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Cisco Bug: CSCvt20782 - NVE interface remains up while associated loopbacks are down

Last Modified

Oct 01, 2020

Products (65)

  • Cisco Nexus 9000 Series Switches
  • Cisco Nexus 93600CD-GX Switch
  • Cisco Nexus 9516 Switch
  • Cisco Nexus 3548 Switch
  • Cisco Nexus 92348GC-X Switch
  • Cisco Nexus 3636C-R Switch
  • Cisco Nexus 3548-X Switch
  • Cisco Nexus 9396TX Switch
  • Cisco Nexus 3548-XL Switch
  • Cisco Nexus 92160YC-X Switch
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Known Affected Releases

9.3(3)

Description (partial)

Symptom:
NVE interface remains up while associated loopbacks are down

Conditions:
On a vxlan multisite border leafs, Nexus 93180 series of switches running 9.3.3, the NVE interface will remain up while the multisite timer is running and the associated loopbacks are down.  This situation happens on multisite border leafs with north bound connectivity out of the fabric and with multisite.  If the border leaf reloads or if the nve interface is bounced, the multisite restore timer will start it’s default countdown of 300 seconds.  During this the switch brings down (it administratively disables) the VTEP and multisite loopbacks.  When the NVE/VTEP loopback is brought down by the timer, the NVE interface fails to be brought down with it.  This is the cause of the issue, NVE interface needs to be brought down during the multisite restore timer.  During this timer, the border leaf learns the vxlan fabric host and network routes and then advertises the routes to the north bound external routers attracting traffic and black holing it on the border leaf since it’s vtep loopback is down and can’t deliver it to the fabric. 

If you manually shutdown the NVE/VTEP loopback, the NVE interface will be brought down.  It appears to be an issue with the NVE interface tracking of the VTEP loopback. It looks like the code is specifically looking for the shutdown statement on the loopback interface and not looking at the loopback operational state.
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