Configure MPLS Routing

MPLS routing

All LSPs other than SR (segment routed) LSPs are routed like RSVP LSPs. For MPLS simulation information specific to these types of LSPs, refer to Configure RSVP-TE Routing and Configure Segment Routing.

  • LSPs are established under normal operation: that is, with failures not taken into account.

  • Any LSPs that are affected by the failures are rerouted. Depending on the LSP path settings, reroutes might involve moving to a secondary path, dynamically rerouting the LSPs, or rerouting based on a segment list.

  • Demands are routed using the established LSPs using the specified IGP protocols given the specified failure scenarios.

  • LSP utilizations are calculated from the demand traffic using the specified traffic level.

Supported LSP types

Cisco Crosswork Planning supports these LSP types:

  • SR LSPs: Segment Routing LSPs, which do not use RSVP for routing. You can create SR LSPs using the Cisco Crosswork Planning UI. They are identified with a Type property of SR. For more information, refer to Configure Segment Routing.

  • RSVP LSPs: LSPs established through RSVP. These are commonly known as MPLS TE tunnels. Cisco Crosswork Planning discovers RSVP LSPs, and you can also create them using the Cisco Crosswork Planning UI. They are identified with a Type property of RSVP. For more information, refer to Configure RSVP-TE Routing.


Note

Cisco Crosswork Planning does not model LDP tunnels as LSPs.

Create and visualize LSPs and LSP paths

To simulate MPLS LSPs in the network, you must first set up the LSPs to be routed. Use this task to create and visualize LSPs from the UI.

Procedure

Step 1

Open the plan file (refer to Open plan files ). It opens in the Network Design page.

Step 2

From the toolbar, choose Actions > Insert > LSPs > LSP.

Alternatively, in the Network Summary panel on the right side, click Add icon > LSPs in the LSPs tab.

The LSPs tab is available under the More tab. If it is not visible, then click the Show/hide tables icon (Show/Hide Tables Icon) and check the LSPs check box.

Step 3

Choose the Type, which determines whether this is an RSVP LSP or an SR LSP.

Step 4

In the Name field, enter the name of the LSP.

Step 5

Select the Active or FRR enabled check box.

Step 6

Expand the Source & destination panel. Choose the appropriate source and destination site and node details.

Step 7

(Optional) Expand the other panels (Routing, CSPF, and Other) and enter the relevant parameters.

Step 8

Save your changes.

Step 9

To visualize the LSP in the network plot, select the LSP from the LSPs table. They appear in the plot as purple arrows.

Figure 1. LSP visualization
LSP visualization

  • To add a mesh of LSPs between the selected nodes, use any of these options:

    • From the toolbar, choose Actions > Insert > LSPs > LSP mesh.

    • In the Network Summary panel on the right side, click Add icon > LSP mesh in the LSPs tab.

  • To filter to related information such as related interfaces, source and destination nodes, demands, or LSP paths, select the LSP, click , and choose the appropriate option.

LSP paths

LSPs can be assigned one or more LSP paths. Like LSPs, LSP paths have properties that vary depending on whether the path is for an RSVP LSP or SR LSP. If these properties are omitted, then they are inherited from the LSP. If these properties are set in the LSP path, they override the LSP settings. For information on these properties, refer to Configure RSVP-TE Routing and Configure Segment Routing.

Path options and active path

A path option is a configuration parameter that

  • assigns a numeric value to each LSP path

  • determines the sequence in which paths are established, and

  • enables prioritization of network routes based on operational requirements.

Each LSP path includes a Path option property, which you can set when adding or editing an LSP path. The system attempts to establish LSP paths in order of increasing path option value: path option 1 is tried first, followed by path option 2, and so on. The LSP is routed using the first path that can be successfully established.

Figure 2. Path option
Path option

Alternatively, you can specify which LSP path to use by setting the Active path field under the Routing section (Add/Edit LSP page). Selecting an active path allows you to override the default path option order and explicitly control which path is used for routing.

Create LSP paths

Use this task to create LSP paths.

Procedure

Step 1

Open the plan file (refer to Open plan files). It opens in the Network Design page.

Step 2

In the Network Summary panel on the right side, from the LSPs table, choose the LSPs to which you are adding LSP paths.

Step 3

From the toolbar, choose Actions > Insert > LSPs > LSP Paths, or click Add icon in the LSP Paths table.

The Insert LSP Path window appears.

Step 4

If you are satisfied with the LSPs that you selected in Step 2, click Next. Make changes to the selection, if required.

Step 5

In the Path option field, enter the order in which the LSP path is activated. Lower numbers have preference over higher numbers.

Create LSP Paths

Step 6

If you are creating an LSP path from SR LSPs, proceed to Step 7. If this is an RSVP LSP path, optionally set these properties. For information on these properties, refer to Configure RSVP-TE Routing.

  1. To set the bandwidth, specify the Setup Bandwidth for the LSP path, or specify that it should inherit the bandwidth from the LSP.

  2. To create associated named paths, check this option and complete the name using $1 for the LSP name and $2 for the path option.

  3. If this is a standby LSP path, check Standby, which ensures the paths are always active.

Step 7

Click Next.

Step 8

Make the required changes in the Affinities page to associate the LSP path with affinities.

  1. For each rule (Include, Include any, Exclude), choose whether the LSP path should inherit the LSP affinity rule or whether it should be based on rules defined in the table.

  2. If you chose to use the table, choose the rule for each affinity you are associating with the LSP path.

Step 9

Submit your changes.

Path latency calculations

Cisco Crosswork Planning calculates shortest latency paths for LSPs and demands using these rules:

  • By default, Cisco Crosswork Planning uses the shortest path from the source to the destination of the LSP or demand, where the weight on each interface is the delay value for that interface.

  • If the delay for any interface is zero (as it is by default), a small (0.00001 ms) delay is used instead. This means that if all the delays for the interfaces in the plan are zero, the path with the smallest number of hops is selected.

  • If two paths have the same latency, paths with the smaller number of hops are preferred.

Route demands through LSPs

Routing through intra-area LSPs

Intra-area LSPs are modeled as IGP shortcuts. That is, the source of the demand using the LSP can be a node other than the ingress node into the IGP, and the destination node of the LSP can be a node other than the egress node from the IGP. A demand through intra-area LSPs does not require the LSP to traverse the full demand path.

Each intra-area LSP has a metric that helps determine which traffic is routed through the LSP. By default, autoroute LSPs have a metric equal to the shortest IGP distance from the source to the destination. However, you can configure static metrics for these LSPs that override this default. Static metrics can also be defined as relative to the shortest IGP distance, but these relative metrics are not currently supported in Cisco Crosswork Planning.

Configuration options

Forwarding adjacency (FA) LSPs always have a metric. If not specified, the default is 10. Forwarding adjacency LSP metrics are injected into the IGP so that nodes other than the source node of the LSP are aware of the path length through the forwarding adjacency LSP, and use it in their shortest path calculations.

To edit Autoroute and Forwarding adjacency settings, choose one or more LSPs from the LSP table, click Edit icon to open the Edit page, and edit the values in the Routing section.

Routing demands through inter-area LSPs

Since it is not possible to define metrics distances across ISP areas, there can be no well-defined metric for inter-area LSPs. Therefore, in Cisco Crosswork Planning, a demand only routes through an inter-area LSP if the demand’s endpoints are nodes matching the source and destination of the LSP, interfaces on these nodes, or external ASes whose ingress and egress points through the IGP are these nodes. This requirement is true regardless of the network option settings.

Routing inter-area LSPs

In Cisco Crosswork Planning, all nodes in a single AS are assumed to belong to a single IGP. If the plan file contains more than one AS, all IGPs defined in these ASes are of the same type. For information on how nodes are assigned to areas or levels, refer to Simulate Traffic Flow from Source to Destination Using Demands.

An inter-area LSP is an LSP whose source node and destination node have no areas in common. If available, inter-area LSPs follow actual paths, regardless of whether doing so violates the required order of routing through areas. For example, if following an actual path, an inter-area can enter and leave an OSPF area 0 more than once.

To understand the protocols that determine routing order when setting up inter-area LSPs, refer to Order of routing through areas. Other factors that determine how the inter-area LSPs are routed include whether the LSP type is RSVP or SR, and whether you have selected to require explicit hops at ABRs. For more information, refer to Explicit and dynamic inter-area LSP routing.


Note

  • Inter-area Fast Reroute LSPs and inter-area IGP shortcut LSPs are not supported. If the source and destination nodes of a Fast Route LSP are in different areas, the LSP is not routed.

  • To successfully route traffic, demands must also match the privacy requirements. Autoroute, Forwarding adjacency (FA) properties, and LSP metrics are ignored. For more information on privacy, refer to Routing demands through private LSPs.

Order of routing through areas

Regardless of the LSP type and whether explicit hops are required, inter-area LSPs route through the backbone areas, where “backbone” means area 0 for OSPF or the Level 2 area for IS-IS.

  • If there are three or more areas, backbone areas must be between the source and destination nodes. Typically, there are no more than three areas and therefore, the backbone area must be in the middle. For example, an OSPF inter-area LSP would route from area 1 to area 0 (backbone) and then to area 2.

  • If there are only two areas, there can only be one backbone area, and either the source or the destination node must be in the backbone area.

Explicit and dynamic inter-area LSP routing

An OSPF ABR is a node that belongs to both area 0 and other OSPF areas. An IS-IS ABR is a node that belongs to both the Level 2 area and another IS-IS level.

There are two modes of routing inter-area LSPs:

  • Explicit hop mode: Requires explicit hops to be set on ABR nodes. This approach simulates actual router behavior where ABR explicit hops are required.

  • Dynamic mode: Does not require explicit hops at ABR nodes and allows routing an LSP dynamically across multiple areas. Though this does not simulate actual router behavior, it is useful for planning inter-area LSP routes.

Configuration option

These modes are specified using the network option LSP routing requires ABR explicit hops in the Label Switched Paths section. If this option is selected, inter-area LSPs are routed based on explicit hops set on the ABR nodes.

  • An inter-area RSVP LSP must contain a named path, and the named path must contain explicit hops at ABRs for each required area crossing.

  • An inter-area SR LSP must contain a segment list, and the segment list must contain explicit node hops at ABRs for each required area crossing.

If this option is not selected, inter-area LSPs are routed dynamically and explicit hops at ABRs are not required. To leave one area and enter another, the inter-area LSP routes to the closest ABR in the current area that also borders the area it is entering.

Routing demands through private LSPs

A private LSP is a special LSP that

  • carries traffic dedicated to specific demands only

  • simulates the operation of MPLS Layer 2 VPNs, providing an exclusive route for the associated demands, and

  • interrupts all traffic associated with the LSP if it fails.

Configuration and identification

To configure LSPs that simulate Layer 2 VPNs, use one of these two methods:

  • Create dedicated demands for existing LSPs. The created demands will match the LSPs in source and destination. For more information, refer to Create private demands for existing LSPs.

  • Create private LSPs from existing demands. The created LSPs will match the existing demands in source and destination. For more information, refer to Create private LSPs for demands.

System indicators for private LSPs include:

  • LSPs table: The Private column is set to true.

  • Demands table columns: The Private LSP name and Private LSP source columns are set to true.

Create private demands for existing LSPs

Use this task to assign specific traffic parameters to LSPs and mark the demands as private.

Before you begin

Ensure that LSPs currently exist in the network model.

Procedure

Step 1

Open the plan file (refer to Open plan files). It opens in the Network Design page.

Step 2

From the toolbar, choose Actions > Insert > LSPs > Demands for LSPs.

Alternatively, in the Network Summary panel on the right side, click Add icon > Demands for LSPs in the LSPs tab.

The LSPs tab may be available under the More tab. If it is not visible, then click the Show/hide tables icon (Show/Hide Tables Icon) and check the LSPs check box.

Figure 3. Create demand for LSPs page
Create private demands for existing LSPs

Step 3

From the LSPs list, select the LSPs for which you want to create demands.

Step 4

Select the service class to which these LSPs belong.

Step 5

Set the demand traffic to equal the LSP setup bandwidth, the LSP traffic measurements, or zero.

Step 6

Check the Mark LSPs as private check box.

Step 7

Submit your changes.

The newly created demands are highlighted in the Demands table.

Create private LSPs for demands

Use this task to add private LSPs to selected demands within your plan file to control bandwidth assignments and mark paths as private.

Before you begin

Ensure that demands exist in the plan file.

Procedure

Step 1

Open the plan file (refer to Open plan files). It opens in the Network Design page.

Step 2

From the toolbar, choose Actions > Insert > LSPs > LSPs for demands.

Alternatively, in the Network Summary panel on the right side, click Add icon > LSPs for demands in the LSPs tab.

The LSPs tab may be available under the More tab. If it is not visible, then click the Show/hide tables icon (Show/Hide Tables Icon) and check the LSPs check box.

Figure 4. Demands selection page
Create private LSPs for demands

Step 3

In the list of demands, select the demands for which you want to create LSPs.

Step 4

Set the bandwidth traffic to a specific demand traffic or to zero.

Step 5

Check the Mark LSPs as private check box.

Step 6

Submit your changes.

The newly created LSPs are highlighted in the LSPs table.

Configure automatic demand deletion for private LSPs

Use this task to delete demands when associated private LSPs are removed from the plan file.

By default, when you delete a private LSP, the related demand remains in the system.

Procedure

Step 1

Open the plan file (refer to Open plan files). It opens in the Network Design page.

Step 2

In the toolbar, click or choose Actions > Edit > Network options.

The Network options page opens.

Step 3

Click the Advanced tab.

Step 4

In the Demands section, ensure that these check boxes are selected.

  • Unrouted if the private LSPs are unrouted

  • Removed if the private LSPs are removed

Step 5

Save your changes.

Load sharing between LSPs

Two or more LSPs with the same source and destination (and metrics, if these are defined) loadshare traffic between them. How the load is shared between the LSPs is determined by the LSP Loadshare property. By default, LSPs have a Loadshare property of 1, and thus route traffic between them in equal proportions. Changing the Loadshare value changes the distribution of LSP traffic and interface traffic in proportion to these values.

Loadshare ratio examples

If two LSPs are parallel, and one has a Loadshare property of 2 and one has a Loadshare property of 1, there will be a 2:1 ratio of traffic shared between them. The top half of Figure 67: Examples of two parallel LSPs with equal loadsharing and 2:1 loadsharing shows an example of two parallel LSPs that are routed using strict explicit paths. Each has a Loadshare value of 1, which means the traffic is routed using a 1:1 loadshare ratio so that each LSP carries 50% of the traffic. In contrast, the lower half shows the same parallel LSPs with a 2:1 ratio. That is, one LSP has a Loadshare value of 2, and one has a Loadshare property value of 1. The LSP with a Loadshare value of 2 carries 66% of the traffic, while the other carries 33%.

Figure 5. Examples of two parallel LSPs with equal loadsharing and 2:1 loadsharing
Two parallel LSPs with equal loadsharing Two parallel LSPs with 2:1 loadsharing

Each LSP has a path showing the percentage of traffic that crosses the LSP as a result of the Loadshare value for that LSP. The format is <path option>:<loadshare percentage>. Although loadshare applies only to path option 1, the LSP itself might be routed along a different path.

Note that this percentage may or may not be the same as the Loadshare value in the LSPs table. This is because the Loadshare value is relative to the other Loadshare values for parallel LSPs. For this reason, if manually editing the Loadshare property, we recommend that you consider the entire set of parallel LSPs. Note also that because an LSP can be in multiple sets of parallel LSPs, the percentage on its path can differ.

To optimize these Loadshare values, use the LSP Loadshare Optimization tool. For information, refer to LSP loadshare optimization.

Global simulation parameters

Cisco Crosswork Planning lets you set global parameters that affect how LSPs are routed or rerouted.

To access these options, click or choose Actions > Edit > Network options in the toolbar, then click the Simulation tab.

Figure 6. Global simulation parameters
Global simulation parameters

By default, Cisco Crosswork Planning simulates the state of the network once it has fully responded to a failure. Specifically, this is the network state after LSPs have re-established new routes around the failure, and the IGP has fully reconverged. This is called the IGP and LSP reconvergence simulation mode.

Other simulation modes include Fast reroute (FRR), Autobandwidth convergence, and Autobandwidth convergence (including failures). For more information on these modes, refer to Configure RSVP-TE Routing.

Optimization tool behavior

The optimization tools only work in IGP and LSP reconvergence mode. If you attempt to run an optimization tool in a different convergence mode, the system prompts you to confirm; if you proceed, the simulation automatically switches to IGP and LSP reconvergence mode.

Set LSP establishment order

Use this task for testing different routing outcomes based on varying establishment orders.

Cisco Crosswork Planning establishes LSPs in the order in which they appear in the plan. The routing of a specific LSP might depend on previously established LSP routes. You can modify this order by changing a random seed. Cisco Crosswork Planning then establishes LSPs in a random order that is determined by this number. Although you cannot predict the order based on the number, if you use the same number multiple times, Cisco Crosswork Planning establishes the LSPs in the same order each time. For example, varying the LSP establishment order lets you check whether certain orders result in higher utilizations.

Procedure

Step 1

In the toolbar, click or choose Actions > Edit > Network options.

The Network options page opens.

Step 2

In the Label switched paths section under the Simulation tab, enter a number in the LSP establishment order seed field. The default is 0.

Step 3

Save your changes.

LSP simulation diagnostics

To help troubleshoot RSVP LSP and LSP path simulations, Cisco Crosswork Planning analyzes simulation routes and provides reasons for certain types of routing behavior. The simulation diagnostics tool identifies why an LSP is not routed, why an LSP is routed away from its actual path, and why an LSP is not following the shortest TE path.

The diagnostic reports assume that all other LSPs, except for the one being tested, have been routed. That is, Cisco Crosswork Planning calculates whether an LSP can route on the actual path after all other routed LSPs have had their bandwidth reserved.

Note that running a report overwrites the previous report of the same type. For example, an LSPs diagnostic report would overwrite the previous LSPs report, but not the LSP path diagnostic report.

Run LSP simulation diagnostics

Use this task to run simulation diagnostics.

Procedure

Step 1

Open the plan file (refer to Open plan files). It opens in the Network Design page.

Step 2

From the toolbar, choose Actions > Tools > Diagnostics > LSP simulation or LSP path simulation.

Step 3

Select the LSPs or the LSP paths you want to optimize.

Step 4

Click Submit.

A diagnostic report is automatically generated. You can access this report at any time by choosing Actions > Reports > Generated reports, and then clicking the LSP Routing Diagnostics or LSP Path Routing Diagnostics link in the right panel.

Simulation diagnostics for LSP routing failures

Simulation diagnostics provide reasons that explain why an LSP or LSP path fails to route during simulation. This information helps identify specific reasons for routing failures during simulation.

The table lists the reasons and a brief description to assist in troubleshooting:

Table 1. LSP simulation diagnostic reasons

Reason

Description

Affinities

The affinity settings prevent the LSP or LSP path from routing.

Available BW

There is insufficient bandwidth to route the LSP or LSP path.

Explicit Hops

The route is determined by a named path that contains one or more explicit hops.

Hop Limit

The hop limit is too low.

Invalid Actual Path

The actual path is invalid and cannot be interpreted as an LSP route.

No Actual Path

The LSP does not have an actual path.

No Attempt

The LSP path is not routed because it is not a standby path and it is not the lowest routable path option for the LSP.

No Destination

There is no destination defined. The collected network might not contain the destination node of the LSP.

Simulation Option

The simulation option to use actual paths is not enabled.

TE not enabled

There are interfaces that the LSP or LSP path traverses that are not TE enabled.

Topology

The source and destination are disconnected.