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19 Spanning Tree Protocol
3.
(config)# interface fastethernet 0/3
(config-if)# switchport mode trunk
(config-if)# spanning-tree portfast trunk
(config-if)# exit
Specifies port 0/3 for the trunk port, so that PortFast functionality is applied. It is not
applied by default to the trunk port. The trunk parameter needs to be specified to
specify each port.
(2) Setting BPDU guards
BPDU guard functionality puts ports for which PortFast is applied in inactive status when
they receive BPDUs. Normally, PortFast functionality is used to specify a port that is not a
redundant path, assuming that no Spanning Tree switch exists ahead of the port. This is set
to avoid unintended topology changes caused by received BPDUs.
Points to note
In order to set BPDU guard functionality, PortFast functionality must be set at the
same time. The
command can be used to apply BPDU guards by default to all ports to which the
PortFast functionality is applied. To disable the BPDU guard for a port after it has
been applied by default, use the
command.
Command examples
1.
(config)# spanning-tree portfast default
(config)# spanning-tree portfast bpduguard default
Sets PortFast functionality for all access ports, protocol ports, and MAC ports. It also
sets BPDU guard functionality for all ports to which PortFast functionality is applied.
2.
(config)# interface fastethernet 0/1
(config-if)# spanning-tree bpduguard disable
(config-if)# exit
Sets BPDU guard functionality to not be used on port 0/1 (access port). Normal
PortFast functionality is applied to port 0/1.
3.
(config)# interface fastethernet 0/2
(config-if)# switchport mode trunk
(config-if)# spanning-tree portfast trunk
(config-if)# exit
Sets PortFast functionality for port 0/2 (trunk port). It also sets BPDU guard
functionality. Because PortFast functionality is not applied by default to trunk ports, it
is set for each port. If BPDU guard functionality is set by default, BPDU guards are
applied automatically when PortFast functionality is set. If it is not set by default, it
can be set using the
19.13.3 Setting BPDU filters
BPDU filter functionality discards any received BPDUs, and prevents BPDUs from being
sent. Normally, ports that are not redundant path are assumed to be specified.
346
spanning-tree portfast bpduguard default
spanning-tree bpduguard disable
spanning-tree bpduguard enable
configuration
configuration
configuration command.
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