What will happen if you use multiple spanning-tree features in a single interface?

[Sagar Hiremath]

Hi Guys,

I have a configuration where in i see multiple spanning-tree features been enabled on a port. I know we use portfast for access ports and root guard between trunk ports. I would like to know how the below port would behave given the config it has?

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interface GigabitEthernet4/34
description sagar--
switchport access vlan 436
switchport mode dynamic desirable
switchport voice vlan 711
auto qos voip cisco-phone
flowcontrol send desired
qos trust device cisco-phone
macro description host-voip
spanning-tree portfast
spanning-tree guard root
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Is there a sequential order that one of these features would be preferred over others? 

Please share your views and valuable info.

Thank you!

Sagar Hiremath

[Georg Pauwen]

Hello,

in your example, portfast takes effect first, it effectively 'enables' the port. Root guard makes sure that the port on which it is configured is the designated port.  If the bridge receives superior STP BPDUs on that port, root guard moves this port to a root-inconsistent STP state, but for that to happen, it has to be in forwarding state first, and that is what portfast does.

Does that make sense ?