The root cause here is likely related to multicast forwarding behavior:
Multicast forwarding may follow a single path based on unicast routing decisions (shortest-path trees or RPF lookup).
Equal-cost Layer 3 links do not always achieve perfect load balancing for multicast traffic since the multicast flow may hash consistently to a particular path.
Applying a more granular load-balancing hash algorithm on SW1 allows better distribution of flows across multiple links by considering additional packet header fields (e.g., Layer 4 ports, source/destination IP).
This is directly aligned with CCDE v3.1 design goals:
Avoiding overutilization by improving hashing entropy.
Preserving consistent unicast and multicast performance.
Leveraging hardware-based load balancing optimizations.
Why other options are incorrect:
A and B: Adding or bundling links doesn ' t address poor hashing distribution.
D: The issue is identified at SW1 (where hashing decisions are made).
E: Filtering IGMP joins may block legitimate receivers, not a valid solution.
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