Nexus 5K + FEX -- Major Negotiation issues with vendor equipment.

[andrew-perry]

We currently are using  FEX (N2K-C2348UPQ-10GE) uplinked to a redundant pair of Nexus 5672UPs.  

We are getting around 30% negotiation failure with all of the following scenarios/variables:

• Auto-Negotiate
• 1000/Full
• spanning-tree port type edge
• spanning-tree bpduguard disable
• spanning-tree bpdufilter enable
• no cdp enable
• no lldp transmit
• link debounce time 0
• no mdix auto

We have physically checked/replaced fiber & SFPs.   If we move the interface to a different FEX port, same issue.   If we move the interface directly onto the Nexus 5K, we do NOT experience this issue (but we lost our redundancy).  The vendor has run debug on the negotiation and they wait 40ms for Auto-Neg (which doesnt work), then they wait an additional 40ms for 1000/Full.  But that times out.    What might the timers be on the FEX ports for Auto-Negotiation/standard negotiation vs the Nexus 5k?  Is there a way to speed up the negotiation on the FEX units to fall within these parameters?

[balaji.bandi]

we need more information is this FEX single home or dual homed? is nexus vPC?

can you share some configuration and FEX outputs

here is some troubleshoot tips :

https://www.cisco.com/c/en/us/support/docs/switches/nexus-2000-series-fabric-extenders/200265-Troubleshooting-Fabric-Extender-FEX-Pe.html

[andrew-perry]

This is a dual-homed FEX, using vPCs
Sample::

interface port-channel102
description vpc to Site05-5k-fex102
switchport mode fex-fabric
no lacp suspend-individual
fex associate 102
vpc 102

Would removing the HW queue limit on the FEX interfaces help in this scenario ? 

[balaji.bandi]

i do not see as per the FEX config, we need more information.

we need some information any policies ? on nexus ?

[mohAmed khAdr]

what code/image you running? Have you run a bug check? 

This should be straightforward based on conf you have on parent 5k. Conf is good.

So, I ain't sure what else it could be, other than maybe you need an image update.

HTH

mohamed