IF I remove vlan 922 do I still need to have spanning-tree portfast when I will assign this port to UPS? I just need a port setup without voice VLAN and in layer two network

interface GigabitEthernet2/0/47
 switchport access vlan 921
 switchport mode access
 switchport voice vlan 922
 spanning-tree portfast

2 Answers 2


Portfast is used to immediately start sending frames by skipping the blocking, listening and learning steps of STP. It should normally be used on access (end-device) interfaces.

For access interfaces, portfast is normally used with bpduguard to shut down the interface if another switch is connected to the access interface in order to prevent STP loops that can create broadcast storms that will kill the network.

You can globally enable portfast and bpduguard. This will only affect access interfaces, not trunks (you normally do not want it on trunk interfaces to other switches), unless you add the trunk keyword. You can do this with the global commands:

spanning-tree portfast default
spanning-tree portfast bpduguard default

That relieves you from having to enable and disable the commands on the interfaces as you change interfaces between trunk and access interfaces.


The portfast option may and should be used on all end-node ports.

By default, a port participating in the spanning tree changes to blocked mode on "link up", dropping all incoming frames. Only when the switch can be sure that there's no bridge located there (no BPDU is received within hello time) the port changes to forwarding mode. This causes a problem with a node that assumes full connectivity once its port has successfully linked ("link up"), especially with DHCP clients.

The portfast option makes the port skip that blocked state and immediately enter forwarding mode when the link comes up. Loops are still detected by spanning tree but only when the first BPDU arrives, so the loop may remain in place for the hello time at most. This may cause the beginning of a broadcast storm, but most often that can be mitigated by limiting the broadcast bandwidth on port (to anything between 5 and 50 percent).

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.