PCE Working Group Q. Zhao
Internet-Draft Z. Li
Intended status: Standards Track D. Dhody
Expires: December 21, 2018 S. Karunanithi
Huawei Technologies
A. Farrel
Juniper Networks, Inc
C. Zhou
Cisco Systems
June 19, 2018

PCEP Procedures and Protocol Extensions for Using PCE as a Central Controller (PCECC) of SR-LSPs
draft-zhao-pce-pcep-extension-pce-controller-sr-03

Abstract

The Path Computation Element (PCE) is a core component of Software- Defined Networking (SDN) systems. 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.

PCE was developed to derive paths for MPLS Label Switched Paths (LSPs), which are supplied to the head end of the LSP using the Path Computation Element Communication Protocol (PCEP). But SDN has a broader applicability than signaled (G)MPLS traffic-engineered (TE) networks, and the PCE may be used to determine paths in a range of use cases. PCEP has been proposed as a control protocol for use in these environments to allow the PCE to be fully enabled as a central controller.

A PCE-based central controller (PCECC) can simplify the processing of a distributed control plane by blending it with elements of SDN and without necessarily completely replacing it. Thus, the LSP can be calculated/setup/initiated and the label forwarding entries can also be downloaded through a centralized PCE server to each network devices along the path while leveraging the existing PCE technologies as much as possible.

This document specifies the procedures and PCEP protocol 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 a segment routing network and telling the edge routers what instructions to attach to packets as they enter the network.

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/.

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This Internet-Draft will expire on December 21, 2018.

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Table of Contents

1. Introduction

The Path Computation Element (PCE) [RFC4655] was developed to offload path computation function from routers in an MPLS traffic-engineered network. Since then, the role and function of the PCE has 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 Path Computation Element Communication Protocol (PCEP) [RFC5440]. This protocol was later extended to allow a PCE to send unsolicited requests to the network for LSP establishment [RFC8281].

[RFC8283] introduces the architecture for PCE as a central controller 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.

[I-D.zhao-pce-pcep-extension-for-pce-controller] specify the procedures and PCEP protocol 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). [I-D.ietf-spring-segment-routing] provides an introduction to SR architecture. The corresponding IS-IS and OSPF extensions are specified in [I-D.ietf-isis-segment-routing-extensions] and [I-D.ietf-ospf-segment-routing-extensions] , respectively. It relies on a series of forwarding instructions being placed in the header of a packet. The segment routing architecture supports operations that can be used to steer packet flows in a network, thus providing a form of traffic engineering. [I-D.ietf-pce-segment-routing] specify the SR specific PCEP extensions.

PCECC may further use PCEP protocol for SR SID (Segment Identifier) distribution on the SR nodes with some benefits.

This document specifies the procedures and PCEP protocol extensions when a PCE-based controller is also responsible for configuring the forwarding actions on the routers (SR SID distribution in this case), in addition to computing the paths for packet flows in a segment routing network and telling the edge routers what instructions to attach to packets as they enter the network.

1.1. 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.

2. Terminology

Terminologies used in this document is same as described in the draft [RFC8283] and [I-D.ietf-teas-pcecc-use-cases].

3. PCECC SR

[I-D.ietf-pce-segment-routing] specifies extensions to PCEP that allow a stateful PCE to compute, update or initiate SR-TE paths. An ingress node of an SR-TE path appends all outgoing packets with a list of MPLS labels (SIDs). This is encoded in SR-ERO subobject, capable of carrying a label (SID) as well as the identity of the node/adjacency label (SID).

The notion of segment and SID is defined in [I-D.ietf-spring-segment-routing], which fits the MPLS architecture [RFC3031] as the label which is managed by a local allocation process of LSR (similarly to other MPLS signaling protocols) [I-D.ietf-spring-segment-routing-mpls]. The SR information such as node/adjacency label (SID) is flooded via IGP as specified in [I-D.ietf-isis-segment-routing-extensions] and [I-D.ietf-ospf-segment-routing-extensions].

As per [RFC8283], PCE as a central controller can allocate and provision the node/prefix/adjacency label (SID) via PCEP.

Rest of the processing is similar to existing stateful PCE with SR mechanism.

For the purpose of this document, it is assumed that label range to be used by a PCE is set on both PCEP peers. Further, a global label range is assumed to be set on all PCEP peers in the SR domain.

4. PCEP Requirements

Following key requirements for PCECC-SR should be considered when` designing the PCECC based solution:

5. Procedures for Using the PCE as the Central Controller (PCECC) in Segment Routing

5.1. Stateful PCE Model

Active stateful PCE is described in [RFC8231]. PCE as a central controller (PCECC) reuses existing Active stateful PCE mechanism as much as possible to control the LSP.

5.2. New LSP Functions

This document uses the same PCEP messages and its extensions which are described in [I-D.zhao-pce-pcep-extension-for-pce-controller] for PCECC-SR as well.

PCEP messages PCRpt, PCInitiate, PCUpd are also used to send LSP Reports, LSP setup and LSP update respectively. The extended PCInitiate message described in [I-D.zhao-pce-pcep-extension-for-pce-controller] is used to download or cleanup central controller's instructions (CCIs) (SR SID in scope of this document). The extended PCRpt message described in [I-D.zhao-pce-pcep-extension-for-pce-controller] is also used to report the CCIs (SR SIDs) from PCC to PCE.

[I-D.zhao-pce-pcep-extension-for-pce-controller] specify an object called CCI for the encoding of central controller's instructions. This document extends the CCI by defining a new object-type for segment routing. The PCEP messages are extended in this document to handle the PCECC operations for SR.

5.3. PCECC Capability Advertisement

During PCEP Initialization Phase, PCEP Speakers (PCE or PCC) advertise their support of PCECC extensions. A PCEP Speaker includes the "PCECC Capability" sub-TLV, described in [I-D.zhao-pce-pcep-extension-for-pce-controller].

A new S-bit is added in PCECC-CAPABILITY sub-TLV to indicate support for PCECC-SR. A PCC MUST set S-bit in PCECC-CAPABILITY sub-TLV and include SR-PCE-CAPABILITY sub-TLV ([I-D.ietf-pce-segment-routing]) in OPEN Object (inside the the PATH-SETUP-TYPE-CAPABILITY TLV) to support the PCECC SR extensions defined in this document. If S-bit is set in PCECC-CAPABILITY sub-TLV and SR-PCE-CAPABILITY sub-TLV is not advertised in OPEN Object, PCE SHOULD send a PCErr message with Error-Type=19 (Invalid Operation) and Error-value=TBD(SR capability was not advertised) and terminate the session.

5.4. PCEP session IP address and TEDB Router ID

PCE may construct its TEDB by participating in the IGP ([RFC3630] and [RFC5305] for MPLS-TE; [RFC4203] and [RFC5307] for GMPLS). An alternative is offered by BGP-LS [RFC7752] and [I-D.dhodylee-pce-pcep-ls].

PCEP [RFC5440] speaker MAY use any IP address while creating a TCP session. It is important to link the session IP address with the Router ID in TEDB for successful PCECC operations.

During PCEP Initialization Phase, PCC SHOULD advertise the TE mapping information. Thus a PCC includes the "Node Attributes TLV" [I-D.dhodylee-pce-pcep-ls] with "IPv4/IPv6 Router-ID of Local Node", in the OPEN Object for this purpose. [RFC7752] describes the usage as auxiliary Router-IDs that the IGP might be using, e.g., for TE purposes. If there are more than one auxiliary Router-ID of a given type, then multiple TLVs are used to encode them.

If "IPv4/IPv6 Router-ID" TLV is not present, the TCP session IP address is directly used for the mapping purpose.

5.5. LSP Operations

The PCEP messages pertaining to PCECC-SR MUST include PATH-SETUP-TYPE TLV [I-D.ietf-pce-lsp-setup-type] with PST=TBD in the SRP object to clearly identify the PCECC-SR LSP is intended.

5.5.1. PCECC Segment Routing (SR)

Segment Routing (SR) as described in [I-D.ietf-spring-segment-routing] depends on "segments" that are advertised by Interior Gateway Protocols (IGPs). The SR-node allocates and advertises the SID (node, adj etc) and flood via the IGP. This document proposes a new mechanism where PCE allocates the SID (label/index/SID) centrally and uses PCEP to advertise the SID. In some deployments PCE (and PCEP) are better suited than IGP because of centralized nature of PCE and direct TCP based PCEP session to the node.

5.5.1.1. PCECC SR Node/Prefix SID allocation

Each node (PCC) is allocated a node-SID by the PCECC. The PCECC sends PCInitiate message to update the label map of each node to all the nodes in the domain. The TE router ID is determined from the TEDB or from "IPv4/IPv6 Router-ID" Sub-TLV [I-D.dhodylee-pce-pcep-ls], in the OPEN Object Section 5.4.

It is RECOMMENDED that PCEP session with PCECC SR capability to use a different session IP address during TCP session establishment than the node Router ID in TEDB, to make sure that the PCEP session does not get impacted by the SR Node/Prefix Label maps (Section 5.4).

If a node (PCC) receives a PCInitiate message with a CCI encoding a SID, out of the range set aside for the SRGB, it MUST send a PCErr message with Error-type=TBD (PCECC failure) and Error-value=TBD (SID out of range) and MUST include the SRP object to specify the error is for the corresponding label update via PCInitiate message.

On receiving the label map, each node (PCC) uses the local information to determine the next-hop and download the label forwarding instructions accordingly. The PCInitiate message in this case MUST NOT have LSP object but uses the new FEC object defined in this document.

    
               +---------+                           +-------+
               |PCC      |                           |  PCE  |
               |192.0.2.3|                           +-------+
        +------|         |                               |
        | PCC  +---------+                               |
        | 192.0.2.2| |                                   |
 +------|          | |                                   |
 |PCC   +----------+ |                                   |
 |192.0.2.1| |       |                                   |
 +---------+ |       |                                   |
     |       |       |                                   |
     |<------- PCInitiate, FEC=192.0.2.1---------------- | Label Map
     |       |       |      CC-ID=X                      | update
     |------- PCRpt,CC-ID=X  --------------------------->|
     |Find   |       |                                   |
     |Nexthop|<------- PCInitiate, FEC=192.0.2.1-------- | Label Map
     |locally|       |             CC-ID=Y               | update
     |       |-----  PCRpt,CC-ID=Y  -------------------->|
     |       |       |                                   |
     |       |       |<--- PCInitiate, FEC=192.0.2.1---- | Label Map
     |       |       |                 CC-ID=Z           | update
     |       |       |---- PCRpt,CC-ID=Z  -------------->|
     |       |       |                                   |

        

The forwarding behavior and the end result is similar to IGP based "Node-SID" in SR. Thus, from anywhere in the domain, it enforces the ECMP-aware shortest-path forwarding of the packet towards the related node.

PCE relies on the Node/Prefix Label cleanup using the same PCInitiate message.

The above example Figure 1 depict FEC and PCEP speakers that uses IPv4 address. Similarly IPv6 address (such as 2001:DB8::1) can be used during PCEP session establishment as well in FEC object as described in this specification.

5.5.1.2. PCECC SR Adjacency Label allocation

[I-D.ietf-pce-segment-routing] extends PCEP 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.

For PCECC SR, 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 label map of each Adj to the corresponding nodes in the domain. Each node (PCC) download the label forwarding instructions accordingly. Similar to SR Node/Prefix Label allocation, the PCInitiate message in this case MUST NOT have LSP object but uses the new FEC object defined in this document.

         
                 +---------+                         +-------+
                 |PCC      |                         |  PCE  |
                 |192.0.2.3|                         +-------+
          +------|         |                             |
          | PCC  +---------+                             |
          | 192.0.2.2| |                                 |
   +------|          | |                                 |
   |PCC   +----------+ |                                 |
   |192.0.2.1|  |      |                                 |
   +---------+  |      |                                 |
       |        |      |                                 |
       |<------ PCInitiate, FEC=192.0.2.1 / ------------ | Label Map
       |        |      |        192.0.2.2                | update
       |        |      |    CC-ID=A                      |
       |------- PCRpt,CC-ID=A  ------------------------->|
       |        |      |                                 |
       |        |<----- PCInitiate, FEC=192.0.2.2------- | Label Map
       |        |      |                192.0.2.1        | update
       |        |      |            CC-ID=B              |
       |        |-----  PCRpt,CC-ID=B  ----------------->|
       |        |      |                                 |

        

The forwarding behavior and the end result is similar to IGP based "Adj-SID" in SR.

The Path Setup Type for segment routing MUST be set for PCECC SR = TBD (see Section 7.2). All PCEP procedures and mechanism are similar to [I-D.ietf-pce-segment-routing].

PCE relies on the Adj label cleanup using the same PCInitiate message.

The above example Figure 2 depict FEC and PCEP speakers that uses IPv4 address. Similarly IPv6 address (such as 2001:DB8::1, 2001:DB8::2) can be used during PCEP session establishment as well in FEC object as described in this specification.

5.5.1.3. Redundant PCEs

[I-D.litkowski-pce-state-sync] describes synchronization mechanism between the stateful PCEs. The SR SIDs allocated by a PCE MUST also be synchronized among PCEs for PCECC SR state synchronization. Note that the SR SIDs are independent to the PCECC-SR LSP, and remains intact till any topology change. The redundant PCEs MUST have a common view of all SR SIDs allocated in the domain.

5.5.1.4. Re Delegation and Cleanup

[I-D.zhao-pce-pcep-extension-for-pce-controller] describes the action needed for CCIs for the Basic PCECC LSP on this terminated session. Similarly actions should be applied for the SR SID as well.

5.5.1.5. Synchronization of Label Allocations

[I-D.zhao-pce-pcep-extension-for-pce-controller] describes the synchronization of Central Controller's Instructions (CCI) via LSP state synchronization as described in [RFC8231] and [RFC8232]. Same procedures should be applied for SR SIDs as well.

6. PCEP messages

As defined in [RFC5440], a PCEP message consists of a common header followed by a variable-length body made of a set of objects that can be either mandatory or optional. An object is said to be mandatory in a PCEP message when the object must be included for the message to be considered valid. For each PCEP message type, a set of rules is defined that specify the set of objects that the message can carry. An implementation MUST form the PCEP messages using the object ordering specified in this document.

6.1. Central Control Instructions

6.1.1. The PCInitiate message

The PCInitiate Message defined in [RFC8281] and extended in [I-D.zhao-pce-pcep-extension-for-pce-controller] is further extended to support SR based central control instructions.

     <PCInitiate Message> ::= <Common Header>
                              <PCE-initiated-lsp-list>
  Where:
     <Common Header> is defined in [RFC5440]

     <PCE-initiated-lsp-list> ::= <PCE-initiated-lsp-request>
                                  [<PCE-initiated-lsp-list>]

     <PCE-initiated-lsp-request> ::= 
                          (<PCE-initiated-lsp-instantiation>|
                           <PCE-initiated-lsp-deletion>|
                           <PCE-initiated-lsp-central-control>)

     <PCE-initiated-lsp-central-control> ::= <SRP> 
                                             (<LSP>
                                             <cci-list>)|
                                             (<FEC>
                                             <CCI>)

     <cci-list> ::=  <CCI>
                     [<cci-list>]

  Where:
      <PCE-initiated-lsp-instantiation> and 
      <PCE-initiated-lsp-deletion> are as per 
      [RFC8281]. 

     The LSP and SRP object is defined in [RFC8231].          

The format of the extended PCInitiate message is as follows:

When PCInitiate message is used to distribute SR SIDs, the SRP, FEC and CCI objects MUST be present. The error handling for missing SRP or CCI object is as per [I-D.zhao-pce-pcep-extension-for-pce-controller]. If the FEC object is missing, the receiving PCC MUST send a PCErr message with Error-type=6 (Mandatory Object missing) and Error-value=TBD (FEC object missing).

To cleanup the SRP object must set the R (remove) bit.

6.1.2. The PCRpt message

The PCRpt message can be used to report the SR instructions received from the central controller (PCE) during the state synchronization phase.

      <PCRpt Message> ::= <Common Header>
                          <state-report-list>
   Where:

      <state-report-list> ::= <state-report>[<state-report-list>]

      <state-report> ::= (<lsp-state-report>|
                          <central-control-report>) 

      <lsp-state-report> ::= [<SRP>]
                             <LSP>
                             <path>

      <central-control-report> ::= [<SRP>] 
                                   (<LSP>
                                   <cci-list>)|
                                   (<FEC>
                                   <CCI>)

      <cci-list> ::=  <CCI>
                      [<cci-list>]   


    Where:
      <path> is as per [RFC8231] and the LSP and SRP object are 
      also defined in [RFC8231].

The format of the PCRpt message is as follows:

When PCRpt message is used to report the label map allocations, the FEC and CCI objects MUST be present. The error handling for CCI object is as per [I-D.zhao-pce-pcep-extension-for-pce-controller]. If the FEC object is missing, the receiving PCC MUST send a PCErr message with Error-type=6 (Mandatory Object missing) and Error-value=TBD (FEC object missing).

7. PCEP Objects

7.1. OPEN Object

7.1.1. PCECC Capability sub-TLV

[I-D.zhao-pce-pcep-extension-for-pce-controller] defined the PCECC-CAPABILITY TLV.

A new S-bit is defined in PCECC-CAPABILITY sub-TLV for PCECC-SR:


    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           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                             Flags                           |S|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        

S (PCECC-SR-CAPABILITY - 1 bit): If set to 1 by a PCEP speaker, it indicates that the PCEP speaker is capable for PCECC-SR capability and PCE would allocate node and Adj label on this session.

7.2. PATH-SETUP-TYPE TLV

The PATH-SETUP-TYPE TLV is defined in [I-D.ietf-pce-lsp-setup-type]. PST = TBD is used when Path is setup via PCECC SR mode.

On a PCRpt/PCUpd/PCInitiate message, the PST=TBD indicates that this LSP was setup via a PCECC-SR based mechanism where either the SIDs were allocated/instructed by PCE via PCECC mechanism.

7.3. CCI Object

The Central Control Instructions (CCI) Object is used by the PCE to specify the forwarding instructions is defined in [I-D.zhao-pce-pcep-extension-for-pce-controller]. This document defines another object-type for SR purpose.


 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        |N|E|V|L|O|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
//                  SID/Label/Index (variable)                 //
+---------------------------------------------------------------+
|                                                               |
//                        Optional TLV                         //
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        

CCI Object-Type is TBD for SR as below -

The field CC-ID is as described in [I-D.zhao-pce-pcep-extension-for-pce-controller]. Following new fields are defined for CCI Object-Type TBD -

MT-ID:
Multi-Topology ID (as defined in [RFC4915]).
Algorithm:
Single octet identifying the algorithm the SID is associated with. See [I-D.ietf-ospf-segment-routing-extensions].
Flags:
is used to carry any additional information pertaining to the CCI. The O bit was defined in [I-D.zhao-pce-pcep-extension-for-pce-controller], this document further defines following bits-
SID/Label/Index:
According to the V and L flags, it contains either:
A 32-bit index defining the offset in the SID/Label space advertised by this router.
A 24-bit label where the 20 rightmost bits are used for encoding the label value.

7.4. FEC Object

The FEC Object is used to specify the FEC information and MAY be carried within PCInitiate or PCRpt message.

FEC Object-Class is TBD.


   FEC Object-Type is 1 'IPv4 Node ID'.
   
    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      IPv4 Node ID                             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   FEC Object-Type is 2 'IPv6 Node ID'.

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                      IPv6 Node ID (16 bytes)                //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   FEC Object-Type is 3 'IPv4 Adjacency'.

    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                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   FEC Object-Type is 4 'IPv6 Adjacency'.

    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)                //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   FEC Object-Type is 5 'Unnumbered Adjacency with IPv4 NodeIDs'.

    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                         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


        

The FEC objects are as follows:

IPv4 Node ID: where IPv4 Node ID is specified as an IPv4 address of the Node. FEC Object-type is 1, and the Object-Length is 4 in this case.

IPv6 Node ID: where IPv6 Node ID is specified as an IPv6 address of the Node. FEC Object-type is 2, and the Object-Length is 16 in this case.

IPv4 Adjacency: where Local and Remote IPv4 address is specified as pair of IPv4 address of the adjacency. FEC Object-type is 3, and the Object-Length is 8 in this case.

IPv6 Adjacency: where Local and Remote IPv6 address is specified as pair of IPv6 address of the adjacency. FEC Object-type is 4, and the Object-Length is 32 in this case.

Unnumbered Adjacency with IPv4 NodeID: where a pair of Node ID / Interface ID tuples is used. FEC Object-type is 5, and the Object-Length is 16 in this case.

Binding ID: TBD

8. Security Considerations

The security considerations described in [I-D.zhao-pce-pcep-extension-for-pce-controller] apply to the extensions described in this document.

9. Manageability Considerations

9.1. Control of Function and Policy

A PCE or PCC implementation SHOULD allow to configure to enable/disable PCECC SR capability as a global configuration.

9.2. Information and Data Models

[RFC7420] describes the PCEP MIB, this MIB can be extended to get the PCECC SR capability status.

The PCEP YANG module [I-D.ietf-pce-pcep-yang] could be extended to enable/disable PCECC SR capability.

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.

9.6. Impact On Network Operations

PCEP implementation SHOULD allow a limit to be placed on the rate of PCLabelUpd messages 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 TLV

[I-D.zhao-pce-pcep-extension-for-pce-controller] defines the PCECC-CAPABILITY TLV and requests that IANA creates a registry to manage the value of the PCECC-CAPABILITY TLV's Flag field. IANA is requested to allocate a new bit in the PCECC-CAPABILITY TLV Flag Field registry, as follows:

Bit Description Reference
31 S((PCECC-SR-CAPABILITY)) This document

10.2. New Path Setup Type Registry

IANA is requested to allocate new PST Field in PATH- SETUP-TYPE TLV. The allocation policy for this new registry should be by IETF Consensus. The new registry should contain the following value:

Value Description Reference
TBD Traffic engineering path is This document
setup using PCECC-SR mode

10.3. PCEP Object

IANA is requested to allocate new registry for FEC PCEP object.

Object-Class Value Name Reference
TBD FEC This document
Object-Type : 1 IPv4 Node ID
Object-Type : 2 IPv6 Node ID
Object-Type : 3 IPv4 Adjacency
Object-Type : 4 IPv6 Adjacency
Object-Type : 5 Unnumbered Adjacency
with IPv4 NodeID

10.4. 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
---------- -------
6
Mandatory Object missing.
Error-value = TBD :
FEC object missing

19
Invalid operation.
Error-value = TBD :
SR capability was not advertised

11. Acknowledgments

We would like to thank Robert Tao, Changjing Yan, Tieying Huang and Avantika for their useful comments and suggestions.

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.
[RFC3630] Katz, D., Kompella, K. and D. Yeung, "Traffic Engineering (TE) Extensions to OSPF Version 2", RFC 3630, DOI 10.17487/RFC3630, September 2003.
[RFC4203] Kompella, K. and Y. Rekhter, "OSPF Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005.
[RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L. and P. Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC 4915, DOI 10.17487/RFC4915, June 2007.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, DOI 10.17487/RFC5305, October 2008.
[RFC5307] Kompella, K. and Y. Rekhter, "IS-IS Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, DOI 10.17487/RFC5440, March 2009.
[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.
[RFC7752] Gredler, H., Medved, J., Previdi, S., Farrel, A. and S. Ray, "North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGP", RFC 7752, DOI 10.17487/RFC7752, March 2016.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[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.
[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.

12.2. Informative References

[RFC3031] Rosen, E., Viswanathan, A. and R. Callon, "Multiprotocol Label Switching Architecture", RFC 3031, DOI 10.17487/RFC3031, January 2001.
[RFC4655] Farrel, A., Vasseur, J. and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, DOI 10.17487/RFC4655, August 2006.
[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.
[RFC7399] Farrel, A. and D. King, "Unanswered Questions in the Path Computation Element Architecture", RFC 7399, DOI 10.17487/RFC7399, October 2014.
[RFC7491] King, D. and A. Farrel, "A PCE-Based Architecture for Application-Based Network Operations", RFC 7491, DOI 10.17487/RFC7491, March 2015.
[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.
[RFC8283] Farrel, A., Zhao, Q., 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.
[I-D.ietf-teas-pcecc-use-cases] Zhao, Q., Li, Z., Khasanov, B., Ke, Z., Fang, L., Zhou, C., Communications, T. and A. Rachitskiy, "The Use Cases for Using PCE as the Central Controller(PCECC) of LSPs", Internet-Draft draft-ietf-teas-pcecc-use-cases-01, May 2017.
[I-D.ietf-pce-lsp-setup-type] Sivabalan, S., Tantsura, J., Minei, I., Varga, R. and J. Hardwick, "Conveying path setup type in PCEP messages", Internet-Draft draft-ietf-pce-lsp-setup-type-10, May 2018.
[I-D.ietf-pce-pcep-yang] Dhody, D., Hardwick, J., Beeram, V. and J. Tantsura, "A YANG Data Model for Path Computation Element Communications Protocol (PCEP)", Internet-Draft draft-ietf-pce-pcep-yang-07, March 2018.
[I-D.zhao-pce-pcep-extension-for-pce-controller] Zhao, Q., Li, Z., Dhody, D., Karunanithi, S., Farrel, A. and C. Zhou, "PCEP Procedures and Protocol Extensions for Using PCE as a Central Controller (PCECC) of LSPs", Internet-Draft draft-zhao-pce-pcep-extension-for-pce-controller-08, June 2018.
[I-D.ietf-pce-segment-routing] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W. and J. Hardwick, "PCEP Extensions for Segment Routing", Internet-Draft draft-ietf-pce-segment-routing-11, November 2017.
[I-D.ietf-isis-segment-routing-extensions] Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., Gredler, H., Litkowski, S., Decraene, B. and J. Tantsura, "IS-IS Extensions for Segment Routing", Internet-Draft draft-ietf-isis-segment-routing-extensions-17, June 2018.
[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", Internet-Draft draft-ietf-ospf-segment-routing-extensions-25, April 2018.
[I-D.litkowski-pce-state-sync] Litkowski, S., Sivabalan, S. and D. Dhody, "Inter Stateful Path Computation Element communication procedures", Internet-Draft draft-litkowski-pce-state-sync-03, April 2018.
[I-D.dhodylee-pce-pcep-ls] Dhody, D., Lee, Y. and D. Ceccarelli, "PCEP Extension for Distribution of Link-State and TE Information.", Internet-Draft draft-dhodylee-pce-pcep-ls-10, March 2018.
[I-D.ietf-spring-segment-routing] Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., Litkowski, S. and R. Shakir, "Segment Routing Architecture", Internet-Draft draft-ietf-spring-segment-routing-15, January 2018.
[I-D.ietf-spring-segment-routing-mpls] Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., Litkowski, S. and R. Shakir, "Segment Routing with MPLS data plane", Internet-Draft draft-ietf-spring-segment-routing-mpls-14, June 2018.

Appendix A. Contributor Addresses

Udayasree Palle
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka  560066
India

EMail: udayasreereddy@gmail.com

Mahendra Singh Negi 
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka  560066
India

EMail: mahendrasingh@huawei.com

Katherine Zhao
Huawei Technologies
2330 Central Expressway
Santa Clara, CA  95050
USA

EMail: katherine.zhao@huawei.com

Boris Zhang
Telus Ltd.
Toronto
Canada

EMail: boris.zhang@telus.com
      
        

Authors' Addresses

Quintin Zhao Huawei Technologies 125 Nagog Technology Park Acton, MA 01719 USA EMail: quintin.zhao@huawei.com
Zhenbin Li Huawei Technologies Huawei Bld., No.156 Beiqing Rd. Beijing , 100095 China EMail: lizhenbin@huawei.com
Dhruv Dhody Huawei Technologies Divyashree Techno Park, Whitefield Bangalore, Karnataka 560066 India EMail: dhruv.ietf@gmail.com
Satish Karunanithi Huawei Technologies Divyashree Techno Park, Whitefield Bangalore, Karnataka 560066 India EMail: satishk@huawei.com
Adrian Farrel Juniper Networks, Inc UK EMail: adrian@olddog.co.uk
Chao Zhou Cisco Systems EMail: choa.zhou@cisco.com