Cisco NX-OS: Fabric Extender (FEX)

Nexus 2000 Series Fabric Extenders acts as a remote line card of N7K or N5K chassis.

N2K FEX – ToR – Top of the Rack
N5K/N7K – EoR – End of the Row

Why?

  • Solve the problem of wiring cables in the data center. Keep all cables inside the rack as much as possible
  • Simplify the management and reduce number of management devices. All management performed on Parent Switch (management/upgrade etc)

Limitations and Parent Switches

  • No local switching inside the N2K FEX
  • 5K as FEX’s Parent
    • static pinning (ports on N2K pinned to the uplink port)
    • vPC topologies
    • FEX ports are L2 switchports
  • 7K as FEX’s Parent
    • not all line cards support FEX
    • static pinning only
      • FEX link must be Port-Channel
    • FEX ports are L2 switchports or native L3 routed interfaces
  • L2 FEX ports are STP “edge” ports
    • run BPDUGuard -> not switch could be connected to the FEX port

FEX configuration

1. Enable FEX feature:

on N5K:

feature fex

on N7K:

install feature-set fex
feature-set fex

2. Configure downlinks to FEX

on N5K:

interface e1/6 - 7
    switchport mode fex-fabric
    fex associate 102

on N7K (must be Port-Channel):

interface e1/6 - 7
    channel-group 101 mode on
int po101
    switchport 
    switchport mode fex-fabric 
    fex associate 101

FEX should be discovered by Parent:

show fex
show fex detail

FEX Pinning

When static pinning?
– there is a critical server on the FEX port that should not be oversubscribed
– BUT with loosing redundancy because there is no automatic re-pinning

show int e1/6 fex-intf
show int e1/7 fex-intf

conf t
fex 102
    pinning max-links 2
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