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Cisco FabricPath: Enhancing TRILL: Standards Compatible

Cisco's announcement about FabricPath at CiscoLive cleared up the confusion about what FabricPath actually is. Cisco indicated that Nexus customers would have to choose between Cisco's own layer 2 multi-path protocol or TRILL, the other multi-path bridging standard that Cisco is supporting. A choice like that could cause lock-in to Cisco's proprietary protocol and product line. Cisco was also light on details about how FabricPath ehnahces TRILL. We asked Cisco for clarification on these points.

FabricPath is an implementation of the IETF's TRILL protocol and Cisco has committed to support both multi-path protocols on the Nexus product line simultaneously. It will be able interconnect Cisco Nexus switches and non-Cisco switches into a single multi-path network.

Cisco's multi-path protocol is called Layer 2 Multi-Pathing (L2MP). It is based on the IETF's Transparent Interconnection of Lots of Links (TRILL), but it isn't TRILL exactly. TRILL is not ratified by the IETF, but the work has progressed to the point that Cisco is confident that the standards concerning packet encapsulation and framing is far enough along that it can be built into new physical interfaces. The control plane, which manages the routing paths through the layer two networks, are in discussion and could change before the standard is finalized. Cisco would implement any changes via software updates. A Packet Pusher Podcast  with Omar Sultan, senior solution manager, Cisco Data Center Solutions and Greg Ferro, network architect and consultant, fills in some details on the impact of FabricPath on data center strategy.

FabricPath is a suite of technologies that includes TRILL. FabricPath enhances layer 2 multi-pathing by incorporating non-FabricPath switches in the fabric, uses conversational learning of MAC addresses, and computes different topologies based on local policies. These enhancements are the claimed value-add that Cisco has built into FabricPath beyond TRILL.

FabricPath switches can support switches that don't have FabricPath using virtual Port Channels (vPC). vPC is used to bond two uplinks that are connected to different switches, and both uplinks can be used simultaneously. Port channels and link aggregation can bond multiple links together between two switches without introducing a loop in the network.vPC creates a bonded Ethernet link between one switch and two other switches providing a redundant active/active path. Since FabricPath is only available on the  Nexus 7000, that would include all other Nexsus switches and any other switch that supports vPC.

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