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Ask the Expert- SD-WAN

A VLAN interface in MSFC does not come up on a Cisco Catalyst 6500 or 6000 series switch that runs CatOS system software


Core issue

This happens if  the router VLAN interfaces does not fulfill the following general conditions to be in up/up state

  • VLAN exists and is in active status on the switch VLAN database.  

  • VLAN interface exists on the router and is not administratively down.  

  • At least one L2 (access port or trunk) port exists and has a link up on this VLAN. The latest implementation of the autostate feature allows synchronization to Spanning-Tree Protocol (STP) port status.  

    A VLAN interface will be brought up after the L2 port has had time to converge (that is, transition from listening-learning to forwarding). This will prevent routing protocols and other features from using the VLAN interface as if it were fully operational. This also prevents other problems, such as routing black holes, from occurring.  

  • At least one L2 (access port or trunk) port is in spanning-tree forwarding state on the VLAN.  


To resolve this issue, create a corresponding VLAN in the Catalyst OS (CatOS) and associate one or more ports to this VLAN. If there are no switch ports in the corresponding VLAN connected to active devices, or no trunk port has been configured with the corresponding VLAN, the MSFC VLAN interface does not come up.

This is the same behavior witnessed with a standard router interface when nothing is connected to the interface. Both a corresponding VLAN in the switch and a connected port in that VLAN must be created for the MSFC to come up.

For additional information, refer to these documents:

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