How do you update and migrate P2MP label switching in MPLS?

1 RSVP-TE P2MP Extension

Resource Reservation Protocol-Traffic Engineering (RSVP-TE) is a signaling protocol that establishes and maintains label switched paths (LSPs) in MPLS networks. The RSVP-TE P2MP extension allows the creation of P2MP LSPs, where a single source node can send packets to multiple destination nodes along a shared tree. To update and migrate P2MP label switching using the RSVP-TE P2MP extension, you need to configure the source node to initiate the P2MP LSP setup, the transit nodes to allocate and forward labels along the tree branches, and the destination nodes to join and leave the tree as needed.

2 BGP P2MP Extension

Border Gateway Protocol (BGP) is a routing protocol that exchanges network reachability information between autonomous systems (ASes). The BGP P2MP extension allows the distribution of P2MP LSP information using BGP messages. To update and migrate P2MP label switching using the BGP P2MP extension, you need to configure the source node to advertise the P2MP LSP attributes, the transit nodes to process and propagate the BGP messages, and the destination nodes to request and receive the P2MP LSP information.

3 Label Allocation Modes

One of the challenges of P2MP label switching is how to allocate labels for the P2MP LSPs. There are two main modes of label allocation: downstream unsolicited (DU) and downstream on demand (DoD). In DU mode, the transit nodes allocate labels for the P2MP LSPs and send them to the upstream nodes without waiting for a request. In DoD mode, the transit nodes allocate labels for the P2MP LSPs only when they receive a request from the upstream nodes. The choice of label allocation mode depends on the trade-off between scalability and efficiency.

4 Label Merging and Retention

Another challenge of P2MP label switching is how to handle label merging and retention. Label merging is the process of using the same label for multiple P2MP LSPs that share a common branch. Label retention is the process of keeping the labels for the P2MP LSPs that are no longer active. Label merging can reduce the label space consumption and improve the forwarding performance, but it can also increase the complexity and overhead of label management. Label retention can facilitate the recovery and reactivation of P2MP LSPs, but it can also waste the label resources and memory.

5 Label Switching Routers and Forwarding Equivalence Classes

The final challenge of P2MP label switching is how to classify and identify the packets that belong to different P2MP LSPs. The devices that perform label switching are called label switching routers (LSRs). The LSRs use a concept called forwarding equivalence class (FEC) to group packets that have the same forwarding behavior. The FEC can be based on various criteria, such as the source address, the destination address, the protocol type, or the application type. The LSRs assign labels to the FECs and use them to forward packets along the P2MP LSPs.

6 Label Switching Operations and Procedures

To update and migrate P2MP label switching in MPLS, you need to follow some basic operations and procedures. First, you need to establish the P2MP LSPs using either the RSVP-TE P2MP extension or the BGP P2MP extension. Second, you need to allocate labels for the P2MP LSPs using either the DU mode or the DoD mode. Third, you need to manage label merging and retention according to your network requirements and preferences. Fourth, you need to define the FECs for the P2MP LSPs and assign labels to them. Fifth, you need to perform label switching on the packets that match the FECs and send them to the appropriate destination nodes.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?