An LSP that is configured on the router is referred to as a PCC-initiated LSP. An LSP that is not configured on the router, but is instead created by the PCE at the request of an application or a service instantiation, is referred to as a PCE-initiated LSP.
The SR OS supports three different modes of operations for PCC-initiated LSPs which are configurable on a per-LSP basis.
When the path of the LSP is computed and updated by the router acting as a PCE Client (PCC), the LSP is referred to as a PCC-initiated and PCC-controlled LSP.
A PCC-initiated and PCC-controlled LSP has the following characteristics:
The LSP can contain strict or loose hops, or a combination of both.
CSPF is supported for RSVP-TE LSPs. Local path computation takes the form of hop-to-label translation for SR-TE LSPs.
LSPs can be reported to synchronize the LSP database of a stateful PCE server using the pce-report option. In this case, the PCE acts in passive stateful mode for this LSP. The LSP path cannot be updated by the PCE. In other words, the control of the LSP is maintained by the PCC.
When the path of the LSP is computed by the PCE at the request of the PCC, it is referred to as a PCC-initiated and PCE-computed LSP.
A PCC-initiated and PCE-computed LSP has the following characteristics:
The user must enable the path-computation-method pce option for the LSP so that the PCE can perform path computations at the request of the PCC only. The PCC retains control.
LSPs can be reported to synchronize the LSP database of a stateful PCE server using the pce-report option. In this case, the PCE acts in passive stateful mode for this LSP.
When the path of the LSP is updated by the PCE following a delegation from the PCC, it is referred to as a PCC-initiated and PCE-controlled LSP.
A PCC-initiated and PCE-controlled LSP has the following characteristics:
The user must enable the pce-control option for the LSP so that the PCE can perform path updates following a network event without an explicit request from the PCC. The PCC delegates full control.
The user must enable the pce-report option for LSPs that cannot be delegated to the PCE. The PCE acts in active stateful mode for this LSP.
SR OS also supports PCE-initiated LSPs. PCE-initiated LSPs allow a WAN SDN controller (such as the NSP) to automatically instantiate an LSP based on a service or application request. Only SR-TE PCE-initiated LSPs are supported.
The instantiated LSP does not have a configuration on the network routers and, consequently, is treated the same way as an auto-LSP. The parameters of the LSP are provided using policy lookup in the NSP and are passed to the PCC using PCEP in accordance with RFC 8281. Missing LSP parameters are added using a default or specified LSP template on the PCC.
PCE-initiated LSPs have the following characteristics:
The user must enable pce-initiated-lsp sr-te to enable the PCC to accept and process the PCInitiate messages from the PCE.
The user must configure one or more LSP templates of type pce-init-p2p-srte for SR-TE LSPs. A default template is supported that is used for LSPs for which no ID or an ID of 0 is included in the PCInitiate message. The user must configure at least one default PCE-initiated LSP template.
PCE-initiated LSPs are a form of SR-TE auto-LSP and are available to the same forwarding contexts. See Forwarding contexts supported with SR-TE auto-LSP. Similar to other auto-LSPs, PCE-initiated messages are installed in the TTM and are therefore available to advanced policy-based services using auto-bind such as VPRN and E-VPN. However, PCE-initiated LSPs cannot be used with provisioned SDPs.