FabricPath (FP) is a L2 Routing = “MAC-in-MAC” Routing. FabricPath is Cisco proprietary and works in the same way as TRILL (Transparent Interconnection of Lots of Links) that is an IETF standard.

  • FP: to remove STP from the topology
  • vPC: only 2 switches
  • FP: full mesh, partial mesh, triangle, square etc


  • Classical Ethernet (CE)
    • regular ethernet with regular flooding, regular STP
  • Leaf Switch
    • connects CE domain to FP domain
  • Spine Switch
    • FP bacbone switch with all ports in the FP domain only
  • FP Core Ports
    • links on Leaf up to Spine or Spine to Spine
    • ie the switchport mode fabricpath links
  • CE Edge Ports
    • links on Leaf connecting to regular CE domain
    • ie NOT the switchport mode fabricpath links

FabricPath Control Plane

  • IS-IS for L2 Routing
  • Goal is to compute SPT (Shortest Path Tree) between all FabricPath nodes
  • Why IS-IS?
    • uses its own L3 transport (IP is not required)
    • natively extensible (supports new TLVs: switch id etc)
    • natively supports ECMP (Equal-cost multi-path routing)

FP switch ID - identifies the node in the IS-IS SPT

by deafult auto generated

(config)# fabricpath swith-id

show fabricpath switch-id
show fabricpath isis adjacency

FabricPath data plane

  • CE frames are encapsulated with new FabricPath header (only Nexus 7K F1 & F2 and Nexus 5500 only)
  • FabricPath header has SRC and DST FP Switch IDs

Traditional MAC learning

  • Learn SRC MAC of all received traffic
  • flood traffic to elict response from DST
  • leard SRC MAC of DST from its response

Conversational MAC learning

  • only learn SRC MAC if it already knows DST MAC

Note: FP Leaf Switches must be STP Root for Classical Ethernet domain

FabricPath Header

  • OMAC: Outer MAC address
  • OSA: Outer Source address
  • ODA: Outer Destination address
  • Switch ID: Used for source and destination switches
  • Ether type: Same as Classical Ethernet
  • TTL: Same as Classical Ethernet
  • FTag (Forwarding Tag): Used for traffic forwarding in the FabricPath domain

FabricPath Configuration

1. Enable FabricPath

conf t
install feature-set faricpath
feature-set fabricpath

2. Configure FabricPath VLAN - specify which VLANs will be tunneled over FP. It changes the MAC learning from Traditional to Conversational learning

vlan 10
   mode fabricpath 

3. Configure FP Core Port

int g1/0/1
   switchport mode fabricpath

FabricPath License

Requires a separate license - ENHANCED_LAYER2_PKG: