PCE Communication Protocol (PCEP) Extensions for Using the PCE as a Central Controller (PCECC) for Segment Routing over IPv6 (SRv6) Segment Identifier (SID) Allocation and Distribution.
draft-ietf-pce-pcep-extension-pce-controller-srv6-02
| Document | Type | Active Internet-Draft (pce WG) | |
|---|---|---|---|
| Authors | Zhenbin Li , Shuping Peng , Xuesong Geng , Mahendra Singh Negi | ||
| Last updated | 2024-02-04 | ||
| Replaces | draft-dhody-pce-pcep-extension-pce-controller-srv6 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | (None) | ||
| IESG | IESG state | I-D Exists | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | (None) |
draft-ietf-pce-pcep-extension-pce-controller-srv6-02
PCE Working Group Z. Li
Internet-Draft S. Peng
Intended status: Standards Track X. Geng
Expires: 7 August 2024 Huawei Technologies
M. Negi
RtBrick Inc
4 February 2024
PCE Communication Protocol (PCEP) Extensions for Using the PCE as a
Central Controller (PCECC) for Segment Routing over IPv6 (SRv6) Segment
Identifier (SID) Allocation and Distribution.
draft-ietf-pce-pcep-extension-pce-controller-srv6-02
Abstract
The PCE is a core component of Software-Defined Networking (SDN)
systems. A PCE-based Central Controller (PCECC) can simplify the
processing of a distributed control plane by blending it with
elements of SDN without necessarily completely replacing it.
Segment Routing (SR) technology leverages the source routing and
tunneling paradigms. Each path is specified as a set of "segments"
encoded in the header of each packet as a list of Segment Identifiers
(SIDs).
This document specifies the procedures and Path Computation Element
Communication Protocol (PCEP) extensions when a PCE-based controller
is also responsible for configuring the forwarding actions on the
routers, in addition to computing the paths for packet flows in the
SRv6 (SR in IPv6) network and telling the edge routers what
instructions to attach to packets as they enter the network. PCECC
is further enhanced for SRv6 SID allocation and distribution.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on 7 August 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
3. PCECC SRv6 . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. PCEP Requirements . . . . . . . . . . . . . . . . . . . . . . 6
5. Procedures for Using the PCE as a Central Controller (PCECC) in
SRv6 . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Stateful PCE Model . . . . . . . . . . . . . . . . . . . 6
5.2. New Functions . . . . . . . . . . . . . . . . . . . . . . 6
5.3. PCECC Capability Advertisement . . . . . . . . . . . . . 7
5.4. PCEP session IP address and TED Router-ID . . . . . . . . 8
5.5. SRv6 Path Operations . . . . . . . . . . . . . . . . . . 8
5.5.1. PCECC Segment Routing in IPv6 (SRv6) . . . . . . . . 8
5.5.1.1. PCECC SRv6 Node/Prefix SID Allocation . . . . . . 8
5.5.1.2. PCECC SRv6 Adjacency SID Allocation . . . . . . . 9
5.5.1.3. Redundant PCEs . . . . . . . . . . . . . . . . . 9
5.5.1.4. Re-Delegation and Cleanup . . . . . . . . . . . . 10
5.5.1.5. Synchronization of SRv6 SID Allocations . . . . . 10
5.5.1.6. Binding SID . . . . . . . . . . . . . . . . . . . 10
5.5.1.7. Anycast SID . . . . . . . . . . . . . . . . . . . 10
6. PCEP Messages . . . . . . . . . . . . . . . . . . . . . . . . 10
7. PCEP Objects . . . . . . . . . . . . . . . . . . . . . . . . 10
7.1. OPEN Object . . . . . . . . . . . . . . . . . . . . . . . 10
7.1.1. PCECC Capability sub-TLV . . . . . . . . . . . . . . 10
7.2. SRv6 Path Setup . . . . . . . . . . . . . . . . . . . . . 11
7.3. CCI Object . . . . . . . . . . . . . . . . . . . . . . . 11
7.4. FEC Object . . . . . . . . . . . . . . . . . . . . . . . 12
8. Security Considerations . . . . . . . . . . . . . . . . . . . 13
9. Manageability Considerations . . . . . . . . . . . . . . . . 13
9.1. Control of Function and Policy . . . . . . . . . . . . . 13
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9.2. Information and Data Models . . . . . . . . . . . . . . . 13
9.3. Liveness Detection and Monitoring . . . . . . . . . . . . 14
9.4. Verify Correct Operations . . . . . . . . . . . . . . . . 14
9.5. Requirements On Other Protocols . . . . . . . . . . . . . 14
9.6. Impact On Network Operations . . . . . . . . . . . . . . 14
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
10.1. PCECC-CAPABILITY sub-TLV . . . . . . . . . . . . . . . . 14
10.2. PCEP Object . . . . . . . . . . . . . . . . . . . . . . 14
10.3. PCEP-Error Object . . . . . . . . . . . . . . . . . . . 15
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 15
12.1. Normative References . . . . . . . . . . . . . . . . . . 15
12.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. Contributor Addresses . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
The PCE [RFC4655] was developed to offload the path computation
function from routers in an MPLS traffic-engineered (TE) network. It
can compute optimal paths for traffic across a network and can also
update the paths to reflect changes in the network or traffic
demands. Since then, the role and function of the PCE have grown to
cover a number of other uses (such as GMPLS [RFC7025]) and to allow
delegated control [RFC8231] and PCE-initiated use of network
resources [RFC8281].
According to [RFC7399], Software-Defined Networking (SDN) refers to a
separation between the control elements and the forwarding components
so that software running in a centralized system, called a
controller, can act to program the devices in the network to behave
in specific ways. A required element in an SDN architecture is a
component that plans how the network resources will be used and how
the devices will be programmed. It is possible to view this
component as performing specific computations to place traffic flows
within the network given knowledge of the availability of network
resources, how other forwarding devices are programmed, and the way
that other flows are routed. This is the function and purpose of a
PCE, and the way that a PCE integrates into a wider network control
system (including an SDN system) is presented in [RFC7491].
In early PCE implementations, where the PCE was used to derive paths
for MPLS Label Switched Paths (LSPs), paths were requested by network
elements (known as Path Computation Clients (PCCs)), and the results
of the path computations were supplied to network elements using the
PCE Communication Protocol (PCEP) [RFC5440]. This protocol was later
extended to allow a PCE to send unsolicited requests to the network
for LSP establishment [RFC8281].
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[RFC8283] introduces the architecture for PCE as a central controller
(PCECC) as an extension of the architecture described in [RFC4655]
and assumes the continued use of PCEP as the protocol used between
PCE and PCC. [RFC8283] further examines the motivations and
applicability for PCEP as a Southbound Interface (SBI), and
introduces the implications for the protocol.
[I-D.ietf-teas-pcecc-use-cases] describes the use cases for the PCECC
architecture.
[RFC9050] specify the procedures and PCEP extensions for using the
PCE as the central controller for static LSPs, where LSPs can be
provisioned as explicit label instructions at each hop on the end-to-
end path.
Segment Routing (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). [RFC8402] provides an introduction to the
SR architecture. The corresponding IS-IS and OSPF extensions are
specified in [RFC8667] and [RFC8665], respectively. It relies on a
series of forwarding instructions being placed in the header of a
packet in the form of a list of segments forming the path, called the
Segment List. Segment Routing can be applied to the IPv6
architecture with the Segment Routing Header (SRH) [RFC8754]. A
segment is encoded as an IPv6 address. An ordered list of segments
is encoded as an ordered list of IPv6 addresses in the routing
header. The active segment is indicated by the Destination Address
of the packet. Upon completion of a segment, a pointer in the new
routing header is incremented and indicates the next segment. The
segment routing architecture supports operations that can be used to
steer packet flows in a network, thus providing a form of traffic
engineering. [RFC8664] and [I-D.ietf-pce-segment-routing-ipv6]
specify the SR specific PCEP extensions.
The PCECC may perform centralized allocation of SR Segment
Identifiers (SIDs) and use PCEP to distribute them to the SR nodes.
The SR nodes continue to rely on IGP for distributed computation
(nexthop selection, protection etc) where PCE (and PCEP) does only
the allocation and distribution of SRv6 SIDs in the network. Note
that the topology at PCE is still learned via existing mechanisms.
A PCE-based central controller may be responsible for computing the
paths for packet flows in an MPLS Segment Routing (SR-MPLS) network
and for telling the edge routers what instructions to attach to
packets as they enter the network.
[I-D.ietf-pce-pcep-extension-pce-controller-sr] specifies the
procedures and PCEP extensions when a PCE-based controller is
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additionally responsible for configuring the forwarding actions on
routers in an SR-MPLS network (i.e., for SR- MPLS SID distribution).
This document extends those procedures to include SRv6 SID
distribution as well.
2. Terminology
Terminologies used in this document is the same as described in
[RFC8283] and [I-D.ietf-pce-segment-routing-ipv6].
2.1. 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.
3. PCECC SRv6
[RFC8664] specifies extensions to PCEP that allow a stateful PCE to
compute, update, or initiate SR-TE paths for MPLS dataplane. An
ingress node of an SR-TE path includes a list of MPLS labels (SIDs)
in all outgoing packets This is encoded in SR-ERO subobject, capable
of carrying a label (SID) as well as the identity of the node/
adjacency label (SID). [I-D.ietf-pce-segment-routing-ipv6] extends
the procedure to include support for SRv6 paths.
As per [RFC8754], an SRv6 Segment is a 128-bit value. "SRv6 SID" or
simply "SID" are often used as a shorter reference for "SRv6
Segment". Further details are in an illustration provided in
[RFC8986]. SR is applied to the IPv6 data plane using the SRH. An
SR path can be derived from an IGP Shortest Path Tree (SPT), but SR-
TE paths might not follow the IGP SPT. Such paths may be chosen by a
suitable network planning tool, or a PCE and provisioned on the
ingress node. [I-D.ietf-pce-segment-routing-ipv6] specifies the
SRv6-ERO subobject capable of carrying an SRv6 SID as well as the
identity of the node/adjacency represented by the SID.
[RFC8283] examines the motivations and applicability for PCECC and
use of PCEP as an SBI. Section 3.1.5. of [RFC8283] highlights the
use of PCECC for configuring the forwarding actions on the routers
and assuming responsibility for managing the identifier space. It
simplifies the processing of a distributed control plane by blending
it with elements of SDN and without necessarily completely replacing
it. This allows the operator to introduce the advantages of SDN
(such as programmability) into the network. Further, Section 3 of
[I-D.ietf-teas-pcecc-use-cases] describes some of the scenarios where
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the PCECC technique could be useful. Section 4 of [RFC8283] also
describes the implications on the protocol when used as an SDN SBI.
The operator needs to evaluate the advantages offered by PCECC
against the operational and scalability needs of the PCECC Section 9.
As per [RFC8283], PCECC can allocate the node/prefix/adjacency label
(SID) and provision them via PCEP. As per
[I-D.ietf-teas-pcecc-use-cases] this is also applicable to SRv6 SIDs.
The rest of the processing is similar to existing stateful PCE for
SRv6 [I-D.ietf-pce-segment-routing-ipv6].
4. PCEP Requirements
Following key requirements for PCECC-SRv6 should be considered when
designing the PCECC-based solution:
* A PCEP speaker supporting this document needs to have the
capability to advertise its PCECC-SRv6 capability to its peers.
* PCEP procedures need to allow for PCC-based SRv6 SID allocations.
* PCEP procedures need to provide a means to update (or clean up)
the SRv6 SID to the PCC.
* PCEP procedures need to provide a means to synchronize the SRv6
SID allocations between the PCE and the PCC in the PCEP messages.
5. Procedures for Using the PCE as a Central Controller (PCECC) in SRv6
5.1. Stateful PCE Model
Active stateful PCE is described in [RFC8231]. A PCE as a Central
Controller (PCECC) reuses the existing active stateful PCE mechanism
as much as possible to control the LSPs.
5.2. New Functions
The PCEP messages PCRpt, PCInitiate, and PCUpd are used to send LSP
reports, LSP setup, and LSP update respectively. [RFC9050] describes
the use of the PCInitiate message with a new objects called the CCI
for encoding the central controller instructions.
[I-D.ietf-pce-pcep-extension-pce-controller-sr] defines a CCI object-
type for SR-MPLS.
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This document uses the same PCEP messages and their extensions as
described in [RFC9050] and
[I-D.ietf-pce-pcep-extension-pce-controller-sr]. It extends their
use to PCECC-SRv6. In particular, this document defines a new CCI
object-type for SRv6 with type=TBD3.
5.3. PCECC Capability Advertisement
During the PCEP initialization phase, PCEP speakers (PCE or PCC)
advertise their support of and willingness to use PCEP extensions for
the PCECC. A PCEP speaker includes the PCECC-CAPABILITY sub-TLV in
the PATH-SETUP-TYPE-CAPABILITY TLV as per [RFC9050].
[I-D.ietf-pce-pcep-extension-pce-controller-sr] defines the S bit in
the PCECC-CAPABILITY sub-TLV to indicate support for PCECC-SR-MPLS.
This document defines another bit (the I bit) to indicate PCECC
support for SRv6. A PCC MUST set the I bit in the PCECC-CAPABILITY
sub-TLV and include the SRv6-PCE-CAPABILITY sub-TLV
([I-D.ietf-pce-segment-routing-ipv6]) in the OPEN object (inside the
PATH-SETUP-TYPE-CAPABILITY TLV) to support the PCECC SRv6 extensions
defined in this document.
Implementations that are not aware of the meaning of the I bit will
ignore it per Section 7.1.1 of [RFC9050]. Implementations that are
not aware of the SRv6-PCE-CAPABILITY sub-TLV but receive one in the
PATH-SETUP-TYPE-CAPABILITY TLV with the PST value of 3 set (per
[I-D.ietf-pce-segment-routing-ipv6], will respond as described in
Section 5 of [RFC8408].
If the I bit is set in PCECC-CAPABILITY sub-TLV and the SRv6-PCE-
CAPABILITY sub-TLV is not advertised, or is advertised without the I
bit set, in the OPEN object, a receiver that implements this
specification MUST:
* send a PCErr message with Error-Type=19 (Invalid Operation) and
Error-value=TBD4 (SRv6 capability was not advertised) and
* terminate the session.
The rest of the processing is as per [RFC9050] and
[I-D.ietf-pce-pcep-extension-pce-controller-sr].
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5.4. PCEP session IP address and TED Router-ID
As described in [I-D.ietf-pce-pcep-extension-pce-controller-sr], it
is important to link the session IP address with the Router-ID in the
Traffic Engineering Database (TED) for successful PCECC-SRv6
operations. Note that the session IP needs be different from the
IPv6 address for the SID to avoid any impact on the PCEP session when
the SRv6 SID is allocated. The Router-ID TLVs are specified in
[I-D.ietf-pce-pcep-extension-pce-controller-sr] and are used to
advertise the TE mapping information.
5.5. SRv6 Path Operations
[RFC8664] specifies the PCEP extension to allow a stateful PCE to
compute and initiate SR-TE paths, as well as a PCC to request a path
subject to certain constraint(s) and optimization criteria in SR
networks. [I-D.ietf-pce-segment-routing-ipv6] extends it to support
SRv6.
The Path Setup Type for SRv6 (PST=3) is used on the PCEP session with
the Ingress as per [I-D.ietf-pce-segment-routing-ipv6].
5.5.1. PCECC Segment Routing in IPv6 (SRv6)
Segment Routing (SR) as described in [RFC8402] depends on "segments"
that are advertised by Interior Gateway Protocols (IGPs). The SR-
node allocates and advertises the SID (node, adj, etc) and floods
them via the IGP. This document describes a new mechanism where PCE
allocates the SRv6 SID centrally and uses PCEP to distribute them to
all nodes. In some deployments, PCE (and PCEP) are better suited
than IGP because of the centralized nature of PCE and direct TCP
based PCEP sessions to the node. Note that only the SRv6 SID
allocation and distribution is done by the PCEP, all other SRv6
operations (nexthop selection, protection, etc) are still done by the
node (and the IGPs).
5.5.1.1. PCECC SRv6 Node/Prefix SID Allocation
Each node (PCC) is allocated a node SRv6 SID by the PCECC. The PCECC
sends the PCInitiate message to update the SRv6 SID table of each
node. The TE Router-ID is determined from the TED or from "IPv4/IPv6
Router-ID" TLVs [I-D.ietf-pce-pcep-extension-pce-controller-sr], in
the OPEN Object.
On receiving the SRv6 node SID allocation, each node (PCC) uses the
local routing information to determine the next-hop and download the
forwarding instructions accordingly. The PCInitiate message uses the
FEC object [I-D.ietf-pce-pcep-extension-pce-controller-sr].
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On receiving the SRv6 node SID allocation:
For the local SID, the node (PCC) needs to update SID with
associated function (END function in this case) in "My Local SID
Table" ([RFC8986]).
For the non-local SID, the node (PCC) uses the local routing
information to determine the next-hop and download the forwarding
instructions accordingly.
The forwarding behavior and the end result are similar to IGP based
"Node-SID" in SRv6. Thus, from anywhere in the domain, it enforces
the ECMP-aware shortest-path forwarding of the packet towards the
related node as per [RFC8402].
PCE relies on the Node/Prefix SRv6 SID clean up using the same
PCInitiate message as per [RFC8281].
5.5.1.2. PCECC SRv6 Adjacency SID Allocation
For PCECC-SRv6, apart from node-SID, Adj-SID is used where each
adjacency is allocated an Adj-SID by the PCECC. The PCECC sends
PCInitiate message to update the SRv6 SID entry for each adjacency to
all nodes in the domain. Each node (PCC) download the SRv6 SID
instructions accordingly. Similar to SRv6 Node/Prefix Label
allocation, the PCInitiate message in this case uses the FEC object.
The forwarding behavior and the end result is similar to IGP based
"Adj-SID" in SRv6 as per [RFC8402].
The handling of adjacencies on the LAN subnetworks is specified in
[RFC8402]. PCECC MUST assign Adj-SID for every pair of routers in
the LAN. The rest of the protocol mechanism remains the same.
PCE relies on the Adj label clean up using the same PCInitiate
message as per [RFC8281].
5.5.1.3. Redundant PCEs
[I-D.ietf-pce-state-sync] describes the synchronization mechanism
between the stateful PCEs. The SRv6 SIDs allocated by a PCE MUST
also be synchronized among PCEs for PCECC-SRv6 state synchronization.
Note that the SRv6 SIDs are independent of the SRv6 paths, and remain
intact until any topology change. The redundant PCEs MUST have a
common view of all SRv6 SIDs allocated in the domain.
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5.5.1.4. Re-Delegation and Cleanup
[RFC9050] describes the action needed for CCIs for the static LSPs on
a terminated session. Same holds true for the CCI for SRv6 SID as
well.
5.5.1.5. Synchronization of SRv6 SID Allocations
[RFC9050] describes the synchronization of CCIs via the LSP state
synchronization as described in [RFC8231] and [RFC8232]. Same
procedures are applied for the SRv6 SID CCIs.
5.5.1.6. Binding SID
Another SID called binding SID is described in
[I-D.ietf-pce-binding-label-sid]. The PCECC mechanism can also be
used to allocate the binding SID for SRv6.
A procedure for binding label/SID allocation is described in
[I-D.ietf-pce-binding-label-sid] and is applicable for all path setup
types (including SRv6 paths).
5.5.1.7. Anycast SID
As per [RFC8402], an anycast segment or Anycast-SID enforces the
ECMP-aware shortest-path forwarding towards the closest node of the
anycast set. Note that the SRv6 anycast prefix segments can also be
allocated and distributed in the same way as described in
Section 5.5.1.1.
6. PCEP Messages
The PCEP messages are as per
[I-D.ietf-pce-pcep-extension-pce-controller-sr].
7. PCEP Objects
7.1. OPEN Object
7.1.1. PCECC Capability sub-TLV
[RFC9050] defined the PCECC-CAPABILITY sub-TLV.
A new I-bit is defined in PCECC-CAPABILITY sub-TLV for PCECC-SRv6:
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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=1 | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |I|S|L|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
[Editor's Note - The above figure is included for ease of the reader
but should be removed before publication.]
I (PCECC-SRv6-CAPABILITY - 1 bit - TBD1): If set to 1 by a PCEP
speaker, it indicates that the PCEP speaker is capable of PCECC-SRv6
capability and the PCE allocates the Node and Adj SRv6 SID on this
session.
7.2. SRv6 Path Setup
The PATH-SETUP-TYPE TLV is defined in [RFC8408]. A PST value of 3 is
used when Path is setup via SRv6 mode as per
[I-D.ietf-pce-segment-routing-ipv6]. The procedure for SRv6 path
setup as specified in [I-D.ietf-pce-segment-routing-ipv6] remains
unchanged.
7.3. CCI Object
The Central Control Instructions (CCI) Object is used by the PCE to
specify the controller instructions is defined in [RFC9050]. This
document defines another object-type for SRv6 purpose.
CCI Object-Type is TBD3 for SRv6 as 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| CC-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MT-ID | Algorithm | Flags |B|P|G|C|N|E|V|L|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | SRv6 Endpoint Function |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SRv6 Identifier |
| (128-bit) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID |
| Structure |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Optional TLV //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The field CC-ID is as described in [RFC9050]. The field MT-ID,
Algorithm, Flags are defined in
[I-D.ietf-pce-pcep-extension-pce-controller-sr].
Reserved: MUST be set to 0 while sending and ignored on receipt.
SRv6 Endpoint Function: 16-bit field representing supported functions
associated with SRv6 SIDs.
SRv6 Identifier: 128-bit IPv6 addresses representing SRv6 segment.
SID Structure: 64-bit field formatted as per "SID Structure" in
[I-D.ietf-pce-segment-routing-ipv6]. The sum of all four sizes in
the SID Structure must be lower or equal to 128 bits. According to
[I-D.ietf-pce-segment-routing-ipv6], if the sum of all four sizes
advertised in the SID Structure is larger than 128 bits, the
corresponding SRv6 SID is considered invalid and a PCErr message with
Error-Type = 10 ("Reception of an invalid object") and Error-Value =
37 ("Invalid SRv6 SID Structure") is returned.
7.4. FEC Object
The FEC Object is used to specify the FEC information and MAY be
carried within PCInitiate or PCRpt message.
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FEC Object (and various Object-Types) are described in
[I-D.ietf-pce-pcep-extension-pce-controller-sr]. SRv6 Node SID MUST
includes the FEC Object-Type 2 for IPv6 Node. SRv6 Adjacency SID
MUST include the FEC Object-Type=4 or 6 for IPv6 adjacency. Further
FEC object types could be added in future extensions.
8. Security Considerations
As per [RFC8283], the security considerations for a PCE-based
controller are a little different from those for any other PCE
system. That is, the operation relies heavily on the use and
security of PCEP, so consideration should be given to the security
features discussed in [RFC5440] and the additional mechanisms
described in [RFC8253]. It further lists the vulnerability of a
central controller architecture, such as a central point of failure,
denial of service, and a focus for interception and modification of
messages sent to individual Network Elements (NEs).
The PCECC extension builds on the existing PCEP messages; thus, the
security considerations described in [RFC5440], [RFC8231], [RFC8281],
[RFC9050], and [I-D.ietf-pce-pcep-extension-pce-controller-sr]
continue to apply.
As per [RFC8231], it is RECOMMENDED that these PCEP extensions only
be activated on mutually-authenticated and encrypted sessions across
PCEs and PCCs belonging to the same administrative authority, using
Transport Layer Security (TLS) [RFC8253] as per the recommendations
and best current practices in [RFC9325] (unless explicitly set aside
in [RFC8253]).
9. Manageability Considerations
9.1. Control of Function and Policy
A PCE or PCC implementation SHOULD allow to configure to enable/
disable PCECC SRv6 capability as a global configuration. The
implementation SHOULD also allow setting the local IP address used by
the PCEP session.
9.2. Information and Data Models
[RFC7420] describes the PCEP MIB, this MIB can be extended to get the
PCECC SRv6 capability status.
The PCEP YANG module [I-D.ietf-pce-pcep-yang] could be extended to
enable/disable PCECC SRv6 capability.
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9.3. Liveness Detection and Monitoring
Mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already
listed in [RFC5440].
9.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation
verification requirements in addition to those already listed in
[RFC5440] and [RFC8231].
9.5. Requirements On Other Protocols
PCEP extensions defined in this document do not put new requirements
on other protocols. It is expected that PCECC based mechanisms
described in this document are not used in conjunction with the IGP
based mechanism, though different SID allocated and distributed via
both mechanisms can coexist.
9.6. Impact On Network Operations
PCEP implementation SHOULD allow a limit to be placed on the rate of
PCInitiate/PCUpd messages (as per [RFC8231]) sent by PCE and
processed by PCC. It SHOULD also allow sending a notification when a
rate threshold is reached.
10. IANA Considerations
10.1. PCECC-CAPABILITY sub-TLV
[RFC9050] defines the PCECC-CAPABILITY sub-TLV and requests that IANA
creates a registry to manage the value of the PCECC-CAPABILITY sub-
TLV's Flag field. IANA is requested to allocate a new bit in the
PCECC-CAPABILITY sub-TLV Flag Field registry, as follows:
+======+==============+===============+
| Bit | Description | Reference |
+======+==============+===============+
| TBD1 | SRv6 (I-bit) | This document |
+------+--------------+---------------+
Table 1
10.2. PCEP Object
IANA is requested to allocate a new code-point for the new CCI
object-type in "PCEP Objects" sub-registry as follows:
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+====================+======+=============+===============+
| Object-Class Value | Name | Object-Type | Reference |
+====================+======+=============+===============+
| 44 | CCI | | [RFC9050] |
+--------------------+------+-------------+---------------+
| | | TBD3: SRv6 | This document |
+--------------------+------+-------------+---------------+
Table 2
10.3. PCEP-Error Object
IANA is requested to allocate new error types and error values within
the "PCEP-ERROR Object Error Types and Values" sub-registry of the
PCEP Numbers registry for the following errors:
+============+===============================+===========+
| Error-Type | Meaning | Reference |
+============+===============================+===========+
| 19 | Invalid Operation | |
+------------+-------------------------------+-----------+
| | Error-value = TBD4: SRv6 | This |
| | capability was not advertised | document |
+------------+-------------------------------+-----------+
Table 3
11. Acknowledgments
Thanks to Adrian Farrel for review and suggested text.
12. References
12.1. 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>.
[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>.
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[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>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
[I-D.ietf-pce-segment-routing-ipv6]
Li, C., Kaladharan, P., Sivabalan, S., Koldychev, M., and
Y. Zhu, "Path Computation Element Communication Protocol
(PCEP) Extensions for Segment Routing leveraging the IPv6
dataplane", Work in Progress, Internet-Draft, draft-ietf-
pce-segment-routing-ipv6-21, 1 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
segment-routing-ipv6-21>.
[RFC9050] Li, Z., Peng, S., Negi, M., Zhao, Q., and C. Zhou, "Path
Computation Element Communication Protocol (PCEP)
Procedures and Extensions for Using the PCE as a Central
Controller (PCECC) of LSPs", RFC 9050,
DOI 10.17487/RFC9050, July 2021,
<https://www.rfc-editor.org/info/rfc9050>.
[I-D.ietf-pce-pcep-extension-pce-controller-sr]
Li, Z., Peng, S., Negi, M. S., Zhao, Q., and C. Zhou, "PCE
Communication Protocol (PCEP) Extensions for Using PCE as
a Central Controller (PCECC) for Segment Routing (SR) MPLS
Segment Identifier (SID) Allocation and Distribution.",
Work in Progress, Internet-Draft, draft-ietf-pce-pcep-
extension-pce-controller-sr-08, 1 January 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
pcep-extension-pce-controller-sr-08>.
[I-D.ietf-pce-binding-label-sid]
Sivabalan, S., Filsfils, C., Tantsura, J., Previdi, S.,
and C. Li, "Carrying Binding Label/Segment Identifier
(SID) in PCE-based Networks.", Work in Progress, Internet-
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Draft, draft-ietf-pce-binding-label-sid-16, 27 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
binding-label-sid-16>.
12.2. Informative References
[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[RFC7025] Otani, T., Ogaki, K., Caviglia, D., Zhang, F., and C.
Margaria, "Requirements for GMPLS Applications of PCE",
RFC 7025, DOI 10.17487/RFC7025, September 2013,
<https://www.rfc-editor.org/info/rfc7025>.
[RFC7399] Farrel, A. and D. King, "Unanswered Questions in the Path
Computation Element Architecture", RFC 7399,
DOI 10.17487/RFC7399, October 2014,
<https://www.rfc-editor.org/info/rfc7399>.
[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>.
[RFC7491] King, D. and A. Farrel, "A PCE-Based Architecture for
Application-Based Network Operations", RFC 7491,
DOI 10.17487/RFC7491, March 2015,
<https://www.rfc-editor.org/info/rfc7491>.
[RFC9325] Sheffer, Y., Saint-Andre, P., and T. Fossati,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
2022, <https://www.rfc-editor.org/info/rfc9325>.
[RFC8232] Crabbe, E., Minei, I., Medved, J., Varga, R., Zhang, X.,
and D. Dhody, "Optimizations of Label Switched Path State
Synchronization Procedures for a Stateful PCE", RFC 8232,
DOI 10.17487/RFC8232, September 2017,
<https://www.rfc-editor.org/info/rfc8232>.
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[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>.
[RFC8283] Farrel, A., Ed., Zhao, Q., Ed., Li, Z., and C. Zhou, "An
Architecture for Use of PCE and the PCE Communication
Protocol (PCEP) in a Network with Central Control",
RFC 8283, DOI 10.17487/RFC8283, December 2017,
<https://www.rfc-editor.org/info/rfc8283>.
[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>.
[RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", RFC 8665,
DOI 10.17487/RFC8665, December 2019,
<https://www.rfc-editor.org/info/rfc8665>.
[RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
Extensions for Segment Routing", RFC 8667,
DOI 10.17487/RFC8667, December 2019,
<https://www.rfc-editor.org/info/rfc8667>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.
[I-D.ietf-teas-pcecc-use-cases]
Li, Z., Dhody, D., Zhao, Q., Ke, Z., and B. Khasanov, "The
Use Cases for Path Computation Element (PCE) as a Central
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Controller (PCECC).", Work in Progress, Internet-Draft,
draft-ietf-teas-pcecc-use-cases-13, 8 January 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-teas-
pcecc-use-cases-13>.
[I-D.ietf-pce-pcep-yang]
Dhody, D., Beeram, V. P., Hardwick, J., and J. Tantsura,
"A YANG Data Model for Path Computation Element
Communications Protocol (PCEP)", Work in Progress,
Internet-Draft, draft-ietf-pce-pcep-yang-22, 11 September
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
pce-pcep-yang-22>.
[I-D.ietf-pce-state-sync]
Litkowski, S., Sivabalan, S., Li, C., and H. Zheng, "Inter
Stateful Path Computation Element (PCE) Communication
Procedures.", Work in Progress, Internet-Draft, draft-
ietf-pce-state-sync-06, 2 January 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-pce-
state-sync-06>.
Appendix A. Contributor Addresses
Dhruv Dhody
Huawei
India
EMail: dhruv.ietf@gmail.com
Authors' Addresses
Zhenbin Li
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing
100095
China
Email: lizhenbin@huawei.com
Shuping Peng
Huawei Technologies
Huawei Bld., No.156 Beiqing Rd.
Beijing
100095
China
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Email: pengshuping@huawei.com
Xuesong Geng
Huawei Technologies
China
Email: gengxuesong@huawei.com
Mahendra Singh Negi
RtBrick Inc
N-17L, 18th Cross Rd, HSR Layout
Bangalore 560102
Karnataka
India
Email: mahend.ietf@gmail.com
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