Multicast Fast Reroute Over Remote Loop-Free Alternate Backup Path
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing multicast protocols face challenges in establishing remote loop-free alternate (RLFA) backup paths due to multicast control plane unawareness of data plane traffic tunneling and differences between unicast and multicast network views, leading to multicast join looping and failure in establishing MoFRR protection.
Innovation Solution
A modified PIM control message with a new message type and an additional field to indicate the address of a RLFA network device is used, allowing network devices to forward the message along the RLFA backup path instead of the source, enabling PIM to support MoFRR over RLFA backup paths.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If PIM is used to signal the RLFA backup path, then multicast traffic can be routed over the backup path, but multicast join looping occurs and the backup path may not be established
Solution Approach 1:
The PIM control message is segmented into two types: modified PIM control messages for signaling along the RLFA backup path, and conventional PIM control messages for signaling toward the source. This segmentation allows the control plane to distinguish between backup path signaling and source-directed signaling, preventing multicast join looping while enabling backup path establishment.
Solution Approach 2:
The modified PIM control message acts as an intermediary mechanism that bridges the control plane and data plane. By introducing this intermediate signaling format with a different message type, the system enables the control plane to be aware of data plane traffic tunneling over RLFA paths without requiring full integration of RLFA logic into the standard PIM protocol.
2Ease of operation
If network devices forward PIM control messages toward the source, then multicast distribution trees are built correctly, but multicast join looping occurs in the RLFA backup path
Solution Approach 1:
Different forwarding behaviors are applied locally based on message type: modified PIM control messages are forwarded toward the RLFA network device along the backup path, while conventional PIM control messages are forwarded toward the source. This local differentiation in forwarding behavior allows each message type to follow the appropriate path without causing loops.
Solution Approach 2:
The PIM control message includes a message type parameter that changes its routing behavior. By setting the message type to indicate a modified PIM control message, the message is routed along the RLFA backup path; by using the conventional message type, the message is routed toward the source. This parameter-based routing control prevents loops while maintaining correct multicast distribution.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Techniques are described for enhancements to Protocol Independent Multicast (PIM) to support multicast only fast re-route (MoFRR) over a remote loop free alternate (RLFA) backup path in a network. This disclosure describes a modified PIM control message having a new PIM message type and an additional field to indicate an address of a RLFA network device in the RLFA backup path. According to techniques of this disclosure, network devices along the RLFA backup path are configured to forward the modified PIM control message toward the RLFA network device instead of toward a source of a requested multicast group. When the RLFA network device receives the modified PIM control message, the RLFA network device is configured to forward a conventional PIM control message towards the source of the requested multicast group. In this way, PIM can be used to provide MoFRR over a RLFA backup path.