Troubleshooting Cisco “FEX Fabric Up to Identity-Mismatch” Message

If you are seeing this error message when configuring a Cisco FEX with more than 1 uplink to the same switch, follow the below setups to troubleshoot

Switch(config-if)# sho int e1/11
Ethernet1/11 is down (FEX identity mismatch)

Syslog Messages During configuration

2019 Apr 11 16:23:02 Switch %FEX-5-FEX_PORT_STATUS_NOTI: Uplink-ID 2 of Fex 0 that is connected with Ethernet1/11 changed its status from Discovered to Created
2019 Apr 11 16:23:02 Switch %FEX-5-FEX_PORT_STATUS_NOTI: Uplink-ID 2 of Fex 102 that is connected with Ethernet1/11 changed its status from Created to Configured

Switch(config-if)# 2019 Apr 11 16:23:09 Switch %ETHPORT-5-SPEED: Interface Ethernet1/11, operational speed changed to 10 Gbps
2019 Apr 11 16:23:09 Switch %ETHPORT-5-IF_DUPLEX: Interface Ethernet1/11, operational duplex mode changed to Full
2019 Apr 11 16:23:09 Switch %ETHPORT-5-IF_RX_FLOW_CONTROL: Interface Ethernet1/11, operational Receive Flow Control state changed to off
2019 Apr 11 16:23:09 Switch %ETHPORT-5-IF_TX_FLOW_CONTROL: Interface Ethernet1/11, operational Transmit Flow Control state changed to off
2019 Apr 11 16:23:09 Switch %FEX-5-FEX_PORT_STATUS_NOTI: Uplink-ID 0 of Fex 102 that is connected with Ethernet1/11 changed its status from Configured to Fabric Up
2019 Apr 11 16:23:09 Switch %FEX-2-FEX_PORT_STATUS_CRIT: Uplink-ID 2 of Fex 102 that is connected with Ethernet1/11 changed its status from Fabric Up to Identity-Mismatch

Why Is this happening??

When a FEX connects to a Nexus switch the Nexus Switch assigns the FEX an ID. If the switch tries to assign a different ID to different port on the same FEX, the “Identity-Mismatch” will occur.

Verification by running “Show interface fax-fabric”

As the below shows, FEX with serial number: FOX1930GDBQ was assigned two different FEX IDs:

  • 102
  • 104

FEX ID 104 was assigned first. When 102 was assigned, it caused a mismatch.

sho interface fex-fabric 
     Fabric      Fabric       Fex       FEX           Fex      
Fex  Port      Port State    Uplink    Model         Serial    
---------------------------------------------------------------
101    Eth1/3        Active     1      N2K-C2232PP-10GE   SSI1634047R
101    Eth1/4        Active     2      N2K-C2232PP-10GE   SSI1634047R
103    Eth1/5        Active     1     N2K-C2248TP-E-1GE   SSI16270C8Z
105    Eth1/6        Active     1      N2K-C2232PP-10GE   SSI15510STZ
104   Eth1/10        Active     1     N2K-C2248TP-E-1GE   FOX1930GDBQ
102   Eth1/11  Identity-Mismatch     2     N2K-C2248TP-E-1GE   FOX1930GDBQ
105   Eth1/12        Active     2      N2K-C2232PP-10GE   SSI15510STZ
---   Eth1/13    Discovered     1     N2K-C2248TP-E-1GE   FOX1930GDE3
---   Eth1/14    Discovered     2     N2K-C2248TP-E-1GE   FOX1930GDE3

How to Fix this?

Fix the cabling physically by swapping the cables to how you want it physically setup

If the desire was to be consistent in the cabling diagram, then it would be best not to deviate from a standard since standards are hard to come by these days 🙂

Reconfigure it based on our it’s already cabled

If there is less of a standard, then just reconfigure the switch

  • Default the interface
    • default interface e1/11
  • configure the misconfigured interface e1/11 with the same configure from FEX ID 104 (interface e1/10)
    • Switch(config-if)# show run int e1/10
      
                      !Command: show running-config interface Ethernet1/10
                      !Time: Thu Apr 11 16:27:05 2019
      
                      version 7.3(2)N1(1)
      
                      interface Ethernet1/10
                        description FEX104 grid DL37-1G
                        switchport mode fex-fabric
                        fex associate 104
                        no snmp trap link-status
                        channel-group 104
                      
  • Now the FEXs are happy
    • Switch# show interface fex-fabric 
                           Fabric      Fabric       Fex       FEX           Fex      
                      Fex  Port      Port State    Uplink    Model         Serial    
                      ---------------------------------------------------------------
                      101    Eth1/3        Active     1      N2K-C2232PP-10GE   SSI1634047R
                      101    Eth1/4        Active     2      N2K-C2232PP-10GE   SSI1634047R
                      103    Eth1/5        Active     1     N2K-C2248TP-E-1GE   SSI16270C8Z
                      105    Eth1/6        Active     1      N2K-C2232PP-10GE   SSI15510STZ
                      104   Eth1/10        Active     1     N2K-C2248TP-E-1GE   FOX1930GDBQ
                      104   Eth1/11        Active     2     N2K-C2248TP-E-1GE   FOX1930GDBQ
                      105   Eth1/12        Active     2      N2K-C2232PP-10GE   SSI15510STZ
                      102   Eth1/13        Active     1     N2K-C2248TP-E-1GE   FOX1930GDE3
                      102   Eth1/14        Active     2     N2K-C2248TP-E-1GE   FOX1930GDE3
                      

About Daniel Fredrick

Technology enthusiast, Programmer, Network Engineer CCIE# 17094

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