Point-to-Multipoint LSPs

A point-to-multipoint MPLS LSP is an RSVP-signaled LSP with a single source and multiple destinations. By taking advantage of the MPLS packet replication capability of the network, point-to-multipoint LSPs avoid unnecessary packet replication at the inbound (ingress) router. Packet replication takes place only when packets are forwarded to two or more different destinations requiring different network paths.

This process is illustrated in Figure 2. Router PE1 is configured with a point-to-multipoint LSP to Routers PE2, PE3, and PE4. When Router PE1 sends a packet on the point-to-multipoint LSP to Routers P1 and P2, Router P1 replicates the packet and forwards it to Routers PE2 and PE3. Router P2 sends the packet to Router PE4.

Point-to-Multipoint LSP Properties

The following are some of the properties of point-to-multipoint LSPs:

• A point-to-multipoint LSP allows you to use MPLS for point-to-multipoint data distribution. This functionality is similar to that provided by IP multicast.
• You can add and remove branch LSPs from a main point-to-multipoint LSP without disrupting traffic. The unaffected parts of the point-to-multipoint LSP continue to function normally.
• You can configure a node to be both a transit and an outbound (egress) router for different branch LSPs of the same point-to-multipoint LSP.
• You can enable link protection on a point-to-multipoint LSP. Link protection can provide a bypass LSP for each of the branch LSPs that make up the point-to-multipoint LSP. If any of the primary paths fails, traffic can be quickly switched to the bypass.
• You can configure sub-paths either statically or dynamically.
• You can enable graceful restart on point-to-multipoint LSPs.

Point-to-Multipoint LSP Configuration

To set up a point-to-multipoint LSP, you configure the primary LSP from the ingress router and the branch LSPs that carry traffic to the egress routers. In addition to the conventional LSP configuration, you specify a path name on the primary LSP and this same path name on each branch LSP.

By default, the branch LSPs are dynamically signaled by means of CSPF and require no configuration. You can alternatively configure the branch LSPs as a static path.

For more information and configuration instructions, see the JUNOS MPLS Applications Configuration Guide.