Hello Bimckenz,
This is because Fabric Extender N2K purpose being to provide end-host connectivity to servers / host. As a result Bridge Protocol Data Unit (BPDU) Guard is enabled on all its host interfaces.
If you connect a bridge or switch to a FEX host interface, that interface is placed in an error-disabled state when a BPDU is received. You cannot disable BPDU Guard on a N2K host interface.
http://www.cisco.com/en/US/docs/switches/datacenter/nexus2000/sw/configuration/guide/rel_521/b_Configuring_the_Cisco_Nexus_2000_Series_Fabric_Extender_rel_5_2_chapter_01.html#con_1197054
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The intersting alternative would be to use Flex Links feature on the 2960 (equivalent to disable STP and to retain basic link redundancy).
http://www.cisco.com/en/US/docs/switches/lan/catalyst2960/software/release/12.2_58_se/configuration/guide/swflink.html
I have used it for blade Cisco 3020 systems and no incident since the installation 2 years ago.
- bpdufilter on the 2960 uplink would also be an alternative but be careful.
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Best regards.
Karim
