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  • Eiji Tanioka thinks this is interesting:

Before Phase 3, spoke-to-spoke tunnels were established through regional hubs. In Phase 3, spoke-to-spoke tunnels are established directly with each other, bypassing both the regional and central hubs.


Cover of CCIE Professional Development Series Network Security Technologies and Solutions


Phase2 is for single-region design, so spoke-to-spoke tunnel between region needs "HUB-TO-HUB' connection.