Supported Platforms
Configuring Primary and Branch LSPs for Point-to-Multipoint LSPs
A point-to-multipoint MPLS label-switched path (LSP) is an RSVP LSP with multiple destinations. By taking advantage of the MPLS packet replication capability of the network, point-to-multipoint LSPs avoid unnecessary packet replication at the ingress router. For more information about point-to-multipoint LSPs, see Point-to-Multipoint LSPs Overview.
To configure a point-to-multipoint LSP, you need to configure the primary LSP from the ingress router and the branch LSPs that carry traffic to the egress routers, as described in the following sections:
Configuring the Primary Point-to-Multipoint LSP
A point-to-multipoint LSP must have a configured primary point-to-multipoint LSP to carry traffic from the ingress router. The configuration of the primary point-to-multipoint LSP is similar to a signaled LSP. See Configuring the Ingress Router for MPLS-Signaled LSPs for more information. In addition to the conventional LSP configuration, you need to specify a path name for the primary point-to-multipoint LSP by including the p2mp statement:
You can include this statement at the following hierarchy levels:
- [edit protocols mpls label-switched-path lsp-name]
- [edit logical-systems logical-system-name protocols mpls label-switched-path lsp-name]
You can enable the optimization timer for point-to-multipoint LSPs. See Optimizing Signaled LSPs for more information.
Configuring a Branch LSP for Point-to-Multipoint LSPs
The primary point-to-multipoint LSP sends traffic to two or more branch LSPs carrying traffic to each of the egress provider edge (PE) routers. In the configuration for each of these branch LSPs, the point-to-multipoint LSP path name you specify must be identical to the path name configured for the primary point-to-multipoint LSP. See Configuring the Primary Point-to-Multipoint LSP for more information.
To associate a branch LSP with the primary point-to-multipoint LSP, specify the point-to-multipoint LSP name by including the p2mp statement:
You can include this statement at the following hierarchy levels:
- [edit protocols mpls label-switched-path lsp-name]
- [edit logical-systems logical-system-name protocols mpls label-switched-path lsp-name]
Note: Any change in any of the branch LSPs of a point-to-multipoint LSP, either due to a user action or an automatic adjustment made by the router, causes the primary and branch LSPs to be resignaled. The new point-to-multipoint LSP is signaled first before the old path is taken down.
The following sections describe how you can configure the branch LSP as a dynamically signaled path using Constrained Shortest Path First (CSPF), as a static path, or as a combination of dynamic and static paths:
Configuring the Branch LSP as a Dynamic Path
By default, the branch LSP for a point-to-multipoint LSP is signaled dynamically using CSPF and requires no configuration.
When a point-to-multipoint LSP is changed, either by the addition or deletion of new destinations or by the recalculation of the path to existing destinations, certain nodes in the tree might receive data from more than one incoming interface. This can happen under the following conditions:
- Some of the branch LSPs to destinations are statically configured and might intersect with statically or dynamically calculated paths to other destinations.
- When a dynamically calculated path for a branch LSP results in a change of incoming interface for one of the nodes in the network, the older path is not immediately torn down after the new one has been signaled. This ensures that any data in transit relying on the older path can reach its destination. However, network traffic can potentially use either path to reach the destination.
- A faulty router at the ingress calculates the paths to two different branch destinations such that a different incoming interface is chosen for these branch LSPs on a router node common to these branch LSPs.
Configuring the Branch LSP as a Static Path
You can configure the branch LSP for a point-to-multipoint LSP as a static path. See Configuring Static LSPs for more information.
