ietf-pce-lsp-setup-type]
Sivabalan, S., Medved, J., Minei, I., Crabbe, E., and R.
Varga, "Conveying path setup type in PCEP messages",
draft-ietf-pce-lsp-setup-type-00 (work in progress),
October 2014.
[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-01 (work in
progress), June 2014.
[I-D.ietf-pce-pcep-mib]
Koushik, K., Stephan, E., Zhao, Q., King, D., and J.
Hardwick, "PCE communication protocol (PCEP) Management
Information Base", draft-ietf-pce-pcep-mib-04 (work in
progress), February 2013.
[I-D.ietf-pce-stateful-pce]
Crabbe, E., Medved, J., Minei, I., and R. Varga, "PCEP
Extensions for Stateful PCE", draft-ietf-pce-stateful-
pce-05 (work in progress), July 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
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[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<http://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, <http://www.rfc-editor.org/info/rfc5462>.
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,
<http://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,
<http://www.rfc-editor.org/info/rfc3473>.
[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,
<http://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, <http://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
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Jan Medved
Cisco Systems, Inc.
170 West Tasman Dr.
San Jose, CA 95134
US
Email: jmedved@cisco.com
Clarence Filsfils
Cisco Systems, Inc.
Pegasus Parc
De kleetlaan 6a, DIEGEM BRABANT 1831
BELGIUM
Email: cfilsfil@cisco.com
Edward Crabbe
Robert Raszuk
Mirantis Inc.
100-615 National Ave.
Mountain View, CA 94043
US
Email: robert@raszuk.net
Victor Lopez
Telefonica I+D
Don Ramon de la Cruz 82-84
Madrid 28045
Spain
Email: vlopez@tid.es
Jeff Tantsura
Ericsson
300 Holger Way
San Jose, CA 95134
USA
Email: jeff.tantsura@ericsson.com
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Wim Henderickx
Alcatel Lucent
Copernicuslaan 50
Antwerp 2018, CA 95134
BELGIUM
Email: wim.henderickx@alcatel-lucent.com
Jon Hardwick
Metaswitch Networks
100 Church Street
Enfield, Middlesex
UK
Email: jon.hardwick@metaswitch.com
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