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Understanding Label-Switched Paths on the NorthStar Controller

 

The NorthStar Controller uses PCEP or Netconf to learn about LSPs in the discovered network topology, and all LSPs and their attributes can be viewed from the NorthStar Controller user interface. However, the LSP type determines whether the Path Computation Client (PCC) or NorthStar Controller maintains the operational and configuration states.

The following LSP types are supported on the NorthStar Controller:

  • PCC-controlled LSP: The LSP is configured locally on the router, and the router maintains both the operational state and configuration state of the LSP. The NorthStar Controller learns these LSPs for the purpose of visualization and comprehensive path computation. Using Netconf, these LSPs can be created or modified in NorthStar.

  • PCC-delegated LSP: The LSP is provisioned on the PCC (router) and has been delegated to the NorthStar Controller for subsequent management. The operational state and configuration state of the LSP is stored in the PCC. For delegated LSPs, the ERO, bandwidth, LSP metric, and priority fields can be changed from the NorthStar Controller user interface. However, the NorthStar Controller can return delegation back to the PCC, in which case, the LSP is reclassified as PCC-controlled.

  • PCE-initiated LSP: The LSP is provisioned from the NorthStar Controller UI. For these LSPs, only the operational state is maintained in the router, and only NorthStar can update the LSP attributes.

    Note

    There are a couple of circumstances under which the NorthStar Controller would discover these LSPs from the router, even though they are PCE-initiated:

    • A PCE-initiated LSP could be created by a controller other than the NorthStar Controller, and then discovered by NorthStar from the router.

    • When you reset the topology in the NorthStar Controller, NorthStar re-learns the LSPs from the router.

The NorthStar Controller supports the discovery, control, and creation of protection LSPs (standby and secondary LSPs). For protection LSPs, the primary, secondary, and standby LSP must be of the same type (PCC-controlled, PCC-delegated, or PCE-initiated). Each LSP can have its own specific bandwidth, setup priority, and hold priority or can use the values of the primary LSP (the default). A primary LSP must always be present for controller-initiated LSPs.

Provisioning Method

NorthStar Controller supports two methods for provisioning and managing LSPs: PCEP and Netconf. When you provision an LSP using PCEP, the LSP is added as a PCE-initiated LSP. When you provision using Netconf, the LSP is added as a PCC-controlled LSP.

Note

At this time, NorthStar Controller supports Netconf provisioning on Juniper devices only.

Table 1 summarizes the provisioning actions available for each type of LSP in the NorthStar Controller.

Table 1: NorthStar Provisioning Actions by LSP Type

LSP Type

Provision LSP

Modify LSP

Delete LSP

PCC-controlled LSP

Netconf

Netconf

Netconf

PCC-delegated LSP

N/A

PCEP

Netconf

PCE-initiated LSP

PCEP

PCEP

PCEP

Note

NorthStar does not offer a way to directly provision a new PCC-delegated LSP. What you can do though, is provision a new PCC-controlled LSP using Netconf and then delegate the LSP to NorthStar Controller by navigating to Applications > Configure LSP Delegation.

In NorthStar, both PCEP and Netconf device collection discover the same LSP attributes (in other words, there are no additional LSP attributes discovered only by device collection).

The following actions are performed or available when LSP provisioning is done via PCEP, but not when done via Netconf:

  • Automatic reprovisioning upon provisioning failure: If provisioning via NETCONF fails, such as when there is a commit failure or the NETCONF session is down, NorthStar does not retry the provisioning and you would need to resubmit the provisioning order. This is applicable to any provisioning for PCC-controlled LSPs and deletion of PCE-delegated LSPs.

  • LSP rerouting: When receiving an LSP down event from the network, NorthStar does not automatically recompute and reprovision a new path for PCC-controlled LSPs.

  • Path Optimization: When you run path optimization, PCC-controlled LSPs are not optimized.

  • Maintenance: PCC-controlled LSPs are not rerouted to avoid scheduled maintenance events.

Routing Method and Path Selection

When provisioning PCC-controlled LSPs via Netconf in NorthStar, you have the option to specify that NorthStar should compute and provision the path for the LSP, or not. You specify this option by setting the LSP routing method:

  • routeByDevice routing method—This is the default routing method when a PCC-controlled LSP is created or learned by NorthStar. When a PCC-controlled LSP has routeByDevice routing method, the NorthStar Controller does not compute and provision a path.

  • Other routing methods (default, delay, and so on)— When a PCC-controlled LSP has a routing method that is not routeByDevice, the NorthStar Controller computes and provisions the path as a strict explicit route when provisioning the LSP. The LSP’s existing explicit route might be modified to a NorthStar-computed strict explicit route. For example, a loose explicit route specified by the user or learned from the router would be modified to a strict explicit route.

    Note

    NorthStar saves the computed strict explicit route with Preferred path selection. This allows NorthStar, when it needs to re-compute the LSP path, to try to follow the strict explicit path, while still enabling it to compute an alternate path if the strict explicit path is no longer valid.

Deletion of LSPs on the Router

When an LSP is removed from the router, and therefore from the network, it is automatically deleted from NorthStar unless it has been modified by a NorthStar user (via the web UI or REST APIs), and therefore has a Persist state associated with it. Any LSP with a Persist state that is deleted from the router would require manual deletion in NorthStar.