Which option does the FabricPath technology use to create loop-free Layer 2 networks?
A.
STP
B.
TTL
C.
fabric tags
D.
FSTP
Explanation:
Well, the dump said “TTL” and I think that’s not entirely true. TTL ends up a looping packet but the loop can
still be there. Fabric path uses IS-IS and the concept of “switch-ids” which could refer to “fabric tags”…
There are also the FTag (Forwarding Tag) which specifies which path the packet traverses… Not very clear.
If the Q was something like: “Which option does the FabricPath technology use to mitigate Layer 2loops?”
I would have answered TTL.
Loop prevention and mitigation is available in the data plane, helping ensure safe forwarding that cannot be matched by any transparent bridging
technology. Cisco FabricPath frames include a timeto-live (TTL) field similar to the one used in IP, and a reverse-path forwarding (RPF) check is also applied.
http://www.cisco.com/c/dam/en/us/products/collateral/switches/nexus-7000-series-switches/at_a_glance_c45-605626.pdf
The advantages of using FabricPath include:
• MAC address scalability with conversational learning
• Spanning Tree Protocol independence: No reliance on Spanning Tree anymore. Each switch has a complete view of the Layer 2 topology, and it calculates the
Layer 2 forwarding table based a shortest-path-first calculation.
• Traffic distribution for unicast: Unicast Layer 2 traffic can take multiple equal-cost Layer 2 paths.
• Traffic distribution for multicast on multiple distribution trees: Multicast traffic can be distributed along two multidestination trees.
• More direct communication paths: Any topology is possible, so cabling two access or edge switches directly to each other creates a direct communication path,
unlike what happens with Spanning Tree.
• Simplicity of configuration: The configuration of FabricPath is very simple. Tuning may still be advised but by default the switches negotiate switch-ids allocation
with a protocol called Dynamic Resource Allocation Protocol (DRAP).
• Loop mitigation with TTL in the frame field: Layer 2 loops, as they are known of today in Spanning-Tree-Protocol-based Layer 2 networks, are mitigated by
dropping frames that have been propagated across too many hops. The Layer 2 FabricPath frames include a Time to Live (TTL) field that is decremented at each
hop. The value of the TTL field is 32.http://www.cisco.com/c/en/us/products/collateral/switches/nexus-5000-series-switches/guide_c07-690079.html