BPDUGuard errdisable

[Dragomir]

I connected a Dell Vrtx chassis with a built in L3 switch to a nexus 2000 fex but the port immediately becomes disabled. Any idea?

[Dragomir]

So since this is a L3 integrated dell switch. Is it possible to hang this off a FEX or does the FEX only support end devices?  I have bpduguard enabled on this port

this is the config on the port connected to the switch

version 6.1(2)

interface Ethernet101/1/19

  no description

  lacp port-priority 32768

  lacp rate normal

  switchport

  switchport mode access

  no switchport dot1q ethertype

  switchport access vlan 50

  switchport trunk native vlan 1

  switchport trunk allowed vlan 1-4094

  spanning-tree port-priority 128

  spanning-tree cost auto

  spanning-tree link-type auto

  spanning-tree port type edge

  spanning-tree bpduguard enable

  no spanning-tree bpdufilter

  speed auto

  duplex auto

  flowcontrol receive off

  flowcontrol send on

  link debounce time 100

  no beacon

  delay 1

  snmp trap link-status

  logging event port link-status default

  logging event port trunk-status default

  no ip dhcp snooping trust

  no ip arp inspection trust

  no ip verify source dhcp-snooping-vlan

  no shutdown

[InayathUlla Sharieff]

Tony,

Yes usually Fex are to be used only to connect the servers not to any third party switches.

One way to do it is configure the switch not to send BPDU, the HIF of the FEX will be able to connect to a switch. However, you can have a protential STP loop in your networ. Hense, this is not recommended.

From 5.2.1, by default the host interfaces are Layer 3. Hence you can connect it to switch if you want to keep it just Layer 3.

But if you want to keep the port as layer 2, then as Jeye mentioned, bpduguard is enabled by default.

Now when you connect a switch to FEX, it will send out a BPDU and hence the FEX port will get err-disabled.

If you want to connect a switch to those port then you need to enable bpdu filter on the switch interface which connects to FEX. This will prevent any BPDU going from switch to FEX and hence it will work out for you.

Always care should be taken when you enable bpdu filter since that will not help you if you have spanning-tree loop since you are not passing BPDUs.

For more reference:

http://www.cisco.com/en/US/partner/docs/switches/datacenter/nexus2000/sw/configuration/guide/rel_521/Configuring_the_Cisco_Nexus_2000_Series_Fabric_Extender_rel_5_2_chapter1.html#con_1046083

HTH

Regards

Inayath

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[Salvador Antonio Quintanilla Mendoza · Accepted solution]

try enabling  the spanning-tree bpdufilter feature on the interface.

[Dragomir]

Hi

Yes that enabled the port. But will it cause any loops? does enabling the bpdufilter on this port cause any problems?

I actually have 4 ports on this switch that I need to connect to the FEX. Would enabling bpdufilter on all 4 ports cause problems or do I need to setup some etherchannel?

thanks

[Leo Laohoo · Accepted solution]

BPDU Guard, on the FEX 2K is PERMANENTLY enabled by default.  You will not be able to disable it.

On the DELL L3 switch, disable STP portfast and see if this works.

[Dragomir]

ok I disabled STP on the L3 Dell and the interface came up.

on the fex I see this

sh spanning-tree interface ethernet 101/1/19 detail

Port 4196 (Ethernet101/1/19) of VLAN0050 is designated forwarding

   Port path cost 4, Port priority 128, Port Identifier 128.4196

   Designated root has priority 16434, address d867.d907.ffc1

   Designated bridge has priority 16434, address d867.d907.ffc1

   Designated port id is 128.4196, designated path cost 0

   Timers: message age 0, forward delay 0, hold 0

   Number of transitions to forwarding state: 1

   The port type is edge

   Link type is point-to-point by default

   Bpdu guard is enabled

   Bpdu filter is enabled by default

   BPDU: sent 11, received 0

BPDUs are being sent. Is that going to cause a loop?

[Dragomir]

if I added another link and disabled STP portfast on it, would that be a problem?

[Leo Laohoo]

if I added another link and disabled STP portfast on it, would that be a problem?

No it won't because STP will take the full 55-second cycle.

[Dragomir]

looks like this caused a problem. with 2 links on the switch attached to the fex and both enabled caused a loop. why would one be ok and 2 not?

[Dragomir]

why would 2 switch links connected to the fex cause a loop? both ports were spantree disabled

[Leo Laohoo]

If both ports have STP disabled, it will not cause a loop because STP will do it's job.

[Dragomir]

stp was disabled only on the dell switch. not on the fex. i initially have only stp disabled on one of the dell switch ports and there was no loop. After i disbaled stp for the second link and did a shut and no shut on the cisco port side, everything came to a halt