Guest

Preview Tool

Cisco Bug: CSCun16599 - N7K SVI may go down even when there are active ports in the VLAN

Last Modified

Nov 01, 2018

Products (1)

  • Cisco Nexus 7000 Series Switches

Known Affected Releases

6.2(8)FM(0.21)

Description (partial)

Symptom:
In a few scenarios the SVI (interface VLAN) on the Nexus 7000 can go down even when there are layer 2 ports carrying the VLAN with STP in forwarding state for those VLANs

Conditions:
This happens when changes are made that invloves removing and re-adding VLANs on a port or bouncing a port/port-channel carrying any VLANs.

To validate if the Nexus 7000 is susceptible to this failure, check the following output.

N7K# show spanning-tree summary
<snip>

Name                   Blocking Listening Learning Forwarding STP Active
---------------------- -------- --------- -------- ---------- ----------
VLAN0040                     0         0        0          1          1
VLAN0049                     0         0        0          1          1
VLAN0100                     0         0        0          3          3
VLAN0101                     0         0        0          3          3
VLAN0102                     0         0        0          3          3
VLAN0103                     0         0        0          3          3


N7K# show spanning-tree internal flc-info
VlanId    FwdPorts   LC Bitmap  FwdPorts per LC
---------------------------------------------------------
VLAN0040         1  0x08000000  LC3:1
VLAN0049         1  0x08000000  LC3:1
VLAN0100         3  0x08000000  LC3:1
VLAN0101         3  0x08000000  LC3:1
VLAN0102         3  0x08000000  LC3:1
VLAN0103         3  0x08000000  LC3:1

If you notice Forwarding counter in "show spanning-tree summary" matches the FWDPorts counter in "show spanning-tree internal flc-info"

If you see a few VLANs missing or you see the FWDPorts counter less than what you see in "show spanning-tree summary" , the box is in a broken state and could end up bringing down those SVIs when changes are being made or link flaps.
Bug details contain sensitive information and therefore require a Cisco.com account to be viewed.

Bug Details Include

  • Full Description (including symptoms, conditions and workarounds)
  • Status
  • Severity
  • Known Fixed Releases
  • Related Community Discussions
  • Number of Related Support Cases
Bug information is viewable for customers and partners who have a service contract. Registered users can view up to 200 bugs per month without a service contract.