We have a 4500, and are looking into future server virtualisation, and as such, the switch ports that are connected to the servers are configured as trunk ports, and given ports are configured as follows:
switchport trunk encapsulation dot1q
switchport mode trunk
logging event link-status
spanning-tree portfast trunk
As we have 25 VLANs configured on this switch, it appears that each interface configured along these lines adds 25 instances to STP.
Due to the number of ports configured this way, the STP process is constantly running at around 35% CPU, so I was looking at ways of cutting this useage down.
My question is as follows, based on the following links (I appreciate that these links are based on 6500, but I assume that this specific process is the same):
"STP PortFast causes a Layer 2 LAN interface configured as an access port to enter the forwarding state immediately, bypassing the listening and learning states"
"When configured for PortFast, a port is still running the spanning tree protocol."
"PortFast BPDU filtering can also be configured on a per-port basis. When PortFast BPDU filtering is explicitly configured on a port, it does not send any BPDUs and drops all BPDUs it receives."
Question 1: Does the above imply that if a port is configured as portfast, that it still continues to send BPDUs out of this port? If it does, could anybody point me to a summary example of why it would do this?
Question 1a: If it does, will BPDU filtering (on a per-port basis) cut down the amount of processing, or will the BPDU essentially still get processed before it is dropped?
Question 1b: Again, if it does, will cutting down on the allowed VLANs with 'switchport trunk allowed vlan' command cut the CPU useage down?
Question 2: If a portfast port doesnt send BPDUs, and only a few ports on the switch are not configured as portfast, would there be any other reason why the CPU useage for this process would be so high?
Question 3: I am currently trying to get my head around MST - does anybody think this would be a potential option, and if so, does MST have to be configured on all of the switches? What could be the consequences of misconfiguring this?
Question 4: If i dont want the ports connected to the servers to participate in STP, would there be any issues with disabling STP on this port?
Any help would be greatly appreciated.