When a service provider does not support multicast over their Layer 3 VPN, the enterprise can useGRE tunnels between Customer Edge (CE) devicesto transport multicast traffic. This method allows the customer to encapsulate multicast packets in unicast GRE packets, which are routable through the provider’s non-multicast core.
In this scenario, the most scalable and immediate solution is to establish a GRE tunnel betweenC2 (in the head office CE router path)andC4 (at the branch office). This setup ensures that multicast traffic originating at the head office is tunneled directly to the multicast receivers, bypassing the service provider’s non-multicast-aware core.
This strategy is directly aligned with CCDE v3.1 principles, which emphasize:
Minimizing service provider dependency
Providing a scalable, customer-controlled overlay solution
Ensuring protocol compatibility across domains
Why other options are incorrect:
A: Tunnel between CE1 and CE2 is less optimal, as it may not originate or terminate at the exact multicast endpoints.
C: Tunnel between C1 and C4 is less aligned with CE-to-CE design expectations and may bypass required edge security/policy controls.
D: 2547oDMVPN is more complex and intended for full-scale VPN overlays, not quick multicast solutions.
E: Draft Rosen requires service provider support, which is currently unavailable, hence not a valid short-term option.
This solution ensures operational simplicity and future scalability with minimal provider dependency, which are core principles outlined in the CCDE v3.1 design methodology.
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