draft-ietf-pce-stateful-pce-21 describes Stateful Path Computation Element Protocol (PCEP) enables a router to report and optionally delegate Label Switched Paths (LSPs) which is established using either Resource Reservation Protocol (RSVP) protocol or Segment Routing Traffic Engineering (SR-TE) to a stateful Path Computation Element (PCE). An LSP delegated to a PCE can be updated by the PCE and a stateful PCE can compute and provide the path of an LSP to the Path Computation Client (PCC).

The PCEP Extensions for PCE-initiated LSP Setup in a Stateful PCE Model (draft-ietf-pce-pce-initiated-lsp-11) specifies a set of extensions to PCEP to enable stateful control of TE LSPs across PCEP sessions in compliance with RFC4657. The PCEP Extensions for PCE-initiated LSP Setup in a Stateful PCE Model provides information about the following:

• Configuring LSPs on a PCC

• Delegating control of LSP to a PCE

The SR: PCE Initiated LSPs feature allows a client to create, setup, control, and delete an LSP from PCE server, which controls creating and deleting LSP on PCC through an PCE initiate message. PCE initiated LSP is automatically delegated to the PCE server that initiated the LSP. A PCE client processes an LSP initiate message. By using the LSP initiate message, PCE client can create or delete LSP.

When a failover occurs on a route processor (RP), the failover results in the RP being disconnected from the network. To reestablish the connection, the PCE server has to resend LSP initiate message to reclaim PCE Initiated LSPs on a client, else PCE initiated LSPs created by the client are automatically deleted.

You must use the pce command for establishing a PCEP session with PCC. The force auto-route command is used to advertise an LSP within an area via the autoroute announce message and across areas via the autoroute destination message. The decision to use autoroute announce or autoroute destination is performed by a device depending on the destination IP address. Enabling the force auto-route command for an initiated LSP allows automatic routing of traffic through a TE tunnel instead of routing traffic via manually configuring static routes. The autoroute announce message installs routes announced by the destination router and downstream routers into the routing table of a headend device that can be reached through a tunnel.

The PCC configuration includes IP addresses for each PCE (both primary and standby or more). The precedence for each PCE can be explicitly specified. If the precedence for two PCEs is same, PCE with smaller IP address has a higher precedence.

The SR: PCE Initiated LSPs feature supports single and redundant PCE operations. In a single PCE operation, when a PCE fails, PCC waits until the state timeout expiry (60 seconds) to remove the LSP.

In a redundant PCE operation, if a Representational state transfer (REST) call is initiated to a standby PCE before the expiry of the timer, the initiated LSP is retained else, the LSP is removed.

Note	The REST call must be initiated again to a standby PCE if the primary PCE fails, and the call must include the standby PCE IP address.

In a redundant PCE operation, PCC configurations include both primary and standby IP addresses for an LSP and the IP address with a lower precedence becomes the primary PCE. The IP addreseses are compared incase of equal priority.

Perform this task to configure a PCEP session PCE server XR based XTC server.

configure terminal
pce
 address ipv4 192.0.2.1 
end

The IP address 192.0.2.1 is the IP address of the transport controller.

configure terminal
 mpls traffic-eng pcc peer 192.0.2.1 source 203.0.113.1 force-autoroute
 end

In the above code snippet, 192.0.2.1 is PCE IP address and 203.0.113.1 is PCC source address for establishing a PCEP session.

configure terminal
mpls traffic-eng pcc peer 192.0.2.1 source 203.0.113.1 force autoroute precedence 255
mpls traffic-eng pcc peer 192.0.2.2 source 203.0.113.1 force-autoroute precedence 100
end

In the above code snippet, 100 is a lower precedence than 255, which is the default precedence. Therefore, the device with IP address 192.0.2.2 becomes the primary PCE and the device with 192.0.2.1 becomes the standby PCE.

mpls traffic-eng reoptimize