Logical Router Multicast Routing via Backplane RPF Check
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Solution Overview
Problem
Multicast routing protocols face challenges in preventing loops when using reverse path forwarding (RPF) checks in logical routers with separated packet handlers, as the unicast routing information does not account for the backplane link between east/west and north/south packet handlers, leading to failed RPF checks and potential packet discarding.
Innovation Solution
The solution involves using a modified RPF check in the north/south packet handler that identifies an entry for the source in unicast routing information and ensures the multicast traffic passes the check by referencing multicast routing information, which indicates the correct interface for receiving multicast packets, thereby avoiding loop detection failures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a logical router uses separated north/south and east/west packet handlers with standard RPF checks, then device complexity is reduced through separation of functions, but multicast routing reliability deteriorates due to loop detection failures
Solution Approach 1:
The logical router is segmented into separate north/south packet handlers and east/west packet handlers, each handling specific traffic directions. This segmentation reduces device complexity by distributing routing functions across specialized components while maintaining overall router functionality through coordinated operation.
Solution Approach 2:
A backplane link serves as an intermediary connection between the east/west packet handler and north/south packet handler. This intermediary enables traffic flow between separated handlers while allowing the system to maintain routing reliability through proper interface identification and RPF check coordination.
2Ease of operation
If the logical router uses unicast routing information for RPF checks, then the routing process is simplified, but multicast packet delivery deteriorates due to failed RPF checks on backplane-received traffic
Solution Approach 1:
The RPF check process is customized for the backplane link interface, recognizing that traffic received from the backplane has different characteristics than standard interface traffic. By applying local quality adjustments to the RPF check logic specifically for backplane-received multicast packets, the system maintains simplified overall routing while ensuring proper multicast packet delivery validation.
Solution Approach 2:
The RPF check parameters are modified to account for backplane link reception. Instead of using standard interface-based RPF verification, the system changes the verification parameter to recognize backplane link as a valid reception path for multicast traffic from east/west handlers, thereby maintaining both simplified operation and improved multicast delivery.
3Reliability
If the logical router performs standard loop detection on multicast packets, then network security is improved, but multicast traffic flow deteriorates due to false positive loop detection in separated handler architecture
Solution Approach 1:
The system performs preliminary identification of the backplane link as a valid reception interface before executing the RPF check on multicast packets. By preparing the routing information in advance to recognize backplane link characteristics, the system prevents false positive loop detections while maintaining security, allowing legitimate multicast traffic to flow through the separated handler architecture without unnecessary blocking.
Data Source
AI summary
The technology disclosed herein enables multicast network traffic to pass an RPF check in a logical router having separated packet handlers. In a particular embodiment, a method includes, in a north/south packet handler of a first logical router, receiving first network traffic from an east/west packet handler of the logical router. The first network traffic is multicast network traffic and the logical router is a first hop router for the first network traffic from a source of the first network traffic. The method further includes identifying an entry for the source in unicast routing information for unicast network traffic. Identifying the entry indicates that the first network traffic passes a reverse path forwarding (RPF) check. In response to the first network traffic passing the RPF check, the method includes transferring the first network traffic from the north/south packet handler to a next hop for the first network traffic indicated by first multicast routing information.