Internet DRAFT - draft-negi-pce-segment-routing-ipv6
draft-negi-pce-segment-routing-ipv6
PCE Working Group M. Negi
Internet-Draft C. Li
Intended status: Standards Track Huawei Technologies
Expires: August 10, 2019 S. Sivabalan
Cisco Systems
P. Kaladharan
RtBrick Inc
February 6, 2019
PCEP Extensions for Segment Routing leveraging the IPv6 data plane
draft-negi-pce-segment-routing-ipv6-04
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.
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
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, Segment Routing 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 draft describes the extensions
required for Segment Routing support for IPv6 data plane in Path
Computation Element communication Protocol (PCEP).
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.
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
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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 August 10, 2019.
Copyright Notice
Copyright (c) 2019 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview of PCEP Operation in SRv6 Networks . . . . . . . . . 5
3.1. Operation Overview . . . . . . . . . . . . . . . . . . . 6
3.2. SRv6-Specific PCEP Message Extensions . . . . . . . . . . 6
3.3. Object Formats . . . . . . . . . . . . . . . . . . . . . 6
3.3.1. The OPEN Object . . . . . . . . . . . . . . . . . . . 6
3.3.1.1. The SRv6 PCE Capability sub-TLV . . . . . . . . . 6
3.3.1.2. Exchanging the SRv6 Capability . . . . . . . . . 8
3.3.2. The RP/SRP Object . . . . . . . . . . . . . . . . . . 9
3.3.3. ERO Object . . . . . . . . . . . . . . . . . . . . . 9
3.3.3.1. SR-ERO Subobject . . . . . . . . . . . . . . . . 10
3.3.3.2. ERO Processing . . . . . . . . . . . . . . . . . 12
3.3.4. RRO Object . . . . . . . . . . . . . . . . . . . . . 13
3.3.4.1. SR-RRO Subobject . . . . . . . . . . . . . . . . 13
3.4. Security Considerations . . . . . . . . . . . . . . . . . 14
3.5. IANA Considerations . . . . . . . . . . . . . . . . . . . 14
3.5.1. PCEP Objects . . . . . . . . . . . . . . . . . . . . 14
3.5.1.1. ERROR Objects . . . . . . . . . . . . . . . . . . 14
3.5.1.2. TLV Type Indicators . . . . . . . . . . . . . . . 14
3.5.1.3. New Path Setup Type . . . . . . . . . . . . . . . 15
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3.6. The NAI Type field . . . . . . . . . . . . . . . . . . . 15
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. Normative References . . . . . . . . . . . . . . . . . . 15
5.2. Informative References . . . . . . . . . . . . . . . . . 16
Appendix A. Contributor . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
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)
[I-D.ietf-6man-segment-routing-header]. 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
[I-D.ietf-isis-segment-routing-extensions], and
[I-D.ietf-ospf-ospfv3-segment-routing-extensions].
As per [I-D.ietf-6man-segment-routing-header], 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.filsfils-spring-srv6-network-programming].
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.
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[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 [I-D.ietf-pce-segment-routing], 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 [I-D.ietf-pce-segment-routing].
[I-D.ietf-pce-segment-routing] specifies PCEP extensions for
supporting a SR-TE LSP for MPLS data plane. This document extends
[I-D.ietf-pce-segment-routing] 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].
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].
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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 of IPv6 SID representing a path in IPv6
SR domain)
3. Overview of PCEP Operation in SRv6 Networks
Basic operations for PCEP speakers is as per
[I-D.ietf-pce-segment-routing]. 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.
[I-D.ietf-pce-segment-routing] defined 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
[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 extends the "SR-ERO subobject" defined in
[I-D.ietf-pce-segment-routing] to carry IPv6 SID(s) (IPv6 Addresses).
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:
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o Defines a new PCEP capability for SRv6
o Update the SR-ERO and SR-RRO sub-object for SRv6
o Defines a new path setup type carried in the PATH-SETUP-TYPE and
PATH-SETUP-TYPE-CAPABILITY TLVs.
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 [I-D.ietf-pce-segment-routing]
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 3.3.1.1).
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
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.
3.3. Object Formats
3.3.1. The OPEN Object
3.3.1.1. 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.
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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 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 |L|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value | MSD-Type | MSD-Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// ... //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MSD-Type | MSD-Value | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SRv6-PCE-CAPABILITY sub-TLV format
The code point for the TLV type (TBD1) is to be defined by IANA. The
TLV length is variable.
The value comprise of -
Reserved: 2 octet, this field MUST be set to 0 on transmission,
and ignored on receipt.
Flags: 2 octet, one bit is currently assigned in this document.
L 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.
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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.bashandy-isis-srv6-extensions]; MSD-
Value (1 octet) is as per [RFC8491].
The TLV format is compliant with the PCEP TLV format defined in
[RFC5440]. That is, the TLV is composed of 2 octets for the type, 2
octets specifying the TLV length, and a Value field. 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.
3.3.1.2. 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 L 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 L 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 L 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 L 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.").
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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.bashandy-isis-srv6-extensions]; [I-D.dawra-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.
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 [I-D.ietf-pce-segment-routing].
The L 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 L flag and not include
(MSD-Type,MSD-Value) in an outbound message to a PCC. Similarly, a
PCC MUST ignore any (MSD-Type,MSD-Value) 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.
3.3.2. 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.
3.3.3. ERO Object
In order to support SRv6, the SR-ERO subobject is used
[I-D.ietf-pce-segment-routing]. This documents extends the SR-ERO
subobject. All the processing rules remains the same.
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3.3.3.1. SR-ERO Subobject
For supporting SRv6, a new NAI Type (NT) is defined, the format of
SR-ERO sub object remains the same as defined in
[I-D.ietf-pce-segment-routing].
When the NAI Type (NT) indicates SRv6, then the SR-ERO subobject
represent a SRv6 segment and include a field SRv6I (SRv6 Identifier)
in place of NAI (Node or Adjacency Identifier) defined in
[I-D.ietf-pce-segment-routing]. The 32 bit SID is not used for SRv6
and MUST NOT be included. The format of SR-ERO subobject is
reproduced with the SRv6I field as 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type | Length | NT | Flags |F|S|C|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (not included) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6I (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SR-ERO Subobject Format
The description of all the flags and fields is as per
[I-D.ietf-pce-segment-routing].
For SRv6 segments, a new NT (NAI Type) is assigned by IANA as TBD3.
For SRv6 segments (when NT is TBD3), M and C flag MUST NOT be set.
The S flag MUST be set and SID field MUST NOT be included. The F bit
MUST NOT be set.
If these flags are not set properly, the subobject MUST be considered
malformed and the PCEP speaker react as per the error handling
described in Section 3.3.3.2.
The SRv6I format is as 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SRv6 Identifier |
| (128-bit) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRv6NT| Flags | Function Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// NAI (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: SR-ERO Subobject's SRv6I Format
SRv6 Identifier is the 128 bit IPv6 addresses representing SRv6
segment.
SRv6NT is the SRv6 NAI Type which indicates the interpretation for
NAI (Node or Adjacency Identifier) as per
[I-D.ietf-pce-segment-routing].
Flags is the 12 bit field, no flag bits are currently defined in
this document. This MUST be set to 0 and ignored on receipt.
Function Code is is the 16 bit field representing supported
functions associated with SRv6 SIDs. This information is optional
and included only for maintainability. Following function codes
are currently defined -
0: Reserved
1: End Function
2: End.DX6 Function
3: End.DT6 Function
4: End.X Function
NAI field [I-D.ietf-pce-segment-routing] contains the NAI
associated with the SRv6 Identifier. Depending on the value of
SRv6NT, the NAI can have different formats.
When SRv6NT value is 1, the NAI is as per the 'IPv6 Node ID'
format defined in [I-D.ietf-pce-segment-routing], which specify
an IPv6 address. This is used to identify the owner of the
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SRv6 Identifier. This is optional, as the LOC (the locater
portion) of the SRv6 SID serves a similar purpose.
When SRv6NT value is 2, the NAI is as per the 'IPv6 Adjacency'
format defined in [I-D.ietf-pce-segment-routing], which specify
a pair of IPv6 addresses. This is used to identify the IPv6
Adjacency and used with the SRv6 Adj-SID.
Note that when SRv6NT value is 0, NAI is not included and MUST
be NULL.
[Editor's Note - Add IPv6 unnumbered adjacency, once done by
[I-D.ietf-pce-segment-routing]]
3.3.3.2. ERO Processing
The ERO and SR-ERO subobject processing remains as per [RFC5440] and
[I-D.ietf-pce-segment-routing].
The NT MUST only be TDB3, if the PST=TBD3 is set in the PCEP message
and SRv6-PCE-CAPABILITY sub-TLV is exchanged with the PCEP peer. In
case a PCEP speaker receives the SR-ERO subobject with NT indicating
SRv6 segment, when the PST is not set to TBD3 or SRv6-PCE-CAPABILITY
sub-TLV was not exchanged, it MUST send a PCErr message with Error-
Type = 19 ("Invalid Operation") and Error-Value = TBD4 ("Attempted
SRv6 when the capability was not advertised"). A PCEP speaker that
does not recognize the NT value, it would behave as per
[I-D.ietf-pce-segment-routing].
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 MAY 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 [I-D.ietf-pce-segment-routing].
When a PCEP speaker detects that all subobjects of ERO are not
identical to SRv6, 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
[I-D.ietf-pce-segment-routing].
When a PCEP speaker receives an SR-ERO subobject for SRv6 segment, M,
C and F flag MUST NOT be set and S flag MUST be set. 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") as per
[I-D.ietf-pce-segment-routing]. The PCEP speaker MAY include the
malformed SR-ERO object in the PCErr message as well.
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3.3.3.2.1. Interpreting the SR-ERO
The SR-ERO contains a sequence of subobjects. According to
[I-D.ietf-spring-segment-routing-policy], each SR-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 SR-ERO
subobject represents the second segment, and so on.
The PCC interprets the SR-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.
3.3.4. RRO Object
In order to support SRv6, the SR-RRO Subobject is used
[I-D.ietf-pce-segment-routing]. All other processing rules remains
the same.
3.3.4.1. SR-RRO Subobject
For SRv6 segments, a new NT (NAI Type) is assigned by IANA as TBD3,
the format of SR-RRO sub object remains the same as the SR-ERO
subobject, but without the L flag [I-D.ietf-pce-segment-routing].
When the NAI Type (NT) indicates SRv6, then the SR-RRO subobject
represent a SRv6 segment and include a field SRv6I (SRv6 Identifier)
in place of NAI (Node or Adjacency Identifier) defined in
[I-D.ietf-pce-segment-routing]. The 32 bit SID MUST NOT be included.
The format of SR-RRO subobject is reproduced with the SRv6I field as
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 (not included) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// SRv6I (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: SR-RRO Subobject Format
The description of all fields and flags is as per SR-ERO subobject.
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Processing rules of SR-RRO subobject are identical to those of SR-ERO
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").
3.4. Security Considerations
The security considerations described in [RFC5440], [RFC8231] and
[RFC8281], [I-D.ietf-pce-segment-routing], are applicable to this
specification. No additional security measure is required.
3.5. IANA Considerations
This document requests IANA to include (I) bit in flags registry for
SR-ERO and SR-RRO sub-objects. Other changes are defined as:
3.5.1. PCEP Objects
3.5.1.1. 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)
19 Invalid Operation
Error-value = TBD4 (Attempted SRv6 when the
capability was not advertised)
3.5.1.2. TLV Type Indicators
IANA is requested to make the assignment of the new code points for
the existing "PCEP TLV Type Indicators" registry as follows:
Value Meaning Reference
----- ------- ---------
TBD1 SRv6-PCE-CAPABILITY This Document
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3.5.1.3. New Path Setup Type
[RFC8408] 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
----- ----------- ---------
TBD2 SRv6 (SRH) technique This Document
3.6. The NAI Type field
As per [I-D.ietf-pce-segment-routing], a new subregistery for "PCEP
SR-ERO NAI Types" was created. IANA is requested to make the
assignment of the new code points in the afore-mentioned registry as
follows:
Value Description Reference
----- ------- ---------
TBD3 NAI is an SRv6 segment This Document
4. Acknowledgements
The authors would like to thank Jeff Tentsura for suggestions
regarding SRv6 MSD Types.
5. References
5.1. 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>.
[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>.
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[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>.
[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>.
[I-D.ietf-pce-segment-routing]
Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "PCEP Extensions for Segment Routing",
draft-ietf-pce-segment-routing-14 (work in progress),
October 2018.
5.2. 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>.
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[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>.
[I-D.ietf-6man-segment-routing-header]
Filsfils, C., Previdi, S., Leddy, J., Matsushima, S., and
d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header
(SRH)", draft-ietf-6man-segment-routing-header-16 (work in
progress), February 2019.
[I-D.ietf-isis-segment-routing-extensions]
Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
Gredler, H., and B. Decraene, "IS-IS Extensions for
Segment Routing", draft-ietf-isis-segment-routing-
extensions-22 (work in progress), December 2018.
[I-D.ietf-ospf-ospfv3-segment-routing-extensions]
Psenak, P. and S. Previdi, "OSPFv3 Extensions for Segment
Routing", draft-ietf-ospf-ospfv3-segment-routing-
extensions-23 (work in progress), January 2019.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
bogdanov@google.com, b., and P. Mattes, "Segment Routing
Policy Architecture", draft-ietf-spring-segment-routing-
policy-02 (work in progress), October 2018.
[I-D.filsfils-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J.,
daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
Network Programming", draft-filsfils-spring-srv6-network-
programming-06 (work in progress), October 2018.
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[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-02 (work in progress), September
2018.
[I-D.bashandy-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extensions to Support Routing over IPv6
Dataplane", draft-bashandy-isis-srv6-extensions-04 (work
in progress), October 2018.
[I-D.dawra-idr-bgpls-srv6-ext]
Dawra, G., Filsfils, C., Talaulikar, K., Chen, M.,
daniel.bernier@bell.ca, d., Uttaro, J., Decraene, B., and
H. Elmalky, "BGP Link State extensions for IPv6 Segment
Routing(SRv6)", draft-dawra-idr-bgpls-srv6-ext-04 (work in
progress), September 2018.
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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
Authors' Addresses
Mahendra Singh Negi
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
EMail: mahendrasingh@huawei.com
Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
EMail: chengli13@huawei.com
Siva Sivabalan
Cisco Systems
EMail: msiva@cisco.com
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Prejeeth Kaladharan
RtBrick Inc
Bangalore, Karnataka
India
EMail: prejeeth@rtbrick.com
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