PCEP extensions in support of SR-TE LSPs

To manage the path of an SR-TE LSP, the PCE and PCC both implement the following extensions to PCEP in support of segment routing:

• An SR-PCE-CAPABILITY TLV in the OPEN object to indicate support of segment routing tunnels by the PCE and the PCC during PCEP session initialization.

• The PCC and PCE support all PCEP capability TLVs defined in this chapter, and always advertise them. If the OPEN object received from a PCEP speaker does not contain one or more of the capabilities, the PCE or the PCC does not use them during that specific PCEP session.

• A Path Setup Type TLV for SR-TE LSPs to be included in the Stateful PCE Request Parameters (SRP) object during the path report (PCRpt) messages by the PCC.

  A Path Setup Type TLV with a value of 1 identifies an SR-TE LSP.

• A Segment Routing ERO and an RRO with subobjects, referred to as SR-ERO and SR-RRO subobjects, which encode the SID information in the PCRpt messages.

• The PCE implementation supports the Segment-ID (SID) Depth value in the METRIC object. This is always signaled by the PCC in the PCEP OPEN object as part of the as SR-PCE-CAPABILITY TLV. It is referred to as the Maximum Stack Depth (MSD). In addition, the per-LSP value for the max-sr-labels option, if configured, is signaled by the PCC to the PCE in the Segment-ID (SID) Depth value in a METRIC object for both a PCE-computed LSP and a PCE-controlled LSP. PCE computes and provides the full explicit path with the TE-links specified. If there is no path with the number of hops lower than the MSD value, or the Segment-ID (SID) Depth value if signaled, a reply with no path is returned to the PCC. For a PCC-controlled LSP, if the label stack returned by the TE-DB’s hop-to-label translation exceeds the per-LSP maximum SR label stack size, the LSP is brought down.

• If the Path Setup Type (PST) TLV is not included in the PCReq message, the PCE or PCC must assume the message is for an RSVP-TE LSP.

Table: PCEP segment routing extension objects and TLVs describes the segment routing extension objects and TLVs supported in the SR OS.