Multicast Link Trace CFM in Ethernet Networks
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Solution Overview
Problem
In Ethernet networks, nodes that perform Reverse Path Forwarding Check (RPFC) based on the source MAC address struggle to properly trace multicast trees due to incorrect forwarding of Link Trace Messages, leading to extraneous transmissions and inability to identify broken links effectively.
Innovation Solution
Implementing a secondary RPFC process in the control plane that combines source and payload information to prevent incorrect forwarding of Link Trace Messages, while preserving the originating MEP's Source MAC Address in the header, allowing proper tracing of multicast trees even when nodes update the packet content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If nodes update the source MAC address when forwarding Link Trace Messages, then the forwarding information is kept current, but the ability to trace multicast trees accurately is lost
Solution Approach 1:
The patent segments the source address information into two parts: the original source MAC address (preserved in the message payload) and the interface identifier (extracted from the incoming interface). This allows the forwarding node to update the source address with interface information for efficient forwarding while preserving the original source identity for accurate tracing.
Solution Approach 2:
The patent introduces an intermediary mechanism where the forwarding node extracts the interface identifier from the incoming interface and uses it as part of the new source address. This intermediary interface identifier serves as a mediator that enables both efficient forwarding (by identifying the correct outgoing interface) and accurate tracing (by preserving the path information).
2Reliability
If Reverse Path Forwarding Check is performed based on source MAC address, then forwarding correctness is verified, but multicast tree tracing fails due to address updates
Solution Approach 1:
The patent performs preliminary extraction of the interface identifier from the incoming interface before updating the source address. This preliminary action ensures that the interface information is captured and preserved in the forwarding decision process, allowing RPFC to verify forwarding correctness while the original source identity is preserved in the message payload for tracing purposes.
Solution Approach 2:
The patent segments the source address verification into two components: the interface identifier (used for RPFC to verify forwarding correctness) and the original source MAC address (preserved for tracing). This segmentation allows both forwarding correctness verification and original source identity preservation to coexist.
Data Source
AI summary
Multicast link trace Connectivity Fault Management (CFM) is implemented in an Ethernet network by causing nodes on the network which perform Reverse Path Forwarding Check (RPFC) based on packet Source Address (SA) to not update the packet SA when updating the content of the CFM message. Alternatively multicast CFM is implemented by causing nodes on the network to update the packet SA when the content of the CFM message is updated, but cause a secondary RPFC process to be implemented by a control process in connection with processing the CFM message. The secondary RPFC process is based on a combination of source and content contained in the payload of the CFM message.