Multihome Multicast Join Routing with Limited Flood Domains
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Solution Overview
Problem
In PIM networks with multihomed provider edges, the independent join and traffic decisions lead to mismatched routing, causing inefficient flooding and resource waste due to random selection of edge routers for multicast traffic.
Innovation Solution
Implementing a multiphase PFM-SD mechanism that creates a limited flood domain with boundary routers having specific routing and link information to directly route multicast joins to the active edge router, limiting flooding and ensuring accurate routing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If PIM joins are flooded throughout the network using longest prefix matching, then all routers can potentially receive and process join requests, but network bandwidth is wasted due to unnecessary flooding to routers that cannot make final routing decisions
Solution Approach 1:
The network is segmented into a limited flood domain consisting only of boundary routers. Instead of flooding PIM joins to all routers in the network, the system segments the flooding scope to only those routers (boundary routers) that are positioned to make final decisions about which edge router to send joins to. This segmentation eliminates unnecessary flooding to intermediate routers that cannot make routing decisions, thereby reducing network bandwidth consumption while maintaining effective join request delivery.
2Device complexity
If spine routers randomly select an edge router for multihomed sources, then the routing decision is simple to implement, but mismatches occur between join decisions and traffic decisions leading to inefficient routing
Solution Approach 1:
Boundary routers perform preliminary actions by locally storing information from source announcements before actual multicast traffic needs to be routed. When a source announcement is received indicating which edge router the multicast source is active on, boundary routers store this information in advance. This preliminary storage of routing information enables boundary routers to make accurate routing decisions when PIM joins arrive, eliminating the need for random selection and preventing mismatches between join and traffic decisions, thereby improving multicast traffic efficiency without significantly increasing device complexity.
3Measurement precision
If source announcement information is stored at all routers, then any router can make accurate routing decisions, but memory resources are wasted by routers that do not need to make routing decisions
Solution Approach 1:
The system applies local quality by giving different functional roles to different routers based on their positions in the network topology. Boundary routers, which are positioned to make final routing decisions, are equipped with the capability to store and use source announcement information. Intermediate routers that do not make routing decisions do not store this information. This localized allocation of storage and decision-making capabilities ensures that memory resources are used only where needed, maintaining routing decision accuracy at boundary routers while avoiding memory waste at intermediate routers.
Data Source
AI summary
A method comprises, at routers of a network configured to provide connectivity from a multicast receiver to edge routers multihomed to a multicast source of multicast traffic on an Ethernet segment: creating a limited flood domain for the Ethernet segment, wherein the limited flood domain includes boundary routers positioned to make a final decision as to which of the edge routers to send a multicast join for the multicast traffic; by the boundary routers, upon receiving a source announcement that announces the multicast source is active on a particular edge router of the Ethernet segment, locally storing information, provided by the source announcement, which includes a multicast address for the multicast source and identifies a link to the particular edge router; and by boundary router of the boundary routers, upon receiving the multicast join, sending the multicast join to the particular edge router using the multicast address and the link.