Cisco CCDE v3.0 | CCDE 400-007 Question # 71 Topic 8 Discussion

Cisco FabricPath is a Layer 2 multipath technology that blends traditional Layer 2 Ethernet with routing technologies to enable loop-free forwarding and scalability. Two critical mechanisms used to mitigate loops:

C. RPF (Reverse Path Forwarding) Check: FabricPath applies a reverse path forwarding check, similar to multicast, to verify the source of a frame and discard duplicates arriving on unexpected paths.

D. TTL Header: FabricPath adds a Time-To-Live (TTL) field to Layer 2 frames, which is not present in traditional Ethernet. This prevents indefinite circulation of frames by limiting their lifetime in the network—much like in IP.

These elements allow FabricPath to prevent broadcast storms and loops in multipath Layer 2 topologies, addressing legacy STP limitations with efficient loop-avoidance methods.

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