Cisco NX-OS: FabricPath (FP)

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

Components:

• 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: