CISCO-IOS - FEX Commands

FEX Discovery and Status Commands

Show FEX Inventory

Displays detected FEX units and their operational state.

show fex

Example output fields:

FEX number
Description
State (Online, Offline, Configured)
Model
Serial number

Show Detailed FEX Information

show fex detail

Includes:

Pinning status
Fabric interfaces
Power state
Host interface count

Show FEX Hardware Inventory

show inventory fex

Useful for RMA and asset tracking.

Show FEX Environment

show environment fex

Displays:

Temperature sensors
Fan status
Power supply status

FEX Association and Configuration

Configure FEX ID

configure terminal
fex <fex-id>
description Rack-01-FEX

Constraints:

FEX ID range depends on platform
ID must match physical FEX

Associate Fabric Interfaces

configure terminal
interface ethernet1/1
switchport mode fex-fabric
fex associate <fex-id>

Best practices:

Use port-channel for redundancy
Avoid mixing fabric and non-fabric interfaces

Fabric Port-Channel Configuration

configure terminal
interface port-channel10
switchport mode fex-fabric
fex associate <fex-id>

Verify Fabric Pinning

show fex pinning

Shows:

Host interface to fabric interface mapping
Load distribution

Host Interface Commands

Configure Host Interface Range

configure terminal
interface ethernet101/1/1
description Server01-NIC1
switchport
switchport mode access
switchport access vlan 100
spanning-tree port type edge

Notes:

FEX host interfaces do not support L3
All switching logic is handled by parent switch

Host Interface Port-Channel (vPC not supported on host ports)

configure terminal
interface port-channel20
switchport
switchport mode trunk

VLAN and Trunking Behavior on FEX

VLAN Assignment

show vlan fex

Displays VLANs allowed and active per FEX.

Trunk Configuration on Host Interface

configure terminal
interface ethernet101/1/2
switchport mode trunk
switchport trunk allowed vlan 100,200,300

Restrictions:

No dynamic trunk negotiation
VLANs must exist on parent switch

Security Concepts and Commands

FEX Trust Boundary

FEX operates as a remote line card:

No local control plane
No independent security policies

Port Security on Host Interfaces

configure terminal
interface ethernet101/1/3
switchport port-security
switchport port-security maximum 2
switchport port-security violation restrict

DHCP Snooping

configure terminal
ip dhcp snooping
ip dhcp snooping vlan 100
interface ethernet101/1/4
ip dhcp snooping trust

Dynamic ARP Inspection

configure terminal
ip arp inspection vlan 100

Note:

Requires DHCP snooping
Enforced at parent switch

BPDU Guard

configure terminal
interface ethernet101/1/5
spanning-tree bpduguard enable

Monitoring and Performance

Show Interface Status

show interface ethernet101/1/1

Show Interface Counters

show interface counters

Show FEX Statistics

show fex statistics

Includes:

Packet drops
Errors
Fabric utilization

FEX High Availability and Redundancy

Dual-Homed FEX (vPC)

show fex
show vpc

Key concepts:

FEX is dual-attached to two parent switches
Uses vPC domain for redundancy
Control plane remains on parents

Verify FEX vPC Status

show fex detail | include vPC

Software and Compatibility

Show FEX Image Version

show fex version

FEX image is automatically downloaded from parent switch.

Compatibility Check

show compatibility fex

Ensures:

NX-OS version compatibility
Hardware support

FEX Troubleshooting

FEX Not Coming Online

Check:

show fex
show logging | include FEX

Common causes:

Incorrect FEX ID
Unsupported NX-OS version
Fabric ports not in fex-fabric mode

Host Interfaces Down

show interface ethernet101/1/1 status
show fex pinning

Possible reasons:

Fabric port failure
VLAN mismatch
Server NIC down

Fabric Port Issues

show interface ethernet1/1
show interface port-channel10

Check for:

Errors
Speed/duplex mismatch
Incorrect port-channel config

VLAN Not Passing Traffic

show vlan id 100
show interface trunk

Ensure:

VLAN allowed on trunk
VLAN active on parent switch

Useful Links

Cisco Nexus Fabric Extender Configuration Guide

 https://www.cisco.com/c/en/us/support/switches/nexus-2000-series-fabric-extenders/products-installation-and-configuration-guides-list.html

Cisco Nexus 2000 Series Data Sheet

 https://www.cisco.com/c/en/us/products/switches/nexus-2000-series-fabric-extenders/index.html

Cisco NX-OS Command Reference

 https://www.cisco.com/c/en/us/support/ios-nx-os-software/nx-os-software/products-command-reference-list.html

Cisco Validated Designs – Data Center

 https://www.cisco.com/c/en/us/solutions/design-zone/data-center-design-guides.html

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