In order for the PCE and PCC to manage the path of an SR-TE LSP, they both implement the following extensions to PCEP in support of segment routing.
A new Segment Routing capability TLV in the OPEN object to indicate support of segment routing tunnels by the PCE and the PCC during PCEP session initialization. This TLV is referred to as the SR-PCE-CAPABILITY TLV.
The PCC and PCE support all PCEP capability TLVs defined in this chapter, and will 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 will not use them during that specific PCEP session.
A new Path Setup Type TLV for SR-TE LSPs to be included in the Stateful PCE Request Parameters (SRP) Object during path report (PCRpt) messages by the PCC.
A Path Setup Type TLV with a value of 1 identifies an SR-TE LSP.
A new Segment Routing ERO and RRO with sub-objects, referred to as SR-ERO and SR-RRO sub-objects, which encode the SID information in 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 will compute and provide the full explicit path with 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 will be 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 it is for an RSVP-TE LSP.
Table 1 describes the segment routing extension objects and TLVs supported in the SR OS.
|
TLV, Object, or Message |
Contained in Object |
Contained in Message |
|---|---|---|
|
SR PCE CAPABILITY TLV |
OPEN |
OPEN |
|
Path Setup Type (PST) TLV |
SRP |
PCReq, PCRep, PCRpt |
|
SR-ERO Sub-object |
ERO |
PCRep, PCRpt |
|
SR-RRO Sub-object |
RRO |
PCReq, PCRpt |
|
Segment-ID (SID) Depth Value in METRIC Object |
METRIC |
PCReq, PCRpt |