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Changing a Fex port back to a Switchport


Hello all,

Basically I am trying to use Wireshark to do a packet capture on a Nexus 5010. I want to do a monitor session on on the switch so I can capture from a source port to a destination port on the same switch. I can configure the source port but when I go to configure the destination port I get "

ERROR: Eth102/1/4: Configuration not allowed on fex interface". I have tried to reconfigure this port as a switchport but "switchport mode access" command does not take. I don't want to make any changes to any other ports but this one. What am I missing? Anyones help would be greatly appreciated.

7 Replies 7

Reza Sharifi
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under interface e102/1/4, can you try



"switchport mode access"

Can you post switcport ?

What is the error message?


Hi Reza,

Here's the error I'm seeing:

NX01(config-monitor)# destination interface e100/1/20

ERROR: Eth100/1/20: Configuration not allowed on fex interface

And here's the running config

interface Ethernet100/1/20

  switchport access vlan 51

  spanning-tree port type edge

  no shutdown

Thanks for reading!

Joshua Senft

The command for changing a routed port back to a switch port is simply "switchport".

Sent from Cisco Technical Support iPad App

The responses so far have focused on the commands on a normal Ethernet switch to make an interface back into a layer 2 switch access port. I think that they have missed one important aspect of the original post and of the follow up from Bob. The issue is not so much about making the port into an access port but is about making the port the destination for SPAN/monitor. The interface mentioned in the original post was Eth102/1/4 and in Bob's post it was Ethernet100/1/20. In both cases these are interfaces on the subsidiary N2K and not interfaces on the 5010. Ethernet100/1/20 may be configured on the parent Nexus switch but this interface is, by definition, part of a FEX connection and you can not treat it like a normal Ethernet switch port and make it into a SPAN/monitor destination port.





Hi Richard,

Thanks for commenting.  Further supporting your assertion, I found an interface on the FEX (100/1/44) with no existing configuration on it and it threw the same error when I tried to make it a destination SPAN port. 

Because the DESTINATION command throws the same error on an uncofigured port, that seems to mean that if it IS a config issue, the issue is elsewhere.

interface Ethernet 100/1/44

interface Ethernet 100/1/45

  switchport access vlan 54

  no shutdown

Thanks again,


  Fexes are basically like old dumb hubs so it doesn't surprise me that

you can't span to them because all the brains for them is basically in the N5K .

Hi Glen,

That's the same direction the senior (señor) guys around here provided: no processing or decision making power in a fex.

Thanks for weighing in.


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