PCEP Developer Guide

Overview

This section provides an overview of feature odl-bgpcep-pcep-all . This feature will install everything needed for PCEP (Path Computation Element Protocol) including establishing the connection, storing information about LSPs (Label Switched Paths) and displaying data in network-topology overview.

PCEP Architecture

Each feature represents a module in the BGPCEP codebase. The following diagram illustrates how the features are related.

PCEP Dependency Tree

PCEP Dependency Tree

Key APIs and Interfaces

PCEP

Session handling

32-pcep.xml defines only pcep-dispatcher the parser should be using (global-pcep-extensions), factory for creating session proposals (you can create different proposals for different PCCs (Path Computation Clients)).

<module>
 <type xmlns:prefix="urn:opendaylight:params:xml:ns:yang:controller:pcep:impl">prefix:pcep-dispatcher-impl</type>
 <name>global-pcep-dispatcher</name>
 <pcep-extensions>
  <type xmlns:pcepspi="urn:opendaylight:params:xml:ns:yang:controller:pcep:spi">pcepspi:extensions</type>
  <name>global-pcep-extensions</name>
 </pcep-extensions>
 <pcep-session-proposal-factory>
  <type xmlns:pcep="urn:opendaylight:params:xml:ns:yang:controller:pcep">pcep:pcep-session-proposal-factory</type>
  <name>global-pcep-session-proposal-factory</name>
 </pcep-session-proposal-factory>
 <boss-group>
  <type xmlns:netty="urn:opendaylight:params:xml:ns:yang:controller:netty">netty:netty-threadgroup</type>
  <name>global-boss-group</name>
 </boss-group>
 <worker-group>
  <type xmlns:netty="urn:opendaylight:params:xml:ns:yang:controller:netty">netty:netty-threadgroup</type>
  <name>global-worker-group</name>
 </worker-group>
</module>

For user configuration of PCEP, check User Guide.

Parser

The base PCEP parser includes messages and attributes from RFC5441, RFC5541, RFC5455, RFC5557 and RFC5521.

Registration

All parsers and serializers need to be registered into Extension provider. This Extension provider is configured in initial configuration of the parser-spi module (32-pcep.xml).

<module>
 <type xmlns:prefix="urn:opendaylight:params:xml:ns:yang:controller:pcep:spi">prefix:pcep-extensions-impl</type>
 <name>global-pcep-extensions</name>
 <extension>
  <type xmlns:pcepspi="urn:opendaylight:params:xml:ns:yang:controller:pcep:spi">pcepspi:extension</type>
  <name>pcep-parser-base</name>
 </extension>
 <extension>
  <type xmlns:pcepspi="urn:opendaylight:params:xml:ns:yang:controller:pcep:spi">pcepspi:extension</type>
  <name>pcep-parser-ietf-stateful</name>
 </extension>
 <extension>
  <type xmlns:pcepspi="urn:opendaylight:params:xml:ns:yang:controller:pcep:spi">pcepspi:extension</type>
  <name>pcep-parser-ietf-initiated</name>
 </extension>
 <extension>
  <type xmlns:pcepspi="urn:opendaylight:params:xml:ns:yang:controller:pcep:spi">pcepspi:extension</type>
  <name>pcep-parser-sync-optimizations</name>
 </extension>
</module>

  • pcep-parser-base - will register parsers and serializers implemented in pcep-impl module

  • pcep-parser-ietf-stateful - will register parsers and serializers of draft-ietf-pce-stateful-pce-07 implementation

  • pcep-parser-ietf-initiated - will register parser and serializer of draft-ietf-pce-pce-initiated-lsp-00 implementation

  • pcep-parser-sync-optimizations - will register parser and serializers of draft-ietf-pce-stateful-sync-optimizations-03 implementation

Stateful module is a good example of a PCEP parser extension.

Configuration of PCEP parsers specifies one implementation of Extension provider that will take care of registering mentioned parser extensions: SimplePCEPExtensionProviderContext. All registries are implemented in package pcep-spi.

Parsing

Parsing of PCEP elements is mostly done equally to BGP, the only exception is message parsing, that is described here.

In BGP messages, parsing of first-level elements (path-attributes) can be validated in a simple way, as the attributes should be ordered chronologically. PCEP, on the other hand, has a strict object order policy, that is described in RBNF (Routing Backus-Naur Form) in each RFC. Therefore the algorithm for parsing here is to parse all objects in order as they appear in the message. The result of parsing is a list of PCEPObjects, that is put through validation. validate() methods are present in each message parser. Depending on the complexity of the message, it can contain either a simple condition (checking the presence of a mandatory object) or a full state machine.

In addition to that, PCEP requires sending error message for each documented parsing error. This is handled by creating an empty list of messages errors which is then passed as argument throughout whole parsing process. If some parser encounters PCEPDocumentedException, it has the duty to create appropriate PCEP error message and add it to this list. In the end, when the parsing is finished, this list is examined and all messages are sent to peer.

Better understanding provides this sequence diagram:

Parsing

Parsing

PCEP IETF stateful

This section summarizes module pcep-ietf-stateful. The term stateful refers to draft-ietf-pce-stateful-pce and draft-ietf-pce-pce-initiated-lsp in versions draft-ietf-pce-stateful-pce-07 with draft-ietf-pce-pce-initiated-lsp-00.

We will upgrade our implementation, when the stateful draft gets promoted to RFC.

The stateful module is implemented as extensions to pcep-base-parser. The stateful draft declared new elements as well as additional fields or TLVs (type,length,value) to known objects. All new elements are defined in yang models, that contain augmentations to elements defined in pcep-types.yang. In the case of extending known elements, the Parser class merely extends the base class and overrides necessary methods as shown in following diagram:

Extending existing parsers

Extending existing parsers

All parsers (including those for newly defined PCEP elements) have to be registered via the Activator class. This class is present in both modules.

In addition to parsers, the stateful module also introduces additional session proposal. This proposal includes new fields defined in stateful drafts for Open object.

PCEP segment routing (SR)

PCEP Segment Routing is an extension of base PCEP and pcep-ietf-stateful-07 extension. The pcep-segment-routing module implements draft-ietf-pce-segment-routing-01.

The extension brings new SR-ERO (Explicit Route Object) and SR-RRO (Reported Route Object) subobject composed of SID (Segment Identifier) and/or NAI (Node or Adjacency Identifier). The segment Routing path is carried in the ERO and RRO object, as a list of SR-ERO/SR-RRO subobjects in an order specified by the user. The draft defines new TLV - SR-PCE-CAPABILITY TLV, carried in PCEP Open object, used to negotiate Segment Routing ability.

The yang models of subobject, SR-PCE-CAPABILITY TLV and appropriate augmentations are defined in odl-pcep-segment-routing.yang.
The pcep-segment-routing module includes parsers/serializers for new subobject (SrEroSubobjectParser) and TLV (SrPceCapabilityTlvParser).

The pcep-segment-routing module implements draft-ietf-pce-lsp-setup-type-01, too. The draft defines new TLV - Path Setup Type TLV, which value indicate path setup signaling technique. The TLV may be included in RP(Request Parameters)/SRP(Stateful PCE Request Parameters) object. For the default RSVP-TE (Resource Reservation Protocol), the TLV is omitted. For Segment Routing, PST = 1 is defined.

The Path Setup Type TLV is modeled with yang in module pcep-types.yang. A parser/serializer is implemented in PathSetupTypeTlvParser and it is overriden in segment-routing module to provide the aditional PST.

PCEP Synchronization Procedures Optimization

Optimizations of Label Switched Path State Synchronization Procedures for a Stateful PCE draft-ietf-pce-stateful-sync-optimizations-03 specifies following optimizations for state synchronization and the corresponding PCEP procedures and extensions:

  • State Synchronization Avoidance: To skip state synchronization if the state has survived and not changed during session restart.

  • Incremental State Synchronization: To do incremental (delta) state synchronization when possible.

  • PCE-triggered Initial Synchronization: To let PCE control the timing of the initial state synchronization. The capability can be applied to both full and incremental state synchronization.

  • PCE-triggered Re-synchronization: To let PCE re-synchronize the state for sanity check.

PCEP Topology

PCEP data is displayed only through one URL that is accessible from the base network-topology URL:

http://localhost:8181/rests/data/network-topology:network-topology/topology/pcep-topology?content=nonconfig

Each PCC will be displayed as a node:

<node>
 <path-computation-client>
  <ip-address>42.42.42.42</ip-address>
  <state-sync>synchronized</state-sync>
  <stateful-tlv>
   <stateful>
    <initiation>true</initiation>
    <lsp-update-capability>true</lsp-update-capability>
   </stateful>
  </stateful-tlv>
 </path-computation-client>
 <node-id>pcc://42.42.42.42</node-id>
</node>
</source>

If some tunnels are configured on the network, they would be displayed on the same page, within a node that initiated the tunnel:

<node>
 <path-computation-client>
  <state-sync>synchronized</state-sync>
  <stateful-tlv>
   <stateful>
    <initiation>true</initiation>
    <lsp-update-capability>true</lsp-update-capability>
   </stateful>
  </stateful-tlv>
  <reported-lsp>
   <name>foo</name>
   <lsp>
    <operational>down</operational>
    <sync>false</sync>
    <ignore>false</ignore>
    <plsp-id>1</plsp-id>
    <create>false</create>
    <administrative>true</administrative>
    <remove>false</remove>
    <delegate>true</delegate>
    <processing-rule>false</processing-rule>
    <tlvs>
    <lsp-identifiers>
      <ipv4>
       <ipv4-tunnel-sender-address>43.43.43.43</ipv4-tunnel-sender-address>
       <ipv4-tunnel-endpoint-address>0.0.0.0</ipv4-tunnel-endpoint-address>
       <ipv4-extended-tunnel-id>0.0.0.0</ipv4-extended-tunnel-id>
      </ipv4>
      <tunnel-id>0</tunnel-id>
      <lsp-id>0</lsp-id>
     </lsp-identifiers>
     <symbolic-path-name>
      <path-name>Zm9v</path-name>
     </symbolic-path-name>
    </tlvs>
   </lsp>
  </reported-lsp>
  <ip-address>43.43.43.43</ip-address>
 </path-computation-client>
 <node-id>pcc://43.43.43.43</node-id>
</node>

Note that, the <path-name> tag displays tunnel name in Base64 encoding.

API Reference Documentation

Javadocs are generated while creating mvn:site and they are located in target/ directory in each module.