Which two statements correctly describe characteristics of the PortFast feature? (Choose two.) *
A.
STP will be disabled on the port.
B.
PortFast can also be configured on trunk ports.
C.
PortFast is required to enable port-based BPDU guard.
D.
PortFast is used for both STP and RSTP host ports.
E.
PortFast is used for STP-only host ports.
I think C, D, and E are all “mostly true”.
A. is incorrect since BPDUs are still transmitted out the port (BPDU filter stops this transmission of BPDUs).
B. is definitely correct (spanning-tree portfast trunk)
C. BPDU guard is specifically intended to work with Portfast, so I think it should be considered correct even though it is possible to issue the BPDU guard command without having issued the portfast command.
D. is mostly but not completely true because RSTP has “edge” ports, which replace host ports & portfast of STP.
E. If you agree with the statement for D, then E is “mostly true”.
Comments are welcome & appreciated.
I found out that C is not true:
“You also can use the spanning-tree bpduguard enable interface configuration command to enable BPDU guard on any port without also enabling the Port Fast feature. When the port receives a BPDU, it is put it in the error-disabled state.”
http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_55_se/configuration/guide/swstpopt.html#wp1032048
So that leaves only D and E for the 2nd correct statement.
Cisco probably wants you to choose D as the 2nd correct statement because their documentation says of Portfast:
“You can enable this feature if your switch is running PVST+, rapid PVST+, or MSTP.” [PVST+ uses STP, the other two use RSTP]
http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_55_se/configuration/guide/swstpopt.html#wp1032048
The answer D is correct for:
The Cisco implementation maintains that the PortFast keyword be used for edge port configuration.!!!!
Concept Edge Port.
Edge Ports
The edge port concept is already well known to Cisco spanning tree users, as it basically corresponds to the PortFast feature. All ports directly connected to end stations cannot create bridging loops in the network. Therefore, the edge port directly transitions to the forwarding state, and skips the listening and learning stages. Neither edge ports nor PortFast enabled ports generate topology changes when the link toggles. An edge port that receives a BPDU immediately loses edge port status and becomes a normal spanning tree port. At this point, there is a user-configured value and an operational value for the edge port state. The Cisco implementation maintains that the PortFast keyword be used for edge port configuration. This makes the transition to RSTP simpler.